[
{
"id": "authors:k2yjh-zez80",
"collection": "authors",
"collection_id": "k2yjh-zez80",
"cite_using_url": "https://authors.library.caltech.edu/records/k2yjh-zez80",
"type": "article",
"title": "Multi-isotope characterization of 4,4'-DDT isolated from sediment samples via Orbitrap-IRMS",
"author": [
{
"family_name": "Csernica",
"given_name": "Timothy A.",
"clpid": "Csernica-Timothy-A"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "\n
\n
Dichlorodiphenyltrichloroethane (DDT) is an environmental contaminant with a long lifetime and significant toxicity. Stable isotopes provide a tool to trace DDT through the environment. We present an Orbitrap Isotope Ratio Mass Spectrometry (Orbitrap-IRMS) method to measure the isotopic content of two DDT fragment ions: m/z = 235 [M+– CCl3] and m/z = 316 [M+– HCl]. With 3 nmol sample sizes and commercial 4,4’-DDT standards, we observe: for the [M+– CCl3] fragment, δ13C (0.13 ‰); δ37Cl (0.07 ‰); δ13C37Cl (0.19 ‰); δ37Cl37Cl (0.19 ‰); δ13C37Cl37Cl (0.39 ‰); and for the [M+– HCl] fragment, δ37Cl (0.22 ‰); δ37Cl37Cl (0.26 ‰); δ37Cl37Cl37Cl (0.52 ‰). We applied our method to 4,4’-DDT extracted from sediment near the White Point (WP) sewage outflow on the Palos Verdes Shelf, a site with substantial DDT contamination. Resulting precisions were worse for natural samples than standard by a factor of ≈4–5 due to their lower concentrations. Our results for [M+– CCl3] show enrichment vs our standard in δ13C (1.87 ± 0.49 ‰) and δ37Cl (1.23 ± 0.29 ‰) while δ13C37Cl and δ37Cl37Cl follow the stochastic distribution. The multiply substituted results add confidence and are useful for fingerprinting. For [M+– HCl] we see no enrichment in δ37Cl (0.31 ± 1.0 ‰) or δ37Cl37Cl (0.01 ± 1.25 ‰) and possible enrichment in δ37Cl37Cl37Cl (7.81 ± 2.11 ‰). These results are within 2σ of our stochastic error bars and are not evidence of clumped isotope enrichment but should be targeted in future study. Finally, our results place an upper bound on the amount of DDT degradation of 66 %.
\n
\n
\n
The isotopic composition of glucose carries the signature of the environmental and metabolic processes that act on it, but most conventional isotope analytical methods cannot resolve its intramolecular isotopic structure. Here, we present a new method for position-specific isotope analysis (PSIA) of carbon in glucose using electrospray ionization-Orbitrap (ESI-Orbitrap) mass spectrometry. This method measures δ13C values at five unique intramolecular sites in glucose at natural isotope abundance and requires <50 μg of glucose per sample, over 3 orders of magnitude less than similar measurements by nuclear magnetic resonance (NMR). By oxidizing glucose to gluconate to improve both ionization yield and fragmentation behavior and measuring with ESI-Orbitrap, we resolve the isotopic composition of the molecular ion and four fragment ions with analytical precision of 0.5–0.8‰ (2 SE). Using a positionally labeled glucose standard, we demonstrate the accuracy of the measurement for both molecular average and position-specific carbon isotope composition. Our method reproduces intramolecular δ13C patterns previously demonstrated for natural sugars formed through C3 and C4 photosynthetic pathways while enabling substantially higher throughput and sensitivity. This is the first application of Orbitrap-PSIA to a carbohydrate, and it enables the tracing of sugar fluxes in environmental, biomedical, and ecological systems. Future developments could extend the method to include oxygen and hydrogen isotopes, further enhancing its value for investigating glucose dynamics across many natural settings.
\n
Microbial fermentation facilitates the initial breakdown of organic matter into small molecules and is thought to be the rate-limiting step of anoxic organic mineralization. However, fermentation is understudied in modern and ancient biogeochemistry due to a lack of environmental biomarkers. It has long been assumed that fermentation, like respiration, does not express significant carbon isotope fractionations, precluding isotopic signals as a means of studying it in nature. Here, we tested this idea by growing pure cultures of four fermenting bacteria on glucose and measuring the carbon isotope compositions of the organic acids and alcohols produced. We found that fermentation exhibits a strong carbon isotope fractionation, ranging from -6‰ to +16‰, depending on the fermentation product. With bioisotopic models that track site-specific isotope enrichments through metabolism, we constrained the enzymes responsible for these fractionations. Our models reproduced in vivo organic acid δ13C values in all four organisms. These findings demonstrate that acetate 13C-enrichment is likely a widespread signature of fermentation. They also challenge traditional notions of controls on the isotope composition of lipids. Finally, our study suggests that fermentation imposes a trophic carbon isotope fractionation as organic carbon is passed from fermenters to secondary degraders like sulfate reducers. Looking to the geologic past, this trophic fractionation could have imprinted isotopic signals on the three billion year record of sedimentary organic carbon, specifically the inverse δ13C pattern of Precambrian acyclic isoprenoid and n-alkane biomarkers. Pervasive evidence of fermentation in the rock record would suggest its underappreciated role in biogeochemical cycles throughout Earth history.
",
"doi": "10.1073/pnas.2511040122",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences",
"publication_date": "2025-10-10",
"series_number": "41",
"volume": "122",
"issue": "41",
"pages": "e2511040122"
},
{
"id": "authors:hmmtj-jbh33",
"collection": "authors",
"collection_id": "hmmtj-jbh33",
"cite_using_url": "https://authors.library.caltech.edu/records/hmmtj-jbh33",
"type": "article",
"title": "Mars Sample Return Sample Receiving Project Measurement Definition Team Final Report",
"author": [
{
"family_name": "Carrier",
"given_name": "Brandi L.",
"orcid": "0000-0001-9943-7138",
"clpid": "Carrier-Brandi-L"
},
{
"family_name": "Sefton-Nash",
"given_name": "Elliot"
},
{
"family_name": "Graham",
"given_name": "Heather V."
},
{
"family_name": "Herd",
"given_name": "Christopher D.K."
},
{
"family_name": "Bridges",
"given_name": "John C."
},
{
"family_name": "Debaille",
"given_name": "Vinciane"
},
{
"family_name": "Fox",
"given_name": "Allison C."
},
{
"family_name": "French",
"given_name": "Katherine L."
},
{
"family_name": "Haltigin",
"given_name": "Timothy"
},
{
"family_name": "Hausrath",
"given_name": "Elisabeth M."
},
{
"family_name": "Krzesi\u0144ska",
"given_name": "Agata M."
},
{
"family_name": "Paardekooper",
"given_name": "Daniel"
},
{
"family_name": "Rampe",
"given_name": "Elizabeth B.",
"orcid": "0000-0002-6999-0028"
},
{
"family_name": "Schwenzer",
"given_name": "Susanne P.",
"orcid": "0000-0002-9608-0759"
},
{
"family_name": "Viotti",
"given_name": "Michelle",
"clpid": "Viotti-Michelle"
},
{
"family_name": "Duprat",
"given_name": "Jean"
},
{
"family_name": "Ferrari",
"given_name": "Marco",
"orcid": "0000-0002-7447-6146"
},
{
"family_name": "Glamoclija",
"given_name": "Mihaela",
"orcid": "0000-0003-4327-6480"
},
{
"family_name": "Harringon",
"given_name": "Andrea D."
},
{
"family_name": "Hutzler",
"given_name": "Aurore"
},
{
"family_name": "Liu",
"given_name": "Yang",
"clpid": "Liu-Yang"
},
{
"family_name": "Magnabosco",
"given_name": "Cara"
},
{
"family_name": "Marlow",
"given_name": "Jeffrey J."
