@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106873, title ="Sulfate sulfur isotopes and major ion chemistry reveal that pyrite oxidation counteracts CO₂ drawdown from silicate weathering in the Langtang-Trisuli-Narayani River system, Nepal Himalaya", author = "Kemeny, P. C. and Lopez, G. I.", journal = "Geochimica et Cosmochimica Acta", volume = "294", pages = "43-69", month = "February", year = "2021", doi = "10.1016/j.gca.2020.11.009", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201202-083406031", note = "© 2020 Elsevier Ltd. \n\nReceived 14 April 2020, Revised 2 November 2020, Accepted 11 November 2020, Available online 19 November 2020. \n\nP.C.K. is supported by the Fannie and John Hertz Foundation Cohan-Jacobs and Stein Families Fellowship. This research was conducted with government support under and awarded by DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. This research was supported by the US National Science Foundation (grants 1349858 and 1834492). N.F.D. is grateful to the Linde Center for support. The Caltech Environmental Analysis Center is supported by the Linde Center and the Beckman Institute at Caltech. This research was also supported by the German Research Foundation DFG through the Cluster of Excellence ‘CliSAP’ (EXC177), Universität Hamburg. The authors acknowledge the Department of Hydrology and Meteorology (DHM), Government of Nepal, for discharge measurements. Initial computing costs were covered by startup research funds provided by Caltech to F. Tissot. T. Jappinen and P. Bartsch helped with logistics and analysis. The authors are grateful to W. Fischer for helpful conversations and to A. Philips and P. Mateo for advice on the design of figures. We thank the associate editor and three anonymous reviewers for providing insightful comments. \n\nData availability: The measurements of δ³⁴S_(SO₄) and dissolved major ion concentrations described in this article are available as supplementary material. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "33", abstract = "Drawdown of atmospheric carbon dioxide (CO₂) due to silicate weathering in the Himalaya has previously been implicated in Cenozoic cooling. However, over timescales shorter than that of the removal of marine sulfate (SO₄²⁻), the oxidation of pyrite (FeS₂) in weathering systems can counteract the alkalinity flux of silicate weathering and modulate pCO₂. Here we present evidence from ³⁴S/³²S isotope ratios in dissolved SO₄²⁻ (δ³⁴S_(SO₄)), together with dissolved major ion concentrations, that reveals FeS₂ oxidation throughout the Langtang-Trisuli-Narayani River system of the Nepal Himalaya. River water samples were collected monthly to bimonthly throughout 2011 from 16 sites ranging from the Lirung Glacier catchment through the Narayani River floodplain. This sampling transect begins in the High Himalayan Crystalline (HHC) formation and passes through the Lesser Himalayan (LH) formation with upstream influences from the Tethyn Sedimentary Series (TSS). Average δ³⁴S_(SO₄) in the Lirung Glacier outlet is 3.6‰, increases downstream to 6.3‰ near the confluence with the Bhote Kosi, and finally declines to −2.6‰ in the lower elevation sites. Using new measurements of major ion concentrations, inversion shows 62–101% of river SO₄²⁻ is derived from the oxidation of sulfide minerals and/or organic sulfur, with the former process likely dominant. The fraction of H₂SO₄-driven weathering is seasonally variable and lower during the monsoon season, attributable to seasonal changes in the relative influence of shallow and deep flow paths with distinct residence times. Inversion results indicate that the primary control on δ³⁴S SO₄ is lithologically variable isotope composition, with the expressed δ³⁴S value for the LH and TSS formations (median values −7.0–0.0‰ in 80% of samples) lower than that in the HHC (median values −1.7–6.2‰ in 80% of samples). Overall, our analysis indicates that FeS₂ oxidation counteracts much of the alkalinity flux from silicate weathering throughout the Narayani River system such that weathering along the sampled transect exerts minimal impact on pCO₂ over timescales >5–10\u202fkyr and <10\u202fMyr. Moreover, reanalysis of prior datasets suggests that our findings are applicable more widely across several of the frontal Himalayan drainages.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105466, title ="The Dissolution Rate of CaCO₃ in the Ocean", author = "Adkins, Jess F. and Naviaux, John D.", journal = "Annual Review of Marine Science", volume = "13", pages = "57-80", month = "January", year = "2021", doi = "10.1146/annurev-marine-041720-092514", issn = "1941-1405", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200922-074257620", note = "© 2021 by Annual Reviews. \n\nFirst published as a Review in Advance on September 18, 2020. \n\nWe thank the National Science Foundation for its support of this research via awards OCE-1220600, OCE-1559215, OCE-1834492, OCE-1559004, OCE-1220302, and OCE-1834475. We have also benefited from financial support from the Linde Center for Global Environmental Science at Caltech, the Change Happens Foundation, and the Grantham Foundation. Little of this work would have been possible without the technical support of Nick Rollins and intellectual inspiration from Jonathan Erez. Conversations with many colleagues over the years have helped shape our understanding of carbonate dissolution kinetics, but we are especially indebted to Burke Hales and Henry Teng for insightful comments and criticisms along the way. \n\nThe authors are not aware of any affiliations, memberships, funding, or financial holdings that might be perceived as affecting the objectivity of this review.", revision_no = "16", abstract = "The dissolution of CaCO₃ minerals in the ocean is a fundamental part of the marine alkalinity and carbon cycles. While there have been decades of work aimed at deriving the relationship between dissolution rate and mineral saturation state (a so-called rate law), no real consensus has been reached. There are disagreements between laboratory- and field-based studies and differences in rates for inorganic and biogenic materials. Rates based on measurements on suspended particles do not always agree with rates inferred from measurements made near the sediment–water interface of the actual ocean. By contrast, the freshwater dissolution rate of calcite has been well described by bulk rate measurements from a number of different laboratories, fit by basic kinetic theory, and well studied by atomic force microscopy and vertical scanning interferometry to document the processes at the atomic scale. In this review, we try to better unify our understanding of carbonate dissolution in the ocean via a relatively new, highly sensitive method we have developed combined with a theoretical framework guided by the success of the freshwater studies. We show that empirical curve fits of seawater data as a function of saturation state do not agree, largely because the curvature is itself a function of the thermodynamics. Instead, we show that models that consider both surface energetic theory and the complicated speciation of seawater and calcite surfaces in seawater are able to explain most of the most recent data. This new framework can also explain features of the historical data that have not been previously explained. The existence of a kink in the relationship between rate and saturation state, reflecting a change in dissolution mechanism, may be playing an important role in accelerating CaCO₃ dissolution in key sedimentary environments.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105565, title ="A Mechanistic Study of Carbonic Anhydrase Enhanced Calcite Dissolution", author = "Dong, Sijia and Berelson, William M.", journal = "Geophysical Research Letters", volume = "47", number = "19", pages = "Art. No. e2020GL089244", month = "October", year = "2020", doi = "10.1029/2020gl089244", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200925-135425366", note = "© 2020 American Geophysical Union. \n\nIssue Online: 29 September 2020; Version of Record online: 29 September 2020; Accepted manuscript online: 21 September 2020; Manuscript accepted: 14 September 2020; Manuscript revised: 08 September 2020; Manuscript received: 11 June 2020. \n\nThis work was supported by the National Science Foundation (NSF) Ocean Acidification grants (OCE1220600, OCE1220302 and OCE 1559004) and the University of Southern California (USC) Dornsife Doctoral Fellowship. We thank Adam V. Subhas for his helpful discussions in preparing the experiments and the manuscript. \n\nData Availability Statement: Data set for this research is available in this in‐text data citation reference: Dong, S., Berelson, W., Teng, H., Rollins, N., Pirbadian, S., El‐Naggar, M., Adkins, J. (2020). Step velocities during calcite dissolution in seawater with and without carbonic anhydrase, version 1.0. Interdisciplinary Earth Data Alliance (IEDA). https://doi.org/10.26022/IEDA/111627. Accessed 2020‐09‐08.", revision_no = "23", abstract = "Carbonic anhydrase (CA) has been shown to promote calcite dissolution (Liu, 2001, https://doi.org/10.1111/j.1755-6724.2001.tb00531.x; Subhas et al., 2017, https://doi.org/10.1073/pnas.1703604114), and understanding the catalytic mechanism will facilitate our understanding of the oceanic alkalinity cycle. We use atomic force microscopy (AFM) to directly observe calcite dissolution in CA‐bearing solution. CA is found to etch the calcite surface only when in extreme proximity (~1 nm) to the mineral. Subsequently, the CA‐induced etch pits create step edges that serve as active dissolution sites. The possible catalytic mechanism is through the adsorption of CA on the calcite surface, followed by proton transfer from the CA catalytic center to the calcite surface during CO2 hydration. This study shows that the accessibility of CA to particulate inorganic carbon (PIC) in the ocean is critical in properly estimating oceanic CaCO3 and alkalinity cycles.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105004, title ="The ECCO‐Darwin Data‐Assimilative Global Ocean Biogeochemistry Model: Estimates of Seasonal to Multidecadal Surface Ocean pCO₂ and Air‐Sea CO₂ Flux", author = "Carroll, D. and Menemenlis, D.", journal = "Journal of Advances in Modeling Earth Systems", volume = "12", number = "10", pages = "Art. No. e2019MS001888", month = "October", year = "2020", doi = "10.1029/2019ms001888", issn = "1942-2466", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200818-132613563", note = "© 2020 The Author(s). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. \n\nAccepted manuscript online: 26 July 2020; Manuscript accepted: 23 July 2020; Manuscript revised: 15 July 2020; Manuscript received: 03 September 2019. \n\nResearch was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. D. C., D. M., and H. Z. were supported by NASA Biological Diversity, Physical Oceanography, and Modeling, Analysis, and Prediction Programs. M. M. G. and D. S. S. were supported by NASA ROSES‐2017 Grant/Cooperative Agreement NNX15AG92G. S. D. was supported by NASA‐IDS Grant 80NSSC17K0561. J. M. L. was supported by U.S. National Science Foundation grant OCE‐1259388. High‐end computing resources were provided by the NASA Advanced Supercomputing (NAS) Division of the Ames Research Center. The authors acknowledge ideas and advice from the participants in the Satellites to the Seafloor workshop organized by the W. M. Keck Institute for Space Studies. \n\nData Availability Statement: ECCO‐Darwin model fields are available at the website (https://data.nas.nasa.gov/ecco). Platform‐independent instructions for running ECCO‐Darwin simulations are available at the website (https://zenodo.org/badge/doi/10.5281/zenodo.3829965.svg). Copyright 2020 California Institute of Technology. U.S. Government sponsorship acknowledged. All rights reserved.", revision_no = "38", abstract = "Quantifying variability in the ocean carbon sink remains problematic due to sparse observations and spatiotemporal variability in surface ocean pCO₂. To address this challenge, we have updated and improved ECCO‐Darwin, a global ocean biogeochemistry model that assimilates both physical and biogeochemical observations. The model consists of an adjoint‐based ocean circulation estimate from the Estimating the Circulation and Climate of the Ocean (ECCO) consortium and an ecosystem model developed by the Massachusetts Institute of Technology Darwin Project. In addition to the data‐constrained ECCO physics, a Green's function approach is used to optimize the biogeochemistry by adjusting initial conditions and six biogeochemical parameters. Over seasonal to multidecadal timescales (1995–2017), ECCO‐Darwin exhibits broad‐scale consistency with observed surface ocean pCO₂ and air‐sea CO₂ flux reconstructions in most biomes, particularly in the subtropical and equatorial regions. The largest differences between CO₂ uptake occur in subpolar seasonally stratified biomes, where ECCO‐Darwin results in stronger winter uptake. Compared to the Global Carbon Project OBMs, ECCO‐Darwin has a time‐mean global ocean CO₂ sink (2.47 ± 0.50 Pg C year⁻¹) and interannual variability that are more consistent with interpolation‐based products. Compared to interpolation‐based methods, ECCO‐Darwin is less sensitive to sparse and irregularly sampled observations. Thus, ECCO‐Darwin provides a basis for identifying and predicting the consequences of natural and anthropogenic perturbations to the ocean carbon cycle, as well as the climate‐related sensitivity of marine ecosystems. Our study further highlights the importance of physically consistent, property‐conserving reconstructions, as are provided by ECCO, for ocean biogeochemistry studies.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105327, title ="Variability in Sulfur Isotope Records of Phanerozoic Seawater Sulfate", author = "Present, Theodore M. and Adkins, Jess F.", journal = "Geophysical Research Letters", volume = "47", number = "18", pages = "Art. No. e2020GL088766", month = "September", year = "2020", doi = "10.1029/2020gl088766", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200911-133129558", note = "© 2020 American Geophysical Union. \n\nIssue Online: 17 September 2020; Version of Record online: 17 September 2020; Accepted manuscript online: 02 September 2020; Manuscript accepted: 29 August 2020; Manuscript revised: 27 August 2020; Manuscript received: 14 May 2020. \n\nWe thank Caltech DocuServe for obtaining many of the publications containing the compiled data, and John Grotzinger and Joe Kirschvink for thoughtful advising and feedback. Constructive reviews by Akshay Mehra and Julia Wilcots were greatly appreciated. \n\nData Availability Statement: No new data were collected for this study. Data sets compiled for this research are tabulated in the supporting information and referenced below, and the compiled data are deposited in a freely accessible Open Science Framework repository available in Present et al. (2020).", revision_no = "30", abstract = "The δ³⁴S of seawater sulfate reflects processes operating at the nexus of sulfur, carbon, and oxygen cycles. However, knowledge of past seawater sulfate δ³⁴S values must be derived from proxy materials that are impacted differently by depositional and postdepositional processes. We produced new time series estimates for the δ³⁴S value of seawater sulfate by combining 6,710 published data from three sedimentary archives—marine barite, evaporites, and carbonate‐associated sulfate—with updated age constraints on the deposits. Robust features in multiple records capture temporal trends in the δ³⁴S value of seawater and its interplay with other Phanerozoic geochemical and stratigraphic trends. However, high‐frequency discordances indicate that each record is differentially prone to depositional biases and diagenetic overprints. The amount of noise, quantified from the variograms of each record, increases with age for all δ³⁴S proxies, indicating that postdepositional processes obscure detailed knowledge of seawater sulfate's δ³⁴S value deeper in time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104374, title ="Brachiopod δ³⁴S_(CAS) microanalyses indicate a dynamic, climate-influenced Permo-Carboniferous sulfur cycle", author = "Johnson, Daniel L. and Grossman, Ethan L.", journal = "Earth and Planetary Science Letters", volume = "546", pages = "Art. No. 116428", month = "September", year = "2020", doi = "10.1016/j.epsl.2020.116428", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200714-093504749", note = "© 2020 Elsevier B.V. \n\nReceived 6 December 2019, Revised 17 June 2020, Accepted 18 June 2020, Available online 7 July 2020. \n\nTed Present, Guillaume Paris, Jared Marske, Nathan Dalleska, Sharon Bone, and Courtney Roach provided valuable analytical support. We also thank the editor and two anonymous reviewers for thoughtful suggestions that substantially improved this manuscript. This work was supported by National Science Foundation (NSF) grants OCE-1559215, OCE-1737404, OCE-1450528, and MGG-1834492; NASA prime grant NNN12AA01C; Change Happens Foundation; and Grantham Foundation awards to JFA. DLJ additionally thanks the NSF for support through a Graduate Research Fellowship. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "10", abstract = "Early isotopic studies of sulfate in carbonate minerals (carbonate associated sulfate; CAS) suggested that carbonates can provide a reliable, well-dated archive of the marine sulfur cycle through time. However, subsequent research has shown that diagenetic alteration can impose highly heterogeneous CAS sulfur isotopic compositions (δ³⁴S_(CAS)) among different carbonate phases within sediments. Such alteration necessitates targeted sampling of well-preserved, primary carbonate phases. Here, we present a new record of Carboniferous and Early Permian brachiopod δ³⁴S_(CAS) generated from over 130 measurements of microsampled brachiopod shells. Our record refines existing brachiopod δ³⁴S_(CAS) records and confirms a large, ∼6.5‰ δ³⁴S_(CAS) decrease in the Early Carboniferous. Importantly, the record also features a novel 3–5‰ increase in δ³⁴S_(CAS) near the Serpukhovian-Bashkirian boundary (323.4 Ma) that coincides with carbonate δ¹³C and δ¹⁸O increases. Variability in δ³⁴S_(CAS) is minor both within (≤0.3‰) and among (≤2‰) individual co-depositional brachiopod specimens. A taxon-specific δ³⁴S_(CAS) offset is present one species (Composita subtilita) that also exhibits a δ¹³C offset, supporting the existence of biological “vital effects” on δ³⁴S_(CAS). Geologic evidence and mathematical modeling of the Permo-Carboniferous carbon and sulfur cycles suggest that changes in the burial ratio of organic carbon to pyrite sulfur (RC:S) are insufficient to explain the observed mid-Carboniferous δ³⁴S_(CAS) record. We find that changes in the ³⁴S depletion of pyrite relative to seawater sulfate (ε³⁴) or in the δ³⁴S of the input to the ocean (δ³⁴S_(in)) are also needed. Large additions of O₂ from organic carbon burial during the Permo-Carboniferous cannot be entirely compensated for with sulfur cycle changes; lower than modern late Visean pO₂ and/or additional O₂ sinks are needed to keep pO₂ at plausible levels. Based on the geologic context surrounding our record's mid-Carboniferous δ³⁴S_(CAS) increase, we advocate for simultaneous changes in pyrite burial, ε³⁴, and δ³⁴S_(in), driven by sea level or tectonically induced changes in environments of sulfur burial, as a viable mechanism to produce rapid seawater δ³⁴S changes.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104232, title ="Deposition of sulfate aerosols with positive Δ³³S in the Neoarchean", author = "Paris, Guillaume and Fischer, Woodward W.", journal = "Geochimica et Cosmochimica Acta", volume = "285", pages = "1-20", month = "September", year = "2020", doi = "10.1016/j.gca.2020.06.028", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200706-145806917", note = "© 2020 Published by Elsevier Ltd. \n\nReceived 21 February 2020, Revised 23 June 2020, Accepted 24 June 2020, Available online 3 July 2020. \n\nWe thank Dr. LaFlamme, Dr. Marin-Carbonne and one anonymous reviewer for their helpful reviews and Prof. Ono for handling the editorial process. Altogether, they helped us improve this article. We thank Prof. Beukes for his help in accessing the cores and for feedback on the geological context. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Financial support was received from the NSF (grant EAR-1349858 attributed to WWF and JFA). WWF acknowledges support from the Simons Foundation Collaboration on the Origins of Life. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "19", abstract = "Anomalous sulfur isotope compositions present in Archean rocks have been intensely scrutinized over the last 20\u202fyears because they record key aspects of Earth's atmospheric composition prior to the appearance of free molecular oxygen ca. 2.3 billion years ago. These isotopic compositions can be described as mass anomalous fractionations (MAF) and are produced in the atmosphere as UV light interacts with SO₂ molecules. Most interpretations suggest that atmospheric processes generate a reduced S-phase with a positive (³³S-enriched) MAF signature, as measured in pyrites, and an oxidized S-phase with a negative anomaly, as measured in bedded barite deposits. However, recent data for carbonate-associated sulfate (CAS) — a direct proxy for the isotopic composition of sulfur from seawater sulfate — in Neoarchean rocks showed no such negative values, but rather the opposite. To understand if the positive MAF anomalies we measured in Neoarchean CAS reflect secondary processes (diagenetic, metamorphic, handling) instead of original signals of Archean seawater sulfate, we collected additional sample suites with various degrees of preservation and metamorphic alteration across the Campbellrand-Malmani platform in South Africa. Results illustrate that within this comprehensive suite, less-altered samples all contain positive MAF values while secondary processes tend to either remove CAS from the sample and/or decrease the ³³S-enrichment. This positive MAF signal in sulfate is therefore reasonably interpreted as a primary depositional origin, and implies that the assumption that sulfate always carries a negative MAF anomaly throughout the Archean rock record needs to be reconsidered. Our CAS observations suggest that future experiments and calculations should also consider atmospheric and/or sulfur cycling processes that can produce oxidized sulfur with a positive MAF signature.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/103781, title ="An Atomic Force Microscopy Study of Calcite Dissolution in Seawater", author = "Dong, Sijia and Berelson, William M.", journal = "Geochimica et Cosmochimica Acta", volume = "283", pages = "40-53", month = "August", year = "2020", doi = "10.1016/j.gca.2020.05.031", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200609-071637828", note = "© 2020 Elsevier Ltd. \n\nReceived 8 November 2019, Revised 27 May 2020, Accepted 28 May 2020, Available online 6 June 2020. \n\nThis work was supported by NSF Ocean Acidification grants (numbers OCE1220600 and OCE1220302), USC Dornsife Doctoral Fellowship, and Grantham Foundation at Caltech. The authors would like to thank four anonymous journal reviewers, as well as the associate editor Dr. Oleg Pokrovsky, for their insightful comments and suggestions that helped to improve this manuscript. We thank Mina Hong, Zibo Li and Liang Zhao for helpful discussions on AFM operations. We also thank Josh West for his suggestions on the manuscript. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "20", abstract = "We present the first examination of calcite dissolution in seawater using Atomic Force Microscopy (AFM). We quantify step retreat velocity and etch pit density to compare dissolution in seawater to low ionic strength water, and also to compare calcite dissolution under AFM conditions to those conducted in bulk solution experiments (e.g. Subhas et al., 2015, Dong et al., 2018). Bulk dissolution rates and step retreat velocities are slower at high and mid-saturation state (Ω) values and become comparable to low ionic strength water rates at low Ω. The onset of defect-assisted etch pit formation in seawater is at Ω\u202f∼\u202f0.85 (defined as Ω_(critical)), higher than in low ionic strength water (Ω\u202f∼\u202f0.54). There is an abrupt increase in etch pit density (from ∼10⁶ cm⁻² to ∼10⁸ cm⁻²) occurring when Ω falls below 0.7 in seawater, compared to Ω\u202f∼\u202f0.1 in low ionic strength water, suggesting a transition from defect-assisted dissolution to homogeneous dissolution much closer to equilibrium in seawater. The step retreat velocity (v) does not scale linearly with undersaturation (1-Ω) across an Ω range of 0.4 to 0.9 in seawater, potentially indicating a high order correlation between kink rate and Ω for non-Kossel crystals such as calcite, or surface complexation processes during calcite dissolution in seawater.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106974, title ="Marine20—The Marine Radiocarbon Age Calibration Curve (0–55,000 cal BP)", author = "Heaton, Timothy J. and Köhler, Peter", journal = "Radiocarbon", volume = "62", number = "4", pages = "779-820", month = "August", year = "2020", doi = "10.1017/rdc.2020.68", issn = "0033-8222", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201209-105155334", note = "© 2020 by the Arizona Board of Regents on behalf of the University of Arizona. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. \n\nPublished online by Cambridge University Press: 12 August 2020. \n\nWe would like to thank Jeremy Oakley and Richard Bintanja for informative discussions during the development of this work. T.J. Heaton is supported by a Leverhulme Trust Fellowship RF-2019-140\\9, “Improving the Measurement of Time Using Radiocarbon”. M Butzin is supported by the German Federal Ministry of Education and Research (BMBF), as Research for Sustainability initiative (FONA); www.fona.de through the PalMod project (grant numbers: 01LP1505B, 01LP1919A). E. Bard is supported by EQUIPEX ASTER-CEREGE and ANR CARBOTRYDH. Meetings of the IntCal Marine Focus group have been supported by Collège de France. Data are available on the PANGAEA database at doi:10.1594/PANGAEA.914500. \n\nAuthor Contributions: TJH led this study and performed the Bayesian modeling. The general setup of Marine20 has been designed through discussions of the IntCal Marine Focus group led by EB. PK provided simulation results using the BICYCLE model, MB simulation results from the LSG OGCM. The manuscript has been written by TJH with large contributions from PK. RWR performed initial modeling tests incorporating pCO₂ data and recalculated ΔR values in the marine reservoir correction database with Marine20. All other co-authors provided expert knowledge and contributions to both discussions and the writing of the manuscript.", revision_no = "12", abstract = "The concentration of radiocarbon (¹⁴C) differs between ocean and atmosphere. Radiocarbon determinations from samples which obtained their ¹⁴C in the marine environment therefore need a marine-specific calibration curve and cannot be calibrated directly against the atmospheric-based IntCal20 curve. This paper presents Marine20, an update to the internationally agreed marine radiocarbon age calibration curve that provides a non-polar global-average marine record of radiocarbon from 0–55 cal kBP and serves as a baseline for regional oceanic variation. Marine20 is intended for calibration of marine radiocarbon samples from non-polar regions; it is not suitable for calibration in polar regions where variability in sea ice extent, ocean upwelling and air-sea gas exchange may have caused larger changes to concentrations of marine radiocarbon. The Marine20 curve is based upon 500 simulations with an ocean/atmosphere/biosphere box-model of the global carbon cycle that has been forced by posterior realizations of our Northern Hemispheric atmospheric IntCal20 ¹⁴C curve and reconstructed changes in CO₂ obtained from ice core data. These forcings enable us to incorporate carbon cycle dynamics and temporal changes in the atmospheric ¹⁴C level. The box-model simulations of the global-average marine radiocarbon reservoir age are similar to those of a more complex three-dimensional ocean general circulation model. However, simplicity and speed of the box model allow us to use a Monte Carlo approach to rigorously propagate the uncertainty in both the historic concentration of atmospheric ¹⁴C and other key parameters of the carbon cycle through to our final Marine20 calibration curve. This robust propagation of uncertainty is fundamental to providing reliable precision for the radiocarbon age calibration of marine based samples. We make a first step towards deconvolving the contributions of different processes to the total uncertainty; discuss the main differences of Marine20 from the previous age calibration curve Marine13; and identify the limitations of our approach together with key areas for further work. The updated values for ΔR, the regional marine radiocarbon reservoir age corrections required to calibrate against Marine20, can be found at the data base http://calib.org/marine/.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/102077, title ="Sulfur isotope fractionation between aqueous and carbonate-associated sulfate in abiotic calcite and aragonite", author = "Barkan, Yigal and Paris, Guillaume", journal = "Geochimica et Cosmochimica Acta", volume = "280", pages = "317-339", month = "July", year = "2020", doi = "10.1016/j.gca.2020.03.022", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200324-101330481", note = "© 2020 Published by Elsevier Ltd. \n\nReceived 25 July 2019, Accepted 16 March 2020, Available online 24 March 2020. \n\nWe thank Ziv Sade and Nir Galili for discussions. I.H. acknowledges support from a European Research Council Starting Grant (No. 337183). Part of this work was supported by the Tellus program from CNRS/INSU. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.", revision_no = "17", abstract = "Sulfate (SO₄²⁻) incorporated into calcium carbonate minerals enables measurements of sulfur (S) isotope ratios in carbonate rocks. This Carbonate Associated Sulfate (CAS) in marine carbonate minerals is thought to faithfully represent the S isotope composition of the seawater sulfate incorporated into the mineral, with little or no S isotope fractionation in the process. However, comparison between different calcifying species reveals both positive and negative S isotope fractionation between CAS and seawater sulfate, and a large range of S isotope ratios can be found within a single rock sample, depending on the component measured. To better understand the isotopic effects associated with sulfate incorporation into carbonate minerals, we precipitated inorganic calcite and aragonite over a range covering more than two orders of magnitude of sulfate concentration and precipitation rate. Coupled measurements of CAS concentration, S isotope composition and X-ray absorption near-edge spectra (XANES) permit characterization and explanation of the observed dependence of S isotope fractionation between CAS and aqueous sulfate (CAS-SO₄²⁻ isotope fractionation) on sulfate concentration and precipitation rate. In aragonite, the CAS-SO₄²⁻ isotope fractionation is 1.0±0.3‰ and independent of the sulfate (and CAS) concentration. In contrast, the CAS-SO₄²⁻ isotope fractionation in calcite covaries strongly with the sulfate concentration and weakly with the precipitation rate, between values of 1.3±0.1 and 3.1±0.6‰. We suggest that the correlation between aqueous sulfate concentration and CAS-SO₄²⁻– isotope fractionation in calcite reflects a dependence of the equilibrium S isotope fractionation on the concentration of CAS, through the effect of the sulfate impurity on the carbonate mineral’s energetic state.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99432, title ="The carbonic anhydrase activity of sinking and suspended particles in the North Pacific Ocean", author = "Subhas, Adam V. and Adkins, Jess F.", journal = "Limnology and Oceanography", volume = "65", number = "3", pages = "637-651", month = "March", year = "2020", doi = "10.1002/lno.11332", issn = "0024-3590", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191024-091357425", note = "© 2019 Association for the Sciences of Limnology and Oceanography. \n\nIssue Online: 05 March 2020; Version of Record online: 11 October 2019; Manuscript accepted: 22 August 2019; Manuscript revised:\n02 May 2019; Manuscript received: 12 December 2018. \n\nWe thank the entire science party and the R/V Kilo Moana crew on the CDisK‐IV cruise. In particular, we thank Doug Hammond and Alex Sessions for providing the in situ pumps, Nathan Kemnitz, Yi Hou, and Abby Lunstrum for help in working up pump filter and multicore samples, and Will Gray for helping to pick pteropod samples. We greatly thank Brian Hopkinson and two anonymous reviewers for their helpful and insightful comments and suggestions throughout the review process. This manuscript was significantly improved thanks to their efforts. We also acknowledge funding sources from NSF (OCE1220600 and OCE1220302), and the Resnick Sustainability Institute Graduate Fellowship for A.V.S. \n\nConflict of Interest: None declared.", revision_no = "19", abstract = "The enzyme carbonic anhydrase (CA) is crucial to many physiological processes involving CO₂, from photosynthesis and respiration, to calcification and CaCO₃ dissolution. We present new measurements of CA activity along a North Pacific transect, on samples from in situ pumps, sediment traps, discreet plankton samples from the ship's underway seawater line, plankton tows, and surface sediment samples from multicores. CA activity is highest in the surface ocean and decreases with depth, both in suspended and sinking particles. Subpolar gyre surface particles exhibit 10× higher CA activity per liter of seawater compared to subtropical gyre surface particles. Activity persists to 4700\u2009m in the subpolar gyre, but only to 1000\u2009m in the subtropics. All sinking CA activity normalized to particulate organic carbon (POC) follows a single relationship (CA/POC = 1.9\u2009±\u20090.2\u2009×\u200910⁻⁷ mol\u2009mol⁻¹). This relationship is consistent with CA/POC values in subpolar plankton tow material, suspended particles, and core top sediments. We hypothesize that most subpolar CA activity is associated with rapidly sinking diatom blooms, consistent with a large mat of diatomaceous material identified on the seafloor. Compared to the basin‐wide sinking CA/POC relationship, a lower subtropical CA/POC suggests that the inventory of subtropical biomass is different in composition from exported material. Pteropods also demonstrate substantial CA activity. Scaled to the volume within pteropod shells, first‐order CO₂ hydration rate constants are elevated ≥\u20091000× above background. This kinetic enhancement is large enough to catalyze carbonate dissolution within microenvironments, providing observational evidence for CA‐catalyzed, respiration‐driven CaCO₃ dissolution in the shallow North Pacific.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/101096, title ="Stable Isotope Analysis of Intact Oxyanions Using Electrospray Quadrupole-Orbitrap Mass Spectrometry", author = "Neubauer, Cajetan and Crémière, Antoine", journal = "Analytical Chemistry", volume = "92", number = "4", pages = "3077-3085", month = "February", year = "2020", doi = "10.1021/acs.analchem.9b04486", issn = "0003-2700", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200204-073456000", note = "© 2020 American Chemical Society. \n\nReceived: October 1, 2019; Accepted: January 21, 2020; Published: February 3, 2020. \n\nWe thank the reviewers for comments. We are grateful for assistance provided by Roxana Eggleston-Rangel and Brett Lomenick, and thank George Rossmann as well as the companies Peñoles, Crimidesa, Saltex, Airborne Industrial Minerals, and Searles Valley Minerals for providing sulfates. This study was using ESMS instrumentation at the Proteome Exploration Laboratory (supported by Beckman Institute, and NIH 1S10OD02001301). C.N. is a fellow of the Hanse-Wissenschaftskolleg. \n\nThe authors declare no competing financial interest.", revision_no = "20", abstract = "The stable isotopes of sulfate, nitrate, and phosphate are frequently used to study geobiological processes of the atmosphere, ocean, as well as land. Conventionally, the isotopes of these and other oxyanions are measured by isotope-ratio sector mass spectrometers after conversion into gases. Such methods are prone to various limitations on sensitivity, sample throughput, or precision. In addition, there is no general tool that can analyze several oxyanions or all the chemical elements they contain. Here, we describe a new approach that can potentially overcome some of these limitations based on electrospray hyphenated with Quadrupole Orbitrap mass spectrometry. This technique yields an average accuracy of 1–2‰ for sulfate δ³⁴S and δ¹⁸O and nitrate δ¹⁵N and δ¹⁸O, based on in-house and international standards. Less abundant variants such as δ¹⁷O, δ³³S, and δ³⁶S, and the ³⁴S–¹⁸O “clumped” sulfate can be quantified simultaneously. The observed precision of isotope ratios is limited by the number of ions counted. The counting of rare ions can be accelerated by removing abundant ions with the quadrupole mass filter. Electrospray mass spectrometry (ESMS) exhibits high-throughput and sufficient sensitivity. For example, less than 1 nmol sulfate is required to determine ¹⁸O/³⁴S ratios with 0.2‰ precision within minutes. A purification step is recommended for environmental samples as our proposed technique is susceptible to matrix effects. Building upon these initial provisions, new features of the isotopic anatomy of mineral ions can now be explored with ESMS instruments that are increasingly available to bioanalytical laboratories.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94594, title ="Diagenetic controls on the isotopic composition of carbonate‐associated sulphate in the Permian Capitan Reef Complex, West Texas", author = "Present, Theodore M. and Gutierrez, Melissa", journal = "Sedimentology", volume = "66", number = "7", pages = "2605-2626", month = "December", year = "2019", doi = "10.1111/sed.12615", issn = "0037-0746", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190409-130651684", note = "© 2019 The Authors. Sedimentology © 2019 International Association of Sedimentologists. \n\nIssue Online: 19 November 2019; Version of Record online: 01 July 2019; Accepted manuscript online: 05 April 2019; Manuscript accepted: 03 April 2019; Manuscript received: 27 November 2018. \n\nFunding Information: the American Chemical Society Petroleum Research Fund New Directions. Grant Number: 53994‐ND2; Society for Sedimentary Geology (SEPM) Student Research Grant.", revision_no = "17", abstract = "Late Palaeozoic‐age strata from the Capitan Reef in west Texas show facies‐dependent heterogeneity in the sulphur isotopic composition of carbonate‐associated sulphate, which is trace sulphate incorporated into carbonate minerals that is often used to reconstruct the sulphur isotopic composition of ancient seawater. However, diagenetic pore fluid processes may influence the sulphur isotopic composition of carbonate‐associated sulphate. These processes variously modify the sulphur isotopic composition of incorporated sulphate from syndepositional seawater in shelf crest, outer shelf, shelf margin and slope depositional settings. This study used a new multicollector inductively‐coupled plasma mass spectrometry technique to determine the sulphur isotopic composition of samples of individual depositional and diagenetic textures. Carbonate rocks representing peritidal facies in the Yates and Tansill formations preserve the sulphur isotopic composition of Guadalupian seawater sulphate despite alteration of the carbon and oxygen isotopic compositions by meteoric and dolomitizing diagenetic processes. However, sulphur isotopic data indicate that limestones deposited in reef and slope facies in the Capitan and Bell Canyon formations largely incorporate sulphate from anoxic marine‐phreatic pore fluids isotopically modified from seawater by microbial sulphate reduction, despite generally preserving the carbon and oxygen isotopic compositions of Permian seawater. Some early and all late meteoric calcite cements have carbonate‐associated sulphate with sulphur isotopic compositions distinct from that of Permian seawater. Detailed petrographic and sedimentary context for carbonate‐associated sulphate analyses will allow for improved reconstructions of ancient seawater composition and diagenetic conditions in ancient carbonate platforms. The results of this study indicate that carbonate rocks that diagenetically stabilize in high‐energy environments without pore fluid sulphate gradients can provide a robust archive of ancient seawater's sulphur isotopic composition.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96927, title ="Calcite dissolution rates in seawater: Lab vs. in-situ measurements and inhibition by organic matter", author = "Naviaux, John D. and Subhas, Adam V.", journal = "Marine Chemistry", volume = "215", pages = "Art. No. 103684", month = "September", year = "2019", doi = "10.1016/j.marchem.2019.103684", issn = "0304-4203", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190708-154640644", note = "© 2019 Elsevier B.V. \n\nReceived 20 March 2019, Revised 15 June 2019, Accepted 4 July 2019, Available online 5 July 2019.", revision_no = "11", abstract = "Ocean acidification from fossil fuel burning is lowering the mean global ocean saturation state (Ω = [Ca^(2+)][CO_3^(2−)]/K_(sp)′), thus increasing the thermodynamic driving force for calcium carbonate minerals to dissolve. This dissolution process will eventually neutralize the input of anthropogenic CO_2, but the relationship between Ω and calcite dissolution rates in seawater is still debated. Recent advances have also revealed that spectrophotometric measurements of seawater pHs, and therefore in-situ Ωs, are systematically lower than pHs/Ωs calculated from measurements of alkalinity (Alk) and total dissolved inorganic carbon (DIC). The calcite saturation horizon, defined as the depth in the water column where Ω\u202f=\u202f1, therefore shifts by ~5–10% depending on the parameters used to calculate Ω. The “true” saturation horizon remains unknown. To resolve these issues, we developed a new in-situreactor and measured dissolution rates of ^(13)C-labeled inorganic calcite at four stations across a transect of the North Pacific Ocean. In-situ saturation was calculated using both Alk-DIC (Ω_((Alk, DIC))) and Alk-pH (Ω_((Alk, pH))) pairs. We compare in-situ dissolution rates with rates measured in filtered, poisoned, UV-treated seawater at 5 and 21\u202f°C under laboratory conditions. We observe in-situ dissolution above Ω_((Alk, DIC))\u202f=\u202f1, but not above Ω_((Alk, pH))\u202f=\u202f1. We emphasize that marine carbonate system equilibria should be reevaluated and that care should be taken when using proxies calibrated to historical Ω_((Alk, DIC)). Our results further demonstrate that calcite dissolution rates are slower in-situ than in the lab by a factor of ~4, but that they each possess similar reaction orders (n) when fit to the empirical Rate\u202f=\u202fk(1-Ω)^n equation. The reaction orders are n\u202f<\u202f1 for 0.8\u202f<\u202fΩ\u202f<\u202f1 and n\u202f=\u202f4.7 for 0\u202f<\u202fΩ\u202f<\u202f0.8, with the kink in rates at Ω_(crit)\u202f=\u202f0.8 being consistent with a mechanistic transition from step edge retreat to homogenous etch pit formation. We reconcile the offset between lab and in-situ rates by dissolving calcite in the presence of elevated orthophosphate (20\u202fμm) and dissolved organic carbon (DOC) concentrations, where DOC is in the form of oxalic acid (20\u202fμm), gallic acid (20\u202fμm), and D-glucose (100\u202fμm). We find that soluble reactive phosphate has no effect on calcite dissolution rates from pH\u202f5.5–7.5, but the addition of DOC in the form of D-glucose and oxalic acid slows laboratory dissolution rates to match in-situ observations, potentially by inhibiting the retreat rate of steps on the calcite surface. Our lab and in-situ rate data form an envelope around previous in-situ dissolution measurements and may be considered outer bounds for dissolution rates in low/high DOC waters. The lower bound (high DOC) is most realistic for particles formed in, and sinking out of, surface waters, and is described by R_((mol cm-2 s-1))\u202f=\u202f10^(–14.3±0.2)(1-Ω)^(0.11±0.1) for 0.8\u202f<\u202fΩ\u202f<\u202f1, and R_((mol cm-2 s-1))\u202f=\u202f10^(–10.8±0.4)(1-Ω)^(4.7±0.7) for 0\u202f<\u202fΩ\u202f<\u202f0.8. These rate equations are derived from in-situ measurements and may be readily implemented into marine geochemical models to describe water column calcite dissolution.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96625, title ="Stratospheric eruptions from tropical and extra-tropical volcanoes constrained using high-resolution sulfur isotopes in ice cores", author = "Burke, Andrea and Moore, Kathryn A.", journal = "Earth and Planetary Science Letters", volume = "521", pages = "113-119", month = "September", year = "2019", doi = "10.1016/j.epsl.2019.06.006", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190621-110910481", note = "© 2019 Elsevier B.V. \n\nReceived 20 February 2019, Revised 4 June 2019, Accepted 5 June 2019, Available online 20 June 2019. \n\nThis research was funded by a Foster and Coco Stanback postdoctoral fellowship and a Marie Curie Career Integration Grant (CIG14-631752) to AB and a NSF-OCE grant 1340174 and NSF-EAR grant 1349858 to JFA. MS acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 820047). NSF-PLR grant 1204176 to JRM supported collection and analysis of the Tunu2013 core. We thank Sepp Kipfstuhl of the Alfred Wegener Institut for providing the B40 core. We thank Joel Savarino, an anonymous reviewer, and James Rae for comments on this manuscript.", revision_no = "11", abstract = "The record of volcanic forcing of climate over the past 2500 years is based primarily on sulfate concentrations in ice cores. Of particular interest are large volcanic eruptions with plumes that reached high altitudes in the stratosphere, as these afford sulfate aerosols the longest residence time in the atmosphere, and thus have the greatest impact on radiative forcing. Sulfur isotopes measured in ice cores can be used to identify these large eruptions because stratospheric sulfur is exposed to UV radiation, which imparts a time-evolving mass independent fractionation (MIF) that is preserved in the ice. However, sample size requirements of traditional measurement techniques mean that the MIF signal may be obscured, leading to an inconclusive result. Here we present a new method of measuring sulfur isotopes in ice cores by multi-collector inductively coupled plasma mass spectrometry, which reduces sample size requirements by three orders of magnitude. Our method allows us to measure samples containing as little as 10 nmol of sulfur, with a precision of 0.11‰ for δ^(34)S and 0.10‰ for Δ^(33)S, enabling a high-temporal resolution over ice core sulfate peaks. We tested this method on known tropical (Tambora 1815 and Samalas 1257) and extra-tropical (Katmai/Novarupta 1912) stratospheric eruptions from the Tunu2013 ice core in Greenland and the B40 ice core from Antarctica. These high-resolution sulfur isotope records suggest a distinct difference between the signatures of tropical versus extra-tropical eruptions. Furthermore, isotope mass balance on sulfate from extra-tropical eruptions provides a means to estimate the fraction of sulfate deposited that was derived from the stratosphere. This technique applied to unidentified eruptions in ice cores may thus improve the record of explosive volcanism and its forcing of climate.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97049, title ="A Southern Ocean Mechanism for the Interhemispheric Coupling and Phasing of the Bipolar Seesaw", author = "Thompson, Andrew F. and Hines, Sophia K.", journal = "Journal of Climate", volume = "32", number = "14", pages = "4347-4365", month = "July", year = "2019", doi = "10.1175/JCLI-D-18-0621.1", issn = "0894-8755", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190711-083803362", note = "© 2019 American Meteorological Society. \n\nManuscript received 20 September 2018, in final form 19 April 2019. \n\nWe thank Raffaele Ferrari and David Marshall for constructive comments to an earlier draft of this study and three anonymous reviewers for their insightful comments. We acknowledge helpful conversations with Paola Cessi, Malte Jansen, Brad Markle, Emily Newsom, Andrew Stewart, and Laure Zanna. We also thank Feng He for providing the TraCE simulation output. AFT received support from the David and Lucille Packard Foundation and from National Science Foundation (NSF) Grant OCE-1235488; SKH received support from NSF Grant P2C2-1503129 and the Lamont-Doherty Earth Observatory Postdoctoral Fellowship.", revision_no = "8", abstract = "The last glacial period is punctuated by abrupt changes in Northern Hemisphere temperatures that are known as Dansgaard–Oeschger (DO) events. A striking and largely unexplained feature of DO events is an interhemispheric asymmetry characterized by cooling in Antarctica during periods of warming in Greenland and vice versa—the bipolar seesaw. Methane-synchronized ice core records indicate that the Southern Hemisphere lags the Northern Hemisphere by approximately 200 years. Here, we propose a mechanism that produces observed features of both the bipolar seesaw and the phasing of DO events. The spatial pattern of sea ice formation and melt in the Southern Ocean imposes a rigid constraint on where water masses are modified: waters are made denser near the coast where ice forms and waters are made lighter farther north where ice melts. This pattern, coupled to the tilt of density surfaces across the Southern Ocean and the stratification of the ocean basins, produces two modes of overturning corresponding to different bipolar seesaw states. We present evolution equations for a simplified ocean model that describes the transient adjustment of the basin stratification, the Southern Ocean surface density distribution, and the overturning strength as the ocean moves between these states in response to perturbations in North Atlantic Deep Water formation, which we take as a proxy for Greenland temperatures. Transitions between different overturning states occur over a multicentennial time scale, which is qualitatively consistent with the observed Southern Hemisphere lag. The volume of deep density layers varies inversely with the overturning strength, leading to significant changes in residence times. Evidence of these dynamics in more realistic circulation models is discussed.