},
{
"family_name": "Maurel",
"given_name": "Clara"
},
{
"family_name": "McLaurin",
"given_name": "Hannah M."
},
{
"family_name": "Ogliore",
"given_name": "Ryan"
},
{
"family_name": "Pack",
"given_name": "Andreas"
},
{
"family_name": "Pillai",
"given_name": "Segaran"
},
{
"family_name": "Schr\u00f6der",
"given_name": "Christian",
"orcid": "0000-0002-7935-6039"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Siljestr\u00f6m",
"given_name": "Sandra",
"orcid": "0000-0002-4975-6074"
},
{
"family_name": "Steele",
"given_name": "Andrew"
},
{
"family_name": "Teece",
"given_name": "Bronwyn L.",
"clpid": "Teece-Bronwyn-L"
},
{
"family_name": "Tu",
"given_name": "Valerie M."
},
{
"family_name": "Wang",
"given_name": "Kun"
}
],
"abstract": "The joint ESA-NASA Mars Sample Return (MSR) Campaign is slated to be one of the most ambitious undertakings in the history of planetary exploration in that analyses in terrestrial laboratories of pristine, scientifically selected samples from the surface of Mars would provide unprecedented insight into the history, evolution, and potential for Mars to harbor life. The MSR Sample Receiving Project (SRP) Measurement Definition Team (MDT) was jointly chartered by NASA and ESA to propose a set of measurements that should be carried out on samples returned from Mars to meet the needs of science, safety, and curation to aid in facility and other project planning. The executive summary of the MDT report is presented here, while the full text of the report is available in the online supplement for this article.
",
"doi": "10.1177/15311074251382248",
"issn": "1531-1074",
"publisher": "SAGE Publications",
"publication": "Astrobiology",
"publication_date": "2025-10",
"pages": "15311074251382248"
},
{
"id": "authors:jzqk2-pe476",
"collection": "authors",
"collection_id": "jzqk2-pe476",
"cite_using_url": "https://authors.library.caltech.edu/records/jzqk2-pe476",
"type": "article",
"title": "Planning Considerations Related to Contamination Control for the Return and Analysis of Martian Samples",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Magnabosco",
"given_name": "Cara"
},
{
"family_name": "Barton",
"given_name": "Hazel A."
},
{
"family_name": "Burkhardt",
"given_name": "Christoph",
"orcid": "0000-0002-6952-5783"
},
{
"family_name": "Dworkin",
"given_name": "Jason P.",
"orcid": "0000-0002-3961-8997"
},
{
"family_name": "Freissinet",
"given_name": "Caroline"
},
{
"family_name": "French",
"given_name": "Katherine L."
},
{
"family_name": "Glavin",
"given_name": "Daniel P.",
"orcid": "0000-0001-7779-7765"
},
{
"family_name": "Leys",
"given_name": "Natalie"
},
{
"family_name": "Maixner",
"given_name": "Frank"
},
{
"family_name": "Olsson-Francis",
"given_name": "Karen"
},
{
"family_name": "Probst",
"given_name": "Alexander J."
},
{
"family_name": "Quitt\u00e9",
"given_name": "Ghylaine"
},
{
"family_name": "Rampe",
"given_name": "Elizabeth",
"orcid": "0000-0002-6999-0028"
},
{
"family_name": "Steele",
"given_name": "Andrew"
},
{
"family_name": "Carrier",
"given_name": "Brandi L.",
"orcid": "0000-0001-9943-7138",
"clpid": "Carrier-Brandi-L"
},
{
"family_name": "Hays",
"given_name": "Lindsay E."
},
{
"family_name": "Thiessen",
"given_name": "Fiona"
},
{
"family_name": "Paardekooper",
"given_name": "Daniel"
},
{
"family_name": "Hutzler",
"given_name": "Aurore",
"orcid": "0000-0002-6733-0448"
},
{
"family_name": "Harrington",
"given_name": "Andrea D.",
"orcid": "0000-0003-4875-3637"
},
{
"family_name": "Teece",
"given_name": "Bronwyn L.",
"clpid": "Teece-Bronwyn-L"
}
],
"abstract": "The joint National Aeronautics and Space Administration and European Space Agency Mars Sample Return (MSR) Campaign is a proposed multi-mission effort to bring selected geological samples from Mars to Earth for the purpose of scientific investigation. Significant parts of these investigations could be affected by Earth-sourced contamination that is either misinterpreted as having a martian origin or that masks a martian signal. The Mars 2020 Perseverance rover implemented strict contamination control requirements to limit contamination of the samples during sample collection. Contamination control and contamination knowledge requirements have not yet been established for the samples after they arrive on Earth. The MSR Sample Receiving Facility (SRF) Contamination Panel (SCP) was tasked with defining the terrestrial biological, organic, and inorganic contamination limits for martian samples during their residence inside the SRF. To reach our recommendations, the SCP studied (i) the previously proposed limits and rationale of the Organic Contamination Panel, (ii) cleanliness levels achieved for sampling hardware by the M2020 mission, (iii) recent improvements in analytical technology and detection limits, (iv) updated information regarding the organic content of martian samples (e.g., from the Sample Analysis at Mars instrument on the Curiosity rover and laboratory analyses of martian meteorites), and (v) information about the composition and geologic context of samples being collected by the Perseverance rover for return to Earth.",
"doi": "10.1177/15311074251382157",
"issn": "1531-1074",
"publisher": "SAGE Publications",
"publication": "Astrobiology",
"publication_date": "2025-10",
"series_number": "10",
"volume": "25",
"issue": "10",
"pages": "694-724"
},
{
"id": "authors:bk1qm-1b847",
"collection": "authors",
"collection_id": "bk1qm-1b847",
"cite_using_url": "https://authors.library.caltech.edu/records/bk1qm-1b847",
"type": "article",
"title": "Comparing Raman and NanoSIMS for heavy water labeling of single cells",
"author": [
{
"family_name": "Schaible",
"given_name": "George A.",
"orcid": "0000-0002-1031-4682"
},
{
"family_name": "Cliff",
"given_name": "John B.",
"orcid": "0000-0002-7395-5604"
},
{
"family_name": "Crandall",
"given_name": "Jennifer A.",
"orcid": "0000-0002-9051-8481"
},
{
"family_name": "Bougoure",
"given_name": "Jeremy J.",
"orcid": "0000-0002-4869-035X"
},
{
"family_name": "Mathuri",
"given_name": "Michael N.",
"orcid": "0000-0003-0652-7789",
"clpid": "Mathuri-Michael-N"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Atwood",
"given_name": "Joseph"
},
{
"family_name": "Hatzenpichler",
"given_name": "Roland",
"orcid": "0000-0002-5489-3444"
}
],
"editor": [
{
"family_name": "Rotaru",
"given_name": "Amelia-Elena"
}
],
"abstract": "Stable isotope probing (SIP) experiments in conjunction with Raman microspectroscopy (Raman) or nano-scale secondary ion mass spectrometry (NanoSIMS) are frequently used to explore single cell metabolic activity in pure cultures as well as complex microbiomes. Despite the increasing popularity of these techniques, the comparability of isotope incorporation measurements using both Raman and NanoSIMS directly on the same cell remains largely unexplored. This knowledge gap creates uncertainty about the consistency of single-cell SIP data obtained independently from each method. Here, we conducted a comparative analysis of 543 Escherichia coli cells grown in M9 minimal medium in the absence or presence of heavy water (2H2O) using correlative Raman and NanoSIMS measurements to quantify the results between the two approaches. We demonstrate that Raman and NanoSIMS yield highly comparable measurements of 2H incorporation, with varying degrees of similarity based on the mass ratios analyzed using NanoSIMS. The 12C2H/12C1H and 12C22H/12C21H mass ratios provide targeted measurements of C-H bonds but may suffer from biases and background interference, while the 2H/1H ratio captures all hydrogen with lower detection limits, making it suitable for applications requiring comprehensive 2H quantification. Importantly, despite its higher mass resolution requirements, the use of C22H/C21H may be a viable alternative to the use of C2H/C1H due to lower background and higher overall count rates. Furthermore, using an empirical approach in determining Raman wavenumber ranges via the second derivative improved the data equivalency of 2H quantification between Raman and NanoSIMS, highlighting its potential for enhancing cross-technique comparability. These findings provide a robust framework for leveraging both techniques, enabling informed experimental design and data interpretation. By enhancing cross-technique comparability, this work advances SIP methodologies for investigating microbial metabolism and interactions in diverse systems.
",
"doi": "10.1128/spectrum.01659-24",
"pmcid": "PMC12211084",
"issn": "2165-0497",
"publisher": "American Society for Microbiology",
"publication": "Microbiology Spectrum",
"publication_date": "2025-07",
"series_number": "7",
"volume": "13",
"issue": "7",
"pages": "e01659-24"
},
{
"id": "authors:7wd5r-pxy66",
"collection": "authors",
"collection_id": "7wd5r-pxy66",
"cite_using_url": "https://authors.library.caltech.edu/records/7wd5r-pxy66",
"type": "article",
"title": "Dry season dominance of salinity's impact on hydrogen isotope fractionation in Aegiceras corniculatum mangrove lipids",
"author": [
{
"family_name": "Wang",
"given_name": "Yao-Ping",
"orcid": "0000-0003-0994-6030"
},
{
"family_name": "Song",
"given_name": "Zhiguang",
"orcid": "0000-0002-8914-6000"
},
{
"family_name": "Xia",
"given_name": "Jia",
"orcid": "0000-0002-4071-8573"
},
{
"family_name": "Zhan",
"given_name": "Zhao-Wen",
"orcid": "0000-0001-7336-4962"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Silverman",
"given_name": "Shaelyn N.",
"orcid": "0000-0001-9201-6904",
"clpid": "Silverman-Shaelyn-N"
},
{
"family_name": "Gao",
"given_name": "Yuan",
"orcid": "0000-0002-1487-3844"
},
{
"family_name": "Li",
"given_name": "Guopeng"
},
{
"family_name": "He",
"given_name": "Ding",
"orcid": "0000-0001-9620-6115"
}
],
"abstract": "\n
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The hydrogen isotope ratios (δ2H) of mangrove leaf waxes are influenced by both precipitation and water salinity, making them promising proxies for paleohydrologic and paleosalinity reconstructions. However, the mechanism by which salinity affects 2H/1H fractionation remain unclear. While previous studies have shown that fractionation between source and leaf water pools is not the primary driver, it is still uncertain how biosynthetic isotope fractionation contributes to this process and how these effects vary across different seasons. To our knowledge, no studies have directly compared the seasonal variations in isotope fractionation between the dry and wet seasons, which are characteristic of tropical and subtropical regions. To address these questions, we measured δ2H values of n-alkanes and n-fatty acids in the leaves of Aegiceras corniculatum collected from the Zhanjiang estuary during both the dry and wet seasons. We compared these data with δ2H and δ18O values from leaf water, xylem water, estuary surface water, and sediment pore water to discern potential differences in isotopic fractionation mechanisms. Our findings indicate that net 2H/1H fractionation increases with salinity for both C31 n-alkanes (2.5 ± 0.9 ‰ ppt−1) and C16:0 n-fatty acids (1.0 ± 0.2 ‰ ppt−1) during the dry season, whereas no similar such trends were observed in the wet season. These seasonal variations highlight the dominant impact of salinity on hydrogen isotope fractionation in A. corniculatum lipids during the dry season. We also found that salinity-driven fractionation is not solely related to water uptake but rather to physiological responses to high salinity. This finding aligns with previous studies, which indicate that salinity-induced effects on hydrogen isotopic fractionation are primarily driven by physiological adaptations, rather than by salinity-dependent fractionation mechanisms in leaf and xylem water. Building upon this understanding, we propose novel hypotheses: heightened salinity in the dry season reduces photosynthetic efficiency in A. corniculatum due to limited CO2 availability, which in turn triggers increased production of compatible solutes. This may reduce cellular water availability and limit isotopic exchange. Additionally, elevated salinity could intensify carbon metabolism, affecting the residence time of intermediates in the TCA cycle and influencing isotopic water exchange. While we propose these as potential mechanisms, further studies are needed to confirm its role in biosynthetic fractionation and its relationship with water isotopes in mangrove plants. In contrast, during the wet season, increased rainfall dilutes salinity, normalizing photosynthetic and metabolic activity in the mangrove. These findings provide new insights into the mechanisms of isotopic fractionation in mangrove lipids and the role of seasonality in fractionation patterns, which are important for improving paleohydrologic and paleosalinity reconstructions.
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The stable hydrogen isotope compositions of long-chain unsaturated C37 alkenones (δ2HC37) in sediments were measured to estimate palaeohydrological changes over the last 260 kyrs in the northern South China Sea (SCS). Values of δ2HC37 ranged from −212‰ to −166‰, with a value of −212‰ in the surface sediment. The residual δ2H value was estimated by subtracting the global ice volume effect from the hydrogen isotope composition of seawater (δ2Hsw), which was calculated with empirical relationships based on the δ2HC37. δ2Hresidual showed clear glacial-interglacial cycles with lower values during glacials than interglacials, a pattern that is not apparent in the analogous δ18Oresidual record from the same core. The latter was estimated from δ18O of the planktonic foraminifer Globigerinoides ruber by correcting for temperature and ice volume effects. We argue that δ2Hresidual may be better than δ18Oresidual as a record of surface seawater isotope changes in the SCS. The lower δ2Hresidual values during the glacials in the northern SCS were likely due to the La Niña-like conditions in the Western Tropical Pacific and the SCS, which resulted in increased precipitation and suppressed Kuroshio intrusion. Conversely, the higher δ2Hresidual values during the interglacials were likely due to El Niño-like conditions. Alternatively, the “extra” isotopic depletion of precipitation resulting from the reorganization of the regional atmospheric circulation under glacial conditions could also contribute to the lower δ2Hresidual values during the glacials.
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Stable isotope ratios of C1–C5 alkanes, the major constituents of subsurface gaseous hydrocarbons, can provide valuable insights on their origins, transport, and fates. Equilibrium isotope effects are fundamental to interpreting stable isotope signatures, as recognition of them in natural materials indicates reversible processes and constrains the temperatures of equilibrated systems. Hydrogen isotope equilibrium of C1–C5 alkanes is of particular interest because evidence shows that alkyl H can undergo isotopic exchange with coexisting compounds under subsurface conditions. We present the results of a combined experimental and theoretical effort to determine equilibrium hydrogen isotope distributions in mixtures of these hydrocarbon compounds. We created two mixtures: one with C1, C2 and C3 (where C1 indicates methane, C2 ethane, etc., hereinafter called ‘C1–C3 mixture’) and another one with C2, C3, iC4, nC4, iC5 and nC5 (hereinafter called ‘C2–C5 mixture’); in both cases, the mixtures were created to start out of hydrogen isotope equilibrium. We tested the performance of several metal catalysts as aids to H isotopic exchange by exposing these mixtures to different metal catalysts at 100 or 200 °C and analyzing the compound-specific hydrogen isotope ratios of the product gases. The C1–C3 mixture exchanged hydrogen isotopes among the starting gas components rapidly in the presence of Ru/Al2O3 at 200 °C. The isotope ratios reach a steady-state (presumably equilibrium) after 72 h of heating (up to 120 h). The hydrogen isotopic ratios of alkanes in the C2–C5 mixture shifted significantly in the presence of Rh/Al2O3 at 100 °C and C3-C5 compounds approached steady state after 70 h, whereas C2 had not yet reached a steady state D/H ratio after 216 h of heating. We evaluated the reaction progress of isotope exchange for each compound as a function of time with a reaction-network model informed by constraints on chemical kinetics. The model indicates that C3, iC4, nC4, iC5 and nC5 in the C2-C5 mixture reached internal isotope equilibrium after 70 h, hence we used their values to calculate experimental equilibrium results. We also calculated equilibrium isotope fractionations with the Bigeleisen-Mayer theorem using vibrational frequencies computed from the density functional theory (B3LYP/aug-cc-pVTZ). We included torsional conformers and explicit H positions in the calculations. We found that the experimental results from both the 200 \u02daC C1–C3 experiment and 100 \u02daC C2–C5 experiment are consistent with theoretical equilibrium results within experimental uncertainty. Additionally, our reaction-network model for catalyzed hydrogen isotope exchange between alkanes succeeded in fitting our experimental results. This modeling framework can be adjusted to simulate exchange in natural settings for constraining temperature histories and sources of natural gases.