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/95957, title ="Dynamic intermediate waters across the late glacial revealed by paired radiocarbon and clumped isotope temperature records", author = "Hines, Sophia K. V. and Eiler, John M.", journal = "Paleoceanography and Paleoclimatology", volume = "34", number = "7", pages = "1074-1091", month = "July", year = "2019", doi = "10.1029/2019pa003568", issn = "2572-4517", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190530-102320622", note = "© 2019 American Geophysical Union. \n\nReceived 18 JAN 2019; Accepted 24 MAY 2019; Accepted article online 29MAY 2019; Published online 10 JUL 2019. \n\nWe would like to thank Andrew Thompson, Nivedita Thiagarajan, and Julia Gottschalk for helpful discussions. We also acknowledge constructive comments from two anonymous reviewers. S. K. V. H. received support from NSF Grants OCE‐1503129 and OCE‐1204211 and the Lamont‐Doherty Earth Observatory Postdoctoral Fellowship. All data are available in the supplemental tables and will be archived on the NOAA National Centers for Environmental Information.", revision_no = "35", abstract = "Paired radiocarbon and clumped isotope temperature records from U/Th‐dated Desmophyllum dianthus corals in the North Atlantic and Southern Ocean provide unique information about the history of intermediate waters (∼1,500–1,700 m) across the late glacial and deglaciation (∼35–10 ka). These measurements allow for the construction of radiocarbon‐temperature crossplots, which help to identify water mass endmembers at different times across the deglaciation. Radiocarbon and temperature values from the late glacial fall outside the range of modern ocean data from near the sample collection sites. In the North Atlantic, radiocarbon values tend to be much older than the modern, while in the Southern Ocean, they are more often younger than the modern. Reconstructed temperatures vary around respective modern ocean values; however, warm waters are observed at the Last Glacial Maximum and across the deglaciation in the north and south. We interpret our data in the context of the modern hydrography of the Western North Atlantic and Southern Ocean, and we draw upon direct comparisons between sediment core‐derived reconstructions of ocean circulation from the South Indo‐Pacific and our deep‐sea coral data from the Southern Ocean. Our North Atlantic data support accepted patterns of reduced North Atlantic Deep Water formation during Heinrich Stadials 1 and 2. In the Southern Ocean, deep‐sea coral populations respond to changes in ocean structure that are also reflected in a depth profile of δ^(13)C data from New Zealand, and data indicate that there was less influence of Pacific Deep Water between 1,500 and 1,700 m south of Tasmania across much of the deglaciation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94070, title ="Aragonite dissolution kinetics and calcite/aragonite ratios in sinking and suspended particles in the North Pacific", author = "Dong, Sijia and Berelson, William M.", journal = "Earth and Planetary Science Letters", volume = "515", pages = "1-12", month = "June", year = "2019", doi = "10.1016/j.epsl.2019.03.016", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190322-142418170", note = "© 2019 Elsevier B.V. \n\nReceived 8 November 2018, Revised 8 March 2019, Accepted 10 March 2019, Available online 22 March 2019. \n\nThis work was supported by NSF Ocean Acidification grants (numbers OCE1220600 and OCE1220302), USC Dornsife Doctoral Fellowship, Elizabeth and Jerol Sonosky Fellowship, the Sea Grant Fellowship, and the Resnick Sustainability Institute Graduate Fellowship. The authors would like to acknowledge editor Derek Vance, reviewer Jack Middelburg and another anonymous reviewer for their invaluable comments of the original manuscript. We thank the captain and crews on Kilo Moana for their assistance at sea. We also acknowledge Christopher Moore, Loraine Martell-Bonet for their help measuring pH and alkalinity during CDisK-IV; Yi Hou for leak-checking the Niskin Incubators by measuring dissolved Si concentrations; Doug Hammond for providing the in situ pumps; Johnny Stutsman and James Rae for their help deploying and recovering in situ pumps; as well as Abby Lunstrum and Huanting Hu for their help picking out swimmers from the sediment trap samples.", revision_no = "16", abstract = "The lack of consensus on CaCO_3 dissolution rates and calcite to aragonite production and export ratios in the ocean poses a significant barrier for the construction of global carbon budgets. We present here a comparison of aragonite dissolution rates measured in the lab vs. in situ along a transect between Hawaii and Alaska using a ^(13)C labeling technique. Our results show a general agreement of aragonite dissolution rates in the lab versus in the field, and demonstrate that aragonite, like calcite, shows a non-linear response of dissolution rate as a function of saturation state (Ω). Total carbon fluxes along the N. Pacific transect in August 2017, as determined using sediment traps, account for 11∼23 weight % of total mass fluxes in the upper 200 m, with a PIC (particulate inorganic carbon) /POC (particulate organic carbon) mole ratio of 0.2∼0.6. A comparison of fluxes at depths of 100 m and 200 m indicates that 30∼60% PIC dissolves between these depths with 20∼70% attenuation in POC fluxes. The molar ratio of PIC to POC loss is 0.29. The simultaneous loss of PIC and POC in the upper 200 m potentially indicates PIC dissolution driven by organic matter respiration, or metazoan/zooplankton consumption. The calcite/aragonite ratio in trap material is significantly lower in the subtropical gyre than in the subarctic gyre. Aragonite fluxes vary from 0.07 to 0.38 mmol m^(−2) day^(−1) at 100 m, and 0.06 to 0.24 mmol m^(−2) day^(−1) at 200 m along the North Pacific transect, with no specific trend over latitude. The identification of suspended PIC mineral phases by Raman spectroscopy shows the presence of aragonite below 3000 m in the subtropical gyre, but none in the subpolar gyre. These multiple lines of evidence suggest that predictions based on a strictly thermodynamic view of aragonite dissolution, combined with measured aragonite fluxes, underestimate observed alkalinity excess and measured PIC attenuation in sinking particles. Our measured aragonite flux combined with our inorganic dissolution rate only account for 9% and 0.2% of the excess alkalinity observed in the North Pacific (Feely et al., 2004), assuming aragonite sinking rates of 1 m day^(−1) and 100 m day^(−1), respectively. However, respiration-driven dissolution or metazoan/zooplankton consumption, indicated by the simultaneous attenuation of PIC and POC in sediment traps, is able to generate the magnitude of dissolution suggested by observed excess alkalinity.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94932, title ="Spatial patterns of benthic silica flux in the North Pacific reflect upper ocean production", author = "Hou, Yi and Hammond, Douglas E.", journal = "Deep Sea Research Part 1", volume = "148", pages = "25-33", month = "June", year = "2019", doi = "10.1016/j.dsr.2019.04.013", issn = "0967-0637", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-111734892", note = "© 2019 Elsevier Ltd. \n\nReceived 9 August 2018, Revised 12 April 2019, Accepted 22 April 2019, Available online 24 April 2019.", revision_no = "10", abstract = "Diatoms are the dominant algal group that cycles dissolved silicic acid in the ocean; they also play an important role in the oceanic carbon cycle. It is therefore important to quantify the spatial distribution of silica cycling for defining global ocean biogeochemical cycles. On the research cruise CDisK-IV, water samples and sediment cores were collected at 5 stations along a North Pacific transect near 150ºW from 22ºN to 50ºN to evaluate benthic remineralization rates of biogenic silica (bSi). Two independent methods, core incubation and diffusive transport based on porewater profiles, were utilized to estimate benthic silicic acid fluxes, and these independent methods yield fluxes that agree within uncertainties. The benthic fluxes are reported as 0.04\u202f±\u202f0.01, 0.04\u202f±\u202f0.01, 0.05\u202f±\u202f0.01, 0.67\u202f±\u202f0.14, 0.40\u202f±\u202f0.08\u202fmmol Si m^(−2) day^(−1) for Stations 1 to 5, south to north, respectively. Burial fluxes were estimated using measurements of solid phase bSi in sediments and literature values of sediment accumulation rate. Burial efficiencies of bSi at all stations were <5% and show reasonable agreement with previous estimates. When burial rates were added to benthic fluxes to calculate rain rates, the rain observed under the subarctic gyre (Stations 4–5), was far larger than in the lower latitudes of the subtropics (Stations 1–3), corresponding to higher surface diatom productivity at higher latitudes. At the two northern stations, the bottom 500\u202fm of the water column shows a near-bottom increase in silicic acid that is consistent with the measured benthic flux and the estimated vertical eddy diffusivity. Above this horizon, water column density stratification increases and vertical diffusivity decreases, but the silicic acid gradient decreases. This reduction in gradient indicates that above this horizon, horizontal transport by deep waters, rather than vertical diffusion, becomes the dominant process removing the silicic acid released by benthic remineralization.", } @misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99419, title ="Tidal Heating: Lessons from Io and the Jovian System - Final Report", author = "de Kleer, Katherine and McEwen, Alfred S.", month = "June", year = "2019", doi = "10.26206/d4wc-6v82", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191023-151847724", note = "© June 2019. \n\nWe especially thank Michele Judd and others at the Keck Institute for Space Studies for supporting this effort. This research was in part carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.", revision_no = "14", abstract = "Tidal heating is key to the evolution and habitability of many worlds across our solar system and beyond. However, there remain fundamental gaps in our understanding of tidal heating and coupled orbital evolution, which motivated a Keck Institute for Space Studies (KISS) workshop on this topic. The Cassini mission has led to many recent results about ocean worlds and what may become a new paradigm for understanding orbital evolution with tidal heating, the model of resonance locking in the parent planet (Fuller et al., 2016). Resonance locking explains how subsurface oceans may persist over much of geologic time, even in tiny Enceladus. The discovery\nof the Laplace resonance of Io, Europa, and Ganymede orbiting Jupiter led to the prediction of intense tidal heating of Io (Peale et al., 1979); this system provides the greatest potential for advances in the next few decades. Europa Clipper and JUpiter ICy moons Explorer (JUICE) will provide in-depth studies of Europa and Ganymede in the 2030s. The easily observed heat flow of Io, from hundreds of continually erupting volcanoes, makes it an ideal target for further investigation, and the missing link—along with missions in development—to understand the Laplace system. \n\nWe identified five key questions to drive future research and exploration: (Q1) What do volcanic eruptions tell us about the interiors of tidally heated bodies (e.g., Io, Enceladus, and perhaps Europa and Triton)? (Q2) How is tidal dissipation partitioned between solid and liquid materials? (Q3) Does Io have a melt-rich layer, or “magma ocean”, that mechanically decouples the lithosphere from the deeper interior? (Q4) Is the Jupiter/Laplace system in equilibrium (i.e., does the satellite’s heat output equal the rate at which energy is generated)? (Q5) Can stable isotope measurements inform long-term evolution of tidally heated bodies? \n\nThe most promising avenues to address these questions include a new spacecraft mission making close flybys of Io, missions orbiting and landing on key worlds such as Europa and Enceladus, technology developments to enable advanced techniques, closer coupling between laboratory experiments and tidal heating theory, and advances in Earth-based telescopic observations of solar system and extrasolar planets and moons. All of these avenues would benefit from technological developments. An Io mission should: characterize volcanic processes (Q1); test interior models via a set of geophysical measurements coupled with laboratory experiments and theory (Q2 and Q3); measure the rate of Io’s orbital migration (to complement similar measurements expected at Europa and Ganymede) to determine if the Laplace resonance is in equilibrium (Q4); and determine neutral compositions and measure stable isotopes in Io’s atmosphere and plumes (Q5). No new technologies are required for such an Io mission following advances in radiation design and solar power realized for Europa Clipper and JUICE. Seismology is a promising avenue for future exploration, either from landers or remote laser reflectometry, and interferometric synthetic aperture radar (InSAR) could be revolutionary on these active worlds, but advanced power systems plus lower mass and power-active instruments are needed for operation in the outer solar system.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/92712, title ="A Cenozoic Record of Seawater Uranium in Fossil Corals", author = "Gothmann, Anne M. and Higgins, John A.", journal = "Geochimica et Cosmochimica Acta", volume = "250", pages = "173-190", month = "April", year = "2019", doi = "10.1016/j.gca.2019.01.039", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190206-103754732", note = "© 2019 Published by Elsevier Ltd. \n\nReceived 9 August 2018, Accepted 30 January 2019, Available online 6 February 2019. \n\nWe would like to thank Francois L.H. Tissot for helpful comments on multiple drafts of this manuscript as well as Associate Editor, Claudine Stirling, and an anonymous reviewer. We thank Stephen Cairns and Tim Coffer (Smithsonian Institution), Linda Ivany (Syracuse University), Roger Portell (Florida Museum of Natural History), Anne Cohen and Bill Thompson (WHOI), the USGS, and Gregory Dietl (Paleontological Research Institution) for loaning samples. Elizabeth Lundstrom (Princeton University) and Lindsey Hedges (California Institute of Technology) provided critical analytical support. We also thank Sarah Jane White (USGS), Francois Morel (Princeton University) and Will Amidon (Middlebury College) for helpful discussions that improved this manuscript.", revision_no = "19", abstract = "We measured U/Ca ratios, ^4He concentrations, ^(234)U/^(238)U, and ^(238)U/^(235)U in a subset of well-preserved aragonitic scleractinian fossil corals previously described by Gothmann et al. (2015). Comparisons of measured fossil coral He/U ages with the stratigraphic age demonstrate that well-preserved coral aragonite retains most or all of its radiogenic He for 10’s of millions of years. Such samples must be largely or entirely free of alteration, including neomorphism. Measurements of ^(234)U/^(238)U and ^(238)U/^(235)U further help to characterize the fidelity with which the original U concentration has been preserved. Analyses of fossil coral U/Ca show that the seawater U/Ca ratio rose by a factor of 4-5 between the Early Cenozoic and today. Possible explanations for the observed increase include (1) the stabilization of U in seawater due to an increase in seawater [CO_3^(2-)], and a resulting increase in UO_2-CO_3 complexation as originally suggested by Broecker (1971); (2) a decrease in the rate of low-temperature hydrothermal alteration from Early Cenozoic to present, leading to a diminished U sink and higher seawater [U]; or (3) a decrease in uranium removal in reducing sediments, again leading to higher seawater [U].", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94246, title ="The role of the Southern Ocean in abrupt transitions and hysteresis in glacial ocean circulation", author = "Hines, Sophia K. V. and Thompson, Andrew F.", journal = "Paleoceanography and Paleoclimatology", volume = "34", number = "4", pages = "490-510", month = "April", year = "2019", doi = "10.1029/2018pa003415", issn = "2572-4517", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190328-112956704", note = "© 2019 American Geophysical Union. \n\nReceived 6 JUN 2018; Accepted 4MAR 2019; Accepted article online 15MAR 2019; Published online 5 APR 2019. \n\nWe would like to thank Raffaele Ferrari, Emily Newsom, Andrew Stewart, David Marshall, James Rae, and Andrea Burke for helpful discussions, and two anonymous reviewers, whose comments improved the manuscript. S. K. V. H. received support from NSF grants OCE‐1503129 and OCE‐1204211 and the Lamont‐Doherty Earth Observatory Postdoctoral Fellowship. A. F. T. received support from the David and Lucille Packard Foundation and from NSF grant OCE‐1235488. J. F. A. received support from NSF grants OCE‐1503129, OCE‐1737404, and OCE‐1450528. The model code used for this paper will be available on GitHub at the https://github.com/shiness11/DynBoxTwoB4L website.", revision_no = "24", abstract = "High‐latitude Northern Hemisphere climate during the last glacial period was characterized by a series of abrupt climate changes, known as Dansgaard‐Oeschger (DO) events, which were recorded in Greenland ice cores as shifts in the oxygen isotopic composition of the ice. These shifts in inferred Northern Hemisphere high‐latitude temperature have been linked to changes in Atlantic meridional overturning strength. The response of ocean overturning circulation to forcing is non‐linear and a hierarchy of models have suggested that it may exist in multiple steady state configurations. Here, we use a time‐dependent coarse‐resolution isopycnal model with four density classes and two basins, linked by a Southern Ocean to explore overturning states and their stability to changes in external parameters. The model exhibits hysteresis in both the steady‐state stratification and overturning strength as a function of the magnitude of North Atlantic Deep Water (NADW) formation. Hysteresis occurs as a result of two non‐linearities in the model‐‐‐the surface buoyancy distribution in the Southern Ocean and the vertical diffusivity profile in the Atlantic and Indo‐Pacific basins. We construct a metric to assess circulation configuration in the model, motivated by observations from the Last Glacial Maximum, which show a different circulation structure from the modern. We find that circulation configuration is primarily determined by NADW density. The model results are used to suggest how ocean conditions may have influenced the pattern of DO events across the last glacial cycle.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/92252, title ="Precise determination of equilibrium sulfur isotope effects during volatilization and deprotonation of dissolved H_2S", author = "Sim, Min Sub and Sessions, Alex L.", journal = "Geochimica et Cosmochimica Acta", volume = "248", pages = "242-251", month = "March", year = "2019", doi = "10.1016/j.gca.2019.01.016", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190114-132114245", note = "© 2019 Published by Elsevier Ltd. \n\nReceived 16 June 2018, Revised 29 December 2018, Accepted 9 January 2019, Available online 14 January 2019. \n\nThis research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No.2018R1D1A1B07050970) and an Agouron Geobiology Fellowship to MSS, Gordon and Betty Moore Foundation Grant GBMF 3306 to VJO and ALS, NSF award OCE-1436566 to ALS and NSF award OCE-1340174 to JFA. The authors are grateful to Guillaume Paris for assistance for isotope analysis. We also thank Daniel Eldridge, Boswell Wing, and an anonymous reviewer for constructive comments on an earlier version of this manuscript.", revision_no = "19", abstract = "Sulfide (H_2S, HS^−, and S^(2−)) is ubiquitous in marine porewaters as a result of microbial sulfate reduction, constituting the reductive end of the biogeochemical sulfur cycle. Stable isotopes have been widely used to constrain the sulfur cycle, because the redox transformations of sulfur compounds, such as microbial sulfate reduction, often exhibit sizable kinetic isotope effects. In contrast to sulfate ion (SO_4^(2−)), the most abundant form of dissolved sulfur in seawater, H2S is volatile and also deprotonated at near neutral pH. Equilibrium isotope partitioning between sulfide species can therefore overlap with kinetic isotope effects during reactions involving sulfide as either reactant or intermediate. Previous experimental attempts to measure equilibrium fractionation between H_2S and HS− have reached differing results, likely due to solutions of widely varying ionic strength. In this study, we measured the sulfur isotope fractionation between total dissolved sulfide and gaseous H2S at 20.6\u202f±\u202f0.5\u202f°C over the pH range from 2 to 8, and calculated the equilibrium isotope effects associated with deprotonation of dissolved H_2S. By using dilute solutions of Na2S, made possible by the improved sensitivity of mass spectrometric techniques, uncertainty in the first dissociation constant of H2S due to ionic strength could be better controlled. This in turn allowed us to close sulfur isotope mass balance for our experiments and increase the accuracy of the estimated fractionation factor. At equilibrium, aqueous H2S was enriched in ^(34)S by 0.7‰ and 3.1‰ relative to gaseous H_2S and aqueous HS−, respectively. The estimated fractionation between aqueous H_2S and HS^− lies between two earlier experimental reports, but agrees within the uncertainty of the measurements with a recent theoretical calculation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91499, title ="Temperature Dependence of Calcite Dissolution Kinetics in Seawater", author = "Naviaux, John D. and Subhas, Adam V.", journal = "Geochimica et Cosmochimica Acta", volume = "246", pages = "363-384", month = "February", year = "2019", doi = "10.1016/j.gca.2018.11.037", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181205-100011581", note = "© 2018 Published by Elsevier Ltd. \n\nReceived 1 August 2018, Revised 26 November 2018, Accepted 27 November 2018, Available online 5 December 2018. \n\nWe would like to thank the anonymous journal reviewers as well as Oleg Pokrovsky and Henry Teng for the insightful comments and suggestions they gave that helped to improve this manuscript. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1745301, as well as NSF grant Numbers OCE1220302, OCE1559004 and 1559215. John Naviaux and Adam Subhas would also like to thank the Resnick Sustainability Institute at Caltech for fellowship support.", revision_no = "21", abstract = "Knowledge of calcite dissolution kinetics in seawater is a critical component of our understanding of the changing global carbon budget. Towards this goal, we provide the first measurements of the temperature dependence of calcite dissolution kinetics in seawater. We measured the dissolution rates of ^(13)C-labeled calcite in seawater at 5, 12, 21, and 37°C across the full range of saturation states (0 < Ω = Ca^(2+)[CO_3^(2-)/Ksp'< 1). We show that the dissolution rate is non-linearly dependent on Ω and that the degree of non-linearity both increases with temperature, and changes abruptly at “critical” saturation states (Ω_(crit_). The traditional exponential rate law most often utilized in the oceanographic community, R=k(1-Ω)^n, requires different fits to k and n depending upon the degree of undersaturation. Though we calculate a similar activation energy to other studies far from equilibrium (25±2 kJ/mol), the exponential rate law could not be used to mechanistically explain our near equilibrium results. We turn to an alternative framework, derived from crystal nucleation theory, and find that our results are consistent with calcite dissolution kinetics in seawater being set by the retreat of pre-existing edges/steps from Ω=1-0.9, defect-assisted etch pit formation from Ω=0.9-0.75, and finally homogenous etch pit formation from Ω=0.75-0. The Ω_(crit) s for each mechanism are shifted significantly closer to equilibrium than they occur in dilute solutions, such that ocean acidification may cause marine carbonates to enter faster dissolution regimes more readily than would be expected from previous studies. We use the observed temperature dependence for each dissolution mechanism to calculate step kinetic coefficients (β, cm/s), densities of active nucleation sites (n_s, sites/m^2), and step edge free energies (α, mJ/m^2). Homogenous dissolution is well explained within the surface nucleation framework, but defect-assisted dissolution is not. Dissolution is initiated via step-propagation at all temperatures, but the defect-assisted mechanism is skipped over at 5°C, potentially due to a lack of nucleation sites. The surface nucleation framework enhances our understanding of calcite dissolution in seawater, but our results suggest that a complete theory will also need to incorporate the role of solution/surface speciation and complexation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/92242, title ="Role of APS reductase in biogeochemical sulfur isotope fractionation", author = "Sim, Min Sub and Ogata, Hideaki", journal = "Nature Communications", volume = "10", pages = "Art. No. 44", month = "January", year = "2019", doi = "10.1038/s41467-018-07878-4", issn = "2041-1723", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190114-083925177", note = "© 2018 The Author(s).\nThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.\n\nReceived 29 June 2018; Accepted 29 November 2018; Published\n09 January 2019.\n\nData availability:\nData supporting the findings of this study are available within the paper and in the supplementary information file or are available from the corresponding author upon reasonable request.\n\n\nThis work was supported by the Research Resettlement Fund for the new faculty of Seoul National University to M.S.S., the NASA Research Opportunities in Space and Earth Sciences grant award number NNX14AO48G to S.E.M. and V.J.O., JSPS KAKENHI Grant Number 10751084 to S.E.M., and the Gordon and Betty Moore Foundation Grant GBMF 3306 to V.J.O. and A.L.S. This research was a part of the project titled ‘Understanding the deepsea biosphere on seafloor hydrothermal vents in the Indian Ridge (20170411)’, funded by the Ministry of Oceans and Fisheries, Korea. We are grateful for insightful and helpful conversations with Boswell A. Wing, David T. Johnston, David A. Fike, and Itay Halevy. We are especially grateful to Tatsuhiko Yagi and Yoshiki Higuchi for helping with initiating collaboration.\n\nContributions:\nM.S.S. and S.E.M. devised the study. H.O. and W.L. purified APS reductase, and M.S.S. executed enzymatic assay and sulfur isotope measurements. M.S.S. and S.E.M. wrote the first draft of the manuscript, and J.F.A., A.L.S., and V.J.O. contributed to interpretation and writing.\n\nCompeting interests:\nThe authors declare no competing interests.\n", revision_no = "20", abstract = "Sulfur isotope fractionation resulting from microbial sulfate reduction (MSR) provides some of the earliest evidence of life, and secular variations in fractionation values reflect changes in biogeochemical cycles. Here we determine the sulfur isotope effect of the enzyme adenosine phosphosulfate reductase (Apr), which is present in all known organisms conducting MSR and catalyzes the first reductive step in the pathway and reinterpret the sedimentary sulfur isotope record over geological time. Small fractionations may be attributed to low sulfate concentrations and/or high respiration rates, whereas fractionations greater than that of Apr require a low chemical potential at that metabolic step. Since Archean sediments lack fractionation exceeding the Apr value of 20‰, they are indicative of sulfate reducers having had access to ample electron donors to drive their metabolisms. Large fractionations in post-Archean sediments are congruent with a decline of favorable electron donors as aerobic and other high potential metabolic competitors evolved.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/88997, title ="CO_2 storage and release in the deep Southern Ocean on millennial to centennial timescales", author = "Rae, J. W. B. and Burke, A.", journal = "Nature", volume = "562", number = "7728", pages = "569-573", month = "October", year = "2018", doi = "10.1038/s41586-018-0614-0", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180821-155408115", note = "© 2018 Springer Nature Limited. \n\nReceived 06 March 2018; Accepted 29 August 2018; Published 24 October 2018. \n\nData availability: The data produced in this study are available in Extended Data Tables and will also be made available at the NOAA (https://www.ncdc.noaa.gov/paleo/study/25230) and Pangaea data repositories. \n\nThis work was supported by NERC Standard Grant NE/N003861/1 to J.W.B.R. and L.F.R., an NOAA Climate and Global Change VSP Fellowship to J.W.B.R, NERC Standard Grant NE/M004619/1 to A.B. and J.W.B.R., a NERC Strategic Environmental Science Capital Grant to A.B. and J.W.B.R., Marie Curie Career Integration Grant CIG14-631752 to A.B., an ERC consolidator grant to L.F.R., NSF grant OCE-1503129 to J.F.A., and NERC studentships to B.T. and E.L. \n\nReviewer information: Nature thanks C. Buizert and the other anonymous reviewer(s) for their contribution to the peer review of this work.", revision_no = "61", abstract = "The cause of changes in atmospheric carbon dioxide (CO_2) during the recent ice ages is yet to be fully explained. Most mechanisms for glacial–interglacial CO_2 change have centred on carbon exchange with the deep ocean, owing to its large size and relatively rapid exchange with the atmosphere. The Southern Ocean is thought to have a key role in this exchange, as much of the deep ocean is ventilated to the atmosphere in this region. However, it is difficult to reconstruct changes in deep Southern Ocean carbon storage, so few direct tests of this hypothesis have been carried out. Here we present deep-sea coral boron isotope data that track the pH—and thus the CO_2 chemistry—of the deep Southern Ocean over the past forty thousand years. At sites closest to the Antarctic continental margin, and most influenced by the deep southern waters that form the ocean’s lower overturning cell, we find a close relationship between ocean pH and atmospheric CO_2: during intervals of low CO_2, ocean pH is low, reflecting enhanced ocean carbon storage; and during intervals of rising CO_2, ocean pH rises, reflecting loss of carbon from the ocean to the atmosphere. Correspondingly, at shallower sites we find rapid (millennial- to centennial-scale) decreases in pH during abrupt increases in CO_2, reflecting the rapid transfer of carbon from the deep ocean to the upper ocean and atmosphere. Our findings confirm the importance of the deep Southern Ocean in ice-age CO_2 change, and show that deep-ocean CO_2 release can occur as a dynamic feedback to rapid climate change on centennial timescales.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/88053, title ="A Kinetic Pressure Effect on Calcite Dissolution in Seawater", author = "Dong, Sijia and Subhas, Adam V.", journal = "Geochimica et Cosmochimica Acta", volume = "238", pages = "411-423", month = "October", year = "2018", doi = "10.1016/j.gca.2018.07.015", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180720-100933524", note = "© 2018 Elsevier. \n\nReceived 16 January 2018, Accepted 9 July 2018, Available online 20 July 2018. \n\nThis work was supported by NSF Ocean Acidification grants (numbers OCE1220600 and OCE1220302), USC Dornsife Doctoral Fellowship and Elizabeth and Jerol Sonosky Fellowship for Earth and Ocean Sciences. The authors would like to thank Jun Shao for helping with Fig. 1 in this paper using Ocean Data View, and Aaron Celestian for his help with XRD. We acknowledge the work by USC machine shop machinists (Don Wiggins and colleagues) who built our pressure vessel and undergraduate student Laura Morine for her help running alkalinities. We also thank Dr. Alfonso Mucci, Dr. Bernard Boudreau, and two anonymous reviewers for their valuable and constructive comments on the original manuscript draft.", revision_no = "17", abstract = "This study provides laboratory data of calcite dissolution rate as a function of seawater undersaturation state (1-Ω) under variable pressure. ^(13)C-labeled calcite was dissolved in unlabeled seawater and the evolving δ^(13)C composition of the fluid was monitored over time to evaluate the dissolution rate. Results show that dissolution rates are enhanced by a factor of 2-4 at 700 dbar compared to dissolution at the same Ω under ambient pressure (10 dbar). This dissolution rate enhancement under pressure applies over an Ω range of 0.65 to 1 between 10 dbar and 700 dbar. Above 700 dbar (up to 2500 dbar), dissolution rates become independent of pressure. The observed enhancement is well beyond the uncertainty associated with the thermodynamic properties of calcite under pressure (partial molar volume ΔV), and thus should be interpreted as a kinetic pressure effect on calcite dissolution. Dissolution at ambient pressure and higher pressures yield non-linear dissolution kinetics, the pressure effect does not significantly change the reaction order n in Rate = k(1-Ω^)n, which is shown to vary from 3.1±0.3 to 3.8±0.5 from 10 dbar to 700 dbar over Ω = 0.65 to 0.9. Furthermore, two different dissolution mechanisms are indicated by a discontinuity in the rate-undersaturation relationship, and seen at both ambient and higher pressures. The discontinuity, Ω_(critical) = 0.87±0.05 and 0.90±0.03 at 10 dbar and 1050 dbar respectively, are similar within error. The reaction order, n, at Ω > 0.9 is 0.47±0.27 and 0.46±0.15 at 10 dbar and 700 dbar respectively. This Ω_(critical) is considered to be the threshold between step retreat dissolution and defect-assisted dissolution. The kinetic enhancement of dissolution rate at higher pressures is related to a decrease in the interfacial energy barrier at dissolution sites. The impact of pressure on the calcite dissolution kinetics implies that sinking particles would dissolve at shallower depth than previously thought.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87097, title ="Cenozoic record of δ^(34)S in foraminiferal calcite implies an early Eocene shift to deep-ocean sulfide burial", author = "Rennie, Victoria C. F. and Paris, Guillaume", journal = "Nature Geoscience", volume = "11", number = "10", pages = "761-765", month = "October", year = "2018", doi = "10.1038/s41561-018-0200-y", issn = "1752-0894", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180614-093746378", note = "© 2018 Springer Nature Limited. \n\nReceived: 4 February 2018; Accepted: 5 July 2018; Published online: 13 August 2018. \n\nWe thank M. Vautravers for her expertise with Palaeogene foraminifera and S. Misra, G. Antler and W. Fisher for helpful discussions and advice. This work was supported by a ‘Small Sulfur’ NERC grant (NERC NE/H011595/1), the ERC (ERC StG 307582, CARBONSINK to A.V.T.) and a NERC studentship to V.C.F.R. \n\nAuthor Contributions: V.C.F.R. designed the cleaning tests, did the lab work and analysis for trace element analysis and sulfur isotopes, and wrote the model and the paper. G.P. advised on the cleaning tests, did sulfate and sulfur isotope preparation and analysis, was heavily involved in the modelling and wrote the paper. A.L.S. provided equipment and fruitful discussions. S.A. picked the foraminifera for the stable isotope analyses. A.V.T. provided extensive advice and funding at all stages, had the idea for the shift in ^(34)ε_(SO4-pyr) and wrote the paper. J.F.A. provided guidance and lab equipment for lab work and analysis, advised extensively on the model and wrote the paper. \n\nData availability: The authors declare that all the data and MATLAB codes supporting the finding of this study are available within the article and its supplementary information files. \n\nThe authors declare no competing interests.", revision_no = "41", abstract = "Understanding the changes in, and drivers of, isotopic variability of sulfur in seawater sulfate (δ^(34)S_(SO4-sw)) over geological time remains a long-standing goal, particularly because of the coupling between the biogeochemical sulfur and carbon cycles. The early Cenozoic has remained enigmatic in this regard, as the existing seawater sulfate isotopic records appear to be decoupled from the well-defined carbon isotope composition of the ocean. Here, we present a new Cenozoic record of sulfur isotopes, using carbonate-associated sulfate hosted in the calcite lattice of single-species foraminifera. The vastly improved stratigraphy afforded by this record demonstrates that carbon and sulfur cycles, as recorded by their isotopes, are not fully decoupled in the early Cenozoic. With a model driven by partial coupling of the carbon and sulfur cycles, we demonstrate that a change in sulfur isotopic fractionation of the pyrite burial flux best explains the large increase in δ^(34)S_(SO4-sw) ~53 million years ago (Ma) and the subsequent long steady state. We suggest that the locus of pyrite burial changed from shallow epicontinental seas and shelf environments to more open-ocean sediments around 53\u2009Ma. Loss of extensive shelf environments corresponds to Cretaceous–Palaeogene sea-level changes and tectonic reorganization, occurring as the Himalayan arc first collided with Asia.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86993, title ="Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO_2 rise", author = "Studer, Anja S. and Sigman, Daniel M.", journal = "Nature Geoscience", volume = "11", number = "10", pages = "756-760", month = "October", year = "2018", doi = "10.1038/s41561-018-0191-8", issn = "1752-0894", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180612-092939297", note = "© 2018 Springer Nature. \n\nReceived: 23 January 2017; Accepted: 26 June 2018; Published: 30 July 2018. \n\nThis study was supported by Swiss NSF grant PBEZP2_145695 to A.S.S., US NSF grants 1401489 and 1234664 to D.M.S., Swiss NSF grant PZ00P2_142424 to A.M.-G., grants PP00P2-144811 and PP00P2_172915 to S.L.J., by the Deutsche Forschungsgemeinschaft through grant Li1815/4 to J.A.L., by funding from the Swedish Research Council VR-349-2012-6278 to E.M., from the Natural Environment Research Council NE/N003861/1 to L.F.R., and from the French INSU/LEFE Indien Sud to A.M. This research was also supported by ExxonMobil through the Andlinger Center for Energy and the Environment at Princeton University and by the Grand Challenges Program of Princeton University. Cores MD11-3353 and MD12-3396CQ were retrieved during Indien Sud oceanographic cruises (A.M.) and we express our thanks to the crew of the R/V Marion Dufresne as well as the French Polar Institute (IPEV). The authors thank K. Hendry, M. Palmer and B. Heinz for their valuable input, and X. Crosta for his help with diatom species identification. \n\nAuthor Contributions: A.S.S., D.M.S., A.M.-G. and G.H.H. designed the study. A.S.S. performed the δ^(15)N_(db) analyses and wrote the first draft of the manuscript with D.M.S., A.M.-G. and G.H.H. L.M.T., S.L.J. and J.A.L. contributed the ^(230)Th-normalized opal flux data. E.M. and A.M. provided access to the sediment cores and measured the radiocarbon ages for the construction of the age model. L.F.R. and J.F.A. recovered the corals, and X.T.W. generated the coral-bound δ^(15)N data. All authors contributed to the interpretation of the data and provided input to the final manuscript. \n\nData availability: Data supporting the findings of this study are available within the Article and its Supplementary Information files. Data are also available on Pangaea at https://doi.pangaea.de/10.1594/PANGAEA.891436. \n\nThe authors declare no competing interests.", revision_no = "33", abstract = "A rise in the atmospheric CO_2 concentration of ~20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensation in response to deglacial outgassing of oceanic CO_2, and enhanced shallow water carbonate deposition. Here, we compile new and previously published fossil-bound nitrogen isotope records from the Southern Ocean that indicate a rise in surface nitrate concentration through the Holocene. When coupled with increasing or constant export production, these data suggest an acceleration of nitrate supply to the Southern Ocean surface from underlying deep water. This change would have weakened the ocean’s biological pump that stores CO_2 in the ocean interior, possibly explaining the Holocene atmospheric CO_2 rise. Over the Holocene, the circum-North Atlantic region cooled, and the formation of North Atlantic Deep Water appears to have slowed. Thus, the ‘seesaw’ in deep ocean ventilation between the North Atlantic and the Southern Ocean that has been invoked for millennial-scale events, deglaciations and the last interglacial period may have also operated, albeit in a more gradual form, over the Holocene.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/88790, title ="The dissolution behavior of biogenic calcites in seawater and a possible role for magnesium and organic carbon", author = "Subhas, Adam V. and Rollins, Nick E.", journal = "Marine Chemistry", volume = "205", pages = "100-112", month = "September", year = "2018", doi = "10.1016/j.marchem.2018.08.001", issn = "0304-4203", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180813-154925391", note = "© 2018 Elsevier B.V. \n\nReceived 13 February 2018, Revised 25 July 2018, Accepted 2 August 2018, Available online 12 August 2018.", revision_no = "11", abstract = "We present the dissolution kinetics of mixed planktic foraminifera, the benthic foraminifera Amphistegina, the coccolithophore Emiliania huxleyi, and the soft coral Rhythismia fulvum in seawater. Dissolution rates were measured across a large range of saturation states (Ω\u202f=\u202f0.99–0.2) by dissolving ^(13)C-labeled calcites in natural seawater undersaturated with respect to calcite. ^(13)C-label was incorporated into biogenic calcite by culturing marine calcifiers in 13C-labeled natural seawater. Net dissolution rates were calculated as the slope of seawater δ^(13)C versus time in a closed seawater-calcite system. All calcites show distinct, nonlinear, dependencies on seawater saturation state when normalized by mass or by specific surface area. For example, coccolith calcite dissolves at a similar rate to inorganic calcite near equilibrium when normalized by surface area, but dissolves much more slowly far from equilibrium. Mass loss from foraminiferal tests is correlated with a decrease in Mg/Ca of the solid, indicating that Mg-rich phases are preferentially leached out at even mild undersaturations. Dissolution also appears to strongly affect test B/Ca. Finally, we provide an interpretation of surface area-normalized biogenic calcite dissolution rates as a function of their Mg and organic carbon content. Near-equilibrium dissolution rates of all calcites measured here show a strong, nonlinear dependence on Mg content. Far-from-equilibrium dissolution rates decrease strongly as a function of organic carbon content. These results help to build a framework for understanding the underlying mechanisms of rate differences between biogenic calcites, and bear important implications for the dissolution of high-Mg calcites in view of ocean acidification.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/85056, title ="Carbonic anhydrase, coral calcification and a new model of stable isotope vital effects", author = "Chen, Sang and Gagnon, Alexander C.", journal = "Geochimica et Cosmochimica Acta", volume = "236", pages = "179-197", month = "September", year = "2018", doi = "10.1016/j.gca.2018.02.032", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180302-082405447", note = "© 2018 Elsevier Ltd. \n\nReceived 13 June 2017, Accepted 16 February 2018, Available online 2 March 2018. \n\nThis work received support from NSF grant P2C2-1503129. S.C. would like to acknowledge financial support from the China Scholarship Council for Ph.D. study at Caltech. We would also like to thank James Watkins for sharing his Matlab code for the oxygen isotope calculations. We are indebted to editors Tom Marchitto and Ros Rickaby for feedback on the original manuscript. Ted McConnaughey, Vanni Aloisi and an anonymous reviewer provided constructive comments that helped clarify key points of the paper. We dedicate this work to Harry Elderfield for his pioneering contributions to the study of vital effects in biogenic carbonates and many fruitful conversations over the years about the lives of the small and calcareous.", revision_no = "15", abstract = "The stable isotope compositions of biogenic carbonates have been used for paleoceanographic and paleoclimatic reconstructions for decades, and produced some of the most iconic records in the field. However, we still lack a fully mechanistic understanding of the stable isotope proxies, especially the biological overprint on the environmental signals termed “vital effects”. A ubiquitous feature of stable isotope vital effects in marine calcifying organisms is a strong correlation between δ^(18)O and δ^(13)C in a range of values that are depleted from inorganic calcite/aragonite. Two mechanisms have been proposed to explain this correlation, one based on kinetic isotope effects during CO_2(aq)-HCO_3− inter-conversion, the other based on equilibrium isotope exchange during pH dependent speciation of the dissolved inorganic carbon (DIC) pool. Neither mechanism explains all the stable isotope features observed in biogenic carbonates. Here we present a fully kinetic model of biomineralization and its isotope effects using deep-sea corals as a test organism. A key component of our model is the consideration of the enzyme carbonic anhydrase in catalyzing the CO2(aq)-HCO_3− inter-conversion reactions in the extracellular calcifying fluid (ECF). We find that the amount of carbonic anhydrase not only modulates the carbonate chemistry of the calcifying fluid, but also helps explain the slope of the δ^(18)O-δ^(13)C correlation. Differences in CA activity in the biomineralization process can possibly explain the observed range of δ^(18)O-δ^(13)C slopes in different calcifying organisms. A mechanistic understanding of stable isotope vital effects with numerical models can help us develop better paleoceanographic tracers.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/85385, title ="The Li isotope composition of marine biogenic carbonates: Patterns and Mechanisms", author = "Dellinger, Mathieu and West, A. Joshua", journal = "Geochimica et Cosmochimica Acta", volume = "236", pages = "315-335", month = "September", year = "2018", doi = "10.1016/j.gca.2018.03.014", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180320-152210071", note = "© 2018 Elsevier Ltd. \n\nReceived 30 August 2017, Accepted 10 March 2018, Available online 17 March 2018. \n\nThis work was primarily supported by the American Chemical Society Petroleum Research Fund (award 53418-DNI2 to AJW). We thank the Natural History Museum of Los Angeles County for providing bivalve samples. We thank Jonathan Erez and an anonymous reviewer for their constructive comments on the manuscript. MD acknowledges financial support from Durham University and a Marie Curie COFUND International Junior research Fellowship held at Durham University. RAE and JBR acknowledge support from NSF grants OCE #1437166 and 1437371. PPvS and CVU analyzed C. gigas from the List Basin with support from NERC Advanced Fellowship NE/I020571/2 and ERC Consolidator grant 682760 - CONTROLPASTCO2.", revision_no = "21", abstract = "Little is known about the fractionation of Li isotopes during formation of biogenic carbonates, which form the most promising geological archives of past seawater composition. Here we investigated the Li isotope composition (δ^7Li) and Li/Ca ratios of organisms that are abundant in the Phanerozoic record: mollusks (mostly bivalves), echinoderms, and brachiopods. The measured samples include (i) modern calcite and aragonite shells from various species and natural environments (13 mollusk samples, 5 brachiopods and 3 echinoderms), and (ii) shells from mollusks grown under controlled conditions at various temperatures. When possible, the mollusk shell ultrastructure was micro-sampled in order to assess intra-shell heterogeneity. In this paper, we systematically characterize the influence of mineralogy, temperature, and biological processes on the δ^7Li and Li/Ca of these shells and compare with published data for other taxa (foraminifera and corals).\nAragonitic mollusks have the lowest δ^7Li, ranging from +16 to +22‰, echinoderms have constant δ^7Li of about +24‰, brachiopods have δ^7Li of +25 to +28‰, and finally calcitic mollusks have the largest range and highest δ^7Li values, ranging from +25‰ to +40‰. Measured brachiopods have similar δ7Li compared to inorganic calcite precipitated from seawater (δ^7Li of +27 to +29‰), indicating minimum influence of vital effects, as also observed for other isotope systems and making them a potentially viable proxy of past seawater composition. Calcitic mollusks, on the contrary, are not a good archive for seawater paleo–δ^7Li because many samples have significantly higher δ^7Li values than inorganic calcite and display large inter-species variability, which suggests large vital effects. In addition, we observe very large intra-shell variability, in particular for mixed calcite-aragonite shells (over 20‰ variability), but also in mono-mineralic shells (up to 12‰ variability). Aragonitic bivalves have less variable δ^7Li (7‰ variability) compared to calcitic mollusks, but with significantly lower δ^7Li compared to inorganic aragonite, indicating the existence of vital effects. Bivalves grown at various temperatures show that temperature has only a minor influence on fractionation of Li isotopes during shell precipitation. Interestingly, we observe a strong correlation (R^2\u202f=\u202f0.83) between the Li/Mg ratio in bivalve Mytilus edulisand temperature, with potential implications for paleo-temperature reconstructions.\nFinally, we observe a negative correlation between the δ^7Li and both the Li/Ca and Mg/Ca ratio of calcite mollusks, which we relate to biomineralization processes. To explain this correlation, we propose preferential removal of ^6Li from the calcification site of calcite mollusks by physiological processes corresponding to the regulation of the amount of Mg in the calcifying medium. We calculate that up to 80% of the initial Li within the calcification site is removed by this process, leading to high δ^7Li and low Li/Ca in some calcite mollusk specimens. Collectively, these results suggest that Mg (and thus [Li]) is strongly biologically controlled within the calcifying medium of calcite mollusks.\nOverall, the results of this study show that brachiopods are likely to be suitable targets for future work on the determination of paleo-seawater Li isotope composition—an emerging proxy for past weathering and hydrothermal processes.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86968, title ="Riverine evidence for isotopic mass balance in the Earth’s early sulfur cycle", author = "Torres, Mark A. and Paris, Guillaume", journal = "Nature Geoscience", volume = "11", number = "9", pages = "661-664", month = "September", year = "2018", doi = "10.1038/s41561-018-0184-7", issn = "1752-0894", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180611-140642568", note = "© 2018 Springer Nature Limited. \n\nReceived: 5 February 2018; Accepted: 19 June 2018; Published online 23 July 2018. \n\nM.A.T. acknowledges support from the Caltech Texaco Postdoctoral fellowship and the California Alliance for Graduate Education and the Professoriate (AGEP). This work was supported from funds supplied by the David and Lucile Packard Foundation, a Caltech GPS Division Discovery Award (W.W.F), and a grant from the National Science Foundation (EAR-1349858) to W.W.F and J.F.A. This project benefited from the use of instrumentation made available by the Caltech Environmental Analysis Center. All authors acknowledge helpful comments provided by B. Wing on an earlier draft of this manuscript. \n\nAuthor Contributions: G.P. and M.A.T conducted the laboratory analyses. All authors contributed to the sample collection, data analysis and manuscript preparation. \n\nData availability: All original data generated as part of this study are available in Supplementary Tables 2 and 3 and online from the PANGEA repository (https://doi.pangaea.de/10.1594/PANGAEA.890986). The Canadian precipitation chemistry analyses are available online at ec.gc.ca/natchem. Compiled analyses of the sulfur isotopic composition of Archaean sulfides are available in the original publications (see citations in Supplementary Table 1). \n\nCode availability: The code used to generate perform the data analysis can be accessed at github.com/torres-lab. \n\nThe authors have no competing interests.", revision_no = "30", abstract = "During a time of negligible atmospheric pO_2, Earth’s early sulfur cycle generated a spectacular geological signal seen as the anomalous fractionation of multiple sulfur isotopic ratios. The disappearance of this signal from the geologic record has been hypothesized to constrain the timing of atmospheric oxygenation, although interpretive challenges exist. Asymmetry in existing S isotopic data, for example, suggests that the Archaean crust was not mass balanced, with the implication that the loss of S isotope anomalies from the geologic record might lag the rise of atmospheric O_2. Here, we present new S isotopic analyses of modern surface and groundwaters that drain Archaean terrains in order to independently evaluate Archaean S cycle mass balance. Natural waters contain sulfur derived from the underlying bedrock and thus can be used to ascertain its S isotopic composition at scales larger than typical geological samples allow. Analyses of 52 water samples from Canada and South Africa suggest that the Archaean crust was mass balanced with an average multiple S isotopic composition equivalent to the bulk Earth. Overall, our work supports the hypothesis that the disappearance of multiple S isotope anomalies from the sedimentary record provides a robust proxy for the timing of the first rise in atmospheric O_2.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87259, title ="Sulfur isotopes in rivers: Insights into global weathering budgets, pyrite oxidation, and the modern sulfur cycle", author = "Burke, Andrea and Present, Theodore M.", journal = "Earth and Planetary Science Letters", volume = "496", pages = "168-177", month = "August", year = "2018", doi = "10.1016/j.epsl.2018.05.022", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180620-110745106", note = "© 2018 Elsevier B.V. \n\nReceived 6 November 2017, Revised 13 May 2018, Accepted 14 May 2018, Available online 6 June 2018. \n\nThis research was funded by a Foster and Coco Stanback postdoctoral fellowship and a Marie Curie Career Integration Grant (CIG14-631752) to AB. JFA acknowledges the support of NSF-OCE grant 1340174 and NSF-EAR grant 1349858. WF acknowledges the support of a grant from the David and Lucile Packard Foundation.", revision_no = "15", abstract = "The biogeochemical sulfur cycle is intimately linked to the cycles of carbon, iron, and oxygen, and plays an important role in global climate via weathering reactions and aerosols. However, many aspects of the modern budget of the global sulfur cycle are not fully understood. We present new δ^(34)S measurements on sulfate from more than 160 river samples from different geographical and climatic regions—more than 46% of the world's freshwater flux to the ocean is accounted for in this estimate of the global riverine sulfur isotope budget. These measurements include major rivers and their tributaries, as well as time series, and are combined with previously published data to estimate the modern flux-weighted global riverine δ^(34)S as 4.4 ± 4.5‰ (V-CDT), and 4.8 ± 4.9‰ when the most polluted rivers are excluded. The sulfur isotope data, when combined with major anion and cation concentrations, allow us to tease apart the relative contributions of different processes to the modern riverine sulfur budget, resulting in new estimates of the flux of riverine sulfate due to the oxidative weathering of pyrites (1.3 ± 0.2 Tmol S/y) and the weathering of sedimentary sulfate minerals (1.5 ± 0.2 Tmol S/y). These data indicate that previous estimates of the global oxidative weathering of pyrite have been too low by a factor of two. As pyrite oxidation coupled to carbonate weathering can act as a source of CO_2 to the atmosphere, this global pyrite weathering budget implies that the global CO_2 weathering sink is overestimated. Furthermore, the large range of sulfur isotope ratios in modern rivers indicates that secular changes in the lithologies exposed to weathering through time could play a major role in driving past variations in the δ^(34)S value of seawater.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/82819, title ="A Cenozoic record of seawater Mg isotopes in well-preserved fossil corals", author = "Gothmann, Anne M. and Stolarski, Jarosław", journal = "Geology", volume = "45", number = "11", pages = "1039-1042", month = "November", year = "2017", doi = "10.1130/G39418.1", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171031-145632026", note = "© 2017 Geological Society of America. \n\nManuscript received 14 June 2017; Revised manuscript received 13 August 2017; Manuscript accepted 18 August 2017; Published: October 02, 2017. \n\nWe thank Michael Bender and Casey Saenger for their valuable thoughts on this manuscript, and Elizabeth Lundstrom for assistance with Mg isotope measurements. We acknowledge the Princeton BP Amoco Carbon Mitigation Initiative and the Frank Harrison Tuttle Memorial Fund for Invertebrate Studies for their generous support. We thank Dan Schrag, Josh Wimpenny, and an anonymous reviewer for comments that greatly improved this manuscript.", revision_no = "9", abstract = "Reconstructions of seawater Mg isotopic composition (δ^(26)Mg) can provide novel insights into the processes that control the major ion chemistry of seawater over geologic time scales. A key period of interest is the Cenozoic (ca. 65 Ma to today), during which the Mg/Ca ratio of seawater increased by a factor of 2–3. However, two published records of seawater δ^(26)Mg over the Cenozoic disagree, making it difficult to draw conclusions about mechanisms driving seawater Mg/Ca change over the past 65 m.y. Here we present a new record of seawater δ^(26)Mg from a set of well-preserved fossil corals, ranging in age from Paleocene to Recent. Fossil coral δ^(26)Mg decreases by ∼0.3‰ between the early Cenozoic and the Oligocene, then increases by ∼0.15‰ between the Oligocene and present, in strong agreement with the published record derived from bulk pelagic carbonate. Together with this existing record, our fossil coral data suggest that the rise in [Mg]_(seawater) over the Cenozoic was mainly driven by an increase in Mg silicate weathering or a decline in Mg uptake in marine silicates. In contrast, we suggest that changes in the rate of carbonate weathering and dolomite formation likely played a minor, but not insignificant, role in the global Mg cycle over the Cenozoic.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/83437, title ="Climatic and in-cave influences on δ^(18)O and δ^(13)C in a stalagmite from northeastern India through the last deglaciation", author = "Lechleitner, Franziska A. and Breitenbach, Sebastian F. M.", journal = "Quaternary Research", volume = "88", number = "03", pages = "458-471", month = "November", year = "2017", doi = "10.1017/qua.2017.72", issn = "0033-5894", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171127-082617834", note = "© 2017 University of Washington. Published by Cambridge University Press.\n\n\nReceived April 3, 2017; Accepted August 2, 2017, Published online 21 September 2017.\n\nWe gratefully acknowledge financial support from the Swiss\nNational Fond (SNF Sinergia grant CRSI22 132646/1 and grant\nP2EZP2_172213), the German Science Foundation (DFG project\nMA4759/8-1--Impacts of uncertainties in climate data analysis [IUCliD]: approaches to working with measurements as a series of probability distributions--and grant no. RE3994-1/1), the National Natural Science Foundation of China (NSFC) grants 4123054 and 2013CB955902, the U.S. National Science Foundation grant 1103403, and the European Union's Horizon 2020 Research and Innovation program under the Marie Skłodowska-Curie grant agreement no. 691037 (QUEST). We thank our Indian colleagues Bijay Mipun\nand Gregory Diengdoh for their logistic help. We thank Daniel Gebauer for support during fieldwork. We also thank Lydia Zehnder and Stewart Bishop (both at ETH Zürich) for assistance during XRD and stable isotope analysis, respectively. Tim Eglinton is acknowledged for financial support of F.A.L. We thank Ashish Sinha, Max Berkelhammer,\nJames Baldini, Yanjun Cai, and two anonymous reviewers for\nconstructive feedback and fruitful discussions on this and earlier versions of this manuscript. We thank the editors, Matthew Lachniet and Lewis Owen, for feedback and handling of the manuscript.\n", revision_no = "15", abstract = "Northeastern (NE) India experiences extraordinarily pronounced seasonal climate, governed by the Indian summer monsoon (ISM). The vulnerability of this region to floods and droughts calls for detailed and highly resolved paleoclimate reconstructions to assess the recurrence rate and driving factors of ISM changes. We use stable oxygen and carbon isotope ratios (δ^(18)O and δ^(13)C) from stalagmite MAW-6 from Mawmluh Cave to infer climate and environmental conditions in NE India over the last deglaciation (16–6ka). We interpret stalagmite δ^(18)O as reflecting ISM strength, whereas δ^(13)C appears to be driven by local hydroclimate conditions. Pronounced shifts in ISM strength over the deglaciation are apparent from the δ^(18)O record, similarly to other records from monsoonal Asia. The ISM is weaker during the late glacial (LG) period and the Younger Dryas, and stronger during the Bølling-Allerød and Holocene. Local conditions inferred from the δ^(13)C record appear to have changed less substantially over time, possibly related to the masking effect of changing precipitation seasonality. Time series analysis of the δ^(18)O record reveals more chaotic conditions during the late glacial and higher predictability during the Holocene, likely related to the strengthening of the seasonal recurrence of the ISM with the onset of the Holocene.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/81286, title ="Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion", author = "McConnell, Joseph R. and Adkins, Jess F.", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "114", number = "38", pages = "10035-10040", month = "September", year = "2017", doi = "10.1073/pnas.1705595114", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170911-100036004", note = "© 2017 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). https://creativecommons.org/licenses/by-nc-nd/4.0/ \n\nEdited by Wallace S. Broecker, Columbia University, Palisades, NY, and approved August 7, 2017 (received for review April 5, 2017). Published ahead of print September 5, 2017. \n\nWe acknowledge R. von Glasow for help with snowpack model simulations, and J. Stutz and R. Kreidberg for helpful discussions. The US National Science Foundation supported this work [Grants 0538427, 0839093, and 1142166 (to J.R.M.); 1043518 (to E.J.B.); 0538657 and 1043421 (to J.P. Severinghaus); 0538553 and 0839066 (to J.C.-D.); and 0944348, 0944191, 0440817, 0440819, and 0230396 (to K.C.T.)]. We thank the WAIS Divide Science Coordination Office and other support organizations. P.K. and G.K. were funded by Polar Regions and Coasts in a Changing Earth System-II, with additional support from the Helmholtz Climate Initiative. \n\nAuthor contributions: J.R.M. designed research; J.R.M., A.B., N.W.D., P.K., J.L.T., M.M.A., N.J.C., O.J.M., M.S., J.F.A., D.B., J.F.B., E.J.B., J.C.-D., T.J.F., G.K., M.M.G., N.I., K.C.M., R.M., G.P., R.H.R., E.S.S., J.P. Severinghaus, J.P. Steffensen, K.C.T., and G.W. performed research; J.R.M. contributed new reagents/analytic tools; J.R.M., A.B., N.W.D., P.K., J.L.T., M.S., E.J.B., C.B., J.C.-D., G.K., H.-F.G., N.I., K.C.M., and G.W. analyzed data; and J.R.M., A.B., N.W.D., P.K., J.L.T., E.J.B., C.B., H.-F.G., and G.W. wrote the paper. \n\nThe authors declare no conflict of interest. \n\nThis article is a PNAS Direct Submission. \n\nData deposition: The data reported in this work have been deposited with the U.S. Antarctic Program Data Center, www.usap-dc.org/view/dataset/601008. \n\nThis article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1705595114/-/DCSupplemental.", revision_no = "29", abstract = "Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/79839, title ="Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks", author = "Torres, Mark A. and Moosdorf, Nils", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "114", number = "33", pages = "8716-8721", month = "August", year = "2017", doi = "10.1073/pnas.1702953114", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170807-091321702", note = "© 2017 National Academy of Sciences. \n\nEdited by Thure E. Cerling, University of Utah, Salt Lake City, UT, and approved July 5, 2017 (received for review February 21, 2017).\nPublished online before print July 31, 2017. \n\nWe thank three reviewers for constructive comments. M.A.T. was supported by a University of Southern California College Merit Fellowship and a Caltech Texaco Postdoctoral Fellowship, N.M. by a Deutscher Akademischer Austauschdienst exchange fellowship, J.H. by the German Science Foundation (DFG-project HA4472/6-1 and the Cluster of Excellence “CliSAP,” EXC177, Universität Hamburg) and Bundesministerium für Bildung und Forschung Project PALMOD (Ref 01LP1506C), and A.J.W. by National Science Foundation Grant EAR-1455352. Requests for access to the GloRiCh database should be addressed to J. Hartmann at geo@hattes.de. \n\nAuthor contributions: N.M., J.H., and A.J.W. designed research; M.A.T., N.M., and J.H. performed research; M.A.T. and J.F.A. contributed new reagents/analytic tools; M.A.T., N.M., J.H., J.F.A., and A.J.W. analyzed data; and M.A.T. and A.J.W. wrote the paper. \n\nThe authors declare no conflict of interest. \n\nThis article is a PNAS Direct Submission. \n\nThis article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1702953114/-/DCSupplemental.", revision_no = "27", abstract = "Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO_2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO_2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO_2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO_2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O_2. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/79124, title ="Catalysis and chemical mechanisms of calcite dissolution in seawater", author = "Subhas, Adam V. and Adkins, Jess F.", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "114", number = "31", pages = "8175-8180", month = "August", year = "2017", doi = "10.1073/pnas.1703604114", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170717-093236411", note = "© 2017 National Academy of Sciences. \n\nEdited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved June 26, 2017 (received for review March 6, 2017). Published online before print July 18, 2017, doi: 10.1073/pnas.1703604114.\n\nWe acknowledge Alex Gagnon for helpful discussions on the formulation of the box model, and Yunbin Guan for help with SIMS analysis. We also thank Sijia Dong for discussions in general about carbonate dissolution in seawater. We thank Mathis Hain and one anonymous reviewer, whose careful reading and detailed comments greatly improved this manuscript. Thanks go to National Science Foundation Graduate Research Fellowship Program and the Resnick Institute Graduate Fellowships for supporting A.V.S. and J.N. We acknowledge support from NSF Grants OCE1220600 and OCE1220302. \n\nAuthor contributions: A.V.S., J.F.A., N.E.R., J.E., and W.M.B. designed research; A.V.S., N.E.R., and J.N. performed research; A.V.S., J.F.A., N.E.R., J.N., and W.M.B. analyzed data; and A.V.S., J.F.A., J.N., and W.M.B. wrote the paper. \n\nThe authors declare no conflict of interest. \n\nThis article is a PNAS Direct Submission. \n\nThis article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1703604114/-/DCSupplemental.", revision_no = "30", abstract = "Near-equilibrium calcite dissolution in seawater contributes significantly to the regulation of atmospheric CO_2 on 1,000-y timescales. Despite many studies on far-from-equilibrium dissolution, little is known about the detailed mechanisms responsible for calcite dissolution in seawater. In this paper, we dissolve ^(13)C-labeled calcites in natural seawater. We show that the time-evolving enrichment of δ^(13)C in solution is a direct measure of both dissolution and precipitation reactions across a large range of saturation states. Secondary Ion Mass Spectrometer profiles into the ^(13)C-labeled solids confirm the presence of precipitated material even in undersaturated conditions. The close balance of precipitation and dissolution near equilibrium can alter the chemical composition of calcite deeper than one monolayer into the crystal. This balance of dissolution–precipitation shifts significantly toward a dissolution-dominated mechanism below about Ω=\u20090.7. Finally, we show that the enzyme carbonic anhydrase (CA) increases the dissolution rate across all saturation states, and the effect is most pronounced close to equilibrium. This finding suggests that the rate of hydration of CO_2 is a rate-limiting step for calcite dissolution in seawater. We then interpret our dissolution data in a framework that incorporates both solution chemistry and geometric constraints on the calcite solid. Near equilibrium, this framework demonstrates a lowered free energy barrier at the solid–solution interface in the presence of CA. This framework also indicates a significant change in dissolution mechanism at Ω=\u20090.7, which we interpret as the onset of homogeneous etch pit nucleation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/74554, title ="Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway", author = "Sim, Min Sub and Paris, Guillaume", journal = "Geochimica et Cosmochimica Acta", volume = "206", pages = "57-72", month = "June", year = "2017", doi = "10.1016/j.gca.2017.02.024", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170227-143517457", note = "© 2017 Elsevier Ltd. \n\nReceived 30 July 2016, Accepted 18 February 2017, Available online 27 February 2017. \n\nThis work was supported by an Agouron Geobiology Fellowship to MSS and the Gordon and Betty Moore Foundation Grant GBMF 3306 to VJO and ALS.", revision_no = "18", abstract = "Microbial sulfate reduction exhibits a normal isotope effect, leaving unreacted sulfate enriched in ^(34)S and producing sulfide that is depleted in ^(34)S. However, the magnitude of sulfur isotope fractionation is quite variable. The resulting changes in sulfur isotope abundance have been used to trace microbial sulfate reduction in modern and ancient ecosystems, but the intracellular mechanism(s) underlying the wide range of fractionations remains unclear. Here we report the concentrations and isotopic ratios of sulfur metabolites in the dissimilatory sulfate reduction pathway of Desulfovibrio alaskensis. Intracellular sulfate and APS levels change depending on the growth phase, peaking at the end of exponential phase, while sulfite accumulates in the cell during stationary phase. During exponential growth, intracellular sulfate and APS are strongly enriched in ^(34)S. The fractionation between internal and external sulfate is up to 49‰, while at the same time that between external sulfate and sulfide is just a few permil. We interpret this pattern to indicate that enzymatic fractionations remain large but the net fractionation between sulfate and sulfide is muted by the closed-system limitation of intracellular sulfate. This ‘reservoir effect’ diminishes upon cessation of exponential phase growth, allowing the expression of larger net sulfur isotope fractionations. Thus, the relative rates of sulfate exchange across the membrane versus intracellular sulfate reduction should govern the overall (net) fractionation that is expressed. A strong reservoir effect due to vigorous sulfate reduction might be responsible for the well-established inverse correlation between sulfur isotope fractionation and the cell-specific rate of sulfate reduction, while at the same time intraspecies differences in sulfate uptake and/or exchange rates could account for the significant scatter in this relationship. Our approach, together with ongoing investigations of the kinetic isotope fractionation by key enzymes in the sulfate reduction pathway, should provide an empirical basis for a quantitative model relating the magnitude of microbial isotope fractionation to their environmental and physiological controls.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/74232, title ="Lead isotopes in deep-sea coral skeletons: ground-truthing and a first deglacial Southern Ocean record", author = "Wilson, David J. and van de Flierdt, Tina", journal = "Geochimica et Cosmochimica Acta", volume = "204", pages = "350-374", month = "May", year = "2017", doi = "10.1016/j.gca.2017.01.052", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170213-095417473", note = "© 2017 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). \n\nReceived 21 August 2016, Revised 24 January 2017, Accepted 31 January 2017, Available online 9 February 2017. \n\nThis study was supported by Leverhulme Trust grant RPG-398 to TvdF, and NERC grant NE/N001141/1 to TvdF and DJW. We are very grateful to Sophia Hines for assistance with sampling from the Caltech coral collection and for providing published and unpublished U-Th ages; Luke Bridgestock for providing some of the NIST-SRM-981 standard data measured on the 10^(11) Ω resistor; Kirsty Crocket for supplying the coral powder used to prepare the in-house coral Pb standard; and Maxence Paul for establishing the double spike TIMS method at Imperial and for his initial efforts during installation of the 10^(12) Ω resistor. Katharina Kreissig and Barry Coles provided invaluable maintenance of the MAGIC clean labs and mass spectrometers. We further appreciate careful and thoughtful reviews from Wafa Abouchami, Ed Boyle and Marcus Gutjahr, and editorial handling by Claudine Stirling.", revision_no = "23", abstract = "Past changes in seawater lead (Pb) isotopes record the temporal evolution of anthropogenic pollution, continental weathering inputs, and ocean current transport. To advance our ability to reconstruct this signature, we present methodological developments that allow us to make precise and accurate Pb isotope measurements on deep-sea coral aragonite, and apply our approach to generate the first Pb isotope record for the glacial to deglacial mid-depth Southern Ocean.\nOur refined methodology includes a two-step anion exchange chemistry procedure and measurement using a ^(207)Pb-^(204)Pb double spike on a ThermoFinnigan Triton TIMS instrument. By employing a 10^(12) Ω resistor (in place of a 10^(11) Ω resistor) to measure the low-abundance ^(204)Pb ion beam, we improve the internal precision on ^(206,207,208)Pb/^(204)Pb for a 2 ng load of NIST-SRM-981 Pb from typically ∼420 ppm to ∼260 ppm (2 s.e.), and the long term external reproducibility from ∼960 ppm to ∼580 ppm (2 s.d.). Furthermore, for a typical 500 mg coral sample with low Pb concentrations (∼6-10 ppb yielding ∼3-5 ng Pb for analysis), we obtain a comparable internal precision of ∼150-250 ppm for ^(206,207,208)Pb/^(204)Pb, indicating a good sensitivity for tracing natural Pb sources to the oceans. Successful extraction of a seawater signal from deep-sea coral aragonite further relies on careful physical and chemical cleaning steps, which are necessary to remove anthropogenic Pb contaminants and obtain results that are consistent with ferromanganese crusts.\nApplying our approach to a collection of late glacial and deglacial corals (∼12-40 ka BP) from south of Tasmania at ∼1.4-1.7 km water depth, we generated the first intermediate water Pb isotope record from the Southern Ocean. That record reveals millennial timescale variability, controlled by binary mixing between two Pb sources, but no distinct glacial-interglacial Pb isotope shift. Mixing between natural endmembers is fully consistent with our data and points to a persistence of the same Pb sources through time, although we cannot rule out a minor influence from recent anthropogenic Pb. Whereas neodymium (Nd) isotopes in the Southern Ocean respond to global ocean circulation changes between glacial and interglacial periods, Pb isotopes record more localised mixing within the Antarctic Circumpolar Current, potentially further modulated by climate through changing terrestrial inputs from southern Africa or Australia. Such decoupling between Pb and Nd isotopes in the Southern Ocean highlights their potential to provide complementary insights into past oceanographic variability.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/75180, title ="Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age", author = "Wang, Xingchen Tony and Sigman, Daniel M.", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "114", number = "13", pages = "3352-3357", month = "March", year = "2017", doi = "10.1073/pnas.1615718114 ", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170316-111615042", note = "© 2017 National Academy of Sciences. \n\nEdited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved February 15, 2017 (received for review September 20, 2016). \n\nWe thank two anonymous reviewers for their constructive comments. This work was supported by National Science Foundation Grants OCE-1234664 (to M.G.P. and D.M.S.), PLR-1401489 (to D.M.S.), and OCE-1503129 (to J.F.A.), the Charlotte Elizabeth Procter Fellowship of the Graduate School at Princeton University (to X.T.W.), the Grand Challenges Program of Princeton University (D.M.S.), European Research Council Grant 278705 (to L.F.R.), and Natural Environmental Research Council Grant NE/N003861/1 (to L.F.R.). \n\nAuthor contributions: X.T.W., D.M.S., M.G.P., and G.H.H. designed research; X.T.W., D.M.S., and M.G.P. performed research; X.T.W., J.F.A., L.F.R., S.K.H., A.S.S., A.M.-G., and T.C. contributed new reagents/analytic tools; X.T.W. and J.C. analyzed data; and X.T.W. and D.M.S. wrote the paper. \n\nThe authors declare no conflict of interest. \n\nThis article is a PNAS Direct Submission. \n\nThis article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1615718114/-/DCSupplemental.", revision_no = "25", abstract = "The Southern Ocean regulates the ocean’s biological sequestration of CO_2 and is widely suspected to underpin much of the ice age decline in atmospheric CO_2 concentration, but the specific changes in the region are debated. Although more complete drawdown of surface nutrients by phytoplankton during the ice ages is supported by some sediment core-based measurements, the use of different proxies in different regions has precluded a unified view of Southern Ocean biogeochemical change. Here, we report measurements of the ^(15)N/^(14)N of fossil-bound organic matter in the stony deep-sea coral Desmophyllum dianthus, a tool for reconstructing surface ocean nutrient conditions. The central robust observation is of higher ^(15)N/^(14)N across the Southern Ocean during the Last Glacial Maximum (LGM), 18–25 thousand years ago. These data suggest a reduced summer surface nitrate concentration in both the Antarctic and Subantarctic Zones during the LGM, with little surface nitrate transport between them. After the ice age, the increase in Antarctic surface nitrate occurred through the deglaciation and continued in the Holocene. The rise in Subantarctic surface nitrate appears to have had both early deglacial and late deglacial/Holocene components, preliminarily attributed to the end of Subantarctic iron fertilization and increasing nitrate input from the surface Antarctic Zone, respectively.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/74484, title ="The transfer of bomb radiocarbon and anthropogenic lead to the deep North Atlantic Ocean observed from a deep sea coral", author = "Lee, Jong-Mi and Eltgroth, Selene F.", journal = "Earth and Planetary Science Letters", volume = "458", pages = "223-232", month = "January", year = "2017", doi = "10.1016/j.epsl.2016.10.049", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170223-071014897", note = "© 2016 Elsevier B.V. \n\nReceived 1 August 2016, Revised 21 October 2016, Accepted 24 October 2016, Available online 9 December 2016. \n\nWe thank the WHOI Alvin group and the crew of the Atlantis for recovering sample ALV 3701-8. We also thank Rick Kayser for maintaining the PQ2+ ICP-MS for Pb analysis. This work was supported by NSF grants OCE-0926197 and OCE-1503129.", revision_no = "12", abstract = "Deep-ocean, Δ^(14)C, Pb concentrations, and Pb isotopes were reconstructed from a deep-sea coral Enallopsammia rostrata from 1410 m depth off of Bermuda. Our high-resolution time series is created from closely spaced radial cross sections, with samples taken from the center of concentric coral growth bands that we show to be the oldest portion of the section. Prebomb radiocarbon ages from the coral demonstrate that the vertical growth rate of the coral is linear, and the age of the coral is estimated to be 560–630 yr old based on the growth rate. Using this age model to reconstruct Δ^(14)C in deep seawater, we first detect bomb radiocarbon at the coral growth site around 1980, and show that Δ^(14)C increased from −80±1‰−80±1‰ (average 1930–1979) to a plateau at −39±3‰ (1999–2001). Pb/Ca of the coral ranges between 1.1–4.5 nmol/mol during the 16th and 17th centuries, and Pb isotope ratios (^(206)Pb/^(207)Pb = 1.21, ^(208)Pb/^(207)Pb = 2.495) in this period agree with pre-anthropogenic values found in the pelagic sediments of the North Atlantic Ocean basin. Coral Pb/Ca is slightly elevated to 6.2±0.9 nmol/mol between the 1740s and the 1850s and then increases to 25.1±0.2 nmol/mol in the 1990s. The increase in coral Pb/Ca is accompanied by a decrease in coral ^(206)Pb/^(207)Pb and ^(208)Pb/^(207)Pb, indicating that the increase was caused by the infiltration of anthropogenic Pb to the coral growth site. Comparing our data to the surface coral Δ^(14)C and Pb records from Bermuda reveals a time scale of tracer transport from the surface ocean to the coral growth site. Some characteristic features, e.g., the bomb-derived Δ^(14)C increase, appear in the deep ocean approximately 25 yr later than the surface, but the overall increase of Δ^(14)C and Pb in the deep ocean is smaller and slower than the surface, showing the importance of mixing during the transport of these tracers.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/69016, title ="Rapid Organic Matter Sulfurization in Sinking Particles from the Cariaco Basin Water Column", author = "Raven, Morgan Reed and Sessions, Alex L.", journal = "Geochimica et Cosmochimica Acta", volume = "190", pages = "175-190", month = "October", year = "2016", doi = "10.1016/j.gca.2016.06.030", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160714-073258113", note = "© 2016 Elsevier Ltd. \n\nReceived Date: 1 December 2015; Accepted Date: 21 June 2016; Available online 25 June 2016. \n\nWe are grateful to Nathan Dalleska, Fenfang Wu and Guillaume Paris (Caltech) for analytical assistance, and to Eric Tappa (U. of South Carolina) for assistance with samples. We also thank the US National Science Foundation (award OCE-1258991 to R.C.T.) and Fundación La Salle de Ciencias Naturales, Estación de Investigaciones Marinas Isla Margarita (FLASA/EDIMAR) for their continuous effort in maintaining the CARIACO Ocean Time-Series program. This work was supported by NSF Award #OCE-1529120 to A.L.S. and was also funded in part by the Gordon and Betty Moore Foundation through Grant GBMF#3306 to A.L.S. We are grateful for insightful comments from two anonymous reviewers that substantially improved the manuscript and for careful editorial handling by Joseph Werne.", revision_no = "20", abstract = "Organic matter (OM) burial in marine sediments is a potentially important control on global climate and the long-term redox state of the earth’s surface. Still, we have only a limited understanding of the processes that stabilize OM and facilitate its preservation in the geologic record. Abiotic reactions with (poly)sulfides can enhance the preservation potential of OM, but for this process to be significant it needs to compete with OM remineralization, the majority of which occurs before sinking particles reach the sea floor. Here we investigate whether OM sulfurization occurs within sinking particles in the Cariaco Basin, a modern sulfidic marine environment with high rates of OM burial. Proto-kerogen in sinking particles is frequently more sulfur-rich and ^(34)S-depleted than expectations for biomass, with a composition that is difficult to explain by mixing with resuspended or terrigenous material. Instead, it appears that sulfur is being incorporated into OM on a timescale of days in sinking particles. The flux of this abiogenic organic S from particles is equivalent to approximately two-thirds of the total amount of proto-kerogen S at 10 cm depth in underlying sediments (ODP Core 1002B); after 6000 years of more gradual sulfurization reactions, potential water column sources are still equivalent to nearly half of the total proto-kerogen S in Cariaco sediments. Water column sulfurization is most extensive during periods of upwelling and high primary productivity and appears to involve elemental S, possibly via polysulfides. This process has the potential to deliver large amounts of OM to the sediments by making it less available for remineralization, generating OM-rich deposits. It represents a potentially dynamic sink in the global carbon cycle that can respond to changes in environmental conditions, including the size and intensity of O_2-depleted environments. Water column OM sulfurization could also have played a more significant role in the carbon cycle during ocean anoxic events, for example during the Cretaceous.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/70693, title ="The acid and alkalinity budgets of weathering in the Andes–Amazon system: Insights into the erosional control of global biogeochemical cycles", author = "Torres, Mark A. and West, A. Joshua", journal = "Earth and Planetary Science Letters", volume = "450", pages = "381-391", month = "September", year = "2016", doi = "10.1016/j.epsl.2016.06.012", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160930-124814278", note = "© 2016 Elsevier B.V.\n\nReceived 25 November 2015, Revised 8 June 2016, Accepted 9 June 2016, Available online 28 June 2016.\n\nFinancial support was provided by NSF EAR-1227192 and NSF EAR-1455352 to A.J. West. M. Torres was supported by USC and C-DEBI fellowships. K. Clark was supported by NSERC and Clarendon Fund Ph.D. scholarships. We thank ACCA Peru, Incaterra, and CREES for field support; A. Robles Caceres, J.A. Gibaja Lopez, J. Huamán Ovalle, R.J. Abarca Martínez, I. Cuba Torres, A. Alfaro-Tapia, D. Oviedo Licona, A. Ccahuana, and J. Farfan Flores for field assistance. Lou Derry and two anonymous reviewers are thanked for their comments on an earlier version of this manuscript.", revision_no = "20", abstract = "The correlation between chemical weathering fluxes and denudation rates suggests that tectonic activity can force variations in atmospheric pCO_2 by modulating weathering fluxes. However, the effect of weathering on pCO2 is not solely determined by the total mass flux. Instead, the effect of weathering on pCO_2 also depends upon the balance between 1) alkalinity generation by carbonate and silicate mineral dissolution and 2) sulfuric acid generation by the oxidation of sulfide minerals. In this study, we explore how the balance between acid and alkalinity generation varies with tectonic uplift to better understand the links between tectonics and the long-term carbon cycle.\nTo trace weathering reactions across the transition from the Peruvian Andes to the Amazonian foreland basin, we measured a suite of elemental concentrations (Na, K, Ca, Mg, Sr, Si, Li, SO4, and Cl) and isotopic ratios (^(87)Sr/^(86)Sr and δ^(34)S) on both dissolved and solid phase samples. Using an inverse model, we quantitatively link systematic changes in solute geochemistry with elevation to downstream declines in sulfuric acid weathering as well as the proportion of cations sourced from silicates. With a new carbonate-system framework, we show that weathering in the Andes Mountains is a CO_2 source whereas foreland weathering is a CO_2 sink. These results are consistent with the theoretical expectation that the ratio of sulfide oxidation to silicate weathering increases with increasing erosion. Altogether, our results suggest that the effect of tectonically-enhanced weathering on atmospheric pCO_2 is strongly modulated by sulfide mineral oxidation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/70358, title ="Study of thermochemical sulfate reduction mechanism using compound specific sulfur isotope analysis", author = "Meshoulam, Alexander and Ellis, Geoffrey S.", journal = "Geochimica et Cosmochimica Acta", volume = "188", pages = "73-92", month = "September", year = "2016", doi = "10.1016/j.gca.2016.05.026", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160915-075013877", note = "© 2016 Elsevier Ltd. \n\nReceived 26 November 2015; accepted in revised form 13 May 2016; available online 26 May 2016. \n\nAlexander Meshoulam thanks the Ministry of National Infrastructures Energy and Water Resources of Israel for MSc grant. Alon Amrani thanks the Israeli Science Foundation (ISF) Grant Number 1269/12 for partial support of this study. Liu Jinzhong acknowledge the support by the Chinese National Scientific Foundation number 41173069 and 41321001. We are also thank Gilad Antler (Cambridge University, UK) for bulk S analysis of some of the starting materials for interlaboratory comparison. We also grateful to Li Gao (PEERI), Bob Dias (U. S. Geological Survey) and three anonymous referees for helpful comments on an earlier version of this manuscript. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.", revision_no = "14", abstract = "The sulfur isotopic fractionation associated with the formation of organic sulfur compounds (OSCs) during thermochemical sulfate reduction (TSR) was studied using gold-tube pyrolysis experiments to simulate TSR. The reactants used included n-hexadecane (n-C_(16)) as a model organic compound with sulfate, sulfite, or elemental sulfur as the sulfur source. At the end of each experiment, the S-isotopic composition and concentration of remaining sulfate, H_2S, benzothiophene, dibenzothiophene, and 2-phenylthiophene (PT) were measured. The observed S-isotopic fractionations between sulfate and BT, DBT, and H_2S in experimental simulations of TSR correlate well with a multi-stage model of the overall TSR process. Large kinetic isotope fractionations occur during the first, uncatalyzed stage of TSR, 12.4‰ for H_2S and as much as 22.2‰ for BT. The fractionations decrease as the H_2S concentration increases and the reaction enters the second, catalyzed stage. Once all of the oxidizable hydrocarbons have been consumed, sulfate reduction ceases and equilibrium partitioning then dictates the fractionation between H_2S and sulfate (∼17‰).\nExperiments involving sparingly soluble CaSO_4 show that during the second catalytic phase of TSR the rate of sulfate reduction exceeds that of sulfate dissolution. In this case, there is no apparent isotopic fractionation between source sulfate and generated H_2S, as all of the available sulfate is effectively reduced at all reaction times. When CaSO_4 is replaced with fully soluble Na_2SO_4, sulfate dissolution is no longer rate limiting and significant S-isotopic fractionation is observed. This supports the notion that CaSO_4 dissolution can lead to the apparent lack of fractionation between H_2S and sulfate produced by TSR in nature. The S-isotopic composition of individual OSCs record information related to geochemical reactions that cannot be discerned from the δ^(34)S values obtained from bulk phases such as H2S, oil, and sulfate minerals, and provide important mechanistic details about the overall TSR process.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/66907, title ="Sedimentary pyrite δ^(34)S differs from porewater sulfide in Santa Barbara Basin: proposed role of organic sulfur", author = "Raven, Morgan Reed and Sessions, Alex L.", journal = "Geochimica et Cosmochimica Acta", volume = "186", pages = "120-134", month = "August", year = "2016", doi = "10.1016/j.gca.2016.04.037", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160510-131537800", note = "© 2016 Elsevier Ltd. \n\nReceived 10 June 2015, Accepted 19 April 2016, Available online 29 April 2016. \n\nWe gratefully acknowledge the science team and crew of R/V Atlantis cruise AT26-06, especially the efforts of Katherine S Dawson (Caltech), David L. Valentine, Karin Lemkau, and Alex Phillips (UC Santa Barbara). This work benefitted from helpful discussions with Victoria J. Orphan and Guillaume Paris, analytical support from David Lyons (UC Riverside) and Fenfang Wu (Caltech), and assistance with sediment extractions from Emilia S. Hernandez. Funding was provided by the National Science Foundation award OCE1436566 to A.L.S. and the Gordon and Betty Moore Foundation through Grant GBMF#3306 to A.L.S.. This manuscript was much improved by insightful reviews from David Fike (Washington U. in St. Louis), Maya Gomes (Harvard), and Matt Hurtgen (Northwestern U.) and the careful editorial handling of Claire Rollion-Bard.", revision_no = "18", abstract = "Santa Barbara Basin sediments host a complex network of abiotic and metabolic chemical reactions that knit together the carbon, sulfur, and iron cycles. From a 2.1-m sediment core collected in the center of the basin, we present high-resolution profiles of the concentrations and isotopic compositions of all the major species in this system: sulfate, sulfide (∑H_2S), elemental sulfur (S^0), pyrite, extractable organic sulfur (OS), proto-kerogen S, total organic and dissolved inorganic carbon, and total and reducible iron. Below 10 cm depth, the core is characterized by low apparent sulfate reduction rates (<0.01 mM/yr) except near the sulfate-methane transition zone. Surprisingly, pyrite forming in shallow sediments is ∼30‰ more ^(34)S-depleted than coexisting ∑H_2S in porewater. S^0 has the same strongly ^(34)S-depleted composition as pyrite where it forms near the sediment–water interface, though not at depth. This pattern is not easily explained by conventional hypotheses in which sedimentary pyrite derives from abiotic reactions with porewater ∑H_2S or from the products of S^0 disproportionation. Instead, we propose that pyrite formation in this environment occurs within sulfate reducing microbial aggregates or biofilms, where it reflects the isotopic composition of the immediate products of bacterial sulfate reduction. Porewater ∑H_2S in Santa Barbara Basin may be more ^(34)S-enriched than pyrite due to equilibration with relatively ^(34)S-enriched OS. The difference between OS and pyrite δ^(34)S values would then reflect the balance between microbial sulfide formation and the abundance of exchangeable OS. Both OS and pyrite δ34S records thus have the potential to provide valuable information about biogeochemical cycles and redox structure in sedimentary paleoenvironments.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/67634, title ="Calcium isotopes in scleractinian fossil corals since the Mesozoic: Implications for vital effects and biomineralization through time", author = "Gothmann, Anne M. and Bender, Michael L.", journal = "Earth and Planetary Science Letters", volume = "444", pages = "205-214", month = "June", year = "2016", doi = "10.1016/j.epsl.2016.03.012", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160603-073625755", note = "© 2016 Elsevier B.V. \n\nReceived 24 September 2015; Received in revised form 27 February 2016; Accepted 6 March 2016; Available online 7 April 2016. \n\nWe would like to thank Stephen Cairns and Tim Coffer (Smithsonian Institution), Linda Ivany (Syracuse University), Roger Portell (Florida Museum of Natural History), Anne Cohen and Bill Thompson (WHOI), the USGS, and Gregory Dietl (Paleontological Research Institution) for loaning samples. We would also like to thank Alex Gagnon for helpful discussions and Elizabeth Lundstrom, Tom Capo and Phil Gillette for experimental assistance. We would like to acknowledge the Princeton BP Amoco Carbon Mitigation Initiative and the Frank Harrison Tuttle Memorial Fund for Invertebrate studies for their generous support.", revision_no = "13", abstract = "We present a Cenozoic record of δ^(44/40)Ca from well preserved scleractinian fossil corals, as well as fossil coral δ^(44/40)Ca data from two time periods during the Mesozoic (84 and 160 Ma). To complement the coral data, we also extend existing bulk pelagic carbonate records back to ∼80 Ma. The same fossil corals used for this study were previously shown to be excellently preserved, and to be faithful archives of past seawater Mg/Ca and Sr/Ca since ∼200 Ma (Gothmann et al., 2015). We find that the δ^(44/40)Ca compositions of bulk pelagic carbonates from ODP Site 807 (Ontong Java Plateau) and DSDP Site 516 (Rio Grande Rise) have not varied by more than ∼±0.20‰ over the last ∼80 Myr. In contrast, the δ^(44/40)Ca compositions of Mesozoic and Early Cenozoic fossil corals are ∼1‰ lighter than those of modern corals.\nThe observed change in coral δ^(44/40)Ca does not likely reflect secular variations in seawater δ^(44/40)Ca. Instead, we propose that it reflects a vital effect of calcification – specifically, a sensitivity of coral Ca isotope discrimination to changing seawater [Ca] and/or pH. Support for this hypothesis comes from the presence of an empirical correlation between our coral δ^(44/40)Ca record and records of seawater [Ca] and pH since the Mesozoic (Lowenstein et al., 2003 and Hönisch et al., 2012). We explore various mechanisms that could give rise to such a vital effect, including: (1) changes in calcification rate, (2) changes in proton pumping in exchange for Ca^(2+), (3) variable Rayleigh distillation from an isolated calcifying fluid, and (4) changes in the calcium mass balance of the extracellular calcifying fluid (termed here the “leaky Ca model”). We test for the dependence of seawater δ^(44/40)Ca on external seawater [Ca] by measuring the δ^(44/40)Ca of cultured corals grown in seawater solutions with [Ca] ranging from 10 to 15 mmol/kg. Corals grown under elevated [Ca] conditions show a slight, ∼0.15‰ depletion of δ^(44/40)Ca at higher seawater [Ca] – a supportive but not definitive result.