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Amino acids are present in all known life, so identifying the environmental conditions under which they can be synthesized constrains where life on Earth might have formed and where life might be found on other planetary bodies. All known abiotic amino acid syntheses require ammonia, which is only produced in reducing and neutral atmospheres. Here, we demonstrate that the Fe-bearing hydroxide mineral ferroan brucite [Fe_(0.33),Mg_(0.67)(OH)\u2082] can mediate the reaction of nitrate and glyoxylate to form glycine, the simplest amino acid used in life. Up to 97% of this glycine was detected only after acid digestion of the mineral, demonstrating that it had been strongly partitioned to the mineral. The dicarboxylic amino acid 3-hydroxy aspartate was also detected, which suggests that reactants underwent a mechanism that simultaneously produced mono- and dicarboxylic amino acids. Nitrate can be produced in both neutral and oxidizing atmospheres, so reductive amination of nitrate and glyoxylate on a ferroan brucite surface expands origins of life scenarios. First, it expands the environmental conditions in which life's precursors could form to include oxidizing atmospheres. Second, it demonstrates the ability of ferroan brucite, an abundant, secondary mineral in serpentinizing systems where olivine is partly hydrated, to mediate reductive amination. Finally, the results demonstrate the need to consider mineral-bound products when analyzing samples for abiotic amino acid synthesis.
",
"doi": "10.1073/pnas.2408248121",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences",
"publication_date": "2024-10-28",
"series_number": "45",
"volume": "121",
"issue": "45",
"pages": "e2408248121"
},
{
"id": "authors:5y60a-wmb13",
"collection": "authors",
"collection_id": "5y60a-wmb13",
"cite_using_url": "https://authors.library.caltech.edu/records/5y60a-wmb13",
"type": "article",
"title": "Isotopic evidence of acetate turnover in Precambrian continental fracture fluids",
"author": [
{
"family_name": "Mueller",
"given_name": "Elliott P.",
"orcid": "0000-0002-6837-0409",
"clpid": "Mueller-Elliott-P"
},
{
"family_name": "Panehal",
"given_name": "Juliann",
"clpid": "Panehal-Juliann"
},
{
"family_name": "Meshoulam",
"given_name": "Alexander",
"orcid": "0009-0006-0566-0157",
"clpid": "Meshoulam-Alexander"
},
{
"family_name": "Song",
"given_name": "Min",
"orcid": "0000-0002-3291-0282"
},
{
"family_name": "Hansen",
"given_name": "Christian T."
},
{
"family_name": "Warr",
"given_name": "Oliver",
"orcid": "0000-0001-8240-7979"
},
{
"family_name": "Boettger",
"given_name": "Jason",
"orcid": "0000-0002-2853-8772"
},
{
"family_name": "Heuer",
"given_name": "Verena B.",
"orcid": "0000-0002-1856-116X"
},
{
"family_name": "Bach",
"given_name": "Wolfgang",
"orcid": "0000-0002-3099-7142"
},
{
"family_name": "Hinrichs",
"given_name": "Kai-Uwe",
"orcid": "0000-0002-0739-9291"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
},
{
"family_name": "Orphan",
"given_name": "Victoria",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Lollar",
"given_name": "Barbara Sherwood"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "The deep continental crust represents a vast potential habitat for microbial life where its activity remains poorly constrained. Organic acids like acetate are common in these ecosystems, but their role in the subsurface carbon cycle - including the mechanism and rate of their turnover - is still unclear. Here, we develop an isotope-exchange 'clock' based on the abiotic equilibration of H-isotopes between acetate and water, which can be used to define the maximum in situ acetate residence time. We apply this technique to the fracture fluids in Birchtree and Kidd Creek mines within the Canadian Precambrian crust. At both sites, we find that acetate residence times are <1 million years and calculated a rate of turnover that could theoretically support microbial life. However, radiolytic water-rock reactions could also contribute to acetate production and degradation, a process that would have global relevance for the deep biosphere. More broadly, our study demonstrates the utility of isotope-exchange clocks in determining residence times of biomolecules with possible applications to other environments.
",
"doi": "10.1038/s41467-024-53438-4",
"issn": "2041-1723",
"publisher": "Nature Publishing Group",
"publication": "Nature Communications",
"publication_date": "2024-10-23",
"series_number": "1",
"volume": "15",
"issue": "1",
"pages": "9130"
},
{
"id": "authors:1e9z3-ykp92",
"collection": "authors",
"collection_id": "1e9z3-ykp92",
"cite_using_url": "https://authors.library.caltech.edu/records/1e9z3-ykp92",
"type": "article",
"title": "Biosynthetic and catabolic pathways control amino acid \u03b4\u00b2H values in aerobic heterotrophs",
"author": [
{
"family_name": "Silverman",
"given_name": "Shaelyn N.",
"orcid": "0000-0001-9201-6904",
"clpid": "Silverman-Shaelyn-N"
},
{
"family_name": "Wijker",
"given_name": "Reto S.",
"orcid": "0000-0001-5104-9849",
"clpid": "Wijker-Reto-S"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "\n
The hydrogen isotope ratios (δ2HAA values) of amino acids in all organisms are substantially fractionated relative to growth water. In addition, they exhibit large variations within microbial biomass, animals, and human tissues, hinting at rich biochemical information encoded in such signals. In lipids, such δ2H variations are thought to primarily reflect NADPH metabolism. Analogous biochemical controls for amino acids remain largely unknown, but must be elucidated to inform the interpretation of these measurements. Here, we measured the δ2H values of amino acids from five aerobic, heterotrophic microbes grown on different carbon substrates, as well as five Escherichia coli mutant organisms with perturbed NADPH metabolisms. We observed similar δ2HAA patterns across all organisms and growth conditions, which–consistent with previous hypotheses–suggests a first-order control by biosynthetic pathways. Moreover, δ2HAA values varied systematically with the catabolic pathways activated for substrate degradation, with variations explainable by the isotopic compositions of important cellular metabolites, including pyruvate and NADPH, during growth on each substrate. As such, amino acid δ2H values may be useful for interrogating organismal physiology and metabolism in the environment, provided we can further elucidate the mechanisms underpinning these signals.