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/67462, title ="A high-resolution speleothem record of western equatorial Pacific rainfall: Implications for Holocene ENSO evolution", author = "Chen, Sang and Hoffmann, Sharon S.", journal = "Earth and Planetary Science Letters", volume = "442", pages = "61-71", month = "May", year = "2016", doi = "10.1016/j.epsl.2016.02.050", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160527-130608031", note = "© 2016 Elsevier B.V. \n\nReceived 29 October 2015; Received in revised form 23 February 2016; Accepted 28 February 2016; Available online 10 March 2016. \n\nWe would like to thank Gunung Buda and Gunung Mulu National Park crew for field assistance. We are grateful to Lora Wingate who performed the stable isotope analyses. We would also like to thank Rachel Sortor, Rachel Franzblau, Rachel Seltz, Alec Washabaugh and Naomi Huntley for help with micromilling, and Stacy Carolin for help with the U–Th dating. Derek Vance, Kathleen Johnson and an anonymous reviewer provided constructive feedbacks that helped improve the manuscript. The research was supported by NSF grant AGS-1103385.", revision_no = "10", abstract = "The El Niño-Southern Oscillation (ENSO) is the primary driver of interannual climate variability in the tropics and subtropics. Despite substantial progress in understanding ocean–atmosphere feedbacks that drive ENSO today, relatively little is known about its behavior on centennial and longer timescales. Paleoclimate records from lakes, corals, molluscs and deep-sea sediments generally suggest that ENSO variability was weaker during the mid-Holocene (4–6 kyr\u2009BP) than the late Holocene (0–4 kyr\u2009BP). However, discrepancies amongst the records preclude a clear timeline of Holocene ENSO evolution and therefore the attribution of ENSO variability to specific climate forcing mechanisms. Here we present δ^(18)O results from a U–Th dated speleothem in Malaysian Borneo sampled at sub-annual resolution. The δ^(18)O of Borneo rainfall is a robust proxy of regional convective intensity and precipitation amount, both of which are directly influenced by ENSO activity. Our estimates of stalagmite δ^(18)O variance at ENSO periods (2–7 yr) show a significant reduction in interannual variability during the mid-Holocene (3240–3380 and 5160–5230 yr\u2009BP) relative to both the late Holocene (2390–2590 yr\u2009BP) and early Holocene (6590–6730 yr\u2009BP). The Borneo results are therefore inconsistent with lacustrine records of ENSO from the eastern equatorial Pacific that show little or no ENSO variance during the early Holocene. Instead, our results support coral, mollusc and foraminiferal records from the central and eastern equatorial Pacific that show a mid-Holocene minimum in ENSO variance. Reduced mid-Holocene interannual δ^(18)O variability in Borneo coincides with an overall minimum in mean δ^(18)O from 3.5 to 5.5 kyr\u2009BP. Persistent warm pool convection would tend to enhance the Walker circulation during the mid-Holocene, which likely contributed to reduced ENSO variance during this period. This finding implies that both convective intensity and interannual variability in Borneo are driven by coupled air-sea dynamics that are sensitive to precessional insolation forcing. Isolating the exact mechanisms that drive long-term ENSO evolution will require additional high-resolution paleoclimatic reconstructions and further investigation of Holocene tropical climate evolution using coupled climate models.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/65831, title ="Northern Borneo stalagmite records reveal West Pacific hydroclimate across MIS 5 and 6", author = "Carolin, Stacy A. and Cobb, Kim M.", journal = "Earth and Planetary Science Letters", volume = "439", pages = "182-193", month = "April", year = "2016", doi = "10.1016/j.epsl.2016.01.028", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160401-073443500", note = "© 2016 Elsevier B.V. \n\nReceived 16 August 2015; Received in revised form 16 January 2016; Accepted 23 January 2016; Available online 11 February 2016. \n\nWe thank Danja Mewes, Eleanor Middlemas, and Sang Chen for fieldwork assistance, and all the staff at Gunung Mulu National Park World Heritage Site for their dedicated assistance during field expeditions. We also thank Guillaume Paris, Sophie Hines, James Rae, and Andrea Burke for their assistance in U–Th dating, and Hussein Sayani, Pamela Grothe, and Tammy Chang for their assistance in oxygen isotope measurements. The research was funded by NSF PECASE Award #0645291 and NSF AGS Award #1502830 to KMC, NSF AGS award #0903099 to JFA, and a NSF Graduate Research Fellowship to SAC. Permits for this work were granted by the Malaysian Economic Planning Unit, the Sarawak State Planning Unit, and the Sarawak Forestry Department. All data reported in this paper are archived at NCDC (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/speleothem/pacific/gunung-mulu2016.txt).", revision_no = "12", abstract = "Over the past decades, tropical stalagmite δ^(18)O records have provided valuable insight on glacial and interglacial hydrological variability and its relationship to a variety of natural climate forcings. The transition out of the penultimate glaciation (MIS 6) represents an important target for tropical hydroclimate reconstructions, yet relatively few such reconstructions resolve this transition. Particularly, comparisons between Termination 1 and 2 provide critical insight on the extent and influence of proposed climate mechanisms determined from paleorecords and model experiments spanning the recent deglaciation. Here we present a new compilation of western tropical Pacific hydrology spanning 0–160 ky\u2009BP, constructed from eleven different U/Th-dated stalagmite δ^(18)O records from Gunung Mulu National Park in northern Borneo. The reconstruction exhibits significant precessional power in phase with boreal fall insolation strength over the 0–160 ky\u2009BP period, identifying precessional insolation forcing as the dominant driver of hydroclimate variability in northern Borneo on orbital timescales. A comparison with a network of paleoclimate records from the circum-Pacific suggests the insolation sensitivity may arise from changes in the Walker circulation system. Distinct millennial-scale increases in stalagmite δ^(18)O, indicative of reduced regional convection, occur within glacial terminations and may reflect a response to shifts in inter-hemispheric temperature gradients. Our results imply that hydroclimate in this region is sensitive to external forcing, with a response dominated by large-scale temperature gradients.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/65431, title ="Neodymium isotope analyses after combined extraction of actinide and lanthanide elements from seawater and deep-sea coral aragonite", author = "Struve, Torben and van de Flierdt, Tina", journal = "Geochemistry, Geophysics, Geosystems", volume = "17", number = "1", pages = "232-240", month = "January", year = "2016", doi = "10.1002/2015GC006130", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160317-105910625", note = "© 2015 American Geophysical Union. \n\nReceived 5 OCT 2015; Accepted 5 DEC 2015; Accepted article online 14 DEC 2015; Published online 9 JAN 2016. \n\nWe thank the team on the second leg of the first GEOTRACES intercalibration cruise for sample collection, Joanne Goudreau, Kuo Fang Huang, Jurek Bluztajn for help at the WHOI Plasma facility, Martin Fleisher and Sven Kretschmer for discussion, and Derek Vance for sharing his 150Nd spike. Torben Stichel is acknowledged for help during column calibration. All data presented in this manuscript can be found in the table included in the main body of the text. Funding that supported this work was received from the National Science Foundation (NSF 0752402), the Leverhulme Trust (RPG-398), the Natural Environmental Research Council (NE/J021636/1 and NE/N003861/1), the European Research Council (278705), and the Grantham Institute for Climate Change. We thank Marcus Gutjahr and an anonymous reviewer for constructive comments on the manuscript and acknowledge the editorial handling by Yusuke Yokoyama.", revision_no = "12", abstract = "Isotopes of the actinide elements protactinium (Pa), thorium (Th), and uranium (U), and the lanthanide element neodymium (Nd) are often used as complementary tracers of modern and past oceanic processes. The extraction of such elements from low abundance matrices, such as seawater and carbonate, is however labor-intensive and requires significant amounts of sample material. We here present a combined method for the extraction of Pa, Th, and Nd from 5 to 10 L seawater samples, and of U, Th, and Nd from <1 g carbonate samples. Neodymium is collected in the respective wash fractions of Pa-Th and U-Th anion exchange chromatographies. Regardless of the original sample matrix, Nd is extracted during a two-stage ion chromatography, followed by thermal ionization mass spectrometry (TIMS) analysis as NdO+. Using this combined procedure, we obtained results for Nd isotopic compositions on two GEOTRACES consensus samples from Bermuda Atlantic Time Series (BATS), which are within error identical to results for separately sampled and processed dedicated Nd samples (ε_(Nd)\u2009=\u2009−9.20\u2009±\u20090.21 and −13.11\u2009±\u20090.21 for 15 and 2000 m water depths, respectively; intercalibration results from 14 laboratories: ε_(Nd)\u2009=\u2009−9.19\u2009±\u20090.57 and −13.14\u2009±\u20090.57). Furthermore, Nd isotope results for an in-house coral reference material are identical within analytical uncertainty for dedicated Nd chemistry and after collection of Nd from U-Th anion exchange chromatography. Our procedure does not require major adaptations to independently used ion exchange chromatographies for U-Pa-Th and Nd, and can hence be readily implemented for a wide range of applications.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/61966, title ="A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years", author = "Hines, Sophia K. V. and Southon, John R.", journal = "Earth and Planetary Science Letters", volume = "432", pages = "46-58", month = "December", year = "2015", doi = "10.1016/j.epsl.2015.09.038", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20151106-150028884", note = "© 2015 Elsevier B.V. \n\nReceived 5 February 2015, Revised 8 September 2015, Accepted 24 September 2015, Available online 3 November 2015. \n\nWe would like to thank Heather Stoll, the editor of this paper, and three reviewers for their helpful comments. We would also like to acknowledge analytical help from Guillaume Paris. This work was funded by NSF P2C2 grant OCE-1204211.", revision_no = "15", abstract = "The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial–interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow depth range. The record shows three distinct periods of circulation: the MIS 3–2 transition, the LGM/Heinrich Stadial 1 (extending from ∼22 to 16 kyr BP), and the Antarctic Cold Reversal (ACR). The MIS 3–2 transition and the ACR are characterized by abrupt changes in intermediate water radiocarbon while the LGM time period generally follows the atmosphere at a constant offset, in support of the idea that the LGM ocean was at steady state for its ^(14)C distribution. Closer inspection of the LGM time period reveals a 40‰ jump at ∼19 ka from an atmospheric offset of roughly 230‰ to 190‰, coincident with an observed 10–15 m rise in sea level and a southward shift of the Subantarctic and Polar Fronts, an abrupt change not seen in deeper records. During the ACR time period intermediate water radiocarbon is on average less offset from the atmosphere (∼110‰∼110‰) and much more variable. This variability has been captured within the lifetimes of three individual corals with changes of up to 35‰ over ∼40 yr, likely caused by the movement of Southern Ocean fronts. This surprising result of relatively young and variable intermediate water radiocarbon during the ACR seems to go against the canonical idea of reduced circulation and ventilation in the south during this time period. However comparisons with other records from the Southern Ocean highlight zonal asymmetries, which can explain the deviation of our Tasmanian record from those in Drake Passage and the eastern Pacific. These signals seen in Tasmanian intermediate water Δ^(14)C can also be found in Greenland ice core δ^(18)O and East Asian monsoon strength. Throughout the LGM and the deglaciation, our Tasmanian intermediate water record is sensitive to times when the upper and lower cells of the meridional overturning circulation are more or less interconnected, which has important implications for the global climate system on glacial–interglacial time scales.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/61968, title ="Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata", author = "Present, Theodore M. and Paris, Guillaume", journal = "Earth and Planetary Science Letters", volume = "432", pages = "187-198", month = "December", year = "2015", doi = "10.1016/j.epsl.2015.10.005", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20151106-150649239", note = "© 2015 Elsevier B.V. \n\nReceived 18 June 2015; Received in revised form 30 September 2015; Accepted 4 October 2015. \n\nFunding for this work was provided by the American Chemical Society Petroleum Research Fund New Directions grant #53994-ND2, NSF Division of Earth Sciences award EAR-1349858, and the Agouron Institute grant AI-GC17.09.3. We thank David Jones and Benjamin Gill for thoughtful reviews. We thank David Fike and Seth Finnegan for helpful input and field context for the Anticosti Island specimens. We thank Renata Cummins for instruction on how to prepare brachiopod secondary-layer fibrous calcite, and Lindsey Hedges, Fenfang Wu, and Nathan Dalleska for analytical support. We thank Joe Kirschvink for help interpreting rock magnetic data. Thank you to Kristin Bergmann for providing the T. transversa specimen, and Nivedita Thiagarajan for help preparing deep-sea coral samples. Ion chromatography was done at the Caltech Environmental Analysis Center.", revision_no = "21", abstract = "Carbonate Associated Sulfate (CAS) is trace sulfate incorporated into carbonate minerals during their precipitation. Its sulfur isotopic composition is often assumed to track that of seawater sulfate and inform global carbon and oxygen budgets through Earth's history. However, many CAS sulfur isotope records based on bulk-rock samples are noisy. To determine the source of bulk-rock CAS variability, we extracted CAS from different internal sedimentary components micro-drilled from well-preserved Late Ordovician and early Silurian-age limestones from Anticosti Island, Quebec, Canada. Mixtures of these components, whose sulfur isotopic compositions vary by nearly 25‰, can explain the bulk-rock CAS range. Large isotopic variability of sedimentary micrite CAS (^(34)S-depleted from seawater by up to 15‰) is consistent with pore fluid sulfide oxidation during early diagenesis. Specimens recrystallized during burial diagenesis have CAS ^(34)S-enriched by up to 9‰ from Hirnantian seawater, consistent with microbial sulfate reduction in a confined aquifer. In contrast to the other variable components, brachiopods with well-preserved secondary-layer fibrous calcite—a phase independently known to be the best-preserved sedimentary component in these strata—have a more homogeneous isotopic composition. These specimens indicate that seawater sulfate remained close to about 25‰ (V-CDT) through Hirnantian (end-Ordovician) events, including glaciation, mass extinction, carbon isotope excursion, and pyrite-sulfur isotope excursion. The textural relationships between our samples and their CAS isotope ratios highlight the role of diagenetic biogeochemical processes in setting the isotopic composition of CAS.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60223, title ="A novel determination of calcite dissolution kinetics in seawater", author = "Subhas, Adam V. and Rollins, Nick E.", journal = "Geochimica et Cosmochimica Acta", volume = "170", pages = "51-68", month = "December", year = "2015", doi = "10.1016/j.gca.2015.08.011", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150914-094735715", note = "© 2015 Elsevier Ltd.\n\nReceived 2 January 2015; accepted in revised form 11 August 2015; Available online 31 August 2015.\n\nThe authors would like to acknowledge Eric Kleinsasser and Joel Schmidt for help with BET analysis, and Burke Hales for helpful suggestions regarding the solubility of calcites. We also thank the three anonymous reviewers for their comments and criticisms on the original manuscript drafts. This work was supported by an NSF Ocean Acidification grant (numbers OCE1220600 and OCE1220302) and the NSF Graduate Research Fellowship.", revision_no = "12", abstract = "We present a novel determination of the dissolution kinetics of inorganic calcite in seawater. We dissolved ^(13)C-labeled calcite in unlabeled seawater, and traced the evolving δ^(13)C composition of the fluid over time to establish dissolution rates. This method provides sensitive determinations of dissolution rate, which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals. We have determined dissolution rates for two different abiotic calcite materials and three different grain sizes. Near-equilibrium dissolution rates are highly nonlinear, and are well normalized by geometric surface area, giving an empirical dissolution rate dependence on saturation state (Ω) of:\n\nRate (g/cm^2/day) = 7.2 ± 0.6 · 10^(-4) (1-Ω)^(3.9±0.1).\n \nThis result substantiates the non-linear response of calcite dissolution to undersaturation. The bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments. Plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms, implying a criticality in the calcite-seawater system. Finally, our new rate determination has implications for modeling of pelagic and seafloor dissolution. Nonlinear dissolution kinetics in a simple 1-D lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth, and also confirm the importance of respiration-driven dissolution in setting the shape of the calcite lysocline.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/62762, title ="Glacial–interglacial temperature change in the tropical West Pacific: A comparison of stalagmite-based paleo-thermometers", author = "Meckler, A. Nele and Affolter, Stéphane", journal = "Quaternary Science Reviews", volume = "127", pages = "90-116", month = "November", year = "2015", doi = "10.1016/j.quascirev.2015.06.015", issn = "0277-3791", url = "https://resolver.caltech.edu/CaltechAUTHORS:20151210-071155702", note = "© 2015 Elsevier Ltd. \n\nReceived 23 January 2015; Received in revised form 12 June 2015; Accepted 16 June 2015; Available online 3 July 2015. \n\nWe thank Syria Lejau, Jenny Malang, Jud Partin, Andrew Tuen, and Brian Clark for assistance with fieldwork. Stewart Bishop, Madalina Jaggi, Isabel Millán, Sebastian Breitenbach, and Martin Ziegler helped with clumped isotope labwork and method development.\nWe are grateful to Hagit Affek for providing standard data and discussing inter-laboratory differences. Rita Hidalgo contributed to homogenization temperature measurements. We thank the Royal Society SE Rainforest Research Programme for provision of the climatic data at Danum Valley Field Centre used in this paper. This work was supported by the Swiss National Science Foundation through the Sinergia project StalClim (grant CRSI22_132646/1) and Marie-Heim-Vögtlin grant PMPDP2_139701 to ANM.", revision_no = "14", abstract = "In the tropics, geochemical records from stalagmites have so far mainly been used to qualitatively reconstruct changes in precipitation, but several new methods to reconstruct past temperatures from stalagmite material have emerged recently: i) liquid–vapor homogenization of fluid inclusion water ii) noble gas concentrations in fluid inclusion water, iii) the partitioning of oxygen isotopes between fluid inclusion water and calcite, and iv) the abundance of the ^(13)C^(18)O^(16)O (‘clumped’) isotopologue in calcite. We present, for the first time, a direct comparison of these four paleo-thermometers by applying them to a fossil stalagmite covering nearly two glacial–interglacial cycles (Marine Isotope Stages (MIS) 12–9) and to two modern stalagmites, all from northern Borneo. The temperature estimates from the different methods agree in most cases within errors for both the old and recent samples; reconstructed formation temperatures of the recent samples match within 2-sigma errors with measured cave temperatures. However, slight but systematic deviations are observed between noble gas and liquid–vapor homogenization temperatures. Whereas the temperature sensitivity of fluid inclusion δ^(18)O and clumped isotopes is currently debated, we find that the calibration of Tremaine et al. (2011) for fluid inclusion δ^(18)O and a synthetic calcite-based clumped isotope calibration (Ziegler et al., in prep.) yield temperature estimates consistent with the other methods. All methods (with the potential exception of clumped isotopes) show excellent agreement on the amplitude of glacial–interglacial temperature change, indicating temperature shifts of 4–5 °C. This amplitude is similar to the amplitude of Mg/Ca-based regional sea surface temperature records, when correcting for sea level driven changes in cave elevation. Our reconstruction of tropical temperature evolution over the time period from 440 to 320 thousand years ago (ka) adds support to the view that climate sensitivity to varying greenhouse forcing is substantial also in the deep tropics.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60308, title ="Fractionation of iron isotopes during leaching of natural particles by acidic and circumneutral leaches and development of an optimal leach for marine particulate iron isotopes", author = "Revels, Brandi N. and Zhang, Ruifeng", journal = "Geochimica et Cosmochimica Acta", volume = "166", pages = "92-104", month = "October", year = "2015", doi = "10.1016/j.gca.2015.05.034", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150917-161039542", note = "© 2015 Elsevier. \n\nReceived 30 October 2014; accepted in revised form 19 May 2015; available online 30 May 2015. \n\nThe authors would like to thank Angela Rosenberg and Beth Bair for technical assistance with isotopic analyses, and Bob Thunell for providing Cariaco sediment trap samples. This work was supported by National Science Foundation Grants OCE-1131387 and OCE-1334029. RZ was supported by The National Natural Science Foundation of China Grant 41006043. This manuscript was significantly improved by the suggestions of three anonymous reviewers.", revision_no = "11", abstract = "Iron (Fe) is an essential nutrient for life on land and in the oceans. Iron stable isotope ratios (δ^(56)Fe) can be used to study the biogeochemical cycling of Fe between particulate and dissolved phases in terrestrial and marine environments. We have investigated the dissolution of Fe from natural particles both to understand the mechanisms of Fe dissolution, and to choose a leach appropriate for extracting labile Fe phases of marine particles. With a goal of finding leaches which would be appropriate for studying dissolved-particle interactions in an oxic water column, three particle types were chosen including oxic seafloor sediments (MESS-3), terrestrial dust (Arizona Test Dust – A2 Fine), and ocean sediment trap material from the Cariaco basin. Four leaches were tested, including three acidic leaches similar to leaches previously applied to marine particles and sediments (25% acetic acid, 0.01 N HCl, and 0.5 N HCl) and a pH 8 oxalate-EDTA leach meant to mimic the dissolution of particles by organic complexation, as occurs in natural seawater. Each leach was applied for three different times (10 min, 2 h, 24 h) at three different temperatures (25 °C, 60 °C, 90 °C). MESS-3 was also leached under various redox conditions (0.02 M hydroxylamine hydrochloride or 0.02 M hydrogen peroxide). For all three sample types tested, we find a consistent relationship between the amount of Fe leached and leachate δ56Fe for all of the acidic leaches, and a different relationship between the amount of Fe leached and leachate δ^(56)Fe for the oxalate-EDTA leach, suggesting that Fe was released through proton-promoted dissolution for all acidic leaches and by ligand-promoted dissolution for the oxalate-EDTA leach. Fe isotope fractionations of up to 2‰ were observed during acidic leaching of MESS-3 and Cariaco sediment trap material, but not for Arizona Test Dust, suggesting that sample composition influences fractionation, perhaps because Fe isotopes are greatly fractionated during leaching of silicates and clays but only minimally fractionated during dissolution of Fe oxyhydroxides. Two different analytical models were developed to explain the relationship between amount of Fe leached and δ^(56)Fe, one of which assumes mixing between two Fe phases with different δ^(56)Fe and different dissolution rates, and the other of which assumes dissolution of a single phase with a kinetic isotope effect. We apply both models to fit results from the acidic leaches of MESS-3 and find that the fit for both models is very similar, suggesting that isotope data will never be sufficient to distinguish between these two processes for natural materials. Next, we utilize our data to choose an optimal leach for application to marine particles. The oxalate-EDTA leach is well-suited to this purpose because it does not greatly fractionate Fe isotopes for a diversity of particle types over a wide variety of leaching conditions, and because it approximates the conditions by which particulate Fe dissolves in the oceans. We recommend a 2 h leach at 90 °C with 0.1 M oxalate and 0.05 M EDTA at pH 8 to measure labile “ligand-leachable” particulate δ56Fe on natural marine materials with a range of compositions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60074, title ="The Information Content of Pore Fluid δ^(18)O and [CI^-]", author = "Miller, Madeline D. and Simons, Mark", journal = "Journal of Physical Oceanography", volume = "45", number = "8", pages = "2070-2094", month = "August", year = "2015", doi = "10.1175/JPO-D-14-0203.1", issn = "0022-3670", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150904-105720688", note = "© 2015 American Meteorological Society. \n\nManuscript received 25 September 2014, in final form 15 May 2015.\n\nM.D.M. thanks William Jenkins for introduction to the Lomb–Scargle periodogram and Eli Tziperman for many helpful discussions and constructive reviews of drafts of this manuscript. ", revision_no = "11", abstract = "Paleoceanographic proxies indicate that the ocean state during the Last Glacial Maximum (LGM) differed from the modern ocean state. Depth profiles of ocean sediment pore fluid δ^(18)O and [Cl^−] have been used to reconstruct the δ^(18)O and salinity at the LGM. Here, it is investigated whether pore fluid profiles can constrain ocean δ^(18)O and salinity at other times and, simultaneously, their ability to constrain the LGM δ^(18)O and salinity. An inverse framework is developed that relies on Bayesian parameter estimation, thus allowing formal separation of prior assumptions from the information in observations. Synthetic problems are used to explore the information about past ocean tracers that can be recovered from pore fluid profiles. It is concluded that prior knowledge of deep ocean mixing time scales is essential to an accurate inverse estimate of LGM ocean salinity and δ^(18)O from modern pore fluid profiles. The most recent 10 000 years of ocean salinity and δ^(18)O and the error in their estimates are better constrained by the pore fluid profiles than are the LGM values. The inverse estimate of salinity and δ^(18)O is strongly correlated with the estimate of diffusivity of oxygen isotopes and [Cl^−] in sediment pore fluids. Uncertainty on the diffusivity of oxygen isotopes and chloride in sediments is reduced through inversion of the pore fluid profiles, but simultaneous estimation of δ^(18)O or salinity and diffusivity increases the total uncertainty. The error reported in previous work may underestimate the true uncertainty of LGM deep ocean salinity and δ^(18)O.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/58215, title ="Fossil corals as an archive of secular variations in seawater chemistry since the Mesozoic", author = "Gothmann, Anne M. and Stolarski, Jarosław", journal = "Geochimica et Cosmochimica Acta", volume = "160", pages = "188-208", month = "July", year = "2015", doi = "10.1016/j.gca.2015.03.018 ", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150612-130535847", note = "© 2015 Elsevier Ltd.\n\nReceived 17 July 2014; accepted in revised form 16 March 2015; available online 25 March 2015.\n\nWe thank Yunbin Guan (California Institute of Technology) for his help with SIMS analyses, Gerald Poirier (Princeton Imaging and Analysis Center) for assistance with SEM and XRD, and Guillaume Paris (California Institute of Technology) for his help with sulfate concentration analyses. This manuscript has benefitted tremendously from helpful discussions with John M. Eiler (California Institute of Technology), John A. Higgins (Princeton University), Alex C. Gagnon (University of Washington) and helpful comments from Silke Severmann (AE), Tim Lowenstein, and two anonymous reviewers. We also thank Stephen A. Cairns, Tim Coffer (Smithsonian Institution), Roger Portell (Florida Museum of Natural History), the USGS Core Research Center, Bill Thompson (WHOI), Gregory P. Dietl (Paleontological Research Institution), and Linda Ivany (Syracuse University) for contributing samples for this work. The work of JS was supported in part by the Polish-Norwegian Research Programme operated by the National Centre for Research and Development under the Norwegian Financial Mechanism 2009–2014 in the frame of Project Contract No Pol-Nor/196260/81/2013. Cathodoluminescence imaging was performed in the NanoFun Laboratory (Institute of Paleobiology) co-financed by the European Regional Development Fund within the Innovation Economy Operational Programme POIG.02.02.00-00-025/09. We gratefully acknowledge support from the Princeton BP Amoco Carbon Mitigation Initiative, and from the Frank Harrison Tuttle Memorial Fund for Invertebrate studies.", revision_no = "13", abstract = "Numerous archives suggest that the major ion and isotopic composition of seawater have changed in parallel with large variations in geologic processes and Earth’s climate. However, our understanding of the mechanisms driving secular changes in seawater chemistry on geologic timescales is limited by the resolution of data in time, large uncertainties in seawater chemistry reconstructions, and ambiguities introduced by sample diagenesis. We validated the preservation of a suite of ∼60 unrecrystallized aragonitic fossil scleractinian corals, ranging in age from Triassic through Recent, for use as new archives of past seawater chemistry. Optical and secondary electron microscopy (SEM) studies reveal that fossil coral crystal fabrics are similar to those of modern coralline aragonite. X-ray diffractometry (XRD), cathodoluminescence microscopy (CL), and Raman studies confirm that these specimens contain little to no secondary calcite. In order to screen for geochemical changes indicative of alteration, we measured ^(87)Sr/^(86)Sr ratios, clumped isotopes, and trace element ratios sensitive to diagenesis (e.g., Mn/Ca). We retain samples when these tests either fail to identify any diagenetic modifications, or identify specific domains free of detectable alteration.\nUsing the validated fossil coral archive we reconstruct seawater Mg/Ca and Sr/Ca ratios, measured by Secondary Ion Mass Spectrometry (SIMS), back to ∼230 Ma. The effects of temperature on coral trace element incorporation cannot explain the trends observed in our fossil coral Mg/Ca and Sr/Ca data. In agreement with independent records, seawater Mg/Ca molar ratios inferred from corals are low (Mg/Ca ∼1) during the Cretaceous and Jurassic, and increase between the Early Cenozoic and present (Mg/Ca = 5.2). Seawater Sr/Ca ratios from corals vary systematically between ∼8 and 13 mmol/mol since 230 Ma, with maximum values in the Cretaceous and Paleogene. The coral Sr/Ca record disagrees with records from hydrothermal CaCO_3 veins, but is similar to those reconstructed from other biogenic carbonates, especially benthic foraminifera. The agreement between corals and other archives, for both Sr/Ca and Mg/Ca ratios, further validates our records. In return, fossil coral records improve our understanding of past variations in seawater Mg/Ca and Sr/Ca.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60176, title ="The glacial mid-depth radiocarbon bulge and its implications for the overturning circulation", author = "Burke, Andrea and Stewart, Andrew L.", journal = "Paleoceanography", volume = "30", number = "7", pages = "1021-1039", month = "July", year = "2015", doi = "10.1002/2015PA002778", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150910-140031548", note = "© 2015 American Geophysical Union. \n\nReceived 7 JAN 2015; Accepted 27 MAY 2015; Accepted article online 2 JUN 2015; Published online 28 JUL 2015. \n\nThis work was supported by a Foster and Coco Stanback Postdoctoral Fellowship and a Marie Curie Career Integration grant (CIG14-631752) awarded to A.B., and an NSF grant awarded to A.F.T. (OPP-1246460). All radiocarbon data presented in this paper can be found in supplemental tables from previous publications (http://www.sciencemag.org/content/335/6068/557, http://www.sciencemag.org/cgi/doi/10.1126/science.1183627, and http://www.nature.com/ngeo/journal/v3/n8/full/ngeo921.html) or from the GLODAP database (http://cdiac.ornl.gov/oceans/glodap/GlopDV.html) [Key et al., 2004]. Model results are available by request to ALS (astewart@atmos.ucla.edu).\n\nAndrea Burke and Andrew L. Stewart contributed equally to this work.", revision_no = "18", abstract = "Published reconstructions of radiocarbon in the Atlantic sector of the Southern Ocean indicate that there is a mid-depth maximum in radiocarbon age during the Last Glacial Maximum (LGM). This is in contrast to the modern ocean where intense mixing between water masses results in a relatively homogenous radiocarbon profile. Ferrari et al. (2014) suggested that the extended Antarctic sea ice cover during the LGM necessitated a shallower boundary between the upper and lower branches of the meridional overturning circulation. This shoaled boundary lay above major topographic features associated with strong diapycnal mixing, isolating dense southern sourced water in the lower branch of the overturning circulation. This isolation would have allowed radiocarbon to decay and thus provides a possible explanation for the mid-depth radiocarbon age bulge. We test this hypothesis using an idealized, 2-D, residual-mean dynamical model of the global overturning circulation. Concentration distributions of a decaying tracer that is advected by the simulated overturning are compared to published radiocarbon data. We find that a 600\u2009km (~5° of latitude) increase in sea ice extent shoals the boundary between the upper and lower branches of the overturning circulation at 45°S by 600\u2009m and shoals the depth of North Atlantic Deep Water convection at 50°N by 2500\u2009m. This change in circulation configuration alone decreases the radiocarbon content in the mid-depth South Atlantic at 45°S by 40‰, even without an increase in surface radiocarbon age in the source region of deep waters during the LGM.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/54056, title ="Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments", author = "Raven, Morgan Reed and Adkins, Jess F.", journal = "Organic Geochemistry", volume = "80", pages = "53-59", month = "March", year = "2015", doi = "10.1016/j.orggeochem.2015.01.002", issn = "0146-6380", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150126-083217317", note = "© 2015 Elsevier B.V.\n\nReceived Date: 13 February 2014; Revised Date: 22 December 2014; Accepted Date: 7 January 2015; Available online 14 January 2015. \n\nWe thank N. Dalleska and G. Paris at Caltech for significant analytical assistance, and J. Rae, A. Amrani, C. Marotta and A. Subhas for helpful advice. We also thank two anonymous reviewers, whose comments significantly improved the manuscript. Financial support was provided by the National Science Foundation through award EAR-1024919 to A.L.S. and J.F.A. The research is also funded in part by the Gordon and Betty Moore Foundation through Grant GBMF#3306 to A.L.S.", revision_no = "21", abstract = "Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are ^(34)S-enriched relative to coexisting sulfide, and experiments have produced ^(34)S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography – inductively coupled plasma mass spectrometry, to measure the compound-specific sulfur isotopic compositions of volatile organosulfur compounds over a 6 m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in ^(34)S relative to coexisting kerogen and porewater sulfide. We hypothesize that this ^(34)S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon-sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary pore water. The ^(34)S-depleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/53978, title ="Transformation of ENSO-related rainwater to dripwater δ^(18)O variability by vadose water mixing", author = "Moerman, Jessica W. and Cobb, Kim M.", journal = "Geophysical Research Letters", volume = "41", number = "22", pages = "7907-7915", month = "November", year = "2014", doi = "10.1002/2014GL061696", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150122-083840589", note = "© 2014 American Geophysical Union.\n\nReceived 27 August 2014; accepted 24 October 2014; accepted article online 29 October 2014; published online 25 November 2014.\n\nThe authors wish to thank the Gunung Mulu National Park staff, Eleanor Middlemas, Danja Mewes, Sang Chen,\nand Niko Sluzki for their assistance during fieldwork and the Mulu Meteorological Station staff for overseeing the collection of the daily rainfall samples. We also gratefully acknowledge the Mulu Caves Project for providing invaluable information about the Mulu karst system and an anonymous reviewer for comments that greatly improved the manuscript. Permits for this work were\ngranted by the Malaysian Economic Planning Unit, the Sarawak State Planning Unit, and the Sarawak Forestry Department. This work was supported by NSF grant 0645291 to K.M.C., and J.W.M. was funded by a NSF Graduate\nResearch Fellowship. Observational data sets of Mulu rainfall and dripwater isotopes used in this study can be found in the supporting information. M. Bayani Cardenas thanks one anonymous reviewer for his/her assistance\nin evaluating this paper.", revision_no = "22", abstract = "Speleothem oxygen isotopes (δ^(18)O) are often used to reconstruct past rainfall δ^(18)O variability, and thereby hydroclimate changes, in many regions of the world. However, poor constraints on the karst hydrological processes that transform rainfall signals into cave dripwater add significant uncertainty to interpretations of speleothem-based reconstructions. Here we present several 6.5 year, biweekly dripwater δ^(18)O time series from northern Borneo and compare them to local rainfall δ^(18)O variability. We demonstrate that vadose water mixing is the primary rainfall-to-dripwater transformation process at our site, where dripwater δ^(18)O reflects amount-weighted rainfall δ^(18)O integrated over the previous 3–10 months. We document large interannual dripwater δ^(18)O variability related to the El Niño–Southern Oscillation (ENSO), with amplitudes inversely correlated to dripwater residence times. According to a simple stalagmite forward model, asymmetrical ENSO extremes produce significant offsets in stalagmite δ^(18)O time series given different dripwater residence times. Our study highlights the utility of generating multiyear, paired time series of rainfall and dripwater δ^(18)O to aid interpretations of stalagmite δ^(18)O reconstructions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/102998, title ="Neoarchean carbonate-associated sulfate records positive Δ³³S anomalies", author = "Paris, G. and Adkins, J. F.", journal = "Science", volume = "346", number = "6210", pages = "739-741", month = "November", year = "2014", doi = "10.1126/science.1258211", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200505-090328803", note = "© 2014 American Association for the Advancement of Science. \n\nReceived 2 July 2014; accepted 22 September 2014. \n\nWe thank J. Johnson for help with stratigraphic sample collection and fruitful comments; N. Beukes and I. Halevy for helpful discussions; K. Bergmann for assistance with C and O analyses; and C. Ma, T. Present, and J. Johnson for assistance with scanning electron microscopy. We acknowledge support from NSF Division of Earth Sciences award no. EAR-1349858. Assistance from N. Dalleska and use of IC instrumentation in the Environmental Analysis Center at the California Institute of Technology is gratefully acknowledged. G.P. was funded by the Henry and Camille Dreyfus Postdoctoral Program in Environmental Chemistry. W.W.F. acknowledges support from the David and Lucile Packard Foundation. Drill core GKP01 was sampled with support from the Agouron Institute. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393).", revision_no = "14", abstract = "Mass-independent fractionation of sulfur isotopes (reported as Δ³³S) recorded in Archean sedimentary rocks helps to constrain the composition of Earth’s early atmosphere and the timing of the rise of oxygen ~2.4 billion years ago. Although current hypotheses predict uniformly negative Δ³³S for Archean seawater sulfate, this remains untested through the vast majority of Archean time. We applied x-ray absorption spectroscopy to investigate the low sulfate content of particularly well-preserved Neoarchean carbonates and mass spectrometry to measure their Δ³³S signatures. We report unexpected, large, widespread positive Δ³³S values from stratigraphic sections capturing over 70 million years and diverse depositional environments. Combined with the pyrite record, these results show that sulfate does not carry the expected negative Δ³³S from sulfur mass-independent fractionation in the Neoarchean atmosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50323, title ="Neocarchean carbonate-associated sulfate records positive Δ^(33)S anomalies", author = "Paris, G. and Adkins, J. F.", journal = "Science", volume = "346", number = "6410", pages = "739-741", month = "November", year = "2014", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141009-161941084", note = "© 2014 American Association for the Advancement of Science. \n\nReceived for publication 2 July 2014. Accepted for publication 22 September 2014.\n\nWe thank J. Johnson for help with stratigraphic sample collection\nand fruitful comments; N. Beukes and I. Halevy for helpful\ndiscussions; K. Bergmann for assistance with C and O analyses;\nand C. Ma, T. Present, and J. Johnson for assistance with scanning\nelectron microscopy. We acknowledge support from NSF Division\nof Earth Sciences award no. EAR-1349858. Assistance from\nN. Dalleska and use of IC instrumentation in the Environmental\nAnalysis Center at the California Institute of Technology is\ngratefully acknowledged. G.P. was funded by the Henry and\nCamille Dreyfus Postdoctoral Program in Environmental Chemistry.\nW.W.F. acknowledges support from the David and Lucile Packard\nFoundation. Drill core GKP01 was sampled with support from the\nAgouron Institute. Use of the Stanford Synchrotron Radiation\nLightsource, SLAC National Accelerator Laboratory, is supported\nby the U.S. Department of Energy, Office of Science, Office of Basic\nEnergy Sciences under Contract No. DE-AC02-76SF00515. The\nSSRL Structural Molecular Biology Program is supported by\nthe DOE Office of Biological and Environmental Research and\nby the National Institutes of Health, National Institute of General\nMedical Sciences (including P41GM103393).", revision_no = "22", abstract = "Mass-independent fractionation of sulfur isotopes (reported as Δ^(33S) recorded in Archean\nsedimentary rocks helps to constrain the composition of Earth’s early atmosphere and the\ntiming of the rise of oxygen ~2.4 billion years ago. Although current hypotheses predict\nuniformly negative Δ^(33)S for Archean seawater sulfate, this remains untested through the\nvast majority of Archean time.We applied x-ray absorption spectroscopy to investigate the\nlow sulfate content of particularly well-preserved Neoarchean carbonates and mass\nspectrometry to measure their Δ^(33)S signatures. We report unexpected, large, widespread\npositive Δ^(33)S values from stratigraphic sections capturing over 70 million years and diverse\ndepositional environments. Combined with the pyrite record, these results show that\nsulfate does not carry the expected negative Δ^(33)S from sulfur mass-independent\nfractionation in the Neoarchean atmosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50324, title ="Sulfate was a trace constituent of Archean seawater", author = "Crowe, Sean A. and Paris, Guillaume", journal = "Science", volume = "346", number = "6210", pages = "735-739", month = "November", year = "2014", doi = "10.1126/science.1258966", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141009-162752745", note = "© 2014 American Association for the Advancement of Science. \n\nReceived for publication 21 July 2014. Accepted for publication 3 October 2014. \n\nWe thank A. Sturm and C. Henny for help with fieldwork. S. Poulton provided sediment δ^(34)S data. A. Hefford helped compile Archean S-isotope data. Funding to S.A.C. was provided by an Agouron Institute Geobiology Fellowship and a Natural Sciences and Engineering Research Council of Canada Postdoctoral Fellowship. Additional funding was provided by the Danish National Research Foundation (grant no. DNRF53) and the European Research Council. All data are available in the supplementary materials.", revision_no = "27", abstract = "In the low-oxygen Archean world (>2400 million years ago), seawater sulfate concentrations were much lower than today, yet open questions frustrate the translation of modern measurements of sulfur isotope fractionations into estimates of Archean seawater sulfate concentrations. In the water column of Lake Matano, Indonesia, a low-sulfate analog for the Archean ocean, we find large (>20 per mil) sulfur isotope fractionations between sulfate and sulfide, but the underlying sediment sulfides preserve a muted range of δ^(34)S values. Using models informed by sulfur cycling in Lake Matano, we infer Archean seawater sulfate concentrations of less than 2.5 micromolar. At these low concentrations, marine sulfate residence times were likely 10^3 to 10^4 years, and sulfate scarcity would have shaped early global biogeochemical cycles, possibly restricting biological productivity in Archean oceans.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50872, title ="Dynamic intermediate ocean circulation in the North Atlantic during Heinrich Stadial 1: a radiocarbon and neodymium isotope perspective", author = "Wilson, David J. and Crocket, Kirsty C.", journal = "Paleoceanography", volume = "29", number = "11", pages = "1072-1093", month = "November", year = "2014", doi = "10.1002/2014PA002674", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141027-140022061", note = "© 2014 American Geophysical Union. \n\nReceived 20 MAY 2014;\nAccepted 16 SEP 2014;\nAccepted article online 18 SEP 2014;\nPublished online 20 NOV 2014.\n\nData to support this article are provided in Table 1 and Table S1 of the Supporting Information. This study was supported by Natural Environment Research Council grant NE/F016751/1, Marie Curie International Reintegration Grant IRG 230828 and Leverhulme Trust grant RPG-398 to TvdF, as well as a Phillip Leverhulme Prize, Marie Curie International Reintegration Grant and European Research Council grant to LFR. We are grateful for thoughtful reviews from Marcus Gutjahr and an anonymous reviewer and the editorial handling by Heiko Pälike.", revision_no = "26", abstract = "The last deglaciation was characterised by a series of millennial scale climate events that have been linked to deep ocean variability. While often implied in interpretations, few direct constraints exist on circulation changes at mid-depths. Here we provide new constraints on the variability of deglacial mid-depth circulation using combined radiocarbon and neodymium isotopes in 24 North Atlantic deep-sea corals. Their aragonite skeletons have been dated by uranium-series, providing absolute ages and the resolution to record centennial scale changes, while transects spanning the lifetime of a single coral allow sub-centennial tracer reconstruction. Our results reveal that rapid fluctuations of water mass sourcing and radiocarbon affected the mid-depth water column (1.7-2.5\u2009km) on timescales of less than 100\u2009years during the latter half of Heinrich Stadial 1. The neodymium isotopic variability (−14.5 to −11.0) ranges from the composition of the modern northern-sourced waters towards more radiogenic compositions that suggest the presence of a greater southern-sourced component at some times. However, in detail, simple two-component mixing between well-ventilated northern-sourced and radiocarbon-depleted southern-sourced water masses cannot explain all our data. Instead, corals from ~15.0\u2009ka and ~15.8\u2009ka may record variability between southern-sourced intermediate waters and radiocarbon-depleted northern-sourced waters, unless there was a major shift in the neodymium isotopic composition of the northern endmember. In order to explain the rapid shift towards the most depleted radiocarbon values at ~15.4\u2009ka, we suggest a different mixing scenario involving either radiocarbon-depleted deep water from the Greenland-Iceland-Norwegian Seas or a southern-sourced deep water mass. Since these mid-depth changes preceded the Bolling-Allerod warming, and were apparently unaccompanied by changes in the deep Atlantic, they may indicate an important role for the intermediate ocean in the early deglacial climate evolution.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/69348, title ="Development and Initial Biogeochemical Applications of Compound-Specific Sulfur Isotope Analysis", author = "Greenwood, P. F. and Amrani, A.", number = "4", pages = "285-312", month = "September", year = "2014", doi = "10.1039/9781782625025-00285", isbn = "978-1-84973-649-7", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160801-104531843", note = "© 2015 Royal Society of Chemistry. \n\nPG, KG, AH, and MM acknowledge funding support from CSIRO Flagship Collaboration Fund Cluster for Organic Geochemistry of Mineral Systems and KG also from an ARC Discovery Outstanding Research Award. AA thanks Shimon Feinstein, Itay Reznik, and IEI Ltd for the oil shale and oil samples from Aderet 1 drillhole and the support of ISF grant 1269/12. ALS and MRR acknowledge the support of NSF EAR-1024919. Our valued instrument technicians, Guillaume Paris (Caltech), Kai Rankenburg (UWA), and Ward Said-Ahmad (HUJI) are thanked for extensive help in developing, maintaining, and implementing the respective sulfur-CSIA systems. Michael Böttcher is thanked for an insightful peer review which helped improve this manuscript.", revision_no = "12", abstract = "Compound-specific isotope analysis (CSIA) has been extended to the ^(32)S and ^(34)S stable isotopes of sulfur (δ^(34)S) through the combination of gas chromatography (GC) and multi-collector inductively coupled mass spectrometry (ICPMS). The molecular level resolution of sulfur-CSIA is greatly expanding the biogeochemical applications of existing sulfur isotope methods, particularly with respect to organic sulfur compounds. Sulfur participates in a variety of important biogeochemical and redox processes, with distinctive isotopic fractionations accompanying many of these. For example, hydrogen sulfide produced during microbial sulfate reduction can be strongly depleted in ^(34)S (up to 66‰ in δ^(34)S) compared to the source sulfate. An improved understanding of sulfur biogeochemistry at the molecular level will assist in the interpretation of studies of sulfur cycling associated with the modern and paleo-environments. A comparison of δ34S values between organic and inorganic sulfur species may help to illuminate the complex role of sulfur in sedimentary organic diagenesis and the pathways of organic sulfur formation. The δ^(34)S values of individual organic sulfur compounds from natural settings can be currently measured by GC-ICPMS with impressive accuracy, precision (<0.5‰) and sensitivity (≥20 pmol S) over a broad range of analyte volatility. The new sulfur-CSIA capability has already been used to study pathways of early diagenetic organic sulfurisation, volatile sulfur emission from the oceans, oil correlations, thermochemical sulfate reduction of petroleum hydrocarbons, and the relationship between OSCs and mineralising sulfides of large metal deposits.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48557, title ="Isotopic composition of carbonate-bound organic nitrogen in deep-sea scleractinian corals: A new window into past biogeochemical change", author = "Wang, Xingchen T. and Prokopenko, Maria G.", journal = "Earth and Planetary Science Letters", volume = "400", pages = "243-250", month = "August", year = "2014", doi = "10.1016/j.epsl.2014.05.048", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140814-105117352", note = "© 2014 Elsevier B.V. Received 25 March 2014, Revised 10 May 2014, Accepted 26 May 2014, Available online 12 June 2014. We thank Stephen D. Cairns (Smithsonian Institution National Museum of Natural History) and Ewann A. Bertson (NOAA) for providing D. dianthus samples and Eric D. Galbraith for providing the complete NICOPP data set. We also thank two anonymous reviewers for providing insightful comments. This work is supported by NSF grant OCE-1234664 to M.G.P. and B.W., the Grand Challenges Program of Princeton University, the Tuttle Fund of the Department of Geosciences at Princeton University, European Research Council, Marie Curie Reintegration Grant, and The Leverhulme Trust.", revision_no = "15", abstract = "Over the last two decades, the skeletal remains of deep-sea corals have arisen as a geochemical archive of Pleistocene oceanographic change. Here we report the exploration of the isotopic composition of the carbonate-bound organic nitrogen (hereafter, CB-δ^(15)N) in the deep-sea scleractinian coral Desmophyllum dianthus as a possible tool for reconstructing past changes in the ocean nitrogen cycle. The measurement protocol is adapted from a high-sensitivity method for foraminifera shell-bound δ^(15)N. We explored the variability of CB-δ^(15)N within specimens, among corals collected at different depths in a given ocean region, and among different ocean regions. Modern D. dianthus CB-δ^(15)N is strongly correlated with the δ^(15)N of N export as estimated from sediment traps, shallow subsurface nitrate, and surface sediments, suggesting that CB-δ^(15)N is a reliable proxy for δ^(15)N of N export. D. dianthus CB-δ^(15)N is consistently 8–9‰8–9‰ higher than δ^(15)N of N export, indicating that D. dianthus acquires its nutrition primarily from suspended particulate organic matter (POM) that derives from sinking POM, not directly from sinking POM.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45358, title ="Abrupt pre-Bølling–Allerød warming and circulation changes in the deep ocean", author = "Thiagarajan, Nivedita and Subhas, Adam V.", journal = "Nature", volume = "511", number = "7507", pages = "75-78", month = "July", year = "2014", doi = "10.1038/nature13472", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140430-120517933", note = "© 2014 Macmillan Publishers Limited. \n\nReceived 19 August 2013; accepted 7 May 2014. \n\nWe thank J. McManus and M. Miller for discussions. We also thank the captain and crew of the RV Atlantis cruise AT7-35 and the WHOI Deep Submergence Alvin and ABE groups. \n\nAuthor Contributions: N.T. and J.F.A. designed the study. N.T. collected the ^(14)C and Δ_(47) data and compiled the benthic δ^(13)C sections. J.R.S. facilitated and oversaw the 14C measurements and J.M.E. facilitated and oversaw the Δ_(47) measurements. A.V.S. collected the U-series data. J.F.A. facilitated and oversaw the U-series measurements. N.T. and J.F.A. wrote the first draft of the manuscript. All authors contributed to the interpretation and preparation of the final manuscript.\n \nThe authors declare no competing financial interests.\n\nSupplementary Information is available in the online version of the paper.\nN.T. and J.F.A. wrote the first draft of the manuscript. All authors contributed to the\ninterpretation and preparation of the final manuscript.", revision_no = "44", abstract = "Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere—probably linked to changes in deep ocean circulation—occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling–Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling–Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling–Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean’s usual thermal stratification pre-dates the Bølling–Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique feature of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the Bølling–Allerød interstadial.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46175, title ="Antarctic sea ice control on ocean circulation in present and glacial climates", author = "Ferrari, Raffaele and Jansen, Malte F.", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "111", number = "24", pages = "8753-8758", month = "June", year = "2014", doi = "10.1073/pnas.1323922111", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140610-103156370", note = "© 2014 National Academy of Sciences. Freely available online through the PNAS open access option. \n\nPublished online before print June 2, 2014. Edited by Edward A. Boyle, Massachusetts Institute of Technology, Cambridge, MA, and approved April 16, 2014 (received for review December 31, 2013). \n\nL.P. Nadeau helped with figures. All authors acknowledge support from the National Science Foundation. R.F. acknowledges support from the Breene M. Kerr Chair. \n\nAuthor contributions: R.F. designed research; R.F., M.F.J., J.A., A.B., A.L.S., and A.F.T. performed research; R.F. and M.F.J. analyzed data; and R.F. wrote the paper. \n\nThe authors declare no conflict of interest. \n\nThis Direct Submission article had a prearranged editor. \n\nThis article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1323922111/-/DCSupplemental.", revision_no = "25", abstract = "In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean’s role in regulating atmospheric carbon dioxide on glacial–interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49577, title ="Rhizon sampler alteration of deep ocean sediment interstitial water samples, as indicated by chloride concentration and oxygen and hydrogen isotopes", author = "Miller, Madeline D. and Adkins, Jess F.", journal = "Geochemistry Geophysics Geosystems", volume = "15", number = "6", pages = "2401-2413", month = "June", year = "2014", doi = "10.1002/2014GC005308 ", issn = "1525‐2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140911-090321616", note = "© 2014 American Geophysical Union.\n\nReceived 24 FEB 2014;\nAccepted 26 APR 2014;\nAccepted article online 2 MAY 2014;\nPublished online 16 JUN 2014.\n\nThis research was made possible by\nthe Integrated Ocean Drilling Program.\nWe thank all of the IODP Expedition\n339 Scientists and Technical Staff for\ntheir generous support of our\nsampling efforts, and particularly\nChristopher Bennight, Erik Moortgat,\nAlexandrina Tzanova, and Jin Kyoung\nKim for their assistance in the\nshipboard chemistry laboratory.\nRichard Murray provided very helpful\ncomments on a draft of this\nmanuscript and Heather Schrum kindly\nshared the original data used for\nFigure 1. M.D.M. was supported by the\nConsortium for Ocean Leadership,\nboth for participation in IODP\nExpedition 339 and through Post-\nExpedition Award T339A89. M.D.M.\nand J.F.A. were supported by the\nNational Science Foundation’s P2C2\nprogram through grant 1204211.\nD.A.H. was supported by the Natural\nEnvironment Research Council grant\nNE/J017922/1. Data for Figures 2–8 are\navailable as supporting information in\nTable S1.", revision_no = "18", abstract = "Despite their potential to inform past ocean salinity, δ^(18)O, and temperature, high-resolution depth profiles of interstitial water chloride concentration and hydrogen and oxygen isotopes exist in very few locations. One of the primary limitations to the recovery of these depth profiles is that traditional interstitial water sampling requires 5–10 cm whole rounds of the sediment core, which has the potential to interfere with stratigraphic continuity. The Rhizon sampler, a nondestructive tool developed for terrestrial sediment interstitial water extraction, has been proposed for efficient and nondestructive sampling of ocean sediment pore waters. However, there exists little documentation on the reliability and performance of Rhizon samplers in deep ocean sediments, particularly in regard to their effect on chloride concentration and oxygen and hydrogen isotopic measurements. We perform an intercomparison of chloride concentration and oxygen and hydrogen isotopic composition in samples taken using traditional squeezing versus those taken with Rhizon samplers. We find that samples taken with Rhizons have positive biases in both chloride concentration and stable isotopic ratios relative to those taken by squeezing water from sediments in a hydraulic press. The measured offsets between Rhizon and squeeze samples are consistent with a combination of absorption by and diffusive fractionation through the hydrophilic membrane of the Rhizon sampler. These results suggest caution is needed when using Rhizons for sampling interstitial waters in any research of processes that leave a small signal-to-noise ratio in dissolved concentrations or isotope ratios.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46546, title ="Experimental determination of carbonate-associated sulfate δ^(34)S in planktonic foraminifera shells", author = "Paris, Guillaume and Fehrenbacher, Jennifer S.", journal = "Geochemistry, Geophysics, Geosystems", volume = "15", number = "4", pages = "1452-1461", month = "April", year = "2014", doi = "10.1002/2014GC005295", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140627-090728672", note = "© 2014 American Geophysical Union.\n\nReceived 11 February 2014; Accepted 2 April 2014; Accepted article online 4 April 2014; Published online 29 April 2014.\n\nWe gratefully acknowledge the field assistance of Kate Holland, Jordan Snyder, and Lael Vetter and the staff of\nthe Wrigley Marine Science Center and Ann Russell for alkalinity and pH measurements. We also thank Greg\nBaxter for assistance with sample preparation/polishing. NanoSIMS measurements were performed at Caltech with the assistance of Chi Ma. We thank two anonymous reviewers\nand Robert Leeds for their constructive reviews. This research was supported by National Science Foundation\nawards ATM-0903099 (JFA) OCE-0550703 (HJS), and OCE-1261519\n(JSF) and the Camille and Henry Dreyfus Foundation (GP).", revision_no = "11", abstract = "Understanding the coupling of oxygen, carbon, and sulfur cycles in the past is critical for reconstructing the history of biogeochemical cycles, paleoclimatic variations, and oceanic chemistry. The abundance of sulfur isotopes (δ^(34)S) in sulfate from ancient marine carbonates, or carbonate-associated sulfate (CAS), is commonly used, along with other archives (mainly evaporites and barite), to estimate the δ^(34)S of seawater throughout Earth history. Analyses of CAS from hand-picked foraminifera are potentially valuable because this group of organisms is used in numerous paleoceanographic studies. They could provide coupled, high-resolution records of δ^(13)C, δ^(18)O, and δ^(34)S isotopic changes directly linked to orbitally tuned records of climate change through the Cenozoic. Such measurements have not previously been possible due to limitations of sensitivity in conventional IRMS-based techniques. However, the recent development of CAS analysis by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) now allows us to work on samples containing just a few nmol of sulfur with accuracy for δ^(34)S values approaching 0.1‰ and, consequently, to analyze hand-picked samples of foraminifera shells. Here we report the results of culture experiments with the planktonic species Orbulina universa, that establish a shell:seawater δ^(34)S calibration for future applications to the fossil record. Our new method uses <650 μg of carbonate (∼15 shells) per analysis. The results show that S isotopes are fractionated consistently by −1‰ between seawater and O. universa tests. We also demonstrate that O. universa faithfully records the [SO^(2−)_(4)]/[Ca^(2+)] ratio of the seawater in which it grew.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44312, title ="Age and growth of the cold-water scleractinian Solenosmilia\nvariabilis and its reef on SW Pacific seamounts", author = "Fallon, S. J. and Thresher, R. E.", journal = "Coral Reefs", volume = "33", number = "1", pages = "31-38", month = "March", year = "2014", doi = "10.1007/s00338-013-1097-y", issn = "0722-4028", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140314-100054953", note = "© 2013 Springer-Verlag Berlin Heidelberg. Received: 8 May 2013. \n\nAccepted: 21 October 2013. Published online: 16 November 2013. \n\nWe thank E. Anagnostou, A. Beck, W. Cho, A. Gagnon, K. Gowlett-Holmes, S. John, A. Kennedy, H. Kippo, N. Meckler, D. Mills, N. Thiagarajan, D. Staples, and A. Subhas, and in particular, the crews of the ROV Jason and its support vessel RV\nThomas T. Thompson for their professional assistance in the field. We also thank Rachel Wood for help with coral dating. Components of this work were supported by the National Science Foundation, the Australian Department of Environment, Water, Heritage, and the Arts, the Australian Commonwealth Environmental Research Fund, and Australian National Climate Adaptations Research Program. Communicated by Geology Editor Prof. Bernhard Riegl.", revision_no = "9", abstract = "Little is known about growth rates of deep-water reef-forming corals or the rates at which these reefs accumulate. Such information is critical for determining the resilience of the reefs to anthropogenic impacts such as trawling and climate change. We radiocarbon date live-caught and sub-fossil samples of the bioherm-forming coral Solenosmilia variabilis collected from precisely known depths and locations by means of a remotely operated vehicle on seamounts south of Tasmania, Australia. The growth rate of colonies live-caught between 958 and 1,454 m, which spans most of the depth range of the species locally, ranged from 0.84 to 1.25 mm linear extension yr^(−1) and tended to be higher in the deeper-caught material. Analysis of skeletal microstructure suggests annual deposition of growth increments near the growing tips, but not closer to the base, as the skeleton is extended and thickened. Dating of sub-fossil material indicates S. variabilis has been present on Tasmanian seamounts for at least the last 47,000 yrs and a reef accumulation rate of 0.27 mm yr^(−1).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44210, title ="Strong Depth-Related Zonation of Megabenthos on a Rocky Continental Margin (∼700–4000 m) off Southern Tasmania, Australia", author = "Thresher, Ronald and Althaus, Franziska", journal = "PLoS ONE", volume = "9", number = "1", pages = "Art. No. e85872", month = "January", year = "2014", doi = "10.1371/journal.pone.0085872", issn = "1932-6203", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140310-094201992", note = "© 2014 Thresher et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.\n\nReceived: January 20, 2013; Accepted: December 9, 2013; Published: January 22, 2014.\n\nWe thank E. Anagnostou, A. Beck, R. Gurney, S. John, A. Kennedy, H. Kippo, N. Meckler, D. Mills, A. Subhas and N. Thiagarajan, and the crews of the AUV ABE, the ROV Jason and RV Thomas T. Thompson and RV Southern Surveyor for their invaluable and professional assistance in the field,\nS. Cairns, D. Fautin, and K. Moore for taxonomic assistance, E. Druffel for discussions about deep-water carbon sources, P. Brodie for assisting in the photographic analyses and R. Kloser, K. Kemp and an anonymous reviewer for helpful comments on the manuscript. \n\nFunding: Components of this work were supported by the National Science Foundation, the Australian Department of Environment, Water, Heritage, and the Arts, the Australian Commonwealth Environmental Research Fund, a grant of ship time by the Australian National Research Facility, and the CSIRO Wealth from Oceans and Climate Adaptation Flagships. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.\n\nAuthor Contributions:\n\nConceived and designed the experiments: JA RT. Performed the\nexperiments: JA WC AG KG-H DS RT. Analyzed the data: FA PA JD\nKG-H FM RT AW. Wrote the paper: FA JA PA RT AW.\n", revision_no = "15", abstract = "Assemblages of megabenthos are structured in seven depth-related zones between ~700 and 4000 m on the rocky and topographically complex continental margin south of Tasmania, southeastern Australia. These patterns emerge from analysis of imagery and specimen collections taken from a suite of surveys using photographic and in situ sampling by epibenthic sleds, towed video cameras, an autonomous underwater vehicle and a remotely operated vehicle (ROV). Seamount peaks in shallow zones had relatively low biomass and low diversity assemblages, which may be in part natural and in part due to effects of bottom trawl fishing. Species richness was highest at intermediate depths (1000–1300 m) as a result of an extensive coral reef community based on the bioherm-forming scleractinian Solenosmilia variabilis. However, megabenthos abundance peaked in a deeper, low diversity assemblage at 2000–2500 m. The S. variabilis reef and the deep biomass zone were separated by an extensive dead, sub-fossil S. variabilis reef and a relatively low biomass stratum on volcanic rock roughly coincident with the oxygen minimum layer. Below 2400 m, megabenthos was increasingly sparse, though punctuated by occasional small pockets of relatively high diversity and biomass. Nonetheless, megabenthic organisms were observed in the vast majority of photographs on all seabed habitats and to the maximum depths observed - a sandy plain below 3950 m. Taxonomic studies in progress suggest that the observed depth zonation is based in part on changing species mixes with depth, but also an underlying commonality to much of the seamount and rocky substrate biota across all depths. Although the mechanisms supporting the extraordinarily high biomass in 2000–2500 m depths remains obscure, plausible explanations include equatorwards lateral transport of polar production and/or a response to depth-stratified oxygen availability.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44718, title ="The geochemistry of deep-sea coral skeletons: Are view of vital effects and applications for palaeoceanography", author = "Robinson, Laura F. and Adkins, Jess F.", journal = "Deep-Sea Research. Part II, Topical Studies in Oceanography", volume = "99", pages = "184-198", month = "January", year = "2014", doi = "10.1016/j.dsr2.2013.06.005", issn = "0967-0645", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140407-151402708", note = "© 2013 Elsevier Ltd. Available online 19 June 2013. Biology and Geology of Deep-Sea Coral Ecosystems: Proceedings of the Fifth International Symposium on Deep Sea Corals.\n\nThis research was funded by the European Research Council (EC FP7 ERC StG 20101014), the Marie Curie Reintegration Program, and by the Phillip Leverhulme Trust (both to LFR and additionally to TvdF, Grant RPG-398). We acknowledge the constructive input from reviewers and editors who helped to improve this manuscript.", revision_no = "19", abstract = "Deep-sea corals were discovered over a century ago, but it is only over recent years that focused efforts have been made to explore the history of the oceans using the geochemistry of their skeletal remains. They offer a promising archive of past oceanic environments given their global distribution, layered growth patterns, longevity and preservation as well as our ability to date them using radiometric techniques. This paper provides an overview of the current state-of-the-art in terms of geochemical approaches to using deep-sea coral skeletons to explore the history of the ocean. Deep-sea coral skeletons have a wide array of morphologies (e.g. solitary cup corals, branching colonial corals) and materials (calcite, aragonite and proteins). As such their biomineralization strategies are diverse, leading to complex geochemistry within coral skeletons. Notwithstanding these complications, progress has been made on developing methods for reconstructing the oceanographic environment in the past using trace elements and isotopic methods. Promising approaches within certain coral groups include clumped isotopes and Mg/Li for temperature reconstructions, boron isotopes and radiocarbon for carbon cycling, εNd, and radiocarbon for circulation studies and δ^(15)N, P/Ca and Ba/Ca for nutrient tracer studies. Likewise there is now a range of techniques for dating deep-sea corals skeletons (e.g. U-series, radiocarbon), and determining their growth rates (e.g. radiocarbon and ^(210)Pb). Dating studies on historic coral populations in the Atlantic, Southern Ocean and Pacific point to climate and environmental changes being dominant controls on coral populations over millennial and orbital timescales. This paper provides a review of a range of successes and promising approaches. It also highlights areas in which further research would likely provide new insights into biomineralization, palaeoceanography and distribution of past coral populations.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42620, title ="Accurate Mg/Ca, Sr/Ca, and Ba/Ca ratio measurements in carbonates by SIMS and NanoSIMS and an assessment of heterogeneity in common calcium carbonate standards", author = "Gabitov, R. I. and Gagnon, A. C.", journal = "Chemical Geology", volume = "356", pages = "94-108", month = "October", year = "2013", doi = "10.1016/j.chemgeo.2013.07.019", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131121-131800523", note = "© 2013 Elsevier B.V. \n\nReceived 7 April 2012. Received in revised form 20 July 2013. Accepted 22 July 2013. Available online 29 July 2013. \n\nEditor: U. Brand. \n\nWe would like to thank Daniele Cherniak, Anne Cohen, Ellen Druffel, Jonathan Erez, Glenn Gaetani, Kent Ross, and Neil Sturchio for sharing the carbonate standards and bulk analytical data. John Ferry provided the carbonate material used in testing the primary beam size on the NanoSIMS. We also thank Lindsey Hedges for advising on sample preparation. The comments of anonymous reviewers were helpful as well. \n\nThis work was supported by the following grants from NOAA — MIT Seagrant Program: NA100AR4170086 “Autonomous vehicle exploration and sampling of deep-water corals” and NSF: OCE-0929272 “Collecting deep-sea corals from off of Tasmania to measure the history of Southern Ocean radiocarbon concentrations”.", revision_no = "12", abstract = "As archives of past climate variability, the micron and sub-micron scales of element:calcium (Me/Ca) variability in both biogenic and inorganic carbonates contain important geochemical information. Ideally working at smaller and smaller scales leads to higher temporal resolution of past changes, but more often it has revealed the strong overprint of other processes on the climate signal. Therefore, the role of SIMS and NanoSIMS techniques in studying paleoenvironmental proxies continues to increase. We evaluate the accuracy and precision of the CAMECA ims 7F-GEO and NanoSIMS-50L ion probes for measurements of Sr/Ca, Mg/Ca, and Ba/Ca ratios in carbonate minerals. Nine carbonate reference materials were examined for their ^(88)Sr/^(42)Ca, ^(24)Mg/^(42)Ca, and ^(138)Ba/^(42)Ca ratios using a primary O^− beam with spot sizes of 20–40 μm (SIMS) and 0.8–2 μm (NanoSIMS). To assess accuracy, seven of these standards were analyzed for Sr/Ca and Mg/Ca with ID-ICP-MS. Variability in the elemental ratios arising from drift and changes in the tuning of the ims 7F-GEO over a nine month period is smaller than the chemical heterogeneity of the most frequently analyzed standards (OKA and Blue-CC). Across a whole crystal, Blue-CC is more homogeneous (1σ of 2.39% and 1.60% for Sr/Ca and Mg/Ca respectively) than OKA, but in the bulk matrix of OKA there is even less variability (1σ of 0.85% and 0.83% respectively). We find that carbonate samples can be accurately normalized to carbonate standards with significantly different absolute Me/Ca ratios. NanoSIMS intensity ratios follow counting statistics better than ± 1% (2σ) at any one spot, but conversion to Me/Ca ratios increases the uncertainty. Two factors give rise to this limitation. First, the spatial heterogeneity of nominally homogeneous standards can lead to accuracy offsets that are as large as the ranges quoted above. Second, the NanoSIMS generates higher instrumental mass fractionation relative to SIMS. The combination of three different analytical techniques demonstrates that Blue-CC and homogeneous calcite zones in OKA are promising reference materials for precise analyses. Accuracy is crucially dependent on making independent measurements on exactly the same crystal of standard used in the SIMS and NanoSIMS machines.", } @misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/81825, title ="Satellites to the Seafloor: Autonomous Science to Forge a Breakthrough in Quantifying the Global Ocean Carbon Budget", author = "Thompson, Andrew and Kinsey, James C.", month = "October", year = "2013", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170926-084222179", note = "Primary support for this study was provided by the Keck Institute for Space Studies. Additional funding for participants was provided by the Jewitt Foundation.\n\nWe particularly want to thank Michele Judd, Managing Director of the Keck Institute for Space Studies, and her Administrative Assistants, Janet Seid and Sharon Bryant, for\ntheir indefatigable efforts and patience, without which our Study could not have been completed.\n\nThe authors thank Judy Fenwick (WHOI) for her assistance in editing the report.", revision_no = "11", abstract = "Understanding the global carbon budget and its changes is crucial to current and future life on Earth. The marine component represents the largest reservoir of the global carbon cycle. In addition to physical processes that govern carbon fluxes at the air-sea interface and regulate the atmospheric carbon budget, complex internal sources and sinks, including inorganic, geologic, microbiological and biological processes also impact carbon distributions and storage. Therefore, it is essential to observe and understand the whole system. This is a daunting task, as many of the processes are distributed throughout the ocean, laterally and vertically over scales ranging from centimeters to thousands of kilometers. Ship and satellite observations both offer a partial view but, for ships, are either too short term and localized and satellites, despite their large spatial coverage, lack the spatial resolution. Ocean robots, such as deep diving autonomous underwater vehicles (AUVs) and gliders, provide in-situ observations of the seafloor and water column while the surface can be observed in-situ by autonomous surface vehicles (ASVs). Presently, these assets are used disparately with each operating independently and requiring direct human intervention for data interpretation and mission retasking. This paradigm is insufficient for the task of obtaining the millions of in-situ and remote measurements necessary for quantifying the ocean’s contribution to the global carbon cycle. This study brings together scientists, who understand the imperative and scope of quantifying the global carbon budget, with technologists, who may be able to glimpse a possible way of solving it.\n\nA coordinated network of ocean robots and satellites that autonomously interpret data and communicate sampling strategies could significantly advance our ability to monitor the marine carbon (and other biogeochemical) cycles. The principal goal of this study is to determine whether emerging technologies could enable crucial oceanographic and space science investigations to be coordinated to address this scientific challenge and may be the way to address others. Specifically, we will:\n\nestablish a lingua franca between the participants’ different research communities that will enable increased communication;\n\nidentify the observational capabilities required to quantify the carbon cycle;\n\nassess the present capabilities of the ocean robotics, autonomous science, and satellite communities to provide these capabilities;\n\ninvestigate if coordinated ocean robots and satellites using autonomous science can obtain those observations; and\ndevelop a collaborative research agenda aimed at solving these problems.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42346, title ="Distribution of sulphur and magnesium in the red coral", author = "Vielzeuf, Daniel and Garrabou, Joaquim", journal = "Chemical Geology", volume = "355", pages = "13-27", month = "September", year = "2013", doi = "10.1016/j.chemgeo.2013.07.008", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131108-151959930", note = "© 2013 Elsevier B.V. All rights reserved. Received 31 October 2012. Received in revised form 8 July 2013. Accepted 9 July 2013. Available online 15 July 2013. This work has been supported by the Centre National de la Recherche Scientifique (CNRS) – Institut National des Sciences de l'Univers (INSU) through grant ECLIPSE 2005, INTERRVIE 2009, by the Agence Nationale pour la Recherche through ANR CoRo 2011–2015, and by the Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) through internal grants. This work is also part of the European Union COST action TD0903. D.V. also benefited from a financial support by E.M. Stolper for a three month stay at Caltech in 2010. We thank H. Zibrowius for providing generously the samples of fossil red coral, C. Marschal and P. Raffin for supplying some of the present-day red coral colonies, J. Pascual and J. Salat for allowing access to the long-term temperature data series from the Medes Islands (Spain), and N. Bensoussan for his help in the processing of the temperature series from the Riou Island (Marseille, France). Reviews by Andres Rüggeberg and an anonymous reviewer as well as editorial handling by Uwe Brand are gratefully acknowledged. This is contribution ANR CoRo n° 03. ", revision_no = "13", abstract = "The concentrations of major and trace elements were measured in red coral skeletons (Corallium rubrum) by electron microprobe (EMP), isotope dilution inductively coupled mass spectrometry (ID-ICPMS) and laser ablation-ICPMS (LA-ICPMS). The average composition (in mg/kg or ppm) is as follows: Ca: 356300 ± 3200, Mg: 29500 ± 2400, Sr: 2600 ± 250, S: 3100 ± 400, Na: 4200 ± 500, K: 140 ± 20, P: 140 ± 40, B: 28 ± 4, Ba: 9 ± 1, Fe: 8 ± 3, Li: 4 ± 1, Mn: 1 ± 0.5, Pb: 0.5 ± 0.3, U: 0.08 ± 0.05. In terms of Mg, the compositions of the red coral skeletons range from 9 to 15 mol% MgCO_3 with a mean value of 12 ± 1%. Concentrations of sulphur are high (approx. 3000 ppm) and among the highest reported in biogenic calcites. EMP maps (Mg and S) and organic matter (OM) staining show a regular alternation of 100–200 μm wide annual growth rings. Combination of these results with a previous study (Marschal et al., 2004) suggests that Mg-rich rings form during the period spring to early fall, while S-rich rings form immediately after (late autumn and winter). Elemental mapping by EMP shows an unexpected anticorrelation between S and Mg confirmed by LA-ICPMS. This anticorrelation is ascribed to the concomitant presence of S in the organic matter and the anticorrelation between Mg and OM in the skeleton. However, mass balance constraints indicate that in the skeleton sulphur is probably present both as organo-sulphur and structurally substituted sulphur. The studied samples of red coral were collected at various locations and different depths (8–73 m) where the temperature of the sea water was monitored for long periods of time. Although overall decreases of the Mg/Ca and Sr/Ca are observed as a function of depth (and temperature), the use of these ratios as an indication of the sea water temperature (SWT) seems difficult. In addition, a single colony that grew in an area where the temperature was monitored for 30 years did not register the measured increase of SWT of about 1 °C. However, Mg and OM distributions inside skeletons could be good indicators of variations of growth rates on decadal time scales and anomalous ‘summer suffering’ events that could be associated with periods of unusually high SWT conditions. The red coral is thus an example of how growth dynamics (and not temperature alone) affects the chemistry of biominerals.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42618, title ="Trace metal and carbon isotopic variations in cave dripwater and stalagmite geochemistry from northern Borneo", author = "Partin, Judson W. and Cobb, Kim M.", journal = "Geochemistry, Geophysics, Geosystems", volume = "14", number = "9", pages = "3567-3585", month = "September", year = "2013", doi = "10.1002/ggge.20215", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131121-131626968", note = "© 2013 American Geophysical Union.\n\nReceived 11 January 2013; Revised 24 June 2013; Accepted 30 June 2013; Published 5 September 2013.\n\nThe authors wish to thank the staff at Gunung Mulu\nNational Park, especially Jenny Malang and Syria Lejau, who\ncollected the time series of cave dripwaters. We also thank Joseph Gau and Sue Clark of Gunung Mulu National Park, and\nJohnny Baei Hassan of Logan Bunut National Park. Joel Despain, George Prest, Shane Fryer, Jed Mosenfelder, and Brad Hacker provided field assistance during the 2003 field trip to Gunung Buda National Park. Joel Despain, Jean Krejca, Vivian Loftin, Pat Kambesis, and Alan Cressler provided field assistance during the 2006 field trip to Gunung Mulu and Gunung Buda. Nele Meckler and Stacy Carolin provided field assistance during the 2008 field trip to Gunung Mulu. Diego Fernandez provided assistance in the geochemical measurements of dripwaters from the 2003 field trip, while Matt Johnson and Nitya Sharma provided assistance with all other dripwater geochemical measurements. The authors thank two anonymous reviewers for very helpful comments. Funding for this work was provided by NSF-ATM award 0645291 to KMC and NSF-AGS award 0903099 to JFA.\n\n", revision_no = "13", abstract = "We investigate stalagmite trace metal ratios and carbon isotopic composition (δ^(13)C) as potential paleoclimate proxies by comparing cave dripwaters, stalagmites, and bedrock composition from Gunung Mulu and Gunung Buda National Parks in northern Borneo, a tropical rainforest karst site. Three year long, biweekly time series of dripwater Mg/Ca, Sr/Ca, and δ^(13)C from several drips at our site are not correlated with rainfall variability, indicative of a relatively weak relationship between hydroclimate and dripwater geochemistry at our site. However, combining all of the dripwater geochemical data gathered over four field trips to our site (N > 300 samples), we find that drips with highly variable Mg[Sr]/Ca have relatively invariable δ^(18)O values close to the mean. We hypothesize that increased residence times translate into reduced variance in dripwater δ^(18)O through mixing in the epikarst as well as increased Mg[Sr]/Ca values through increased calcite precipitation in the epikarst. Mg/Ca, Sr/Ca, and δ^(13)C time series from three overlapping stalagmites that grew over the last 27 kyrs are characterized by strong centennial-scale variations, and bear little resemblance to previously published, well-reproduced δ^(18)O time series from the same stalagmites. The only shared signal among the three stalagmites' geochemical time series is a relative decrease of 1‰ in δ^(13)C from the Last Glacial Maximum to the Holocene, consistent with a transition from savannah (C4) to rainforest (C3) conditions documented in nearby records. Taken together, our study indicates that stalagmite Mg[Sr]/Ca ratios are poor indicators of hydroclimate conditions at our site, while stalagmite δ^(13)C exhibits some reproducible signals on glacial-interglacial timescales.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/41560, title ="A new method for precise determination of iron, zinc and cadmium stable isotope ratios in seawater by double-spike mass spectrometry", author = "Conway, Tim M. and Rosenberg, Angela D.", journal = "Analytica Chimica Acta", volume = "793", pages = "44-52", month = "September", year = "2013", doi = "10.1016/j.aca.2013.07.025", issn = "0003-2670", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130930-140658632", note = "© 2013 Elsevier B.V. Received 8 March 2013. Received in revised form 24 May 2013. Accepted 8 July 2013. Available online 15 July 2013. We would like to thank Frank Wombacher and Derek Vancefor providing Cd and Zn isotope standards, Ken Bruland and Geoff Smith at UCSC for supplying SAFe standards, Beth Bair at the University of South Carolina for technical support, Paul Field at ESI foruseful discussions on methane, and the Captain and Crew of the R.V. Knorr for collecting samples for us on the US GEOTRACES A03 Transect and the IC1 GEOTRACES cruises. We would also like to thank two anonymous reviewers for their helpful comments. The University of South Carolina and NSF Grant OCE-1131387 funded this study.", revision_no = "16", abstract = "The study of Fe, Zn and Cd stable isotopes (δ^(56)Fe, δ^(66)Zn and δ^(114)Cd) in seawater is a new field, which promises to elucidate the marine cycling of these bioactive trace metals. However, the analytical challenges posed by the low concentration of these metals in seawater has meant that previous studies have typically required large sample volumes, highly limiting data collection in the oceans. Here, we present the first simultaneous method for the determination of these three isotope systems in seawater, using Nobias PA-1 chelating resin to extract metals from seawater, purification by anion exchange chromatography, and analysis by double spike MC-ICPMS. This method is designed for use on only a single litre of seawater and has blanks of 0.3, 0.06 and <0.03 ng for Fe, Zn and Cd respectively, representing a 1–20 fold reduction in sample size and a 4–130 decrease in blank compared to previously reported methods. The procedure yields data with high precision for all three elements (typically 0.02–0.2‰; 1σ internal precision), allowing us to distinguish natural variability in the oceans, which spans 1–3‰ for all three isotope systems. Simultaneous extraction and purification of three metals makes this method ideal for high-resolution, large-scale endeavours such as the GEOTRACES program.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42694, title ="Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements", author = "Hathorne, Ed C. and Gagnon, Alex", journal = "Geochemistry Geophysics Geosystems", volume = "14", number = "9", pages = "3730-3750", month = "September", year = "2013", doi = "10.1002/ggge.20230", issn = "1525‐2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131125-141418131", note = "© 2013 American Geophysical Union. \n\nReceived 27 March 2013; Revised 3 July 2013; Accepted 19 July 2013; Published 23 September 2013.\n\nThanks, Danke and Merci to all participants and laboratories.\nE.C.H. (MARUM Fellowship) and T.F. were supported\nby the DFG-Research Center/Excellence Cluster \"The Ocean\nin the Earth System,\" University of Bremen. The Geological\nSurvey of Japan prepared the reference materials and kindly\nsupplied them for this study. Christina Gnade (MARUM)\nhelped distribute reference powders and collected the data.\nHVM was supported by an AINSE Research Fellowship.", revision_no = "13", abstract = "The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42331, title ="The role of deep ocean circulation in setting glacial climates", author = "Adkins, Jess F.", journal = "Paleoceanography", volume = "28", number = "3", pages = "539-561", month = "September", year = "2013", doi = "10.1002/palo.20046 ", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131108-091133838", note = "© 2013 American Geophysical Union.\n\nReceived 2 January 2013; revised 1 August 2013; accepted 16 August 2013; published 19 September 2013.\n\nThis work has greatly benefited from conversations\nwith many people over the years. Ed Boyle and Danny Sigman have\ntaught me much of what I know about the carbonate system, though any\nmistakes about CO_2 feedbacks in this paper are mine alone. A sabbatical in\nthe CNRS lab at Gif-sur-Yvette provided the time and intellectual space for\nthe initial idea about feedbacks between NADW and AABW formation to\ngerminate into a nascent theory of glacial to interglacial change. I thank them\nimmensely for their hospitality, good humor, and critical ears. My group at\nCaltech has provided both new ideas and a sounding board for this paper during\nits long development. Madeline Miller and Andrea Burke are especially\nthanked for close readings of a fairly complete draft. Two reviewers, Luke\nSkinner and one anonymous, provided a careful, close, and critical reading\nof the manuscript that helped improve it greatly. Finally, Chris Charles was\nan extremely patient editor as well as an important critic of this paper during\nits several incarnations. I am deeply indebted to him for his help. This work\nwas partially supported by NSF grants OCE 1204211 and OCE 0929272.", revision_no = "11", abstract = "The glacial cycles of the Pleistocene involve changes in the circulation of the deep ocean\nin important ways. This review seeks to establish what were the robust patterns of deep-sea\nwater mass changes and how they might have influenced important parts of the last glacial\ncycle. After a brief review of how tracers in the modern ocean can be used to understand the\ndistribution of water masses, I examine the data for biogeochemical, circulation rate, and\nconservative tracers during glacial climates. Some of the robust results from the literature of the\nlast 30 years include: a shoaled version of northern source deep water in the Atlantic, expanded\nsouthern source water in the abyss and deep ocean, salt (rather than heat) stratification of the\nlast glacial maximum (LGM) deep-sea, and several lines of evidence for slower overturning\ncirculation in the southern deep cell. We combine these observations into a new idea for how\nthe ocean-atmosphere system moves from interglacial to glacial periods across a single cycle.\nBy virtue of its influence on the melting of land-based ice around Antarctica, cooling North\nAtlantic Deep Water (NADW) leads to a cold and salty version of Antarctic Bottom Water\n(AABW). This previously underappreciated feedback can lead to a more stratified deep ocean\nthat operates as a more effective carbon trap than the modern, helping to lower atmospheric\nCO_2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a\npositive feedback that drives the system to further cooling.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39775, title ="Varied Response of Western Pacific Hydrology to Climate Forcings over the Last Glacial Period", author = "Carolin, Stacy A. and Cobb, Kim M.", journal = "Science", volume = "340", number = "6140", pages = "1564-1566", month = "June", year = "2013", doi = "10.1126/science.1233797 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130806-094742879", note = "© 2013 American Association for the Advancement of Science. \n\nReceived 7 December 2012; accepted 21 May 2013\nPublished online 6 June 2013.\n\nWe thank N. Meckler, J. Partin, and\nS. Clark (Gunung Mulu National Park) for field assistance;\nJ. Partin for assistance in sample analysis; G. Paris, M. Raven,\nS. Hines, and A. Subhas for assistance in U-Th dating; and\nJ. Lynch-Stieglitz for providing comments on early versions\nof the manuscript. S.A.C, K.M.C., and J.F.A. were involved in\nthe writing and design of this study; A.A.T. and B.C. facilitated\nthe fieldwork for this study; S.A.C, K.M.C., S.L., and J.M.\ncollected samples; and S.A.C. analyzed the samples. The\nresearch was funded by NSF PECASE Award no. 0645291 to\nK.M.C., NSF AGS award no. 0903099 to J.F.A., and a NSF\nGraduate Research Fellowship to S.A.C. Permits for this work\nwere granted by the Malaysian Economic Planning Unit, the\nSarawak State Planning Unit, and the Sarawak Forestry\nDepartment. All data reported in this paper are archived at the\nNational Climatic Data Center (ftp://ftp.ncdc.noaa.gov/pub/data/\npaleo/speleothem/pacific/borneo2013.txt).", revision_no = "14", abstract = "Atmospheric deep convection in the west Pacific plays a key role in the global heat and moisture budgets, yet its response to orbital and abrupt climate change events is poorly resolved. Here, we present four absolutely dated, overlapping stalagmite oxygen isotopic records from northern Borneo that span most of the last glacial cycle. The records suggest that northern Borneo’s hydroclimate shifted in phase with precessional forcing but was only weakly affected by glacial-interglacial changes in global climate boundary conditions. Regional convection likely decreased during Heinrich events, but other Northern Hemisphere abrupt climate change events are notably absent. The new records suggest that the deep tropical Pacific hydroclimate variability may have played an important role in shaping the global response to the largest abrupt climate change events. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/40722, title ="Movement of deep-sea coral populations on climatic timescales", author = "Thiagarajan, Nivedita and Gerlach, Dana", journal = "Paleoceanography", volume = "28", number = "2", pages = "227-236", month = "June", year = "2013", doi = "10.1002/palo.20023 ", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130819-142613103", note = "© 2013 American Geophysical Union.\n\nReceived 13 November 2012; revised 16 February 2013; accepted 21 February 2013; published 30 May 2013.\n\nWe would like to thank the crew of the R/V\nThomas Thompson and R/V Southern Surveyor for their dedicated support\nduring two cruises to the westerly wind belt. We would also like to thank\nJoel Tropp (Caltech) for help with statistical analysis.", revision_no = "34", abstract = "During the past 40,000\u2009years, global climate has moved into and out of a full glacial period, with the deglaciation marked by several millennial-scale rapid climate change events. Here we investigate the ecological response of deep-sea coral communities to both glaciation and these rapid climate change events. We find that the deep-sea coral populations of Desmophyllum dianthus in both the North Atlantic and the Tasmanian seamounts expand at times of rapid climate change. However, during the more stable Last Glacial Maximum, the coral population globally retreats to a more restricted depth range. Holocene populations show regional patterns that provide some insight into what causes these dramatic changes in population structure. The most important factors are likely responses to climatically driven changes in productivity, [O_2] and [CO_3^(2–)].", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39716, title ="MC-ICP-MS measurement of δ^(34)S and Δ^(33)S in small amounts of dissolved sulfate", author = "Paris, Guillaume and Sessions, Alex L.", journal = "Chemical Geology", volume = "345", pages = "50-61", month = "May", year = "2013", doi = "10.1016/j.chemgeo.2013.02.022 ", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130801-142621209", note = "© 2013 Elsevier B.V. \n\nReceived 16 November 2012. Received in revised form 16 February 2013. Accepted 19 February 2013. Available online 5 March 2013. \n\nEditor: U. Brand. \n\nThe authors would like to acknowledge Nathan Dalleska for precious help in using the IC, Eric Kort for helping with Allan variance analyses, Seth John for providing the seawater samples and Nivedita Thiagarajan for the coral sample. We also thank two anonymous reviewers for their comments and suggestions. This work was supported by the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry. The Adkins and Sessions groups are also deeply thanked for feedbacks and support. Thanks also to Vicky Rennie for being a motivated early user of this new method.", revision_no = "12", abstract = "Over the last decade, the use of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has significantly lowered the detection limit of sulfur isotope analyses, albeit typically with decreased precision. Moreover, the presence of isobaric interferences for sulfur prevented accurate analysis of the minor isotopes ^(33)S and ^(36)S. In the present study, we report improved techniques for measuring sulfur isotopes on the MC-ICP-MS Neptune Plus (Thermo Fischer Scientific) using a heated spray chamber coupled to a desolvating membrane (Aridus, Cetac). Working at high mass resolution, we measured δ^(34)S values of natural samples with a typical reproducibility of 0.08–0.15‰ (2sd) on 5 to 40 nmol sulfur introduced into the instrument. We applied this method to two seawater profiles, using 25 μl of sample (700 nmol of sulfate). The average δ^(34)S_(VCDT) value is 20.97 ± 0.10‰ (2sd, n = 25). We show that the amount of sulfate required for an analysis can be decreased to 5 nmol. Because the plasma is sustained by Ar, measurement of ^(36)S is impossible at the current mass resolution due to the presence of ^(36)Ar^+, but a reproducibility of 0.1–0.3‰ (2sd) is achieved on the measurement of mass independent fractionations (Δ^(33)S). This is the first time such precision has been achieved on samples of this size.