\n
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\n
\n
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\n
Sedimentary rocks from the early Eocene Green River Formation comprise the largest known lacustrine oil shale deposits, contain remarkably well-preserved fossils, and provide a unique record of climate evolution across the Early Eocene Climate Optimum, a period of high atmospheric CO2. The depositional environment of these intermountain lakes spanned from relatively fresh and fluvially influenced to expanded and stratified saline closed basin lakes under the influence of the Laramide orogeny and alternating humid and arid climatic conditions. As the surface area of the lakes expanded, alkalinity and salinity increased, with depositional cycles that linked to evaporative cycles and marked by an increasing abundance of organic matter-rich shales (TOC > 10 wt%). Simultaneously, an intriguing 20 ‰ positive shift in the sulfur isotope composition of sulfide minerals and organic sulfur is observed. Given that this trend cannot be simply explained by a change in the source of sulfate delivered to the basin, the evolution of biogeochemical sulfur cycling and the balance of fluxes in response to basin evolution remain unresolved. Here, we combine the sulfur isotope compositions of pyrite, organic sulfur, and carbonate-associated sulfate and molecular proxies of euxinia in samples from the Uinta basin's depocenter. We find that organic matter-rich sediments reflect deposition in a stratified water column with enhanced burial of pyrite and sulfurized organic matter, while organic-lean facies present evidence of, at least transiently, euxinic conditions reaching the photic zone during arid conditions presumably because of evaporation. As the lake became both saline-stratified and euxinic, we observe that δ34S values of all measured sulfur-bearing sedimentary proxies increase and evolve along a 1:1 line, a trend independent of facies that we interpret as reflecting a sulfate-limited system despite saline conditions. The isotopic mass balance of sulfur fluxes implies the existence of a sink of sulfur depleted in 34S that is spatially decoupled from burial in the depocenter. Modeling sulfur biogeochemical processes in a saline stratified lake system allows us to estimate that at least 50 % of the sulfur entering the lake could have been lost from the upper part of the euxinic water column where the fractionation factor imparted by microbial sulfate reduction is expressed. We propose that the overall isotopic enrichment of the system was caused by H2S degassing during arid climate intervals, presumably enhanced by transient water column mixing events. Further, episodic intrusion of euxinic bottom waters into the upper part of the water column might have triggered mass fish and plankton mortality, consequently facilitating the formation of these exceptionally fossiliferous and organic matter-rich rocks. Our study finds that volatile outgassing may be an underappreciated mechanism for the sulfur mass balance of stratified lacustrine systems.
\n
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\n
The abundances of different isotopic forms of a compound, or isotopologues, will vary based on its physical and chemical history. The number of isotopologues increases combinatorically with the size of a molecule, and even small molecules such as amino acids have thousands of potentially observable isotopic variants. However, due to the analytical challenges of separating and observing isotopologues, only a few dimensions of isotopic diversity are routinely measured. Overcoming these challenges requires both an experimental method to observe many isotopic properties and a theoretical framework for interpreting these experiments. In Part 1, we presented such a theoretical framework; here, we demonstrate an experimental method, which we apply to methionine. Our approach uses a Q Exactive HF Orbitrap to perform several “M + N experiments”, where a sample is ionized, a subset of its isotopologues with cardinal mass N daltons greater than the unsubstituted isotopologue is selected and fragmented, and the proportions of all detectable isotopic forms of those fragment ions are quantified. We perform M + 1, M + 2, M + 3, and M + 4 experiments of a methionine sample and standard where the sample has a 100 ‰ enrichment of 13C at the methyl carbon relative to the natural 13C abundance at that position in the standard, and is otherwise identical to the standard. We observe isotopic forms of 8 fragment ion species for each version of the M + N experiment. With the assistance of a forward model of expected mass spectra, we identify isotopic peaks for each fragment ion based on observed mass and abundance, screen these for data quality, and quantify abundances for 146 unique isotopic peaks at precisions of ≈ 0.3–3 ‰. We present our direct observations and use them to reconstruct the concentrations of 19 individual singly, doubly, and triply-substituted isotopologues; doing so gives fewer constraints and broader error bars than working with the direct observations, but may be more interpretable for some applications. We also examine possibilities for measuring additional peaks, which are primarily limited by the detection limit of the Orbitrap-IRMS method. We then suggest some possible uses of our direct measurements for chemical forensics and hypothesis testing. Our results demonstrate the diversity of isotopic constraints currently observable and interpretable for organic molecules.
\n
\n
\n
The ability to detect intramolecular isotopic differences within a single molecule can answer questions about molecule synthesis and alteration across numerous scientific fields. Until recently, intramolecular (i.e., position-specific isotope analysis, PSIA) isotope measurements were laborious, requiring large amounts of analyte or specialized instrumentation. Orbitrap\u2122 mass spectrometers are capable of fragmenting molecules and have the high mass resolution needed to constrain position-specific isotopic differences among the resulting fragment ions. Orbitrap mass spectrometers with electrospray ionization accurately measured the molecular average isotope composition of acetate, nitrate, sulfate, phosphate, and the amino acid methionine, as well as the position-specific isotopic structure of methionine. Here, we document the ability of this method to measure the position-specific carbon isotope structure of the amino acid alanine. Data include measurements of \u00b9\u00b3C-enriched materials to assign specific atoms in fragments to the original molecular structure and detect any recombination of atoms in resultant fragments. We further demonstrate high-precision intramolecular isotope analyses for standards with independently determined position-specific carbon isotope compositions. Isotope data from ESI-Orbitrap-MS agrees with values obtained using gas source isotope ratio mass spectrometry, giving further confidence to this novel approach to PSIA. The carbon isotope analyses by Orbitrap-MS were rapid and required \u223c5 \u03bcg of analyte to obtain both molecular average and position-specific values in triplicate with precision \u22641\u2030.
",
"doi": "10.1016/j.ijms.2023.117128",
"issn": "1387-3806",
"publisher": "Elsevier",
"publication": "International Journal of Mass Spectrometry",
"publication_date": "2023-11",
"volume": "493",
"pages": "117128"
},
{
"id": "authors:ek4s2-8hp23",
"collection": "authors",
"collection_id": "ek4s2-8hp23",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230615-181931196",
"type": "article",
"title": "Position-specific carbon isotopes of Murchison amino acids elucidate extraterrestrial abiotic organic synthesis networks",
"author": [
{
"family_name": "Zeichner",
"given_name": "Sarah S.",
"orcid": "0000-0001-8897-7657",
"clpid": "Zeichner-Sarah-S"
},
{
"family_name": "Chimiak",
"given_name": "Laura",
"orcid": "0000-0002-5047-5421",
"clpid": "Chimiak-Laura"
},
{
"family_name": "Elsila",
"given_name": "Jamie E.",
"orcid": "0000-0002-0008-2590",
"clpid": "Elsila-Jamie-E"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Dworkin",
"given_name": "Jason P.",
"orcid": "0000-0002-3961-8997",
"clpid": "Dworkin-Jason-P"
},
{
"family_name": "Aponte",
"given_name": "Jos\u00e9 C.",
"orcid": "0000-0002-0131-1981",
"clpid": "Aponte-Jos\u00e9-C"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
}
],
"abstract": "The Murchison meteorite is a well-studied carbonaceous chondrite with relatively high concentrations of amino acids thought to be endogenous to the meteorite, in part because they are characterized by carbon isotope (δ13C) values higher than those typical of terrestrial amino acids. Past studies have proposed that extraterrestrial amino acids in the Murchison meteorite could have formed by Strecker synthesis (for α-amino acids), Michael addition (for β-amino acids), or reductive amination, but a lack of constraints have prevented confident discrimination among these possibilities, or assignment of specific formation pathways to each of several specific amino acids. Position-specific carbon isotope analysis differentiates amongst these mechanisms by relating molecular sites to isotopically distinct carbon sources and by constraining isotope effects associated with elementary chemical reactions. Prior measurements of the position-specific carbon isotopic composition of α-alanine from the Murchison CM chondrite demonstrated that alanine’s high δ13CVPDB value is attributable to the amine carbon (δ13CVPDB = +142 ± 20‰), consistent with Strecker synthesis drawing on 13C-rich carbonyl groups in precursors (Chimiak et al., 2021). Here, we measured the δ13C composition of fragment ions generated by electron impact ionization of derivatized \u237a-alanine, β-alanine, and aspartic acid from Murchison via gas chromatography-Fourier transform mass spectrometry. α-Alanine’s amine carbon yielded δ13CVPDB = +109 ± 21‰, which is consistent with the previously measured value and with formation from 13C-rich precursors. β-Alanine’s amine carbon presents a lower δ13CVPDB = +33 ± 24‰, which supports formation from 13C-rich precursors but potentially via a Michael addition mechanism rather than Strecker synthesis. Aspartic acid’s amine carbon has δ13CVPDB = −14 ± 5‰, suggesting synthesis from precursors distinct from those that generated the alanine isomers. These measurements indicate that Murchison amino acids are a mixture of compounds made from different synthesis mechanisms, though some subsets likely drew on the same substrates; this conclusion highlights the complexity of extraterrestrial organic synthesis networks and the potential of emerging methods of isotope ratio analysis to elucidate the details of those networks.