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/40729, title ="Diurnal to interannual rainfall δ^(18)O variations in northern Borneo driven by regional hydrology", author = "Moerman, Jessica W. and Cobb, Kim M.", journal = "Earth and Planetary Science Letters", volume = "369", pages = "108-119", month = "May", year = "2013", doi = "10.1016/j.epsl.2013.03.014", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130820-091932864", note = "© 2013 Elsevier B. V.\n\nReceived 4 October 2012; Received in revised form 11 March 2013; Accepted 13 March 2013; Editor: G. Henderson. Available online 25 April 2013.\n\nThe authors gratefully acknowledge the Mulu Meteorological Station staff for overseeing the collection of the daily rainfall samples, as well as Jenny Malang, Syria Lejau, and the staff at Gunung Mulu National Park for their dedicated assistance during fieldtrips. Permits for this work were granted by the Malaysian Economic Planning Unit, the Sarawak State Planning Unit, and the Sarawak Forestry Department. We also thank Aaron van Pelt of Picarro, Inc., Bruce Vaughn of INSTARR at UC Boulder, and Krystle Stewart for their invaluable assistance during sample analysis and Dr. Emanuele Di Lorenzo for his assistance with the TRMM dataset. This research was supported by NSF Grant 0645291 to KMC, and JWM was funded by a NSF Graduate Research Fellowship.", revision_no = "16", abstract = "The relationship between climate variability and rainfall oxygen isotopic (δ^(18)O) variability is poorly constrained, especially in the tropics, where many key paleoclimate records rely on past rainfall isotopes as proxies for hydroclimate. Here we present a daily-resolved, 5-yr-long timeseries of rainfall δ^(18)O from Gunung Mulu National Park, located in northern Borneo (4°N, 114°E) in the heart of the West Pacific Warm Pool, and compare it to local and regional climatic variables. Daily rainfall δ^(18)O values range from +0.7‰ to −18.5‰ and exhibit a weak but significant inverse relationship with daily local precipitation amount (R=−0.19, p<0.05), consistent with the tropical amount effect. Day-to-day δ^(18)O variability at Mulu is best correlated to regional precipitation amount averaged over the preceding week (R=−0.64, p<0.01). The inverse relationship between Mulu rainfall δ^(18)O and local (regional) precipitation amount increases with increased temporal averaging, reaching R=−0.56 (R=−0.72) on monthly timescales. Large, negative, multi-day rainfall δ^(18)O anomalies of up to 16‰ occur every 30–90 days and are closely associated with wet phases of the intraseasonal Madden–Julian Oscillation. A weak, semi-annual seasonal cycle in rainfall δ^(18)O of 2–3‰ bears little resemblance to seasonal precipitation variability, pointing to a complex sequence of moisture sources and/or trajectories over the course of the year. Interannual rainfall δ^(18)O variations of 6–8‰ are significantly correlated with indices of the El Niño Southern Oscillation, with increased rainfall δ^(18)O during relatively dry El Niño conditions, and vice versa during La Nina events. We find that Mulu rainfall δ^(18)O outperforms Mulu precipitation amount as a tracer of basin-scale climate variability, highlighting the time- and space-integrative nature of rainfall δ^(18)O. Taken together, our results suggest that rainfall δ^(18)O variability at Mulu is significantly influenced by the strength of regional convective activity. As such, our study provides further empirical support for the interpretation of δ^(18)O-based paleo-reconstructions from northern Borneo stalagmites as robust indicators of regional-scale hydroclimate variability, where higher δ^(18)O reflects regional drying.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/37649, title ="Sr/Ca sensitivity to aragonite saturation state in cultured subsamples from a single colony of coral: Mechanism of biomineralization during ocean acidification", author = "Gagnon, Alexander C. and Adkins, Jess F.", journal = "Geochimica et Cosmochimica Acta", volume = "105", pages = "240-254", month = "March", year = "2013", doi = "10.1016/j.gca.2012.11.038", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130327-111017326", note = "© 2012 Elsevier Ltd. \n\nReceived 15 September 2010; accepted in revised form 26 November 2012; available online 10 December 2012. Associate editor: Alfonso Mucci. \n\nNanoSIMS analysis was conducted at the Caltech Center for Microanalysis which is supported in part by the Gordon and Betty Moore Foundation. The confocal laser-scanning microscope is housed and maintained by the Caltech Biological Imaging Center. Will Berelson of USC made his lab available for DIC analysis. Several technicians at Hebrew University, Jerusalem assisted with\nalkalinity titrations. This manuscript benefited from constructive suggestions by several anonymous reviewers as well as the detailed comments and skillful handing of the editor.", revision_no = "14", abstract = "Using a new and rapid NanoSIMS-based method, we quantified the sensitivity of skeletal Sr/Ca in coral to the aragonite saturation state of seawater (Ω_(SW)). Skeletal Sr/Ca is a common proxy for temperature while Ω_(SW) is a parameter that varied in the past ocean and is predicted to change with continued ocean acidification. Five adult branches of the surface coral Stylophora pistillata were grown at different Ω_(SW) from 2.7 to 4.9 (pH of 7.9–8.5) but at a constant temperature of 25 °C. Despite a large range of growth parameters and a twofold range in calcification rates, the average skeletal Sr/Ca of coral exposed to each condition are within 1.2% of each other (2σ std. dev. of the 5 means). Furthermore, the average skeletal Sr/Ca measured in this study agrees with the results of two previous coral culture experiments conducted at the same temperature but where Ω_(SW) was not controlled. These results suggest that aragonite saturation has little or no influence on Sr/Ca paleothermometry over the range of Ω_(SW) investigated. Combined with existing data for low Ω_(SW) conditions, our results were used to elucidate the mechanisms controlling calcifying fluid acid–base chemistry during coral biomineralization. Assuming that coral drive precipitation through alkalinity pumping, our data suggest that this pumping occurs until the calcifying fluid reaches a target pH. Below a threshold Ω_(SW) bounded by 1 < Ω_(SW) < 2.4, however, coral do not pump enough alkalinity to reach the target pH and instead pump a maximal but finite amount of alkalinity. In this low Ω_(SW) regime, calcifying fluid pH is expected to decrease with Ω_(SW). The interplay between these two alkalinity pumping regimes and external seawater composition explain the full range of observed Sr/Ca sensitivity to Ω_(SW) and suggest that surface coral may become increasingly sensitive to ocean acidification below a threshold Ω_(SW) bounded by 1 < Ω_(SW) < 2.4.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42335, title ="Simple, rapid, and cost effective: a screening method for ^(14)C analysis of small carbonate samples", author = "Bush, Shari L. and Santos, Guaciara M.", journal = "Radiocarbon", volume = "55", number = "2-3", pages = "631-640", month = "January", year = "2013", doi = "10.2458/azu_js_rc.55.16192", issn = "0033-8222", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131108-093622193", note = "© 2013 Arizona Board of Regents on behalf of the University of Arizona.\n\nWe wish to thank the 2 anonymous reviewers for the very constructive and detailed suggestions and the editors Mark McClure and Tim Jull.", revision_no = "10", abstract = "We have developed a simple, rapid method to screen carbonates for survey applications, which provides radiocarbon dates with decreased precision at lower cost. The method is based on previous work by Longworth et al. (2011) and involves mixing pulverized CaCO_3 with Fe powder, followed by pressing into aluminum target holders for direct ^(14)C accelerator mass spectrometry (AMS) measurements. An optimum beam current averaging ~10% of those produced by >0.7 mg C graphite targets was obtained for carbonate samples of 0.3–0.5 mg (0.04–0.06 mg C). The precision of the method was evaluated by measuring triplicates of 14C reference materials, as well as by comparing results from this rapid method with results from high-precision AMS measurements on graphite (typically 0.2–0.3%). Measurement reproducibility was ~1.8% (1σ) for samples <10 ka BP, and it increased drastically for older samples. However, t tests on paired samples resulted in p values greater than 0.05, indicating a good correlation between this survey method and the conventional one. An average blank (calcite) of 0.0075 Fm (~39 ka BP) was achieved. The simplicity of the technique allowed us to process and measure 72 deep-sea coral samples in less than 25 hr.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/36163, title ="Precise overgrowth composition during biomineral culture and inorganic precipitation", author = "Gagnon, Alexander C. and DePaolo, Donald J.", journal = "Chemical Geology", volume = "330", pages = "188-196", month = "November", year = "2012", issn = "0009-2541", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130104-093434755", note = "© 2012 Published by Elsevier B.V. Received 2 May 2012. Received in revised form 22 August 2012. Accepted 22 August 2012. Available online 31 August 2012. This work was supported in part by the Director, Office of Science,\nOffice of Basic Energy Sciences, Chemical Sciences Geosciences and Bioscience Program of the U.S. Department of Energy under Contract No. DEAC02-05CH11231. ACG would like to thank Jonathan Erez for his encouragement and for thoughtful discussions; conversations that helped motivate this research. This manuscript benefited from constructive suggestions by two anonymous reviewers.", revision_no = "11", abstract = "We introduce a method to analyze element ratios and isotope ratios in mineral overgrowths. This general technique can quantify environmental controls on proxy behavior for a range of cultured biominerals and can also measure compositional effects during seeded mineral growth. Using a media enriched in multiple stable isotopes, the method requires neither the mass nor the composition of the initial seed or skeleton to be known and involves only bulk isotope measurements. By harnessing the stability and sensitivity of bulk analysis the new approach promises high precision measurements for a range of elements and isotopes. This list includes trace species and select non-traditional stable isotopes, systems where sensitivity and external reproducibility currently limit alternative approaches like secondary ion mass spectrometry (SIMS) and laser ablation mass spectrometry. Since the method separates isotopically labeled growth from unlabeled material, well-choreographed spikes can resolve the compositional effects of different events through time. Among other applications, this feature could be used to separate the impact of day and night on biomineral composition in organisms with photosymbionts.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/35242, title ="The flux of iron and iron isotopes from San Pedro Basin sediments", author = "John, Seth G. and Mendez, Jeffery", journal = "Geochimica et Cosmochimica Acta", volume = "93", pages = "14-29", month = "September", year = "2012", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121101-110258784", note = "© 2012 Elsevier Ltd. Received 20 May 2011; accepted in revised form 3 June 2012; available online 23 June 2012. Associate editor: Mark Rehkamper. ", revision_no = "15", abstract = "Iron is an important nutrient in the ocean, but the different sources and sinks of iron are not well constrained. Here, we use measurements of Fe concentration and Fe stable isotope ratios to evaluate the importance of reducing continental margins as a source of Fe to the open ocean. Dissolved iron concentration ([Fe]) and iron stable isotope ratios (δ^(56)Fe) were measured in the San Pedro and Santa Barbara basins. Dissolved δ^(56)Fe ranges from −1.82‰ to 0.00‰ in the San Pedro Basin and from −3.45‰ to −0.29‰ in the Santa Barbara Basin, and in both basins the lowest δ^(56)Fe values and highest Fe concentrations are found at the bottom of the basin reflecting the input of isotopically light Fe from reducing sediment porewaters. In the San Pedro Basin, we are also able to fingerprint an advective source of Fe from shallow continental shelves next to the basin and the atmospheric deposition of Fe into surface waters. A one-dimensional model of the Fe isotope cycle has been constructed for the deep silled San Pedro Basin. By fitting model output to data, values of several important iron cycle parameters are predicted including a flux of Fe from sediment porewaters into the water column of 0.32–1.14 μmol m^(−2) d^(−1), a first-order dissolved Fe precipitation rate constant of 0.0018–0.0053 d^(−1), a flux δ56Fe of −2.4‰, and an isotope effect for Fe precipitation of Δδ^(56)Fe_(particulate-dissolved) = −0.8‰. Applying our model-predicted Fe cycle parameters to the global ocean suggests that continental margins contribute 4–12% of world ocean dissolved Fe and make the ocean’s Fe lighter by −0.08‰ to −0.26‰. The dramatically negative δ^(56)Fe signature seen in the water column of the San Pedro and Santa Barbara basins demonstrate the utility of Fe isotopes as a tracer for continental margin Fe input from reducing sediments to the oceans, while the isotopic fractionation observed during loss of Fe from the dissolved phase suggests that this signature will be modified by subsequent reactions. Our modeling provides an initial framework for testing how these signals are transmitted into the open ocean.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/35650, title ="GEOTRACES IC1 (BATS) contamination-prone trace element\nisotopes Cd, Fe, Pb, Zn, Cu, and Mo intercalibration", author = "Boyle, Edward A. and John, Seth", journal = "Limnology and Oceanography: Methods", volume = "10", pages = "653-665", month = "September", year = "2012", doi = "10.4319/lom.2012.10.653", issn = "1541-5856", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121127-073916860", note = "© 2012 by the American Society of Limnology and Oceanography, Inc. Submitted 1 August 2011 Revised 19 April 2012 Accepted 29 May 2012. We particularly thank Greg Cutter and Geoff Smith for assistance in obtaining these samples, as well as the other participants who lent a hand in lugging heavy samples up and down the decks of the ship. Rick Kayser prepared materials for the cruise. We thank Nilanjan Chatterjee for electron probe analysis. We thank the officers and crew of the R/V Knorr. The National Science Foundation sponsored the cruise and many of the shipboard participants; in particular E.B. was funded to\nparticipate on the cruise by NSF Grant OCE-0751409 and his\npreparation of this paper was partially supported by grants\nfrom the Kuwait Foundation for the Advancement of Science\n(KFAS) and the Singapore-MIT Alliance for Research and Technology (SMART). This paper is part of the Intercalibration in Chemical Oceanography special issue of L&O Methods that was supported by funding from the U.S. National Science Foundation, Chemical Oceanography Program (Grant OCE-0927285 to G. Cutter).", revision_no = "14", abstract = "We report data on the isotopic composition of cadmium, copper, iron, lead, zinc, and molybdenum at the GEOTRACES IC1 BATS Atlantic intercalibration station. In general, the between lab and within-lab precisions are adequate to resolve global gradients and vertical gradients at this station for Cd, Fe, Pb, and Zn. Cd and Zn isotopes show clear variations in the upper water column and more subtle variations in the deep water; these variations are attributable, in part, to progressive mass fractionation of isotopes by Rayleigh distillation from biogenic uptake and/or adsorption. Fe isotope variability is attributed to heavier crustal dust and hydrothermal sources and light Fe from reducing sediments. Pb isotope variability results from temporal changes in anthropogenic source isotopic compositions and the relative contributions of U.S. and European Pb sources. Cu and Mo isotope variability is more subtle and close to analytical precision. Although the present situation is adequate for proceeding with GEOTRACES, it should be possible to improve the within-lab and between-lab precisions for some of these properties.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39477, title ="The role of ocean cooling in setting glacial southern source bottom water salinity", author = "Miller, M. D. and Adkins, J. F.", journal = "Paleoceanography", volume = "27", number = "3", pages = "Art. No. PA3207", month = "August", year = "2012", doi = "10.1029/2012PA002297 ", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130722-073939346", note = "© 2012 American Geophysical Union.\n\nReceived 23 February 2012; revised 2 May 2012; accepted 20 June 2012; published 4 August 2012.\n\nM.D.M. and J.F.A. received funding from\nthe National Science Foundation under NSF grant OCE-0929272. M.D.M.,\nD.M., and M.P.S. received funding from the ECCO2 project, a contribution\nto the NASA Modeling Analysis and Prediction (MAP) Program. We gratefully\nacknowledge computational resources and support from the NASA\nAdvanced Supercomputing (NAS) Division. We thank Keith Nicholls for\nproviding the data for Figure 1. Anand Gnanadesikan inspired writing the\nsalt tracer code for analyzing the sources of salinity changes. We are grateful\nto Martin Losch for his implementation of the ice shelf code in MITgcm and\nfor helpful discussions about ice shelf and sea ice modeling.", revision_no = "9", abstract = "At the Last Glacial Maximum (LGM), the salinity contrast between northern source deep water and southern source bottom water was reversed with respect to the contrast today. Additionally, Glacial Southern Source Bottom Water (GSSBW) was saltier than Antarctic Bottom Water (AABW), over and above the difference implied by the mean sea level change. This study examines to what extent cold temperatures, through their effect on ice formation and melting, could have caused these differences. Computational sensitivity experiments using a coupled ice shelf cavity–sea ice–ocean model are performed in a Weddell Sea domain, as a representative case study for bottom water formation originating from Antarctic continental shelves. Ocean temperatures at the domain open boundaries are systematically lowered to determine the sensitivity of Weddell Sea water mass properties to a range of cool ocean temperatures. The steady state salinities differ between experiments due to temperature-induced responses of ice shelf and sea ice melting and freezing, evaporation and open boundary fluxes. The results of the experiments indicate that reduced ocean temperature can explain up to 30% of the salinity difference between GSSBW and AABW, primarily due to decreased ice shelf melting. The smallest and most exposed ice shelves, which abut narrow continental shelves, have the greatest sensitivity to the ocean temperature changes, suggesting that at the LGM there could have been a shift in geographical site dominance in bottom water formation. More sea ice is formed and exported in the cold ocean experiments, but the effect of this on salinity is negated by an equal magnitude reduction in evaporation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/32361, title ="The vertical distribution of iron stable isotopes in the North Atlantic near Bermuda", author = "John, Seth G. and Adkins, Jess", journal = "Global Biogeochemical Cycles", volume = "26", pages = "Art. No. GB2034", month = "June", year = "2012", issn = "0886-6236", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120711-132003222", note = "© 2012 American Geophysical Union.\n\nReceived 27 January 2011; accepted 2 May 2012; published 15 June 2012. \n\nThanks to all who helped and participated on the Geotraces Intercalibration I cruise, especially Chief Scientist Greg\nCutter, Ed Boyle, Geoffrey Smith, and the captain and crew of the R/V Knorr.", revision_no = "16", abstract = "Seawater dissolved iron isotope ratios (δ^(56)Fe) have been measured in the North Atlantic near Bermuda. In a full-depth profile, seawater dissolved δ^(56)Fe is isotopically heavy compared to crustal values throughout the water column (δ^(56)Fe_(IRMM-014) = +0.30‰ to +0.71‰). Iron isotope ratios are relatively homogenous in the upper water column (between +0.30‰ to +0.45‰ above 1500 m), and δ^(56)Fe increases below this to a maximum of +0.71‰ at 2500 m, decreasing again to +0.35‰ at 4200 m. The δ^(56)Fe profile is very different from the iron concentration profile; in the upper water column [Fe] is variable while δ^(56)Fe is relatively constant, and in the deeper water column δ^(56)Fe varies while [Fe] remains relatively constant. The δ^(56)Fe profile is also not well correlated with other hydrographic tracers in the North Atlantic such as temperature, salinity, or the concentrations of oxygen, phosphate, silica, and CFC-11. The dissimilarity between δ^(56)Fe profiles and profiles of [Fe] and other hydrographic tracers shows that Fe isotope ratios provide a unique sort of information about ocean chemistry, and they suggest that Fe isotopes may therefore be a valuable new tool for tracing the global sources, sinks, and biogeochemical cycling of Fe. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/32048, title ="Interglacial Hydroclimate in the Tropical West Pacific Through the Late Pleistocene", author = "Meckler, A. N. and Clarkson, M. O.", journal = "Science", volume = "336", number = "6086", pages = "1301-1304", month = "June", year = "2012", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120622-151730519", note = "© 2012 American Association for the Advancement of Science.\n\n22 December 2011; accepted 19 April 2012; Published online 3 May 2012.\n\nWe thank B. Clark, S. Lejau, and J. Malang of Mulu National Park, as well as J. Partin for assistance in the field. A. Tuen (Universiti Malaysia Sarawak) greatly facilitated fieldwork in Sarawak. N. Sharma and K. Stewart are acknowledged for assistance with stable isotope measurements. D. Lund, A. Subhas, and D. Fernandez are\nthanked for assistance and advice with U-Th dating. J. Eiler\nprovided access to his facilities at the California Institute of Technology. Support for this work was provided by the Swiss National Science Foundation (SNF) and the German Research Foundation (DFG) through postdoctoral fellowships to A.N.M.; by the US NSF through grants ATM-0318445 and ATM-0903099 to J.F.A, as well as ATM-0645291 to K.M.C.; and by an Edinburgh University Principal’s Career Development Ph.D. Scholarship to M.O.C.", revision_no = "20", abstract = "Records of atmospheric carbon dioxide concentration (Pco_2) and Antarctic temperature have revealed an intriguing change in the magnitude of interglacial warmth and Pco_2 at around 430,000 years ago (430 ka), but the global climate repercussions of this change remain elusive. Here, we present a stalagmite-based reconstruction of tropical West Pacific hydroclimate from 570 to 210 ka. The results suggest similar regional precipitation amounts across the four interglacials contained in the record, implying that tropical hydroclimate was insensitive to interglacial differences in Pco_2 and high-latitude temperature. In contrast, during glacial terminations, drying in the tropical West Pacific accompanied cooling events in northern high latitudes. Therefore, the tropical convective heat engine can either stabilize or amplify global climate change, depending on the nature of the climate forcing. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/31815, title ="Global climate evolution during the last deglaciation", author = "Clark, Peter U. and Adkins, Jess F.", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "109", number = "19", pages = "E1134-E1142", month = "May", year = "2012", doi = "10.1073/pnas.1116619109", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120605-104736843", note = "© 2012 National Academy of Sciences. \n\nEdited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved January 4, 2012 (received for review October 10, 2011). Published online before print February 13, 2012. \n\nWe thank the National Oceanic and Atmospheric Administration Paleoclimatology program for data archiving, and the many scientists who generously contributed datasets used in our analyses. We also thank the National Science Foundation Paleoclimate Program and the Past Global Changes program for supporting the workshops that led to this synthesis. \n\nAuthor contributions: P.U.C., J.D.S., Z.L., and B.L.O.-B. designed research; P.U.C., J.D.S., and\nJ.X.M. performed research; P.U.C., J.D.S., A.E.C., H.C., Z.L., B.L.O.-B., J.F.A., J.L.B., J.C., S.M.C.,\nW.B.C., B.P.F., F.H., T.C.J., J.L.-S., V.M., J.M., P.I.M., and J.W.W. analyzed data; and P.U.C.,\nJ.D.S., P.A.B., P.J.B., S.B., E.B., A.E.C., D.S.K., T.M.M., A.C.M., C.M., K.P., J.M.R., and C.W.\nwrote the paper.", revision_no = "25", abstract = "Deciphering the evolution of global climate from the end of the Last Glacial Maximum approximately 19 ka to the early Holocene 11 ka presents an outstanding opportunity for understanding the transient response of Earth’s climate system to external and internal forcings. During this interval of global warming, the decay of ice sheets caused global mean sea level to rise by approximately 80 m; terrestrial and marine ecosystems experienced large disturbances and range shifts; perturbations to the carbon cycle resulted in a net release of the greenhouse gases CO_2 and CH_4 to the atmosphere; and changes in atmosphere and ocean circulation affected the global distribution and fluxes of water and heat. Here we summarize a major effort by the paleoclimate research community to characterize these changes through the development of well-dated, high-resolution records of the deep and intermediate ocean as well as surface climate. Our synthesis indicates that the superposition of two modes explains much of the variability in regional and global climate during the last deglaciation, with a strong association between the first mode and variations in greenhouse gases, and between the second mode and variations in the Atlantic meridional overturning circulation. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/31861, title ="Seawater transport during coral biomineralization", author = "Gagnon, Alexander C. and Adkins, Jess F.", journal = "Earth and Planetary Science Letters", volume = "329", pages = "150-161", month = "May", year = "2012", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120608-153059820", note = "© 2012 Elsevier B.V.\nAccepted 2 March 2012. Available online 31 March 2012. Editor: P. DeMenocal.\nNanoSIMS analysis was conducted using an instrument at the Caltech\nCenter for Microanalysis which is supported in part by the Gordon\nand Betty Moore Foundation. The confocal laser-scanning microscope is\nhoused and maintained by the Caltech Biological Imaging Center. This\nmanuscript benefited from constructive suggestions by two anonymous\nreviewers.", revision_no = "24", abstract = "Cation transport during skeletal growth is a key process controlling metal/calcium (Me/Ca) paleoproxy behavior\nin coral. To characterize this transport, cultured corals were transferred into seawater enriched in the rare\nearth element Tb^(3+) as well as stable isotopes of calcium, strontium, and barium. Subsequent NanoSIMS ion\nimages of each coral skeleton were used to follow uptake dynamics. These images show a continuous region\ncorresponding to new growth that is homogeneously enriched in each tracer. Isotope ratio profiles across the\nnew growth boundary transition rapidly from natural abundance ratios to a ratio matching the enriched culture\nsolution. The location of this transition is the same for each element, within analytical resolution. The\nsynchronous incorporation of all these cations, including the dissimilar ion terbium, which has no known biological\nfunction in coral, suggests that: (1) there is cation exchange between seawater and the calcifying\nfluid, and (2) these elements are influenced by similar transport mechanisms consistent with direct and\nrapid seawater transport to the site of calcification. Measured using isotope ratio profiles, seawater transport\nrates differ from place to place on the growing coral skeleton, with calcifying fluid turnover times from 30 min\nto 5.7 h. Despite these differences, all the elements measured in this study show the same transport dynamics\nat each location. Using an analytical geochemical model of biomineralization that includes direct seawater\ntransport we constrain the role of active calcium pumping during calcification and we show that the balance\nbetween seawater transport and precipitation can explain observed Me/Ca variability in deep-sea coral.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/31373, title ="The sulfur-isotopic compositions of benzothiophenes\nand dibenzothiophenes as a proxy for thermochemical\nsulfate reduction", author = "Amrani, Alon and Deev, Andrei", journal = "Geochimica et Cosmochimica Acta", volume = "84", pages = "152-164", month = "May", year = "2012", doi = "10.1016/j.gca.2012.01.023", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120509-102449517", note = "© 2012 Elsevier Ltd. \n\nReceived 31 May 2011; accepted in revised form 20 December 2011; available online 28 January 2012. \n\nAssociate editor: Josef P. Werne. \n\nWe thank Zeev Aizenshtat and Ward Said-Ahamed (Hebrew University, Jerusalem) for the EA-IRMS analysis of bulk S isotopes, and Adam Subhas (California Institute of Technology) for technical assistance with the MC-ICPMS. This study was partially supported by Marathon Oil Company and the Power, Energy and Environmental Research Institute (PEERi). We appreciate the discussions and comments by Tongwei Zhang, Zeev Aizenshtat, Geoffrey Ellis, Clifford Walters, Richard Worden, and an anonymous reviewer that help to improve this manuscript.", revision_no = "20", abstract = "Compound-specific analyses of the ^(34)S/^(32)S isotope ratios of individual organosulfur compounds in Upper Jurassic oil and condensate samples from the Smackover Fm. reveal differences of up to ∼50‰ between compounds. There is a clear distinction between oils altered by thermochemical sulfate reduction (TSR) versus those that are not. Oils that did experience TSR exhibit significant ^(34)S enrichment of benzothiophenes (BTs) compared to dibenzothiophenes (DBTs), while in unaltered oils these compounds have similar isotopic compositions. The δ^(34)S values of BTs are close to those of sulfate-bearing evaporites of the Smackover Fm., whereas the δ^(34)S values of DBTs are spread over a wider range and gradually approach those of the BTs.\nGold-tube hydrous pyrolysis experiments using three representative oils show that isotopic alteration readily occurs under TSR conditions and can significantly affect the δ^(34)S values of individual compounds. Our results indicate that BTs can be a sensitive tracer for TSR as they form readily under TSR conditions, with large ^(34)S enrichments relative to the bulk oil. In contrast, DBTs exhibit relatively small changes in δ^(34)S, preserving their original δ^(34)S values longer than do BTs because of their greater thermal stability and slow rate of formation. We propose that comparison of the δ^(34)S values of BT and DBT can be used to detect TSR alteration of oils from the very early stages up to highly altered oils. The approach should find numerous uses in petroleum exploration, as well as for understanding the basic reaction mechanisms and kinetics of thermochemical sulfate reduction and secondary sulfur incorporation into oils.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/28992, title ="Effects of chronic low carbonate saturation levels on\nthe distribution, growth and skeletal chemistry of\ndeep-sea corals and other seamount megabenthos", author = "Thresher, Ronald E. and Tilbrook, Bronte", journal = "Marine Ecology - Progress Series", volume = "442", pages = "87-99", month = "December", year = "2011", issn = "0171-8630", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120127-092337870", note = "© 2011 Inter-Research. Submitted: December 23, 2010; Accepted: September 15, 2011. Proofs received from author(s): November 15, 2011. We thank E. Anagnostou, A. Beck, W. Cho, A. Gagnon, K. Gowlett-Holmes, S. John, A. Kennedy, H. Kippo, N. Meckler, D. Mills, D. Staples, A. Subhas and N. Thiagarajan; the crews of the autonomous underwater vehicle (AUV) 'ABE', the ROY 'Jason' and the RVs 'Thomas T. Thompson' and 'Southern Surveyor' for their professional assistance in the field; P. Alderslade, S. Cairns, D. Fautin, K. Gowlett-Holmes, F. McEnnulty and K. Moore for taxonomic assistance; A. Agron. K. Berry, E. Innocenti, C. MacRae and S. Peacock for the mineralogical and chemical analyses; R. Matear for discussions about historical shifts in the ASH; E. Butler for advice on measuring organic fractions in corals; M. Keith and the Woods Hole Advanced Imaging and Visualization Laboratory for photographic expertise; and N. Bax, J . Guinotte, R. Matear and 2 anonymous referees for comments on the manuscript. Components of this work were supported by the National Science Foundation; the Australian Department of Environment, Water, Heritage, and the Arts; the Australian Climate Change Science Program; the Australian Commonwealth Environmental Research Fund; and a grant of ship time by the Australian National Research Facility. ", revision_no = "13", abstract = "Ocean acidification has been predicted to reduce the ability of marine organisms to produce carbonate skeletons, threatening their long-term viability and severely impacting marine ecosystems. Corals, as ecosystem engineers, have been identified as particularly vulnerable and important. To determine the sensitivity of corals and allied taxa to long-term exposure to very low carbonate concentrations, we examined the distribution and skeletal characteristics of coral taxa along a natural deep-sea concentration gradient on seamounts of SW Australia. Carbonate under-saturation had little evident effect on the depth distribution, growth or skeletal composition of live scleractinians or gorgonians, with corals growing, often abundantly, in waters as much as 20 to 30% under-saturated. Developmental anomalies in the deepest skeleton-forming anthozoan collected (an isidid gorgonian, at nearly 4 km depth) suggest an absolute low tolerance limit of about 40% under-saturation. Evidence for an effect of acidification on the accumulation of reef structure is ambiguous, with clear indications of dissolution of high-magnesium calcite (HMC) gorgonian skeletons at depths below 2300 m, but also abundant, old scleractinian skeletons well below the aragonite saturation horizon. The latter might be the result of ferromanganese deposition on exposed skeletons, which, however, may render them inhospitable for benthic organisms. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/27800, title ="Modal analysis of the deep-water solitary scleractinian,\nDesmophyllum dianthus, on SW Pacific seamounts: inferred\nrecruitment periodicity, growth, and mortality rates", author = "Thresher, R. E. and Adkins, J.", journal = "Coral Reefs", volume = "30", number = "4", pages = "1063-1070", month = "December", year = "2011", issn = "0722-4028", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111116-094548860", note = "© 2011 Springer-Verlag. Received: 6 January 2011. Accepted: 19 July 2011. Published online: 3 August 2011. Communicated by Biology Editor Dr. Hugh Sweatman. We thank E. Anagnostou, A. Beck, W. Cho, A. Gagnon, K. Gowlett-Holmes, S. John, A. Kennedy, H. Kippo, N. Meckler, D. Mills, D. Staples, and A. Subhas, and the crews of the AUV ABE, the ROV Jason, RV Thomas T. Thompson, and RV Southern Surveyor for their professional assistance in the field. We particularly thank M. Haddon for his assistance with the modal analysis and comments on a draft manuscript. We also thank R. Waller, N. Bax and two anonymous referees for useful comments on the ms. Components of this work were supported by the National Science Foundation, the Australian Department of Environment, Water, Heritage, and the Arts, the Australian Commonwealth Environmental Research Fund and a grant of ship time by the Australian\nNational Research Facility. ", revision_no = "12", abstract = "Little is known about the demography of corals inhabiting deep-sea features due to the logistical difficulties of working at the extreme depths they inhabit. To obtain basic information about growth, mortality, and recruitment dynamics for such a coral, we applied modal analysis to the size frequency distributions of live-caught and sub-fossil specimens of the widely distributed solitary cup coral, Desmophyllum dianthus, collected on SW Pacific seamounts. Comparison of live-caught material collected in 1997 and 2007–2009 indicated modal progression over time and an implied maximum age of approximately 190 years, which is similar to ages determined previously for D. dianthus using radiometric techniques. A log-linear decline in the number of individuals with increasing size further implies a constant adult mortality rate, of 15.1% per annum in 1997 and 9.2% per annum in 2007–2009. The spacing of size modes in the 2007–2009 samples suggests regularly episodic recruitment events, at 22- to 32-year intervals, which may relate to periodic variability in large-scale Southern Ocean circulation. Preliminary analyses of size frequency distributions of the sub-fossil material suggest that the trophodynamics, growth, and adult mortality schedules of D. dianthus in the SW Pacific have remained basically similar throughout the Holocene.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/27799, title ="Extraordinarily high biomass benthic community on Southern Ocean seamounts", author = "Thresher, R. E. and Adkins, J.", journal = "Scientific Reports", volume = "1", pages = "Art. No. 119", month = "October", year = "2011", doi = "10.1038/srep00119", issn = "2045-2322", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111116-092357408", note = "© 2011 Nature Publishing Group. Received 03 August 2011. Accepted 03 October 2011. Published 18 October 2011. We thank E. Anagnostou, B. Barker, A. Beck, W. Cho, J. Cordell, A. Gagnon, R. Gurney, S. John, A. Kennedy, H. Kippo, M. Lewis, F. McEnnulty, N.Meckler, D. Mills,M. Sherlock, D. Staples, A. Subhas and N. Thiagarajan, and the crews of the AUV ABE, the ROV Jason and RV Thomas T. Thompson and RV Southern Surveyor for their invaluable and professional assistance in the field, P. Alderslade, S. Cairns, D. Fautin, M. Mitchel and K. Moore for taxonomic assistance, P. Brodie and J. Dowdney for assisting in the photographic analyses, T. Trull for discussion regarding the radiocarbon analyses, J. Guinotte and R. Matear for\ndiscussions on regional patterns of productivity and export, and N. Bax, F. McEnnulty and the NSR sub-editor,M. Scardi, for valuable comments on the ms. This work was supported by the U.S. National Science Foundation, the Australian Department of Environment, Water, Heritage, and the Arts, the Australian Commonwealth Environmental Research\nFund Marine Biodiversity Hub, and a grant of ship time by the Australian National Research Facility.\n\nAuthor contributions:\nR.E.T. and J.A. organised, coordinated and secured support for the Jason and ABE field programs, and with K. G.-H. undertook the field observations; S.J.F. did the radiocarbon\nanalyses; F.A. and A.W. oversaw the quantitative analysis of photographic images; and R.E.T. did the wet weight analyses. All five authors contributed to writing the ms.", revision_no = "19", abstract = "We describe a previously unknown assemblage of seamount-associated megabenthos that has by far the highest peak biomass reported in the deep-sea outside of vent communities. The assemblage was found at depths of 2–2.5 km on rocky geomorphic features off the southeast coast of Australia, in an area near the Sub-Antarctic Zone characterised by high rates of surface productivity and carbon export to the deep-ocean. These conditions, and the taxa in the assemblage, are widely distributed around the Southern mid-latitudes, suggesting the high-biomass assemblage is also likely to be widespread. The role of this assemblage in regional ecosystem and carbon dynamics and its sensitivities to anthropogenic impacts are unknown. The discovery highlights the lack of information on deep-sea biota worldwide and the potential for unanticipated\nimpacts of deep-sea exploitation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/25081, title ="Carbonate clumped isotope thermometry of deep-sea corals\nand implications for vital effects", author = "Thiagarajan, Nivedita and Adkins, Jess", journal = "Geochimica et Cosmochimica Acta", volume = "75", number = "16", pages = "4416-4425", month = "August", year = "2011", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110824-141241026", note = "© 2011 Elsevier Ltd.\n\nReceived 1 March 2010; accepted in revised form 4 April 2011; available online 17 May 2011.\n\nWe would like to thank Weifu Guo and Alexander Gagnon for\nhelpful conversations. We would also like to thank Rinat Gabitov and two anonymous reviewers for their comments. We also thank The National Museum of Natural History for lending us deep-sea coral samples.", revision_no = "15", abstract = "Here we calibrate the carbonate clumped isotope thermometer in modern deep-sea corals. We examined 11 specimens of three species of deep-sea corals and one species of a surface coral spanning a total range in growth temperature of 2–25 °C. External standard errors for individual measurements ranged from 0.005‰ to 0.011‰ (average: 0.0074‰) which corresponds to ~1-2 °C. External standard errors for replicate measurements of Δ_47 in corals ranged from 0.002‰ to 0.014‰ (average: 0.0072‰) which corresponds to 0.4–2.8 °C. We find that skeletal carbonate from deep-sea corals shows the same relationship of Δ47 (the measure of ^(13)C–^(18)O ordering) to temperature as does inorganic calcite. In contrast, the δ^(13) C and δ^(18)O values of these carbonates (measured simultaneously with Δ_47 for every sample) differ markedly from equilibrium with seawater; i.e., these samples exhibit pronounced ‘vital effects’ in their bulk isotopic compositions. We explore several reasons why the clumped isotope compositions of deep-sea coral skeletons exhibit no evidence of a vital effect despite having large conventional isotopic vital effects.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39798, title ="Past ocean temperatures and coupled U/Th and ^(14)C measurements from deep-sea corals", author = "Thiagarajan, Nivedita and Adkins, Jess", journal = "Mineralogical Magazine", volume = "75", number = "3", pages = "2003-2003", month = "June", year = "2011", issn = "0026-461X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130807-085951657", note = "© 2011 by the Mineralogical Society of Great Britain and Ireland.\n\nOpen Access Article.\n\nPublished online 1 August 2011.\n\n", revision_no = "11", abstract = "Deep-sea corals are a unique archive in paleoceanography. They have large banded skeletons that allow for high\nresolution records and have a high uranium content allowing for accurate calendar ages independent of radiocarbon age\nmeasurements. One problem with using deep-sea corals for long records is that it is difficult to date a large numbers of\ncorals accurately and precisely. Unlike sediment cores, fossil fields of corals have no inherent stratigraphy and each\nindividual coral must be separately dated.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/23209, title ="Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing", author = "Lund, D. C. and Adkins, J. F.", journal = "Paleoceanography", volume = "26", pages = "Art. No. PA1213", month = "March", year = "2011", doi = "10.1029/2010PA001938 ", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110401-143100821", note = "© 2011 American Geophysical Union. \n\nReceived 19 March 2010; accepted 21 December 2010; published 19 March 2011.", revision_no = "18", abstract = "The ocean’s role in regulating atmospheric carbon dioxide on glacial‐interglacial timescales remains an\nunresolved issue in paleoclimatology. Reduced mixing between deep water masses may have aided oceanic\nstorage of atmospheric CO_2 during the Last Glacial Maximum (LGM), but data supporting this idea have\nremained elusive. The δ^(13)C of benthic foraminifera indicate the Atlantic Ocean was more chemically\nstratified during the LGM, but the nonconservative nature of δ^(13)C complicates interpretation of the LGM\nsignal. Here we use benthic foraminiferal δ^(18)O as a conservative tracer to constrain the ratio of meridional\ntransport to vertical diffusivity in the deep Atlantic. Our calculations suggest that the ratio was at least twice\nas large at the LGM. We speculate that the primary cause was reduced mixing between northern and\nsouthern component waters, associated with movement of this water mass boundary away from the zone of\nintense mixing near the seafloor. The shallower water mass boundary yields an order of magnitude increase\nin the volume of southern component water, suggesting its residence time may have increased substantially.\nOur analysis supports the idea that an expanded volume of Antarctic Bottom Water and limited vertical\nmixing enhanced the abyssal ocean’s ability to trap carbon during glacial times.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/22853, title ="An Isotope Dilution ICP-MS Method for the Determination of Mg/Ca and Sr/Ca Ratios in Calcium Carbonate", author = "Fernandez, Diego P. and Gagnon, Alex C.", journal = "Geostandards and Geoanalytical Research", volume = "35", number = "1", pages = "23-37", month = "March", year = "2011", issn = "1639-4488", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110314-105334327", note = "© 2010 The Authors. Geostandards and Geoanalytical Research © 2010 International Association of Geoanalysts.\n\nReceived 05 Jan 09; Accepted 07 Aug 09.\nArticle first published online: 15 Sep. 2010.\n\nThis work was supported by the National Science\nFoundation, Grants OCE-0096373 and OCE-0502642,\nand the Comer Science and Education Foundation, Grant\nCM113. We acknowledge two anonymous reviewers for\ncomments and suggestions than improved this manuscript.", revision_no = "11", abstract = "Mg/Ca and Sr/Ca ratios in calcium carbonate are important components of many palaeoclimate studies. We present an isotope dilution method relying on a single mixed spike containing ^(25)Mg, ^(43)Ca and ^(87)Sr. Dozens of samples per day, as small as 10 μg of carbonate, could be dissolved, spiked and run in an ICP-MS with a precision of 0.8% (2 RSD). Two instruments types, a sector field and a quadrupole ICP-MS, were compared. The best long term precision found was 0.4% (2 RSD), although this increased by up to a factor of two when samples of very different Mg or Sr content were run together in the same sequence. Long term averages for the two instruments concurred. No matrix effects were detected for a range of Ca concentrations between 0.2 and 2 mmol l^(-1). Accuracy, tested by measuring synthetic standard solutions, was 0.8% with some systematic trends. We demonstrate the strength of this isotope dilution method for (a) obtaining accurate results for sample sets that present a broad Mg and Sr range and (b) testing solid carbonates as candidate reference materials for interlaboratory consistency. Mg/Ca and Sr/Ca results for reference materials were in good agreement with values from the literature.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20582, title ="Deep-sea coral aragonite as a recorder for the neodymium isotopic composition of seawater", author = "van de Flierdt, Tina and Robinson, Laura F.", journal = "Geochimica et Cosmochimica Acta", volume = "74", number = "21", pages = "6014-6032", month = "November", year = "2010", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101028-094932327", note = "© 2010 Elsevier Ltd.\n\nReceived 15 March 2010; accepted 27 July 2010. \nAssociate editor: Miryam Bar-Matthews. Available online 6 August 2010.\n\nThis study was supported by NSF Grant OCE-0623107 to\nT.v.d.F. and L.F.R., NSF Grant ANT-063678 to L.F.R., a Marie\nCurie International Reintegration grant (IRG 230828) and NERC Grant NE/F016751/1 to T.v.d.F., and NSF Grant OCE-0929272 to J.F.A. We thank the Lamont geochemistry group for their help in keeping the labs and the mass specs running smoothly, particularly Jenna Cole for initial help in getting familiar with the TIMS, and Sidney Hemming for invaluable discussions while developing the coral measurements on the TIMS. Alex Gagnon is thanked for help with coral sampling. We are very grateful to Stephen\nCairns from the Smithsonian Museum in Washington (DC) for\nlending us the majority of the coral specimen used for this study and for fruitful discussion. Constructive reviews by M. Gutjahr and two anonymous referees, as well as the editorial handling of M. Bar-Matthews are gratefully acknowledged.", revision_no = "14", abstract = "Deep-sea corals have been shown to be useful archives of rapid changes in ocean chemistry during the last glacial cycle. Their aragonitic skeleton can be absolutely dated by U–Th data, freeing radiocarbon to be used as a water-mass proxy. For certain species of deep-sea corals, the growth rate allows time resolution that is comparable to ice cores. An additional proxy is needed to exploit this opportunity and turn radiocarbon data into rates of ocean overturning in the past.\n\nNeodymium isotopes in seawater can serve as a quasi-conservative water-mass tracer and initial results indicate that deep-sea corals may be reliable archives of seawater Nd isotopes. Here we present a systematic study exploring Nd isotopes as a water-mass proxy in deep-sea coral aragonite. We investigated five different genera of modern deep-sea corals (Caryophyllia, Desmophyllum, Enallopsamia, Flabellum, Lophelia), from global locations covering a large potential range of Nd isotopic compositions. Comparison with ambient seawater measurements yields excellent agreement and suggests that deep-sea corals are reliable archives for seawater Nd isotopes.\n\nA parallel study of Nd concentrations in these corals yields distribution coefficients for Nd between seawater and coral aragonite of 1–10, omitting one particular genus (Enallopsamia). The corals and seawater did however not come from exactly the same location, and further investigations are needed to reach robust conclusions on the incorporation of Nd into deep-sea coral aragonite.\n\nLastly, we studied the viability of extracting the Nd isotope signal from fossil deep-sea corals by carrying out stepwise cleaning experiments. Our results show that physical removal of the ferromanganese coating and chemical pre-cleaning have the highest impact on Nd concentrations, but that oxidative/reductive cleaning is also needed to acquire a seawater Nd isotope signal.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/19064, title ="Atmospheric input of manganese and iron to the ocean: Seawater dissolution experiments with Saharan and North American dusts", author = "Mendez, Jeffrey and Guieu, Cecile", journal = "Marine Chemistry", volume = "120", number = "1-4", pages = "34-43", month = "June", year = "2010", issn = "0304-4203", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100715-090913021", note = "© 2008 Elsevier.\nReceived 10 July 2008; accepted 28 August 2008. Available online 9 September 2008. \n\n\nWe would like to acknowledge Marith Reheis (USGS) for kindly\nproviding the U.S. dust, Stéphane Moustier (CEREGE-France) for the\ngrain-size distribution measurements, Kristen Buck (UC Santa Cruz)\nfor the seawater ligand measurements, Diego Fernandez for his\nexpertise with the ICP-mass spectrometer, and James Morgan for\ninsightful discussions. This work was partly supported by the National\nScience Foundation (grant OCE-0502642), by the Comer Science and\nEducation Foundation, and by the European FAIRY Program (Marie\nCurie Int. Fellowships — Contract MOIF-CT-2004-002918).", revision_no = "15", abstract = "Dissolution of wind blown dust is a major source of iron, manganese and other trace nutrients in the ocean.\nKinetic and thermodynamic values for the release of metals from dust are needed for computer models\nwhich incorporate dust as part of their ocean system. Here we investigate both the thermodynamic and\nkinetics parameters involved in the dissolution of metals from dust in seawater. We added dust from the\nSahara and the Western United States in five different concentrations (0.01–5.0 mg/L) representative of those\nconcentrations found in seawater after dust events, to open-ocean Pacific seawater. Sub-sampling of the\nreaction vessels took place on days 1, 2, 4, 7, 14, and 35 for the kinetic study.\nResults show different apparent thermodynamic constants for manganese (Mn) and iron (Fe). The final\nMn concentrations are proportional to the added dust concentration. Fe concentrations reach a maximum\nof less than 2 nM, independent of the quantity and type of dust added. The Fe dissolution kinetics are\nfaster than our sampling resolution. The first order rate constant for the dissolution of Mn from the\nWestern US and Sahara dusts were 0.94 ± 0.04 (nmol Mn/day mg Dust), and 0.22 ± 0.01 (nmol Mn/daymg Dust) respectively. We\nconclude that, Mn concentrations are limited by available Mn on the dust surface, while Fe concentrations\nare limited by the ligand concentrations in the seawater, which ultimately are determined by the\nbiological community.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/18863, title ="Growth rates, stable oxygen isotopes (δ^(18)O), and strontium (Sr/Ca) composition in two species of Pacific sclerosponges (Acanthocheatetes wellsi and Astrosclera willeyana) with δ^(18)O calibration and application to paleoceanography", author = "Grottoli, Andréa G. and Adkins, Jess F.", journal = "Journal of Geophysical Research C", volume = "115", pages = "C06008", month = "June", year = "2010", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100629-165404339", note = "© 2010 American Geophysical Union.\n\nReceived 21 June 2009; accepted 4 January 2010; published 12 June 2010. \n\nWe thank the following people and organizations\nfor their assistance: J. Bauer, M. Cathey, P. Colin, R. Fairbanks,\nO. Gibb, D. Idip, T. Isamu, J. Kloulechad, J. Moots, J. Palardy, D. Purcell,\nR. Richmond, S. Takahashi, Palau International Coral Reef Center, Coral\nReef Research Foundation, Palau Division of Marine Resources, Palau\nMinistry of Resources and Development, Commonwealth of the Northern\nMariana Islands (CNMI) Division of Fish and Wildlife, CNMI Department of Environmental Quality, CNMI Coastal Resources Management, and\nthe University of Guam. FTIR measurements were made by W.R.P.\nand D.M.R. at the U2A beamline of the National Sychrotron Light Source\nat Brookhaven National Lab (DOE BES DE‐AC02‐98CH10886) with the\nsupport of COMPRES (NSF EAR 06‐4958). Major funding for this work\nwas provided to A.G.G. by the American Society for Mass Spectrometry,\nthe Mellon Foundation, and the National Science Foundation (Chemical Oceanography, OCE0426022 and OCE0610487).", revision_no = "15", abstract = "The isotopic and elemental composition of sclerosponge skeletons is used to reconstruct paleoceanographic records. Yet few studies have systematically examined the natural variability in sclerosponge skeletal δ^(18)O, growth, and Sr/Ca, and how that may influence the interpretation of sclerosponge proxy records. Here, we analyzed short records in seven specimens of Acanthocheatetes wellsi (high-Mg calcite, 21 mol% Mg) from Palau, four A. wellsi (high-Mg calcite, 21 mol% Mg) from Saipan, and three Astrosclera willeyana (aragonite) sclerosponges from Saipan, as well as one long record in an A. wellsi specimen from Palau spanning 1945–2001.5. In Saipan, species-specific and mineralogical effects appear to have a negligible effect on sclerosponge δ^(18)O, facilitating the direct comparison of δ^(18)O records between species at a given location. At both sites, A. wellsi δ^(18)O and growth rates were sensitive to environmental conditions, but Sr/Ca was not sensitive to the same conditions. High-resolution δ^(18)O analyses confirmed this finding as both A. wellsi and A. willeyana deposited their skeleton in accordance with the trends in isotopic equilibrium with seawater, though with a 0.27‰ offset in the case of A. willeyana. In the high-Mg-calcite species A. wellsi, Mg may be interfering with Sr incorporation into the skeleton. On multidecadal timescales, A. wellsi sclerosponge δ^(18)O in Palau tracked the Southern Oscillation Index variability post-1977, but not pre-1977, coincident with the switch in the Pacific Decadal Oscillation (PDO) at ~1976. This suggests that water mass circulation in the region is influenced by El Niño— Southern Oscillation variability during positive PDO phases, but not during negative ones.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/18638, title ="Analysis of dissolved iron isotopes in seawater \n", author = "John, Seth G. and Adkins, Jess F.", journal = "Marine Chemistry", volume = "119", number = "1-4", pages = "65-76", month = "April", year = "2010", issn = "0304-4203", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100610-101345765", note = "© 2010 Elsevier B.V.\nReceived 22 July 2009; revised 22 December 2009; accepted 5 January 2010. Available online 18 January 2010. \n", revision_no = "9", abstract = "Iron is an important nutrient in the ocean. Measuring the stable isotopes of dissolved Fe in seawater may help to answer important biogeochemical questions such as what are the sources and sinks for Fe to the oceans, and how is Fe biologically cycled. Because Fe concentrations in seawater are very low, typically less than 1 nM, there are significant challenges both to separate and purify Fe from seawater without introducing contamination, and to accurately analyze δ^(56)Fe on the small quantities of Fe extracted. New techniques are presented here for separation and purification of Fe from seawater by bulk extraction onto a resin with NTA functional groups, followed by anion exchange chromatography. This method recovers 89% of the Fe from 1 L samples of seawater without causing any fractionation of Fe isotopes, with a total blank of 1.1 ± 0.6 ng Fe. To optimize the analytical procedure for small amounts of Fe, the different sources of error in measurement of δ^(56)Fe have been analyzed. For 252 individual analyses of standards and samples, the internal error is well described by the combination of errors from electronic noise on the detectors (Johnson noise), counting statistics, and a third source of error hypothesized to be short-timescale flicker in instrumental mass bias. With the small amounts of iron found in natural seawater samples, error is dominated by Johnson noise and counting statistics. Our analyses also include 160 pairs of “intermediate” replicates in which the same post-purification sample was measured during different analytical sessions, and 141 pairs of “external” replicate analyses for samples prepared from the same original seawater carboy but which were extracted and purified separately. The portion of overall mass spectrometry error that derives from intermediate error has been evaluated by comparing the variance in δ^(56)Fe for a single sample measured during multiple analytical sessions with the internal variance in δ^(56)Fe for the multiple cycles of data that make up each single analysis. The portion of total external error that derives from internal error was determined from variance in δ^(56)Fe for external replicates, compared with internal error based on the variance in cycles for each single analysis. We find that the error for multiple analyses of a sample during different analytical sessions is 1.06 times the internal error, and the external error for analysis of Fe samples which have been separately purified and extracted from the same original seawater is 1.26 times the internal analytical error. Based on this error analysis, we suggest that dissolved Fe isotopes in seawater are best measured by separately extracting the Fe from a single liter of seawater and measuring the entire quantity of extracted Fe in a single short analysis. Using this method, the predicted accuracy for measurements of seawater dissolved δ^(56)Fe ranges from 0.2‰ to 0.05‰ (2σ) for seawater Fe concentrations of 0.1 nM and 1.0 nM, respectively.\n\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/18282, title ="Strong influence of water vapor source dynamics on stable isotopes in precipitation observed in Southern Meghalaya, NE India", author = "Breitenbacha, Sebastian F.M. and Adkins, Jess F.", journal = "Earth and Planetary Science Letters", volume = "292", number = "1-2", pages = "212-220", month = "March", year = "2010", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100513-091934538", note = "© 2010 Elsevier.\nReceived 4 July 2009; revised 22 January 2010; accepted 25 January 2010. Available online 13 February 2010. \n\nWe gratefully acknowledge the co-funding of the PhD work of\nSebastian Breitenbach by the DeutscheForschungsgemeinschaft (DFG)\nand the Davidow Fund at Caltech. Norbert Marwan was supported by\nthe DFG Graduate School GK 1364 “Shaping Earth's Surface in a\nVariable Environment”. JFA and lab work at Caltech were supported by\nNSF grant OCE-0318445. We thank Denis P. Rayen (Laitkynsew, India),\nBrian Kharpran Daly (Shillong, India), Pawel Prokop (Krakow, Poland),\nThomas Arbenz (Matzendorf, Switzerland) and Rolf Siegenthaler\n(Gümligen, Switzerland) for sampling and logistical support.", revision_no = "11", abstract = "To calibrate δ^(18)O time-series from speleothems in the eastern Indian summer monsoon (ISM) region of India, and to understand the moisture regime over the northern Bay of Bengal (BoB) we analyze the δ^(18)O and δD of rainwater, collected in 2007 and 2008 near Cherrapunji, India. δD values range from + 18.5‰ to − 144.4‰, while δ^(18)O varies between + 0.8‰ and − 18.8‰. The Local Meteoric Water Line (LMWL) is found to be indistinguishable from the Global Meteoric Water Line (GMWL). Late ISM (September–October) rainfall exhibits lowest δ^(18)O and δD values, with little relationship to the local precipitation amount. There is a trend to lighter isotope values over the course of the ISM, but it does not correlate with the patterns of temperature and rainfall amount. δ^(18)O and δD time-series have to be interpreted with caution in terms of the ‘amount effect’ in this subtropical region. We find that the temporal trend in δ18O reflects increasing transport distance during the ISM, isotopic changes in the northern BoB surface waters during late ISM, and vapor re-equilibration with rain droplets. Using an isotope box model for surface ocean waters, we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern BoB. Temporal variations in this source can contribute up to 25% of the observed changes in stable isotopes of precipitation in NE India. To delineate other moisture sources, we use backward trajectory computations and find a strong correlation between source region and isotopic composition. Palaeoclimatic stable isotope time-series from northeast Indian speleothems likely reflect changes in moisture source and transport pathway, as well as the isotopic composition of the BoB surface water, all of which in turn reflect ISM strength. Stalagmite records from the region can therefore be interpreted as integrated measures of the ISM strength.\n\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/18673, title ="Compound-Specific δ^(34)S Analysis of Volatile Organics by Coupled GC/Multicollector-ICPMS", author = "Amrani, Alon and Sessions, Alex L.", journal = "Analytical Chemistry", volume = "81", number = "21", pages = "9027-9034", month = "November", year = "2009", doi = "10.1021/ac9016538 ", issn = "0003-2700", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100614-153741613", note = "© 2009 American Chemical Society. \n\nReceived for review July 24, 2009. Accepted September 21, 2009. Publication Date (Web): October 6, 2009. \n\nWe thank Nathan Daleska, Alex Gagnon, Seth John, Magdalena Osburn, and Sean Sylva for assistance with instrumentation and experiments; Tim Lyons, Bill Gillooly, Zeev Aizenshtat, and Ward\nSaid Ahamed for S-isotope analyses of organic standards; Yongchun\nTang for crude oil samples; Charles Douthitt, Johannes Schweiters,\nClaudia Bouman, and Shona McSheehy for advice and support in\nconstructing the instrumentation interface and for useful discussions. \n\nThis work was supported by The Davidow Endowment for Environmental Science and Engineering at Caltech, the Texaco (Prize) postdoctoral fellowship of Caltech to A.A., and NSF Grant OCE-0852362 to J.F.A.", revision_no = "14", abstract = "We have developed a highly sensitive and robust method for the analysis of δ^(34)S in individual organic compounds by coupled gas chromatography (GC) and multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The system requires minimal alteration of commercial hardware and is amenable to virtually all sample introduction methods. Isobaric interference from O_2^+ is minimized by employing dry plasma conditions and is cleanly resolved at all masses using medium resolution on the Thermo Neptune MC-ICPMS. Correction for mass bias is accomplished using standard−sample bracketing with peaks of SF6 reference gas. The precision of measured δ^(34)S values approaches 0.1‰ for analytes containing >40 pmol S and is better than 0.5‰ for those containing as little as 6 pmol S. This is within a factor of 2 of theoretical shot-noise limits. External accuracy is better than 0.3‰. Integrating only the center of chromatographic peaks, rather than the entire peak, offers significant gain in precision and chromatographic resolution with minimal effect on accuracy but requires further study for verification as a routine method. Coelution of organic compounds that do not contain S can cause degraded analytical precision. Analyses of crude oil samples show wide variability in δ^(34)S and demonstrate the robustness and precision of the method in complex environmental samples.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39638, title ="Clumped isotope calibration of modern deep sea corals and implications for vital effects", author = "Thiagarajan, Nivedita and Guo, Weifu", journal = "Geochimica et Cosmochimica Acta", volume = "73", number = "13", pages = "A1324-A1324", month = "June", year = "2009", doi = "10.1016/j.gca.2009.05.016", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130730-082151262", note = "© 2009 Published by Elsevier Ltd.", revision_no = "11", abstract = "Deep-sea corals are a unique archive in paleoceanography.\nThey have large banded skeletons that allow for high\nresolution records and have a high uranium content allowing\nfor accurate calendar ages independent of radiocarbon age\nmeasurements. However, their use as a paleoceanographic\narchive is complicated by the fact that the bulk isotope and\ntrace-metal compositions of their skeletons are generally out\nof isotopic equilibrium with co-existing seawater. We explore\nthe mechanisms of this 'vital' effect through 'clumped\nisotope' analyses of CO_2 evolved by acid digestion of natural\ndeep-sea corals.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39632, title ="Constraints from clumped isotope analyses of a stalagmite on maximum tropical temperature change through the late Pleistocene", author = "Meckler, A. N. and Adkins, J. F.", journal = "Geochimica et Cosmochimica Acta", volume = "73", number = "13", pages = "A863", month = "June", year = "2009", doi = "10.1016/j.gca.2009.05.011", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130729-134243287", note = "© 2009 Published by Elsevier Ltd.", revision_no = "12", abstract = "We analyzed modern and ancient speleothems from caves\nin Northern Borneo (4°N, 115°W) for their carbonate\nisotopologue, or 'clumped isotope', compositions. Although\nthis method of paleothermometry appears to exhibit a common\ncalibration in a variety of carbonates, speleothems have so far\nproven to be difficult archives for this technique. Most\nsamples measured to date are out of equilibrium, yielding\napparent temperatures that are too high [1,2].", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39608, title ="New capabilities for small-scale and high-precision SIMS analyses", author = "Eiler, John M. and Adkins, Jess F.", journal = "Geochimica et Cosmochimica Acta", volume = "73", number = "13", pages = "A321", month = "June", year = "2009", doi = "10.1016/j.gca.2009.05.004", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130726-092553235", note = "© 2009 Published by Elsevier Ltd.", revision_no = "16", abstract = "Secondary ion mass spectrometry (SIMS) has wide application for in situ geochronology, trace element and isotope analysis. Despite the strengths of SIMS techniques, their usefulness has been limited for many problems by the relatively coarse scale of analysis (~10-30 µm), and poor precision for element abundance ratios (~1-10 %, relative). \n\nThree recent innovations in SIMS instrumentation have improved capabilities in both regards, creating opportunities for new kinds of applications: (1) The NanoSIMS provides a reduced primary beam size (typically 100-300 nm; as small as 10's of nm). A conventional SIMS instrument equipped with a Gallium source can achieve similar resolutions, though at the cost of significantly reduced sensitivity. (2) The NanoSIMS is also the first ion microprobe capable of simultaneous detection of elements differing greatly in mass (up to a factor of 22; e.g., ^(12)C and ^(238)U). This allows for multi-collection of most element ratios, much as isotope ratio multi-collection is done on lower-dispersion mass spectrometers. (3) The ims-7f Geo provides a 'pseudo multi-collection' capability. This is intended as a poor-man's instrument for high-precision isotope ratio analysis, but also permits element ratio measurements at greater than normal speed and precision.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/11531, title ="Assessing the ability of the 14C projection-age method to constrain the circulation of the past in a 3-D ocean model", author = "Franke, J. and Schulz, M.", journal = "Geochemistry, Geophysics, Geosystems", volume = "9", number = "8", pages = "Q08003", month = "August", year = "2008", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:FRAggg08", note = "Copyright 2008 by the American Geophysical Union. \n\nReceived 11 January 2008; accepted 19 June 2008; published 6 August 2008. \n\nWe greatly appreciate the constructive discussions with Mea Cock and the constructive comments of two anonymous reviewers that greatly helped to improve this manuscript. This work was supported by the Deutsche Forschungsgemeinschaft\n(DFG).", revision_no = "11", abstract = "Radiocarbon differences between benthic and planktonic foraminifera (B-P ages) and radiocarbon projection ages are both used to determine changes of the past ocean circulation rate. A global 3-D ocean circulation model with a constant modern ocean circulation is used to study which method is less influenced by atmospheric Δ14C variations. Three factors cause uncertainties: first, the long equilibration time of the ocean after atmospheric Δ14C changes; second, different mixing processes in the ocean, which cause an ocean response of smaller amplitude than the atmospheric forcing; and third, the unknown source region and corresponding initial surface 14C reservoir age of subsurface waters. The model suggests that B-P ages and projection ages have lower uncertainties the closer they are to deepwater formation zones. In the North Atlantic the B-P age method is less influenced by atmospheric Δ14C variations than the projection-age method. Projections ages vary less in the Pacific as long as atmospheric Δ14C decreases linearly. A more irregular atmospheric Δ14C evolution leads to age variations of similar magnitude with both methods. On the basis of the model experiment, we suggest a potential improvement of the projection-age method.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39577, title ="Analysis of Mg, Sr, and Ba in deep sea corals using SIMS and ICP-MS", author = "Gabitov, R. I. and Gagnon, A. C.", journal = "Geochimica et Cosmochimica Acta", volume = "72", number = "12", pages = "A287-A287", month = "July", year = "2008", doi = "10.1016/j.gca.2008.05.010", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130725-091547745", note = "© 2008 Published by Elsevier Ltd.\n\n", revision_no = "10", abstract = "Chemical compositons of corals are widely used to\nreconstruct the temperature and composition of the ocean.\nHowever, many corals are heterogeneous in minor and trace\nelements even when they grew at constant temperature and\nseawater composition. The goals of our work are to\ncharacterize and explain Mg, Sr, and Ba distributions across\nknown skeletal features of corals, and to establish how these\ndistributions vary with temperature.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47175, title ="Development of coupled GC/ICPMS for analysis of δ^(34)S in individual organic compounds", author = "Amrani, Alon and Sessions, Alex L.", journal = "Geochimica et Cosmochimica Acta", volume = "72", number = "12", pages = "A20", month = "July", year = "2008", doi = "10.1016/j.gca.2008.05.004", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140714-124754729", note = "© 2008 Elsevier Ltd. \n\nAwards Ceremony Speeches and Abstracts of the 18th Annual V.M. Goldschmidt Conference Vancouver, Canada July, 2008.", revision_no = "12", abstract = "Sulfur (S) is a key component of many biogeochemical\nprocesses and records. Specific redox transitions of sulfur are linked to large stable-isotopic fractionations, and the record of those fractionations is potentially preserved in great detail by organosulfur compounds.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33618, title ="Low reservoir ages for the surface ocean from mid-Holocene Florida corals", author = "Fruffel, Ellen R. M. and Robinson, Laura F.", journal = "Paleoceanography", volume = "23", pages = "Art. No. PA2209", month = "May", year = "2008", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-140427479", note = "© 2008 American Geophysical Union. Received 26 July 2007; accepted 1 February 2008; published 13 May 2008. We thank Tom Guilderson and associates at CAMS for help with the AMS measurements and Rindy Ostermann at WHOI for the stable isotope measurements. We are grateful to Wally Broecker and an anonymous reviewer for their comments on the manuscript. NSF Chemical Oceanography program provided monetary support under grants OCE-9711326, OCE-0137207, and OCE-0551940 (to ERMD). ", revision_no = "11", abstract = "The ^(14)C reservoir age of the surface ocean was determined for two Holocene periods (4908–4955 and 3008–3066 calendar (cal) B.P.) using U/Th-dated corals from Biscayne National Park, Florida, United States. We found that the average reservoir ages for these two time periods (294 ± 33 and 291 ± 27 years, respectively) were lower than the average value between A.D. 1600 and 1900 (390 ± 60 years) from corals. It appears that the surface ocean was closer to isotopic equilibrium with CO_2 in the atmosphere during these two time periods than it was during recent times. Seasonal δ^(18)O measurements from the younger coral are similar to modern values, suggesting that mixing with open ocean waters was indeed occurring during this coral's lifetime. Likely explanations for the lower reservoir age include increased stratification of the surface ocean or increased Δ^(14)C values of subsurface waters that mix into the surface. Our results imply that a more correct reservoir age correction for radiocarbon measurements of marine samples in this location from the time periods ∼3040 and ∼4930 cal years B.P. is ∼292 ± 30 years, less than the canonical value of 404 ± 20 years.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33603, title ="Regional-scale climate influences on temporal variations of rainwater and cave dripwater oxygen isotopes in northern Borneo", author = "Cobb, Kim M. and Adkins, Jess F.", journal = "Earth and Planetary Science Letters", volume = "263", number = "3-4", pages = "207-220", month = "November", year = "2007", doi = "10.1016/j.epsl.2007.08.024", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-100751466", note = "© 2007 Elsevier B.V. Received 23 February 2007; received in revised form 22 August 2007; accepted 22 August 2007. Available online 31 August 2007. Editor: M.L. Delaney. The authors are indebted to Jenny Malang and the\nstaff of Gunung Mulu National Park for fieldtrip and\nsampling assistance, Johnny Baei Hassan for expert\ncaving guidance, and Prof. Andrew Tuen (UNIMAS)\nfor permitting assistance. Joel Despain, George Prest,\nShane Fryer, Jed Mosenfelder, and Brad Hacker\nprovided assistance during the 2003 fieldtrip. Permits\nfor this work were granted by the Malaysian Economic\nPlanning Unit, the Sarawak Forestry Department, and\nthe Sarawak State Planning Unit. Mulu airport rainfall was provided by the Sarawak Department of Irrigation\nand Drainage. The research was funded by NSF grant\nATM-0318445, and by a Comer Abrupt Climate Change\nFellowship.\n", revision_no = "14", abstract = "This study investigates the relationship between large-scale climate variability, rainfall oxygen isotopic composition (δ^(18)O), and cave dripwater δ^(18)O at Gunung Mulu and Gunung Buda National Parks in northern Borneo (4°N, 115°E) on intraseasonal to interannual timescales. A 3-yr timeseries of rainfall δ^(18)O contains prominent seasonal and interannual variability. The seasonal cycle in rainfall δ^(18)O is defined by lighter values of − 10‰ during late boreal summer and heavier values of − 4‰ during late boreal winter, and is poorly correlated to local precipitation, which displays very weak seasonality. Seasonally-varying moisture trajectories likely play a key role in the observed seasonal cycle of rainfall δ^(18)O, driving enhanced fractionation during boreal summer and less fractionation during boreal winter. Dripwater δ^(18)O timeseries display 2‰ seasonal cycles that follow the rainfall δ^(18)O seasonal cycles, with a mean δ^(18)O value equivalent to the mean δ^(18)O of rainfall. Large surveys of cave dripwaters conducted during three fieldtrips to Gunung Mulu/Buda reveal a system-wide response to rainfall δ^(18)O seasonality that supports a relatively short (less than 6months) response time for most drips. During the weak 2005/2006 La Niña event, sustained positive precipitation anomalies are associated with rainfall δ^(18)O values that are 4 to 5‰ lighter than previous years' values, consistent with the tropical “amount effect” observed in both models and data. Dripwater δ^(18)O values are 1 to 2‰ lighter during the weak La Niña event. The importance of the “amount effect” in driving intraseasonal rainfall δ^(18)O anomalies at our site is supported by an 8‰ increase in rainfall δ^(18)O that occurred over the course of two weeks in response to a pronounced decrease in regional convective activity. Dripwater discharge rates underwent a ten-fold decrease during the extended dry period, but dripwater δ^(18)O values remained constant. This study supports the interpretation of stalagmite δ^(18)O records from Gunung Mulu/Buda as paleo-precipitation records that are sensitive to the location and strength of deep convection in the West Pacific Warm Pool.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/19561, title ="Ancient DNA techniques: Applications for deep-water corals", author = "Waller, Rhian G. and Adkins, Jess F.", journal = "Bulletin of Marine Science", volume = "81", number = "3", pages = "351-359", month = "November", year = "2007", issn = "0007-4977", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100820-132119162", note = "© 2007 Rosenstiel School of Marine and Atmospheric Science.\n\nThe authors would like to thank the captains, crew, and scientists of two cruises to the NW\nAtlantic that brought back samples for this study—AT7-34 (Lost City, Chief Scientist D. Kelly,\nUniversity of Washington) and AT7-35 (New England Seamounts, Chief Scientist J. Adkins,\nCaltech). We would also like to thank D. Scheirer (USGS), M. Taviani (CNR), and K. Scanlon\nfor discussions during the initial development of this project. Support for this project was\nprovided by National Science Foundation grants OCE 0096373 (JFA), OCE 0095331 (Daniel\nScheirer, USGS), OCE 0136871 [D. Yoerger (WH OI) and (TMS)], OCE 0624627 (TMS and\nRGW) and NOAA’s Office of Exploration grant NA05OAR4601054 (TMS, RGW, and JFA).\nWe are also grateful for the enabling support of the Ocean Life Institute and the Ocean and\nClimate Change Institute of the Woods Hole Oceanographic Institution, without whose assistance\nthe ongoing pursuit of this project would not be possible.", revision_no = "10", abstract = "The potential applications of ancient DNA (aDNA) techniques have been realized relatively recently, and have been revolutionized by the advent of PCR techniques in the mid 1980s. Although these techniques have been proven valuable in ancient specimens of up to 100,000 yrs old, their use in the marine realm has been largely limited to mammals and fish. Using modifications of techniques developed for skeletons of whales and mammals, we have produced a method for extracting and amplifying aDNA from sub-fossil (not embedded in rock) deep-water corals that has been successful in yielding 351 base pairs of the ITS2 region in sub-fossil Desmophyllum dianthus (Esper, 1794) and Lophelia pertusa (Linnaeus, 1758). The comparison of DNA sequences from fossil and live specimens resulted in clustering by species, demonstrating the validity of this new aDNA method. Sub-fossil scleractinian corals are readily dated using U-series techniques, and so the abundance of directly-dateable skeletons in the world's oceans, provides an extremely useful archive for investigating the interactions of environmental pressures (in particular ocean circulation, climate change) on the past distribution, and the evolution of deep-water corals across the globe.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33644, title ="Deep-sea scleractinian coral age and depth distributions in the northwest Atlantic for the last 225,000 years", author = "Robinson, Laura F. and Adkins, Jess F.", journal = "Bulletin of Marine Science", volume = "81", number = "3", pages = "371-391", month = "November", year = "2007", issn = "0007-4977", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120829-095459243", note = "© 2007 Rosenstiel School of Marine and Atmospheric Science. We gratefully acknowledge the support of The Comer Foundation for Abrupt Climate Change, The Henry Luce Foundation, The American Chemical Society Petroleum Research Fund, NSF Grant Numbers OCE-0096373 and OCE-0095331, and NOAA OE Grant Number\nA05OAR4601054. We would also like to thank the crew, the science parties, and the DSV Alvin and ROV Hercules pilots on RV Atlantis cruise AT7-35 and AT8-1, and the DASS05 expedition to the New England Seamounts.", revision_no = "17", abstract = "Deep-sea corals have grown for over 200,000 yrs on the New England Seamounts in the northwest Atlantic, and this paper describes their distribution both with respect to depth and time. Many thousands of fossil scleractinian corals were collected on a series of cruises from 2003-2005; by contrast, live ones were scarce. On these seamounts, the depth distribution of fossil Desmophyllum dianthus (Esper, 1794) is markedly different to that of the colonial scleractinian corals, extending 750 m deeper in the water column to a distinct cut-off at 2500 m. This cut-off is likely to be controlled by the maximum depth of a notch-shaped feature in the seamount morphology. The ages of D. dianthus corals as determined by U-series measurements range from modern to older than 200,000 yrs. The age distribution is not constant over time, and most corals have ages from the last glacial period. Within the glacial period, increases in coral population density at Muir and Manning Sea-mounts coincided with times at which large-scale ocean circulation changes have been documented in the deep North Atlantic. Ocean circulation changes have an effect on coral distributions, but the cause of the link is not known. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33601, title ="Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum", author = "Partin, Judson W. and Cobb, Kim M.", journal = "Nature", volume = "449", number = "7161", pages = "452-455", month = "September", year = "2007", doi = "10.1038/nature06164", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-100112890", note = "© 2007 Nature Publishing Group, a division of Macmillan Publishers Limited. \n\nReceived 22 February 2007; Accepted 8 August 2007.\n\nWe thank J. Malang, J. Gau and S. Clark of Gunung Mulu\nNational Park and J. Baei Hassan of Logan Bunut National Park for field assistance. J. Despain, G. Prest, S. Fryer, J. Mosenfelder and B. Hacker provided field assistance\nduring the 2003 field trip. A. A. Tuen (UNIMAS) greatly facilitated our 2006 fieldwork in Sarawak. We also thank D. Lund for assistance in U–Th dating, and J. Lynch-Stieglitz and M. Schmidt for providing comments on early versions of the manuscript. The research was funded by NSF-ESH and by a Comer Abrupt Climate Change Fellowship.", revision_no = "24", abstract = "Models and palaeoclimate data suggest that the tropical Pacific climate system plays a key part in the mechanisms underlying orbital-scale and abrupt climate change. Atmospheric convection over the western tropical Pacific is a major source of heat and moisture to extratropical regions, and may therefore influence the global climate response to a variety of forcing factors. The response of tropical Pacific convection to changes in global climate boundary conditions, abrupt climate changes and radiative forcing remains uncertain, however. Here we present three absolutely dated oxygen isotope records from stalagmites in northern Borneo that reflect changes in west Pacific warm pool hydrology over the past 27,000\u2009years. Our results suggest that convection over the western tropical Pacific weakened 18,000–20,000\u2009years ago, as tropical Pacific and Antarctic temperatures began to rise during the early stages of deglaciation. Convective activity, as inferred from oxygen isotopes, reached a minimum during Heinrich event 1 (ref. 10), when the Atlantic meridional overturning circulation was weak, pointing to feedbacks between the strength of the overturning circulation and tropical Pacific hydrology. There is no evidence of the Younger Dryas event in the stalagmite records, however, suggesting that different mechanisms operated during these two abrupt deglacial climate events. During the Holocene epoch, convective activity appears to track changes in spring and autumn insolation, highlighting the sensitivity of tropical Pacific convection to external radiative forcing. Together, these findings demonstrate that the tropical Pacific hydrological cycle is sensitive to high-latitude climate processes in both hemispheres, as well as to external radiative forcing, and that it may have a central role in abrupt climate change events.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33595, title ="Sr/Ca and Mg/Ca vital effects correlated with skeletal architecture in a scleractinian deep-sea coral and the role of\nRayleigh fractionation", author = "Gagnon, Alexander C. and Adkins, Jess F.", journal = "Earth and Planetary Science Letters", volume = "261", number = "1-2", pages = "280-295", month = "September", year = "2007", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-091252247", note = "© 2007 Elsevier B.V. Received 29 November 2006; received in revised form 15 May 2007; accepted 3 July 2007. Available online 17 July 2007. Editor: H. Elderfield. Special thanks to Dr. Stephen Cairns and The Smithsonian Institution National Museum of Natural History for allowing the analysis of the deep-sea coral specimens in this study. A.C.G. would like to thank D. Rees of the California Institute of Technology for continued scientific advice and guidance. Comments by Glen Gaetani and Anne Cohen as well as two anonymous reviewers contributed to improving this manuscript.", revision_no = "15", abstract = "Deep-sea corals are a new tool in paleoceanography with the potential to provide century long records of deep ocean change at sub-decadal resolution. Complicating the reconstruction of past deep-sea temperatures, Mg/Ca and Sr/Ca paleothermometers in corals are also influenced by non-environmental factors, termed vital effects. To determine the magnitude, pattern and mechanism of vital effects we measure detailed collocated Sr/Ca and Mg/Ca ratios, using a combination of micromilling and isotope-dilution ICP-MS across skeletal features in recent samples of Desmophyllum dianthus, a scleractinian coral that grows in the near constant environment of the deep-sea. Sr/Ca variability across skeletal features is less than 5% (2σ relative standard deviation) and variability of Sr/Ca within the optically dense central band, composed of small and irregular aragonite crystals, is significantly less than the surrounding skeleton. The mean Sr/Ca of the central band, 10.6 ± 0.1 mmol/mol (2σ standard error), and that of the surrounding skeleton, 10.58±0.09 mmol/mol, are statistically similar, and agree well with the inorganic aragonite Sr/Ca-temperature relationship at the temperature of coral growth. In the central band, Mg/Ca is greater than 3 mmol/mol, more than twice that of the surrounding skeleton, a general result observed in the relative Mg/Ca ratios of D. dianthus collected from separate oceanographic locations. This large vital effect corresponds to a ∼ 10 °C signal, when calibrated via surface coral Mg/Ca-temperature relationships, and has the potential to complicate paleoreconstructions. Outside the central band, Mg/Ca ratios increase with decreasing Sr/Ca. We explain the correlated behavior of Mg/Ca and Sr/Ca outside the central band by Rayleigh fractionation from a closed pool, an explanation that has been proposed elsewhere, but which is tested in this study by a simple and general relationship. We constrain the initial solution and effective partition coefficients for a Rayleigh process consistent with our accurate Metal/Ca measurements. A process other than Rayleigh fractionation influences Mg in the central band and our data constrain a number of possible mechanisms for the precipitation of this aragonite. Understanding the process affecting tracer behavior during coral biomineralization can help us better interpret paleoproxies in biogenic carbonates and lead to an improved deep-sea paleothermometer.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33591, title ="Simulating the transient evolution and abrupt change of Northern Africa atmosphere–ocean–terrestrial ecosystem in the Holocene", author = "Liu, Z. and Wang, Y.", journal = "Quaternary Science Reviews", volume = "26", number = "13-14", pages = "1818-1837", month = "July", year = "2007", doi = "10.1016/j.quascirev.2007.03.002 ", issn = "0277-3791", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-081630088", note = "© 2007 Elsevier Ltd. Received 30 July 2006; received in revised form 22 February 2007; accepted 1 March 2007. The authors would like to thank Drs. M. Claussen, P. Hoelzmann and an anonymous reviewer for helpful comments. This work is supported by ESH/NSF. The computation is performed at NCAR CSL.", revision_no = "14", abstract = "We present the first synchronously coupled transient simulation of the evolution of the northern Africa climate-ecosystem for the last 6500 years in a global general circulation ocean–atmosphere–terrestrial ecosystem model. The model simulated the major abrupt vegetation collapse in the southern Sahara at about 5 ka, consistent with the proxy records. Local precipitation, however, shows a much more gradual decline with time, implying a lack of strong positive vegetation feedback on annual rainfall during the collapse. The vegetation change in northern Africa is driven by local precipitation decline and strong precipitation variability. In contrast, the change of precipitation is dominated by internal climate variability and a gradual monsoonal climate response to orbital forcing. In addition, some minor vegetation changes are also simulated in different regions across northern Africa\nThe model also simulated a gradual annual mean surface cooling in the subtropical North Atlantic towards the latest Holocene, as well as a reduced seasonal cycle of SST. The SST response is caused largely by the insolation forcing, while the annual mean cooling is also reinforced by the increased coastal upwelling near the east boundary. The increased upwelling results from a southward retreat of the North Africa monsoon system, and, in turn, an increased northeasterly trade wind. The simulated changes of SST and upwelling are also largely consistent with marine proxy records, albeit with a weaker magnitude in the model.\nThe mismatch between the collapse of vegetation and gradual transition of rainfall suggests that the vegetation collapse is not caused by a strong positive vegetation feedback. Instead, it is suggested that the Mid-Holocene collapse of North African vegetation is caused mainly by a nonlinear response of the vegetation to a precipitation threshold in the presence of strong climate variability. The implication to the modeling and observations is also discussed.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33619, title ="Atlantic Meridional Overturning Circulation During the Last Glacial Maximum", author = "Lynch-Stieglitz, Jean and Adkins, Jess F.", journal = "Science", volume = "316", number = "5821", pages = "66-69", month = "April", year = "2007", doi = "10.1126/science.1137127 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-142253528", note = "© 2007 American Association for the Advancement of Science.\n\nWe thank the Scientific Committee on Ocean Research,\nIMAGES, and NSF for their support of the Working Group\non Past Ocean Circulation and the workshop that was\nheld on this topic in March 2005 at Georgia Tech. We\nalso thank the scientists who contributed their ideas to\nthis review through their participation in that workshop\nand the ORMEN/VAMOC Workshop on LGM ocean circulation in Amsterdam in October 2005. We thank T. Bickert for providing data for Fig. 1.", revision_no = "16", abstract = "The circulation of the deep Atlantic Ocean during the height of the last ice age appears to have been quite different from today. We review observations implying that Atlantic meridional overturning circulation during the Last Glacial Maximum was neither extremely sluggish nor an enhanced version of present-day circulation. The distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the Atlantic only slightly greater than today. However, evidence from multiple water-mass tracers supports a different distribution of deep-water properties, including density, which is dynamically linked to circulation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33629, title ="Characterization and role of carbonic anhydrase\nin the calcification process of the azooxanthellate coral\nTubastrea aurea", author = "Tambutté, Sylvie and Tambutté, Eric", journal = "Marine Biology", volume = "151", number = "1", pages = "71-83", month = "March", year = "2007", issn = "0025-3162", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-153725990", note = "© 2006 Springer-Verlag.\n\nReceived: 8 May 2006; Accepted: 9 August 2006; Published online: 30 September 2006.\n\nWe thank Prof. François Morel from Princeton University and Mak Saïto from the Woods Hole Oceanographic Institution for providing the antibody, anti-bcarbonic anhydrase from Synecchococcus sp. This study was conducted as part of the Centre Scientifique de Monaco 2000–2004 research program. It was supported by the Government of the Principality of Monaco and by the California Institute of Technology, USA.", revision_no = "13", abstract = "In zooxanthellate corals, the photosynthetic fixation of carbon dioxide and the precipitation of CaCO_3 are intimately linked both spatially and temporally making it difficult to study carbon transport mechanisms involved in each pathway. When studying Tubastrea aurea, a coral devoid of zooxanthellae, we can focus on carbon transport mechanisms involved only in the calcification process. We performed this study to characterize T. aurea carbonic anhydrase and to determine its role in the calcification process. We have shown that inhibition of tissular carbonic anhydrase activity affects the calcification rate. We have\nmeasured the activity of this enzyme both in the tissues\nand in the organix matrix extracted from the skeleton. Our results indicate that organic matrix proteins, which\nare synthesized by the calcifying tissues, are not only\nstructural proteins, but they also play a crucial catalytic\nrole by eliminating the kinetic barrier to interconversion\nof inorganic carbon at the calcification site. By\nimmunochemistry we have demonstrated the presence of a protein both in the tissues and in the organic matrix, which shares common features with prokaryotic carbonic anhydrases.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33606, title ="Temporal stability of the neodymium isotope signature of the Holocene to glacial North Atlantic", author = "van der Flierdt, Tina and Robinson, Laura F.", journal = "Paleoceanography", volume = "21", number = "4", pages = "Art. No. PA4102", month = "November", year = "2006", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-104043357", note = "© 2006 American Geophysical Union. Received 17 March 2006; revised 8 July 2006; accepted 19 July 2006; published 25 November 2006. This study was supported by the Comer\nScience and Education Foundation and the Vetlesen Foundation Climate Center at LDEO. We thank Marty Q. Fleisher, N. Gary Hemming, Anna Cipriani, Allison M. Franzese, and Jennifer M. Cole for their help in keeping the labs and the mass specs running smoothly. We also thank two anonymous reviewers for their productive comments. This is Lamont contribution 6977.", revision_no = "16", abstract = "The neodymium isotopic composition of marine precipitates is increasingly recognized as a powerful tool for identifying changes in ocean circulation and mixing on million year to millennial timescales. Unlike nutrient proxies such as δ^(13)C or Cd/Ca, Nd isotopes are not thought to be altered in any significant way by biological processes, and thus they can serve as a quasi-conservative water mass tracer. However, the application of Nd isotopes in understanding the role of thermohaline circulation in rapid climate change is currently hindered by the lack of direct constraints on the signature of the North Atlantic end-member through time. Here we present the first results of Nd isotopes measured in U-Th-dated deep-sea corals from the New England seamounts in the northwest Atlantic Ocean. Our data are consistent with the conclusion that the Nd isotopic composition of North Atlantic deep and intermediate water has remained nearly constant through the last glacial cycle. The results address long-standing concerns that there may have been significant changes in the Nd isotopic composition of the North Atlantic end-member during this interval and substantiate the applicability of this novel tracer on millennial timescales for paleoceanography research. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33615, title ="A deep-sea coral record of North Atlantic radiocarbon through the Younger Dryas: Evidence for intermediate water/deepwater reorganization", author = "Eltgroth, Selene F. and Adkins, Jess F.", journal = "Paleoceanography", volume = "21", number = "4", pages = "Art. No. PA4207", month = "November", year = "2006", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-123314699", note = "© 2006 American Geophysical Union.\nReceived 12 July 2005; revised 25 May 2006; accepted 28 June 2006; published 17 November 2006.