",
"doi": "10.1016/j.gca.2023.06.010",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2023-08-15",
"volume": "355",
"pages": "210-221"
},
{
"id": "authors:1fr4h-f9m65",
"collection": "authors",
"collection_id": "1fr4h-f9m65",
"cite_using_url": "https://authors.library.caltech.edu/records/1fr4h-f9m65",
"type": "article",
"title": "Oceanic nutrient rise and the late Miocene inception of Pacific oxygen-deficient zones",
"author": [
{
"family_name": "Wang",
"given_name": "Xingchen Tony",
"orcid": "0000-0001-5316-789X"
},
{
"family_name": "Wang",
"given_name": "Yuwei"
},
{
"family_name": "Auderset",
"given_name": "Alexandra",
"orcid": "0000-0002-6316-4980"
},
{
"family_name": "Sigman",
"given_name": "Daniel M.",
"orcid": "0000-0002-7923-1973"
},
{
"family_name": "Ren",
"given_name": "Haojia",
"orcid": "0000-0002-1769-4243"
},
{
"family_name": "Mart\u00ednez-Garc\u00eda",
"given_name": "Alfredo",
"orcid": "0000-0002-7206-5079"
},
{
"family_name": "Haug",
"given_name": "Gerald H.",
"orcid": "0000-0001-7534-4420"
},
{
"family_name": "Su",
"given_name": "Zhan"
},
{
"family_name": "Zhang",
"given_name": "Yi Ge",
"orcid": "0000-0001-7331-1246"
},
{
"family_name": "Rasmussen",
"given_name": "Birger",
"orcid": "0000-0002-2745-0904"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Fischer",
"given_name": "Woodward",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
}
],
"abstract": "The modern Pacific Ocean hosts the largest oxygen-deficient zones (ODZs), where oxygen concentrations are so low that nitrate is used to respire organic matter. The history of the ODZs may offer key insights into ocean deoxygenation under future global warming. In a 12-My record from the southeastern Pacific, we observe a >10\u2030 increase in foraminifera-bound nitrogen isotopes (\u00b9\u2075N/\u00b9\u2074N) since the late Miocene (8 to 9 Mya), indicating large ODZs expansion. Coinciding with this change, we find a major increase in the nutrient content of the ocean, reconstructed from phosphorus and iron measurements of hydrothermal sediments at the same site. Whereas global warming studies cast seawater oxygen concentrations as mainly dependent on climate and ocean circulation, our findings indicate that modern ODZs are underpinned by historically high concentrations of seawater phosphate.
",
"doi": "10.1073/pnas.2204986119",
"pmcid": "PMC9659387",
"issn": "0027-8424",
"publisher": "Proceedings of the National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences",
"publication_date": "2022-11-08",
"series_number": "45",
"volume": "119",
"issue": "45",
"pages": "e2204986119"
},
{
"id": "authors:z8ang-3hv34",
"collection": "authors",
"collection_id": "z8ang-3hv34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221010-454096500.14",
"type": "article",
"title": "Quantifying Isotopologue Reaction Networks (QIRN): A modelling tool for predicting stable isotope fractionations in complex networks",
"author": [
{
"family_name": "Mueller",
"given_name": "Elliott P.",
"orcid": "0000-0002-6837-0409",
"clpid": "Mueller-Elliott-P"
},
{
"family_name": "Wu",
"given_name": "Fenfang",
"orcid": "0000-0003-1134-280X",
"clpid": "Wu-Fenfang"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Natural-abundance stable isotope compositions are powerful tools for understanding complex processes across myriad scientific disciplines. However, quantitative interpretation of these signals often requires equally complex models. Previous stable isotope models have treated isotopic compositions as intrinsic properties of molecules or atoms (e.g. \u03b4\u00b9\u00b3C, \u00b9\u00b3R, etc.). This has proven to be a computationally efficient but inflexible approach. Here, we present a new isotope modelling software tool that combines computational strategies used in metabolic modeling with an understanding of natural isotope fractionations from the geosciences, called Quantifying Isotopologue Reaction Networks (QIRN, \"churn\"). QIRN treats isotopic properties as distributions of discrete isotopologues, i.e. molecules with different numbers and distributions of isotopic substitutions. This approach is remarkably generalizable and computationally tractable, enabling models of reaction networks with unprecedented complexity. QIRN parameterizes reactions as rate law equations with distinct isotopologues as the reactants and products. Isotope effects are implemented as small changes to the relevant isotopologues' rate constants. Running this model forward in time gives the numerical solution for steady state isotopologue abundances. Different subsets of the isotopologue population can then be sampled to quantify numerous isotopic proprieties simultaneously (i.e. compound-specific, site-specific, and multiply-substituted isotope compositions). Furthermore, QIRN can model any physical, chemical or biological process as reversible or irreversible. As such, it incorporates both kinetic and equilibrium isotope effects. It can be readily applied to any isotope system (i.e. C, N, O, etc.), though at present can only track two isotopes of one element at a time. Given its generalizability, QIRN has a diverse range of applications. To demonstrate the flexibility and efficiency of QIRN, we reconstructed previous (intrinsic-property) models of sulfate reduction, abiotic amino acid synthesis, lipid biosynthesis, and photosynthesis. In these examples, QIRN consistently reproduced outputs from prior models and predicted isotopic anomalies that have been measured in nature. With its new approach to isotope modelling, QIRN will expand the potential complexity of modelled reaction networks, help predict isotopic signals that can direct experimental efforts, and provide a more efficient means of modeling emerging isotopic properties such as 'clumped isotopes'.",
"doi": "10.1016/j.chemgeo.2022.121098",
"issn": "0009-2541",
"publisher": "Elsevier",
"publication": "Chemical Geology",
"publication_date": "2022-11-05",
"volume": "610",
"pages": "Art. No. 121098"
},
{
"id": "authors:q058g-0ww96",
"collection": "authors",
"collection_id": "q058g-0ww96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221029-514734200.2",
"type": "article",
"title": "Novel sulfur isotope analyses constrain sulfurized porewater fluxes as a minor component of marine dissolved organic matter",
"author": [
{
"family_name": "Phillips",
"given_name": "Alexandra A.",
"orcid": "0000-0001-5959-5238",
"clpid": "Phillips-Alexandra-A"
},
{
"family_name": "White",
"given_name": "Margot E.",
"orcid": "0000-0002-0095-7641",
"clpid": "White-Margot-E"
},
{
"family_name": "Seidel",
"given_name": "Michael",
"orcid": "0000-0003-0934-1939",
"clpid": "Seidel-Michael"
},
{
"family_name": "Wu",
"given_name": "Fenfang",
"orcid": "0000-0003-1134-280X",
"clpid": "Wu-Fenfang"
},
{
"family_name": "Pavia",
"given_name": "Frank F.",
"orcid": "0000-0003-3627-0179",
"clpid": "Pavia-Frank-J"
},
{
"family_name": "Kemeny",
"given_name": "Preston C.",
"orcid": "0000-0003-1693-4142",
"clpid": "Kemeny-Preston-C"
},
{
"family_name": "Ma",
"given_name": "Audrey C.",
"clpid": "Ma-Audrey-C"
},
{
"family_name": "Aluwihare",
"given_name": "Lihini I.",
"orcid": "0000-0001-5031-9464",
"clpid": "Aluwihare-Lihini-I"
},
{
"family_name": "Dittmar",
"given_name": "Thorsten",
"orcid": "0000-0002-3462-0107",
"clpid": "Dittmar-Thorsten"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Marine dissolved organic matter (DOM) is a major reservoir that links global carbon, nitrogen, and phosphorus. DOM is also important for marine sulfur biogeochemistry as the largest water column reservoir of organic sulfur. Dissolved organic sulfur (DOS) can originate from phytoplankton-derived biomolecules in the surface ocean or from abiotically “sulfurized” organic matter diffusing from sulfidic sediments. These sources differ in 34S/32S isotope ratios (δ34S values), with phytoplankton-produced DOS tracking marine sulfate (21‰) and sulfurized DOS mirroring sedimentary porewater sulfide (∼0 to –10‰). We measured the δ34S values of solid-phase extracted (SPE) DOM from marine water columns and porewater from sulfidic sediments. Marine DOMSPE δ34S values ranged from 14.9‰ to 19.9‰ and C:S ratios from 153 to 303, with lower δ34S values corresponding to higher C:S ratios. Marine DOMSPE samples showed consistent trends with depth: δ34S values decreased, C:S ratios increased, and δ13C values were constant. Porewater DOMSPE was 34S-depleted (∼-0.6‰) and sulfur-rich (C:S ∼37) compared with water column samples. We interpret these trends as reflecting at most 20% (and on average ∼8%) contribution of abiotic sulfurized sources to marine DOSSPE and conclude that sulfurized porewater is not a main component of oceanic DOS and DOM. We hypothesize that heterogeneity in δ34S values and C:S ratios reflects the combination of sulfurized porewater inputs and preferential microbial scavenging of sulfur relative to carbon without isotope fractionation. Our findings strengthen links between oceanic sulfur and carbon cycling, supporting a realization that organic sulfur, not just sulfate, is important to marine biogeochemistry.
\n\n",
"doi": "10.1073/pnas.2209152119",
"pmcid": "PMC9565371",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2022-10-06",
"series_number": "41",
"volume": "119",
"issue": "41",
"pages": "e2209152119"
},
{
"id": "authors:7nk81-60v34",
"collection": "authors",
"collection_id": "7nk81-60v34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220708-948968900",
"type": "article",
"title": "Position-specific carbon isotope analysis of serine by gas chromatography/Orbitrap mass spectrometry, and an application to plant metabolism",
"author": [
{
"family_name": "Wilkes",
"given_name": "Elise B.",
"orcid": "0000-0002-3379-7832",
"clpid": "Wilkes-Elise-B"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Zeichner",
"given_name": "Sarah S.",
"orcid": "0000-0001-8897-7657",
"clpid": "Zeichner-Sarah-S"
},
{
"family_name": "Dallas",
"given_name": "Brooke",
"orcid": "0000-0002-1313-3270",
"clpid": "Dallas-Brooke-H"
},
{
"family_name": "Schubert",
"given_name": "Brian",
"orcid": "0000-0001-9459-2059",
"clpid": "Schubert-Brian"
},
{
"family_name": "Jahren",
"given_name": "A. Hope",
"orcid": "0000-0003-3884-1676",
"clpid": "Jahren-Anne-Hope"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
}
],
"abstract": "Rationale: Position-specific \u00b9\u00b3C/\u00b9\u00b2C ratios within amino acids remain largely unexplored in environmental samples due to methodological limitations. We hypothesized that natural-abundance isotope patterns in serine may serve as a proxy for plant metabolic fluxes including photorespiration. Here we describe an Orbitrap method optimized for the position-specific carbon isotope analysis of serine to test our hypothesis and discuss the generalizability of this method to other amino acids. \n\nMethods: Position-specific carbon isotope ratios of serine were measured using a Thermo Scientific\u2122 Q Exactive\u2122 GC Orbitrap\u2122. Amino acids were hydrolyzed from Arabidopsis biomass, purified from potential matrix interferences, and derivatized alongside standards. Derivatized serine (N,O-bis(trifluoroacetyl)methyl ester) was isolated using gas chromatography, trapped in a reservoir, and purged into the electron ionization source over tens of minutes, producing fragment ions containing different combinations of atoms from the serine-derivative molecule. The \u00b9\u00b3C/\u00b9\u00b2C ratios of fragments with monoisotopic masses of 110.0217, 138.0166, and 165.0037\u2009Da were monitored in the mass analyzer and used to calculate position-specific \u03b4\u00b9\u00b3C values relative to a working standard. \n\nResults: This methodology constrains position-specific \u03b4\u00b9\u00b3C values for nanomole amounts of serine isolated from chemically complex mixtures. The \u03b4\u00b9\u00b3C values of fragment ions of serine were characterized with \u22641\u2030 precisions, leading to propagated standard errors of 0.7\u20135\u2030 for each carbon position. Position-specific \u03b4\u00b9\u00b3C values differed by up to ca 28\u2009\u00b1\u20095\u2030 between serine molecules hydrolyzed from plants grown under contrasting pCO\u2082, selected to promote different fluxes through photosynthesis and photorespiration. The method was validated using pure serine standards characterized offline. \n\nConclusions: This study presents the first Orbitrap-based measurements of natural-abundance, position-specific carbon isotope variation in an amino acid isolated from a biological matrix. We present a method for the precise characterization of isotope ratios in serine and propose applications probing metabolism in plants. We discuss the potential for extending these approaches to other amino acids, paving the way for novel applications.",
"doi": "10.1002/rcm.9347",
"issn": "0951-4198",
"publisher": "Wiley",
"publication": "Rapid Communications in Mass Spectrometry",
"publication_date": "2022-09-30",
"series_number": "18",
"volume": "36",
"issue": "18",
"pages": "Art. No. e9347"
},
{
"id": "authors:hgz8w-55503",
"collection": "authors",
"collection_id": "hgz8w-55503",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220728-730554000",
"type": "article",
"title": "Sulfur cycling at natural hydrocarbon and sulfur seeps in Santa Paula Creek, CA",
"author": [
{
"family_name": "Aronson",
"given_name": "Heidi S.",
"orcid": "0000-0002-6777-0304",
"clpid": "Aronson-Heidi-S"
},
{
"family_name": "Monteverde",
"given_name": "Danielle R.",
"orcid": "0000-0002-0198-8220",
"clpid": "Monteverde-Danielle-R"
},
{
"family_name": "Barnes",
"given_name": "Ben Davis",
"clpid": "Barnes-Ben-Davis"
},
{
"family_name": "Johnson",
"given_name": "Brooke R.",
"clpid": "Johnson-Brooke-R"
},
{
"family_name": "Zawaski",
"given_name": "Mike J.",
"clpid": "Zawaski-Mike-J"
},
{
"family_name": "Speth",
"given_name": "Daan R.",
"orcid": "0000-0002-2361-5935",
"clpid": "Speth-Daan-R"
},
{
"family_name": "Wang",
"given_name": "Xingchen Tony",
"orcid": "0000-0001-5316-789X",
"clpid": "Wang-Xingchen-Tony"
},
{
"family_name": "Wu",
"given_name": "Fenfang",
"orcid": "0000-0003-1134-280X",
"clpid": "Wu-Fenfang"
},
{
"family_name": "Webb",
"given_name": "Samuel M.",
"orcid": "0000-0003-1188-0464",
"clpid": "Webb-Samuel-M"
},
{
"family_name": "Trower",
"given_name": "Elizabeth J.",
"orcid": "0000-0001-9898-5589",
"clpid": "Trower-Elizabeth-J"
},
{
"family_name": "Magyar",
"given_name": "John S.",
"orcid": "0000-0002-3586-8286",
"clpid": "Magyar-John-S"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Fischer",
"given_name": "Woodward W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
},
{
"literal": "Geobiology Course 2017"
},
{
"literal": "Geobiology Course 2018"