\nWe wish to thank Jessie Shing-Lin Wang and Diego Fernandez for help with U-Th sample preparation and analysis at Caltech. We thank the staff of the UC Irvine KCCAMS laboratory and the staff of LLNL-CAMS for help with radiocarbon sample preparation and analysis. We are grateful to Steven Cairns at the Smithsonian for providing one of the samples (YD-3) used in this study and to the crew of the R/V Atlantis and DSV Alvin pilots, whose expertise made it possible for us to collect thousands of fossil samples from the New England seamounts. Luke Skinner and Jean Lynch-Stieglitz provided very helpful reviews of the manuscript. This work was supported by NSF grant OCE\n0096373.", revision_no = "9", abstract = "Our record of Younger Dryas intermediate-depth seawater Δ^(14)C from North Atlantic deep-sea corals supports a link between abrupt climate change and intermediate ocean variability. Our data show that northern source intermediate water (∼1700 m) was partially replaced by (14)^C-depleted southern source water at the onset of the event, consistent with a reduction in the rate of North Atlantic Deep Water formation. This transition requires the existence of large, mobile gradients of Δ^(14)C in the ocean during the Younger Dryas. The Δ^(14)C water column profile from Keigwin (2004) provides direct evidence for the presence of one such gradient at the beginning of the Younger Dryas (∼12.9 ka), with a 100‰ offset between shallow (<∼2400 m) and deep water. Our early Younger Dryas data are consistent with this profile and also show a Δ^(14)C inversion, with 35‰ more enriched water at ∼2400 m than at ∼1700 m. This feature is probably the result of mixing between relatively well ^(14)C ventilated northern source water and more poorly ^(14)C ventilated southern source intermediate water, which is slightly shallower. Over the rest of the Younger Dryas our intermediate water/deepwater coral Δ^(14)C data gradually increase, while the atmosphere Δ^(14)C drops. For a very brief interval at ∼12.0 ka and at the end of the Younger Dryas (11.5 ka), intermediate water Δ^(14)C (∼1200 m) approached atmospheric Δ14C. These enriched Δ^(14)C results suggest an enhanced initial Δ^(14)C content of the water and demonstrate the presence of large lateral Δ^(14)C gradients in the intermediate/deep ocean in addition to the sharp vertical shift at ∼2500 m. The transient Δ^(14)C enrichment at ∼12.0 ka occurred in the middle of the Younger Dryas and demonstrates that there is at least one time when the intermediate/deep ocean underwent dramatic change but with much smaller effects in other paleoclimatic records. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33620, title ="The \"African humid period\" and the record of marine upwelling from excess ^(230)Th in Ocean Drilling Program Hole 658C", author = "Adkins, Jess and deMenocal, Peter", journal = "Paleoceanography", volume = "21", number = "4", pages = "Art. No. PA4203", month = "October", year = "2006", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-142810744", note = "© 2006 American Geophysical Union.\nReceived 26 August 2005; revised 4 February 2006; accepted 13 June 2006; published 20 October 2006.\nWe thank Joe Ortiz for his analysis of the bulk density data and for conversations over the years. Two anonymous\nreviewers improved the clarity of the manuscript. J.F.A.’s work was supported by a LDEO postdoctoral fellowship and by the Lamont Climate Center. NSF grant OCE-0318445 supported J.F.A.’s work on this project at Caltech.", revision_no = "17", abstract = "Using a high-resolution ^(230)Th normalized record of sediment flux, we document the deglacial and Holocene history of North African aridity and coastal upwelling at Ocean Drilling Program Hole 658C. At both the end of the Younger Dryas and after the 8.2 ka event, there are significant drops in terrigenous accumulation at our site, indicating an increase in the monsoon moisture flux over Africa at this time. At 5.5 ka, there is an abrupt end to the “African humid period” and a return to stronger upwelling conditions. For carbonate and opal fluxes the ^(230)Th normalization completely changes the shape of each record based on percentage variations alone. This site is a clear example of how variations in one sediment component can obscure changes in the others, and it demonstrates the need for radionuclide measurements more generally in paleoceanography. By taking our new records and a large amount of previous data from this site we conclude that increases in African moisture are tightly coupled to decreases in coastal upwelling intensity.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/3959, title ="Primary U distribution in scleractinian corals and its implications for U series dating", author = "Robinson, Lauren F. and Adkins, Jess F.", journal = "Geochemistry, Geophysics, Geosystems", volume = "7", number = "5", pages = "Q05022", month = "May", year = "2006", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:ROBggg06", note = "Copyright 2006 by the American Geophysical Union. \n\nReceived 6 September 2005; accepted 10 March 2006; published 24 May 2006 \n\nWe gratefully acknowledge The Comer Foundation for Abrupt Climate Change and the helpful comments of two anonymous reviewers.", revision_no = "5", abstract = "In this study we use microsampling techniques to explore diagenetic processes in carbonates. These processes are important as they can affect the accuracy of U series chronometry. Fission track maps of deep-sea scleractinian corals show a threefold difference between the minimum and maximum [U] in modern corals, which is reduced to a factor of 2 in fossil corals. We use micromilling and MC-ICP-MS to make detailed analyses of the [U] and δ234Uinitial distributions in corals from 218 ka to modern. Within each fossil coral we observe a large range of δ234Uinitial values, with high δ234Uinitial values typically associated with low [U]. A simple model shows that this observation is best explained by preferential movement of alpha-decay produced 234U atoms (alpha-recoil diffusion). Open-system addition of 234U may occur when alpha-recoil diffusion is coupled with a high [U] surface layer, such as organic material. This process can result in large, whole-coral δ234Uinitial elevations with little effect on the final age. The diagenetic pathways that we model are relevant to both shallow-water and deep-sea scleractinian corals since both exhibit primary [U] heterogeneity and may be subject to U addition.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/21014, title ="^(13)C–^(18)O bonds in carbonate minerals: A new kind of paleothermometer", author = "Ghosh, Prosenjit and Adkins, Jess", journal = "Geochimica et Cosmochimica Acta", volume = "70", number = "6", pages = "1439-1456", month = "March", year = "2006", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101124-091221004", note = "© 2005 Elsevier Inc.\n\nReceived 2 August 2005; accepted 10 November 2005. Associate editor: Miryam Bar-Matthews. Available online 3 February 2006. \n\nThis study was conducted in response to Michael Bender's good-natured prodding of J.M.E. and J.F.A.; we thank\nhim for his insightful instincts and persistence. We gratefully\nacknowledge the help of Lisa Welp, who measured the\nd18O values of water from which we grew inorganic calcites,\nMa Chi, who helped with XRD analyses of synthetic\ncarbonates, and Dr. Willi Brand, who provided aliquots of\nMAR-J1 carbonate standard. We also thank the Smithsonian\nInstitute for lending us deep-sea coral samples. This\nwork made use of an instrument purchased with the help\nof NSF Grant EAR-0220066 and the Packard Foundation,\nand benefited from salary support provided by NSF Grant\nEAR-0345905.", revision_no = "11", abstract = "The abundance of the doubly substituted CO_2 isotopologue, ^(13)C^(18)O^(16)O, in CO_2 produced by phosphoric acid digestion of synthetic, inorganic calcite and natural, biogenic aragonite is proportional to the concentration of ^(13)C–^(18)O bonds in reactant carbonate, and the concentration of these bonds is a function of the temperature of carbonate growth. This proportionality can be described between 1 and 50 °C by the function: Δ_(47) = 0.0592 • 10^6 • T^(−2) − 0.02, where Δ_(47) is the enrichment, in per mil, of ^(13)C^(18)O^(16)O in CO_2 relative to the amount expected for a stochastic (random) distribution of isotopes among all CO_2 isotopologues, and T is the temperature in Kelvin. This relationship can be used for a new kind of carbonate paleothermometry, where the temperature-dependent property of interest is the state of ordering of ^(13)C and ^(18)O in the carbonate lattice (i.e., bound together vs. separated into different CO_3^(2−) units), and not the bulk δ^(18)O or δ^(13)C values. Current analytical methods limit precision of this thermometer to ca. ± 2 °C, 1σ. A key feature of this thermometer is that it is thermodynamically based, like the traditional carbonate–water paleothermometer, and so is suitable for interpolation and even modest extrapolation, yet is rigorously independent of the δ^(18)O of water and δ^(13)C of DIC from which carbonate grew. Thus, this technique can be applied to parts of the geological record where the stable isotope compositions of waters are unknown. Moreover, simultaneous determinations of Δ_(47) and δ^(18)O for carbonates will constrain the δ^(18)O of water from which they grew.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33647, title ="Radiocarbon Variability in the Western North Atlantic During the Last Deglaciation", author = "Robinson, Laura F. and Adkins, Jess F.", journal = "Science", volume = "310", number = "5753", pages = "1469-1473", month = "December", year = "2005", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120829-101808337", note = "© 2005 American Association for the Advancement of Science. Received for publication 13 May 2005; accepted 24 October 2005. Published online 3 November 2005.\nWe acknowledge the Comer Foundation for Abrupt\nClimate Change, the Henry Luce Foundation, the\nAmerican Chemical Society Petroleum Research\nFund, and NSF grant numbers OCE-0096373 and\nOCE-0095331. We also thank all members of the\ncruise AT7-35 to the New England Seamounts. ", revision_no = "16", abstract = "We present a detailed history of glacial to Holocene radiocarbon in the deep western North Atlantic from deep-sea corals and paired benthic-planktonic foraminifera. The deglaciation is marked by switches between radiocarbon-enriched and -depleted waters, leading to large radiocarbon gradients in the water column. These changes played an important role in modulating atmospheric radiocarbon. The deep-ocean record supports the notion of a bipolar seesaw with increased Northern-source deep-water formation linked to Northern Hemisphere warming and the reverse. In contrast, the more frequent radiocarbon variations in the intermediate/deep ocean are associated with roughly synchronous changes at the poles. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39384, title ="Carbonate paleothermometry based on abundances of ^(13)C-^(18)O bonds", author = "Eiler, John M. and Ghosh, Prosenjit", journal = "Geochimica et Cosmochimica Acta", volume = "69", number = "10", pages = "A127-A127", month = "May", year = "2005", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130716-083842973", note = "© 2005 Elsevier Ltd. \n\n", revision_no = "10", abstract = "Urey’s carbonate oxygen isotope paleothermometer is a milestone of paleoclimate research but constrains temperature only if the oxygen isotope composition of water from which carbonate grew is known. Moreover, difficulty in recognizing diagenetic overprinting has confounded the interpretation of\ncarbonate oxygen isotope compositions for much of the geological record. We pesent a carbonate paleothermometer based on the formation of bonds between ^(13)C and ^(18)O. This\nordering of rare isotopes can be described by the reaction: Ca^(13)C^(16)O_3 + Ca^(12)C^(18)O^(16)O_2 = Ca^(12)C^(16)O_3 + Ca^(13)C^(18)O^(16)O_2 rxn 1.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33605, title ="Rapid climate change and conditional instability of the glacial deep ocean from the thermobaric effect and geothermal heating", author = "Adkins, Jess F. and Ingersoll, Andrew P.", journal = "Quaternary Science Reviews", volume = "24", number = "5-6", pages = "581-594", month = "March", year = "2005", doi = "10.1016/j.quascirev.2004.11.005", issn = "0277-3791", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-102721930", note = "© 2004 Elsevier Ltd. Accepted 13 November 2004. Early discussions with M. Bender, D. Sigman and T. Schneider helped form our ideas. The manuscript was improved by thoughtful reviews from R. Toggweiller and S. Hostetler. JFA was supported by NSF grant OCE-0096814. ", revision_no = "12", abstract = "Previous results from deep-sea pore fluid data demonstrate that the glacial deep ocean was filled with salty, cold water from the South. This salinity stratification of the ocean allows for the possible accumulation of geothermal heat in the deep-sea and could result in a water column with cold fresh water on top of warm salty water and with a corresponding increase in potential energy. For an idealized 4000 dbar two-layer water column, we calculate that there are ∼10^6J/m^2 (∼0.2J/kg) of potential energy available when a 0.4 psu salinity contrast is balanced by a ∼2°C temperature difference. This salt-based storage of heat at depth is analogous to Convectively Available Potential Energy (CAPE) in the atmosphere. The \"thermobaric effect\" in the seawater equation of state can cause this potential energy to be released catastrophically. Because deep ocean stratification was dominated by salinity at the Last Glacial Maximum (LGM), the glacial climate is more sensitive to charging this \"thermobaric capacitor\" and can plausibly explain many aspects of the record of rapid climate change. Our mechanism could account for the grouping of Dansgaard/Oeschger events into Bond Cycles and for the different patterns of warming observed in ice cores from separate hemispheres.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33593, title ="Growth rates of the deep-sea scleractinia Desmophyllum cristagalli and Enallopsammia rostrata", author = "Adkins, J. F. and Henderson, G. M.", journal = "Earth and Planetary Science Letters", volume = "227", number = "3-4", pages = "481-490", month = "November", year = "2004", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-085352790", note = "© 2004 Elsevier B.V. Received 15 March 2004; received in revised form 6 August 2004; accepted 30 August 2004. Editor: E. Bard. We thank Will Berelson and T.L. Ku at USC for\ntheir help with the ^(209)Po spike. Marty Fleisher at LDEO alpha counted our silver disks and helped interpret the energy spectra. JFA and JSLW were supported by NSF grant OCE-0096373. We also thank the WHOI Alvin group and the crew of the Atlantis for recovering sample ALV 3701-8. ", revision_no = "21", abstract = "With uranium rich skeletons and density bands similar to their surface coral counterparts, deep-sea scleractinia are a promising archive of past climate. To improve the utility of fossil samples as monitors of deep ocean variability, we have measured ^(210)Pb and ^(226)Ra activities in a variety of modern specimens to constrain the range of growth rates. Mechanical and chemical cleaning of each sample are required to isolate the radionuclides trapped in the coral skeleton from surface contaminants. However, in many cases mechanically cleaned samples show the same overall growth rate as parallel transects of samples subjected to the full chemical and mechanical cleaning but with much higher overall activities. Three samples of Desmophyllum cristagalli show a range of vertical extension rates from 0.5 mm/yr to 2 mm/yr, consistent with previous estimates. A single Enallopsammia rostrata from the North Atlantic is over 100 years old. Its average radial growth rate is 0.07 mm/yr, and the clear banding in this direction is not consistent with annual periodicity. A minimum vertical extension rate of 5 mm/yr is estimated from the ^(210)Pb data. Both of these species are found in the fossil record and, with the growth rates determined here, can record about 100 years of climate change. The growth rates will allow the reconstruction of climate at subdecadal resolution in D. cristagalli and even higher resolution in E. rostrata.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/51633, title ="Deep Ocean Overturning — Then and Now", author = "Adkins, Jess F. and Pasquero, Claudia", journal = "Science", volume = "306", number = "5699", pages = "1143-1144", month = "November", year = "2004", doi = "10.1126/science.1105531", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141112-090839762", note = "© 2004 American Association for the Advancement of Science.", revision_no = "9", abstract = "Knowledge of how fast the deep ocean overturned during the last glacial period is important for understanding how Earth's climate could enter such an extremely cold state. Radiocarbon ages from surface and deep-dwelling foraminifera can indirectly measure the overturning rate. In their Perspective, Adkins and Pasquero discuss new data from the glacial Equatorial Pacific (see report by Broecker et al.) that show that at the time of the Last Glacial Maximum, mid-depth waters were about as \"old\" (that is, they had spent as much time below the surface) as they are today. Coupled with other records from the deeper ocean, the data might help to determine what drives the strength of the overturning circulation in the first place.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33614, title ="Oceanic evidence of climate change in southern Australia over the last three centuries", author = "Thresher, Ronald and Rintoul, Stephen R.", journal = "Geophysical Research Letters", volume = "31", number = "7", pages = "Art. No. L07212", month = "April", year = "2004", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-122216658", note = "© 2004 American Geophysical Union.\nReceived 18 October 2003; accepted 11 March 2004; published 13 April 2004.\nWe thank L. Ayliffe, M. Bravington, K. Evans, K. Hayes, C. MacRae, P. Oke and A. B. Pittock for their assistance and valuable discussions. This study was supported by the Australian Fisheries and Research Development Corporation, the Australian Greenhouse Office, and the Land and Water Research Development Corporation.", revision_no = "10", abstract = "Chemical analysis of deepwater octocorals collected at 1000 m depth off southern Australia indicates long-term cooling, beginning in the mid-18th century. This cooling appears to reflect shoaling of isotherms along the continental shelf, that can be related statistically, observationally and by modeling to increasing coastal sea-surface temperatures, that in turn reflect a poleward extension of the SW Pacific boundary current (the East Australian Current). The oceanographic changes implied by the coral record suggest climate change in temperate Australia starting about the time of European settlement. Correlations between temperate Australian and Antarctic indices suggest these long-term changes might also be relevant to Antarctic climate.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33592, title ="Reconstructing Last Glacial Maximum bottom water salinities\nfrom deep-sea sediment pore fluid profiles", author = "Adkins, Jess F. and Schrag, Daniel P.", journal = "Earth and Planetary Science Letters", volume = "216", number = "1-2", pages = "109-123", month = "November", year = "2003", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-082914777", note = "© 2003 Elsevier B.V. Received 31 March 2003; received in revised form 28 August 2003; accepted 5 September 2003. During her stay at Caltech, Kate McIntyre collected many of the [Cl] profiles and provided many helpful comments on the modeling sensitivities. David Hodel, Chris Charles, Peggy Delaney, Alan Mix and all the inorganic chemists worked extremely hard to collect the pore fluid samples during ODP Legs 177 and 202. Reviews from L. Labeyrie, J. Lynch-Stieglitz and B. Boudreau\ngreatly improved the manuscript. This work was supported by NSF Grant numbers OCE-0096814 to J.F.A. and OCE-0096909 to D.P.S.[BARD]", revision_no = "17", abstract = "Deep-sea sediment pore fluids contain a record of past glaciations in their [Cl] and δ^(18)O. The signal of the Last Glacial Maximum (LGM) ice volume increase remains in the pore fluids as a local peak in each of these species. Using a one-dimensional model to account for the diffusive and advective transport within the sediment column since the LGM, the past bottom water salinity and δ^(18)O_(seawater) values can be estimated. The model is most sensitive to the shape of the forcing function used to represent bottom water variations through time, the effective diffusion coefficient, and the scatter in the data. Assuming steady-state compaction, the model is relatively insensitive to the initial condition, the bulk sedimentation rate and the assumed porosity profile, though these last two are measured independently. Overall uncertainties in the relative [Cl] increase at the LGM are between 0.1 and 0.5%, where the mean ocean change is about 3.5%.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33613, title ="Ventilation of the North Atlantic Ocean during the Last Glacial Maximum: A comparison between simulated and observed radiocarbon ages", author = "Meissner, K. J. and Schmittner, A.", journal = "Paleoceanography", volume = "18", number = "2", pages = "Art. No. 1023", month = "April", year = "2003", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-120841334", note = "© 2003 American Geophysical Union.\nReceived 28 January 2002; revised 27 September 2002; accepted 22 October 2002; published 8 April 2003.\nWe would like to thank Lloyd D. Keigwin for providing his submitted manuscript and for his useful comments about\nthe interpretation of his data. Two anonymous reviewers and Matthew England were extraordinarily helpful with an earlier version of this paper. Furthermore, we would like to thank Carl Wunsch for many useful comments\non an earlier version of this manuscript. Michael Eby’s technical support was very appreciated. We are grateful for research grant support under the NSERC Operating, Strategic, CSHD and CFCAS research grant programs. Dáithí A. Stone is gratefully acknowledged for editing English grammar.", revision_no = "9", abstract = "The distribution of radiocarbon during simulations of the Last Glacial Maximum with a coupled ocean-atmosphere-sea ice model is compared with sediment core measurements from the equatorial Atlantic Ceara Rise, Blake Ridge, Caribbean Sea, and South China Sea. During these simulations we introduce a perturbation of North Atlantic freshwater fluxes leading to varying strengths of the Atlantic meridional overturning. The best fit with the observations is obtained for an overturning weakened by 40% compared with today. Further, we simulate the phenomenon of an “age reversal” found in deep sea corals, but we suggest that this indicates rather a sudden interruption of deep water formation instead of an increase in ventilation, which was suggested earlier.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33710, title ="Stable isotopes in deep-sea corals and a new mechanism for “vital effects”", author = "Adkins, J. F. and Boyle, E. A.", journal = "Geochimica et Cosmochimica Acta", volume = "67", number = "6", pages = "1129-1143", month = "March", year = "2003", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-132156981", note = "© 2003 Elsevier Science Ltd. \n\nReceived January 24, 2002; accepted in revised form September 13, 2002.\n\nThis research was supported by NSF grant number\nOCE-0096373 and an NCAR Global Climate Change Postdoctoral\nFellowship to J.F.A. We thank David Lea, Howie Spero, Richard Zeebe, and an anonymous reviewer for constructive comments that improved the article. In addition to the above people, conversations with Jonathan Erez, Francios Morel, Michael Bender, and Jele Bjima have helped to shape our thinking about vital effects. Associate editor: D. Lea", revision_no = "13", abstract = "Offsets from isotopic equilibrium in biogenic carbonates have complicated paleoclimate reconstructions for decades. A new archive of climate, deep-sea corals, is used to evaluate the calcification processes, independent of photosynthesis, that contribute to these offsets. Carbon and oxygen stable isotope data from six modern deep-sea corals show strong linear trends between δ^(13)C and δ^(18)O. Slopes of these trends between samples are similar and range between 1.9 to 2.6 for Δδ^(13)C/Δδ^(18)O. Linear trends intersect isotopic equilibrium for δ^(18)O and are slightly depleted for δ^(13)C. Variations in the isotopic ratios are strongly correlated with the density banding structure. Isotopically depleted aragonite is associated with light, quickly precipitating bands, whereas isotopically enriched points correspond to slowly accumulating, less dense aragonite. The densest white band at the trabecular center is furthest from isotopic equilibrium for both carbon and oxygen. Data from this region fall off the linear trend between δ^(18)O and δ^(13)C. This deviation, where δ^(13)C remains constant while the δ^(18)O continues to decrease, does not support “vital effect” mechanisms that call upon kinetic fractionation to explain offsets from isotopic equilibrium. We propose a new mechanism for vital effects in these deep-sea corals that is based on a thermodynamic response to a biologically induced pH gradient in the calcifying region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33594, title ="Rapid sea-level fall and deep-ocean temperature change since\nthe last interglacial period", author = "Cutler, K. B. and Edwards, R. L.", journal = "Earth and Planetary Science Letters", volume = "206", number = "3-4", pages = "253-271", month = "February", year = "2003", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-085740795", note = "© 2002 Elsevier Science B.V.\nReceived 4 June 2002; received in revised form 12 November 2002; accepted 27 November 2002.\nWe thank J. Chappell for scientific discussions around tropical campfires, helping initiate this project, and facilitating the field work and drilling on the Huon Peninsula; J. Hoff and D.A. Richards for laboratory assistance; C.R. Bentley and J.A. Dorale for informative discussions; R.G. Johnson, E. Wallensky, G.R. Min, J.W. Beck, and the 1988 PNG field team for sample collection\nefforts; and D. Lea and two anonymous reviewers\nfor constructive criticisms that improved the manuscript considerably. Supported by NSF Grants ESH-9809459, EAR-9712037, and ARI-9512334 to R.L.E. K.B.C. was supported by NSF-sponsored grants for Geofluids Research\n(to M. Person) and Research Training (to M. Davis), and the Doctoral Dissertation Fellowship (University of Minnesota).", revision_no = "22", abstract = "We have dated Huon Peninsula, Papua New Guinea and Barbados corals that formed at times since the Last Interglacial Period, applying both ^(230)Th and ^(231)Pa dating techniques as a test of age accuracy. We show that Marine Isotope Stage (MIS) 5e ended prior to 113.1 ± 0.7 kyr, when sea level was −19 m. During MIS 5b sea level was −57 m at 92.6 ± 0.5 kyr, having dropped about 40 m in approximately 10 kyr during the MIS 5c–5b transition. Sea level then rose more than 40 m during the MIS 5b–5a transition, also in about 10 kyr. MIS 5a lasted until at least 76.2 ± 0.4 kyr, at a level of −24 m at that time. Combined with earlier data that places MIS 4 sea level at −81 m at 70.8 kyr, our late MIS 5a data indicate that sea level fell almost 60 m in less than 6 kyr (10.6 m/kyr) during the MIS 5–4 transition. The magnitude of the drop is half that of the glacial–interglacial amplitude and approximately equivalent to the volume of the present-day Antarctic Ice Sheet. During this interval the minimum average rate of net continental ice accumulation was 18 cm/yr, likely facilitated by efficient moisture transport from lower latitudes. At three specific times (60.6 ± 0.3, 50.8 ± 0.3, and 36.8 + 0.2 kyr) during MIS 3, sea level was between −85 and −74 m. Sea level then dropped to −107 m at 23.7 ± 0.1 kyr early in MIS 2, before dropping further to Last Glacial Maximum (LGM) values and then rising to present values during the last deglaciation. Times of rapid sea-level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation, supporting the idea that these factors may have resulted in high water-vapor pressure in moisture sources and efficient moisture transport to high-latitude glaciers, thereby contributing to glacial buildup. We combined our sea-level results with deep-sea δ^(18)O records as a means of estimating the temperature and ice-volume components in the marine δ^(18)O record. This analysis confirms large deep-ocean temperature shifts following MIS 5e and during Termination I. Deep-ocean temperatures changed by much smaller amounts between MIS 5c and 2. Maximum temperature shift in the deep Pacific is about 2°, whereas the shift at a site in the Atlantic is 4°. Under glacial conditions temperatures at both sites are near the freezing point. The shift in the Atlantic is likely caused by a combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33608, title ="The Salinity, Temperature, and δ18O of the Glacial Deep Ocean", author = "Adkins, Jess F. and McIntyre, Katherine", journal = "Science", volume = "298", number = "5599", pages = "1769-1773", month = "November", year = "2002", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-115444522", note = "© 2002 American Association for the Advancement of Science. \n\n17 July 2002; accepted 29 October 2002.\n\nWe thank K. Cuffey for insightful discussions about\nhydrology and E. Boyle and an anonymous reviewer for helpful comments. E. Boyle is thanked for inspiration\nand continued encouragement. E. Goddard provided assistance withlab work. Supported by NSF grant numbers OCE-0096814 to J.F.A. and OCE-0096909 to D.P.S.", revision_no = "10", abstract = "We use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from Ocean Drilling Program cores to reconstruct salinity and temperature of the deep ocean during the Last Glacial Maximum (LGM). Our data show that the temperatures of the deep Pacific, Southern, and Atlantic oceans during the LGM were relatively homogeneous and within error of the freezing point of seawater at the ocean's surface. Our chloride data show that the glacial stratification was dominated by salinity variations, in contrast with the modern ocean, for which temperature plays a primary role. During the LGM the Southern Ocean contained the saltiest water in the deep ocean. This reversal of the modern salinity contrast between the North and South Atlantic implies that the freshwater budget at the poles must have been quite different. A strict conversion of mean salinity at the LGM to equivalent sea-level change yields a value in excess of 140 meters. However, the storage of fresh water in ice shelves and/or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33598, title ="The oxygen isotopic composition of seawater during the Last Glacial Maximum", author = "Schrag, Daniel P. and Adkins, Jess F.", journal = "Quaternary Science Reviews", volume = "21", number = "1-3", pages = "331-342", month = "January", year = "2002", doi = "10.1016/S0277-3791(01)00110-X", issn = "0277-3791", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-095932442", note = "© 2001 Elsevier Science Ltd. \n\nReceived 30 January 2001; Accepted 8 August 2001; Available online 11 December 2001. \n\nThe authors thank Ethan Goddard for technical assistance. Reviews by Art Spivack and Gideon Henderson greatly improved the manuscript. This work was supportedby NSF awards 0096909 to Schrag and 0096814 to Adkins.", revision_no = "12", abstract = "High-resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep-sea sediments from sites in the North and South Atlantic. The data provide direct measurements of changes in the isotopic composition of bottom waters during the Last Glacial Maximum (LGM). Results from Ocean Drilling Program (ODP) Site 981 in the North Atlantic, currently bathed in North Atlantic Deep Water (NADW) reproduces previous results from the Ceara and Bermuda Rises, constraining the glacial–interglacial change in δ^(18)O of the deep Atlantic to be 0.7–0.8‰. Results from Site 984, which is located north of Site 981 and at a shallower water depth, yield a similar value (0.8‰), providing insight into the properties of Glacial North Atlantic Intermediate Water (GNAIW). Sites from ODP Leg 177 in the South Atlantic span the modern boundary between northern and southern sources of deep water. Data from the northern site (1088) yield a similar result to sites in the tropical and North Atlantic (0.7‰). At the southern site (1093), located south of the polar front, the change is substantially larger (1.1‰), representing the change in δ^(18)O of southern source waters since the LGM. These results confirm previous estimates that the global average change in δ^(18)O of seawater is 1.0±0.1‰. Hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations, giving further support to these results. At all sites studied, the temperature of the deep ocean during the LGM, calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera, was within 1°C of the freezing point of seawater.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33602, title ="Radiocarbon dating of deep-sea corals", author = "Adkins, Jess F. and Griffin, Sheila", journal = "Radiocarbon", volume = "44", number = "2", pages = "567-580", month = "January", year = "2002", issn = "0033-8222", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-100130405", note = "© 2002 by the Arizona Board of Regents on behalf of the University of Arizona.\n\nThis work is licensed under a Creative Commons Attribution 3.0 License. \n\n", revision_no = "15", abstract = "Deep-sea corals are a promising new archive of paleoclimate. Coupled radiocarbon and U-series dates allow ^(14)C to be used as a tracer of ocean circulation rate in the same manner as it is used in the modern ocean. Diagnetic alteration of coral skeletons on the seafloor requires a thorough cleaning of contaminating phases of carbon. In addition, 10% of the coral must be chemically leached prior to dissolution to remove adsorbed modern CO_2. A survey of modern samples from the full Δ^(14)C gradient in the deep ocean demonstrates that the coralline CaCO_3 records the radiocarbon value of the dissolved inorganic carbon.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/51667, title ="Dating--Vive la Différence", author = "Adkins, Jess", journal = "Science", volume = "294", number = "5548", pages = "1844-1845", month = "November", year = "2001", doi = "10.1126/science.1067544", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141112-131606095", note = "© 2001 American Association for the Advancement of Science.", revision_no = "9", abstract = "Radiocarbon ages are widely used in archaeology and the geological sciences to date events from the modern to beyond the Last Glacial Maximum. But atmospheric radiocarbon concentrations vary widely at many time scales. In his Perspective, Adkins explains how Siani et al. circumvent this problem, enabling them to determine absolute ages for ocean surface water temperature records. The results help understand how variations in surface radiocarbon reservoir ages relate to climatic changes during the last deglaciation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33609, title ="Pore fluid constraints on deep ocean temperature and salinity during the Last Glacial Maximum", author = "Adkins, J. F. and Schrag, D. P.", journal = "Geophysical Research Letters", volume = "28", number = "5", pages = "771-774", month = "March", year = "2001", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-115449235", note = "© 2001 American Geophysical Union.\nReceived 15 March 2000; accepted 17 July 2000.", revision_no = "9", abstract = "Pore water records of δ^(18)O and [Cl] from ODP Site 1063A on the Bermuda Rise constrain the change in seawater δ^(18)O and salinity from the Last Glacial Maximum (LGM) to the Holocene to be 0.75±0.05‰ and 2.5±0.1% respectively. Coupled with a measured benthic foraminiferal δ^(18)O change, this result means that bottom waters were 4.6±0.8°C cooler than the Holocene at the LGM and therefore at or near the seawater freezing point. Coupled δ^(18)O and chlorinity results give an extrapolated mean ocean LGM to Holocene change in δ^(18)O of 0.95±0.09‰. These data also constrain the past southern source deep‐water salinity to be 35.76±0.04 psu, which is within error of the mean deep ocean value for this time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33596, title ="U-Th dating of deep-sea corals", author = "Cheng, Hai and Adkins, Jess", journal = "Geochimica et Cosmochimica Acta", volume = "64", number = "14", pages = "2401-2416", month = "July", year = "2000", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-093103827", note = "© 2000 Elsevier Science Ltd.\nReceived 24 February 1999; Revised 16 November 1999; Accepted 16 November 1999; Available online 6 July 2000.\nD. Richards and J. Doral provided stimulating discussions about many of the issues raised in this work. S. Cairns helped identify the coral samples. T. Kleindinst of WHOI produced the photograph in Figure 4. We would like to thank G. Henderson and D. Muhs for helpful reviews of the manuscript. JFA thanks the UCAR Post-Doctoral Fellowship Program and LDEO for support during the writing of this paper.", revision_no = "10", abstract = "^(230)Th, ^(232)Th, ^(234)U and ^(238)U compositions of several deep-sea solitary corals, mainly the species Desmophyllum cristagalli, were determined by thermal ionization mass spectrometry (TIMS). It is possible to obtain high precision ages on modern pristine corals that have low [^(232)Th] (5 to a few hundred ppt). However, because older deep-sea corals tend to have higher [^(232)Th] compared to surface corals, and the initial ^(230)Th/^(232)Th ratio is uncertain, older deep-sea corals have larger age uncertainties (± several hundred years for samples with a few thousand ppt ^(232)Th). Therefore, the key hurdle for precise U-Th dating is to remove or account for contaminants which contain elevated ^(232)Th and associated ^(230)Th not due to closed system decay within the coral lattice. A modification of the trace metal cleaning methods used for foraminifera and surface corals can significantly reduce this contamination. By counting the visible growth bands and measuring the mean age of a single septum, the extension rate of D. cristagalli was estimated to be between 0.1 and 3.1 mm/year. In a mean sense, bands appear to be precipitated annually, but this estimate has a large uncertainty. If appropriate tracer calibrations can be established, these corals are therefore suitable to record decadal or sub-decadal oceanographic changes over the course of their lifetime. The δ^(234)U values of all modern samples from different localities and different depths are similar (mean 145.5 ± 2.3‰) and indistinguishable from the data obtained from surface corals. At a precision of about ±2‰, we find no structure in the oceanic profile of δ^(234)U ratios over the top 2000 m of the water column.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33604, title ="Abrupt onset and termination of the African Humid Period:\nrapid climate responses to gradual insolation forcing", author = "deMenocal, Peter and Ortiz, Joseph", journal = "Quaternary Science Reviews", volume = "19", number = "1-5", pages = "347-361", month = "January", year = "2000", issn = "0277-3791", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-101728135", note = "© 1999 Elsevier Science Ltd.\nAvailable online 21 April 2000.\nThe authors would like to thank John Miller and Paula Weiss from the Ocean Drilling Program for their help in the detailed sampling Site 658C. Helpful comments and significant input to this paper were contributed by Bob Anderson, Andre Berger, Martin Claussen, Claude Hillaire-Marcel, George Kukla, and David Rind. Comments by two anonymous reviewers greatly improved the final manuscript. This project was supported by the Marine Geology and Geophysics division of the National Science Foundation. This is LDEO contribution number 5961.", revision_no = "12", abstract = "A detailed (ca. 100 yr resolution) and well-dated (18 AMS ^(14)C dates to 23 cal. ka BP) record of latest Pleistocene–Holocene variations in terrigenous (eolian) sediment deposition at ODP Site 658C off Cap Blanc, Mauritania documents very abrupt, large-scale changes in subtropical North African climate. The terrigenous record exhibits a well-defined period of low influx between 14.8 and 5.5 cal. ka BP associated with the African Humid Period, when the Sahara was nearly completely vegetated and supported numerous perennial lakes; an arid interval corresponding to the Younger Dryas Chronozone punctuates this humid period. The African Humid Period has been attributed to a strengthening of the African monsoon due to gradual orbital increases in summer season insolation. However, the onset and termination of this humid period were very abrupt, occurring within decades to centuries. Both transitions occurred when summer season insolation crossed a nearly identical threshold value, which was 4.2% greater than present. These abrupt climate responses to gradual insolation forcing require strongly non-linear feedback processes, and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non-linear climate sensitivity. The African monsoon climate system is thus a low-latitude corollary to the bi-stable behavior of high-latitude deep ocean thermohaline circulation, which is similarly capable of rapid and large-amplitude climate transitions.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33756, title ="Age Screening of Deep-Sea Corals and the Record of Deep North Atlantic Circulation Change at 15.4ka", author = "Adkins, Jess F. and Boyle, Edward A.", pages = "103-120", month = "January", year = "1999", isbn = "9780306462931", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120831-095218599", note = "© 1999 Kluwer Academic/Plenum Publishers.\nThis is L-DEO contribution 5985.", revision_no = "12", abstract = "Uranium rich, density banded deep-sea corals are a new archive of deep ocean\nbehavior on decadal time scales. Large numbers of samples can be rapidly and inexpensively\nscreened for their-ages using an Inductively Coupled Plasma-Mass Spectrometry\n(ICP-MS) technique. With this new method, 300 samples have been sorted into 5,000\nyear age bins and several dozen of these are useful for coupled precise uranium series\nand radiocarbon dating. Together with Cd/Ca data from a single coral's skeleton, these\ncoupled ages show that there was a rapid and large shift in the deep circulation of the\nwestern north Atlantic at 15.4ka and 1,800m depth. This deep-sea coral signal, also\nfound in sediment records from around the Atlantic, leads the Bolling/Allerod warming\nin the Greenland ice cores by 840 ± 340 years. Coupled ages from the two dating methods\nin the corals also constrain the southern source deep waters to be about 600 years older\nthan their initial value just prior to 15.4ka. This result is in contrast to the modern\nAtlantic where western basin deep waters are on average 100 years old or less.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33599, title ="Deep-Sea Coral Evidence for Rapid Change in Ventilation of the Deep North Atlantic 15,400 Years Ago", author = "Adkins, Jess F. and Cheng, Hai", journal = "Science", volume = "280", number = "5364", pages = "725-728", month = "May", year = "1998", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-100027067", note = "© 1998 American Association for the Advancement of Science. \n\nReceived 18 November 1998; accepted 18 March 1998.\n\nWe thank S. Griffin, C. Masiello, and B. Grant for\nlaboratory assistance. Discussions with D. Sigman, W. S. Broecker, and A. L. van Geen helped improve the manuscript. Supported by the National Science Foundation. J.F.A. was supported by a NASA Global Change fellowship and a grant from Tokyo Electric and Power Company.", revision_no = "11", abstract = "Coupled radiocarbon and thorium-230 dates from benthic coral species reveal that the ventilation rate of the North Atlantic upper deep water varied greatly during the last deglaciation. Radiocarbon ages in several corals of the same age, 15.41 ± 0.17 thousand years, and nearly the same depth, 1800 meters, in the western North Atlantic Ocean increased by as much as 670 years during the 30- to 160-year life spans of the samples. Cadmium/calcium ratios in one coral imply that the nutrient content of these deep waters also increased. Our data show that the deep ocean changed on decadal-centennial time scales during rapid changes in the surface ocean and the atmosphere. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33616, title ="Variability of the North Atlantic thermohaline circulation during the last interglacial period", author = "Adkins, Jess F. and Boyle, Edward A.", journal = "Nature", volume = "390", number = "6656", pages = "154-156", month = "November", year = "1997", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-125041823", note = "© 1997 Macmillan Publishers Ltd. Received 24 March 1997; Accepted 8 September 1997. This research would not have been possible without the extraordinary efforts of the entire IMAGES 101 crew during the summer of 1995 on board the Marion Dufresne. Specifically we thank Yvon Balut, Laurent Labeyrie, Jean-Louie Turon and Franck Bassinot for their efforts on our behalf. We also thank M. M. Rutgers van der Loeff for helpful comments. J.F.A. was supported by a NASA Global Change Fellowship and a grant from the Tokyo Electric and Power Company. NSF provided the funds to collect this core and NOAA funded our work on high-resolution climate records.", revision_no = "17", abstract = "Studies of natural climate variability are essential for evaluating its future evolution. Greenland ice cores suggest that the modern warm period (the Holocene) has been relatively stable for the past 9,000 years. Much less is known about other warm interglacial periods, which comprise less than 10% of the climate record during the past 2.5 million years. Here we present high-resolution ocean sediment records of surface and deep-water variables from the Bermuda Rise spanning the last interglacial period, about 118,000–127,000 years ago. In general, deep-water chemical changes are coincident with transitions in surface climate at this site. The records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates. The relatively stable interglacial period begins and ends with abrupt changes in deep-water flow. We estimate, using ^(230)Th measurements to constrain the chronology, that transitions occur in less than 400 years.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33600, title ="Changing atmospheric Δ^(14)C and the record of deep water paleoventilation ages", author = "Adkins, Jess F. and Boyle, Edward A.", journal = "Paleoceanography", volume = "12", number = "3", pages = "337-344", month = "June", year = "1997", issn = "0883-8305", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120828-100049534", note = "© 1997 American Geophysical Union.\n\nReceived 19 September 1996; accepted 26 January 1997; published 1 June 1997. \n\nWe would like to thank Delia Oppo, Nick Shackleton and Daniel Sigman for helpful discussions. Edouard Bard, J.\nR. Toggweiler and M. L. Delaney provided constructive reviews of the manuscript. J. F. A. was supported by a NASA Global Change Fellowship and a grant from the Tokyo Electric and Power Company. We gratefully acknowledge the support of NSF grant# OCE-94-02198 and NOAA grant # NA46GP0282.", revision_no = "17", abstract = "We propose a new calculation method to better estimate the deep water ventilation age from benthic-planktonic foraminifera ^(14)C ages. Our study is motivated by the fact that changes in atmospheric Δ^(14)C through time can cause contemporary benthic and planktonic foraminifera to have different initial Δ^(14)C values. This effect can cause spurious ventilation age changes to be interpreted from the geologic data. Using a new calculation method, ^(14)C projection ages, we recalculate the data from the Pacific Ocean. Contrary to previous results, we find that the Pacific intermediate and deep waters were about 600 years older than today at the last glacial maximum. In addition, there are possible signals of ventilation age change prior to ice sheet melting and at the Younger Dryas. However, the data are still too sparse to constrain these ventilation transients. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33739, title ="A 120 yr record of widespread contamination from mining of the Iberian pyrite belt", author = "van Geen, A. and Adkins, J. F.", journal = "Geology", volume = "25", number = "4", pages = "291-294", month = "April", year = "1997", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120830-161418780", note = "© 1997 Geological Society of America.\n\nManuscript received September 11, 1996; Revised manuscript received January 8, 1997; Manuscript accepted January 22, 1997.\n\nWe thank J. M. Martin for facilitating surface water\ncollection off the Portuguese coast and S. N. Luoma and M. Bacon for use of their laboratories. National Science Foundation Summer Fellow A. Schmid extended the metal contamination record to Roman times. Sample collection in the Rio Tinto-Odiel was funded by the Office of Naval Research. Collection of sediment cores from the Gulf of Cadiz was funded by the Joint Committee of Science and Technology of the United States–Spain Treaty of Friendship. Lamont-Doherty Earth Observatory contribution no. 5620.", revision_no = "10", abstract = "A metal-enriched seawater plume entering the western Mediterranean Sea through the Strait of Gibraltar originates 300 km to the west in the Rio Tinto estuary of southwestern Spain. Mining of Rio Tinto ore, one of the largest metal-rich sulfide deposits in the world, started well before Roman times. Contemporary Rio Tinto waters draining the region are highly acidic (pH 2.5) with dissolved cadmium, zinc, and copper concentrations 10^5–10^6 times higher than in uncontaminated surface water of the Gulf of Cadiz. Two dated sediment cores from the Spanish continental shelf show that metal inputs to the region increased with the onset of intensive mining activities during the second half of the 19th century. Although the impact of mining may have decreased over the past few decades, the Tinto river and estuary remain highly contaminated.", }