}
],
"abstract": "Biogeochemical cycling of sulfur is relatively understudied in terrestrial environments compared to marine environments. However, the comparative ease of access, observation, and sampling of terrestrial settings can expand our understanding of organisms and processes important in the modern sulfur cycle. Furthermore, these sites may allow for the discovery of useful process analogs for ancient sulfur-metabolizing microbial communities at times in Earth's past when atmospheric O2 concentrations were lower and sulfide was more prevalent in Earth surface environments. We identified a new site at Santa Paula Creek (SPC) in Ventura County, CA\u2014a remarkable freshwater, gravel-bedded mountain stream charged with a range of oxidized and reduced sulfur species and heavy hydrocarbons from the emergence of subsurface fluids within the underlying sulfur- and organic-rich Miocene-age Monterey Formation. SPC hosts a suite of morphologically distinct microbial biofacies that form in association with the naturally occurring hydrocarbon seeps and sulfur springs. We characterized the geology, stream geochemistry, and microbial facies and diversity of the Santa Paula Creek ecosystem. Using geochemical analyses and 16S rRNA gene sequencing, we found that SPC supports a dynamic sulfur cycle that is largely driven by sulfide-oxidizing microbial taxa, with contributions from smaller populations of sulfate-reducing and sulfur-disproportionating taxa. This preliminary characterization of SPC revealed an intriguing site in which to study geological and geochemical controls on microbial community composition and to expand our understanding of sulfur cycling in terrestrial environments.",
"doi": "10.1111/gbi.12512",
"issn": "1472-4677",
"publisher": "Wiley",
"publication": "Geobiology",
"publication_date": "2022-09",
"series_number": "5",
"volume": "20",
"issue": "5",
"pages": "707-725"
},
{
"id": "authors:pmcy9-k6a28",
"collection": "authors",
"collection_id": "pmcy9-k6a28",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220513-557936000",
"type": "article",
"title": "Methods and limitations of stable isotope measurements via direct elution of chromatographic peaks using gas chromotography-Orbitrap mass spectrometry",
"author": [
{
"family_name": "Zeichner",
"given_name": "Sarah S.",
"orcid": "0000-0001-8897-7657",
"clpid": "Zeichner-Sarah-S"
},
{
"family_name": "Wilkes",
"given_name": "Elise B.",
"orcid": "0000-0002-3379-7832",
"clpid": "Wilkes-Elise-B"
},
{
"family_name": "Hofmann",
"given_name": "Amy E.",
"orcid": "0000-0001-6869-5118",
"clpid": "Hofmann-Amy-E"
},
{
"family_name": "Chimiak",
"given_name": "Laura",
"orcid": "0000-0002-5047-5421",
"clpid": "Chimiak-Lsura"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Makarov",
"given_name": "Alexander",
"orcid": "0000-0002-7046-6709",
"clpid": "Makarov-Alexander"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
}
],
"abstract": "The Thermo Scientific\u2122 QExactive Orbitrap\u2122 mass spectrometer combined with a Thermo Scientific\u2122 Trace\u2122 1310 GC enables high-mass-resolution measurements of molecular isotopic structure (e.g., molecular-average, position-specific, and multiple substitution measurements), but thus far has employed non-traditional, slow sample introduction methods and long integrations lasting minutes or tens of minutes to optimize measurement precision. This study examines the performance of the Orbitrap for isotope ratio measurements of analytes eluting directly from the gas chromatograph (GC) as traditional GC peaks \u2014 i.e. eluting over a period of seconds and with rapidly varying signal intensities. Such a measurement holds potential for simultaneous compound identification and isotope ratio measurement of numerous analytes separated by GC within a single acquisition. We applied this \"direct elution\" measurement strategy to molecular and fragment ions of para-xylene, serine, and a mixture of polycyclic aromatic hydrocarbons (PAHs) at natural isotope abundances. We built a mathematical model and used a Monte Carlo simulation to evaluate how variations in data processing decisions and GC peak characteristics (e.g., peak shape and elution timing) affect the accuracy of the resulting absolute isotope ratios and sample-standard comparisons (\u03b4 values). These case studies inform our recommendations for applying direct elution measurements. The method is appropriate for systems with large position-specific, molecular, or multiply-substituted isotopic anomalies (e.g., isotopically labelled or extraterrestrial compounds), and for compounds that produce strong molecular ions. Precisions improve when experiments are designed to (1) target ions with relatively high mass spectral intensities, (2) optimize the number of ions and range of masses admitted into the Orbitrap, and (3) minimize the nominal resolution settings while still separating relevant isobars.",
"doi": "10.1016/j.ijms.2022.116848",
"issn": "1387-3806",
"publisher": "Elsevier",
"publication": "International Journal of Mass Spectrometry",
"publication_date": "2022-07",
"volume": "477",
"pages": "Art. No. 116848"
},
{
"id": "authors:00bft-cpd16",
"collection": "authors",
"collection_id": "00bft-cpd16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220121-870770000",
"type": "article",
"title": "Isotope effects at the origin of life: Fingerprints of the Strecker synthesis",
"author": [
{
"family_name": "Chimiak",
"given_name": "L.",
"orcid": "0000-0002-5047-5421",
"clpid": "Chimiak-Laura"
},
{
"family_name": "Eiler",
"given_name": "J.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
},
{
"family_name": "Sessions",
"given_name": "A.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Blumenfeld",
"given_name": "C.",
"clpid": "Blumenfeld-Carl-M"
},
{
"family_name": "Klatte",
"given_name": "M.",
"clpid": "Klatte-Max"
},
{
"family_name": "Stoltz",
"given_name": "B. M.",
"orcid": "0000-0001-9837-1528",
"clpid": "Stoltz-B-M"
}
],
"abstract": "Strecker synthesis creates \u03b1-amino acids from prebiotically plausible substrates (cyanide, ammonia, and aldehydes) and is widely hypothesized to be a key mechanism in the chemistry that led to life on Earth and on other planets. To better constrain the synthetic environments and precursors of abiotic \u03b1-amino acids, and to determine unique signatures of abiogenic amino acids, we measured the molecular-averaged and site-specific carbon and nitrogen isotope effects for the Strecker synthesis of alanine. The reaction steps of the Strecker synthesis can be divided into two groups: an initial series of reversible amination and nitrile-addition reactions ('equilibration') and a second series of irreversible hydrolysis reactions ('hydrolysis'). The equilibration of cyanide, acetaldehyde, and ammonia with the intermediate, \u03b1-aminopropionitrile (\u03b1-APN), has a measured 55.1\u2030 equilibrium nitrogen isotope effect between the \u00b9\u2075N-rich amine nitrogen in \u03b1-aminopropionitrile and the \u00b9\u2075N-poor ammonia and a 20.0\u2030 equilibrium carbon isotope effect between the \u00b9\u00b3C-poor C-2 site in \u03b1-aminopropionitrile and the \u00b9\u00b3C-rich carbonyl carbon in acetaldehyde. The first irreversible hydrolysis step is inferred to have an up to 10\u2030 normal carbon fractionation (i.e., faster for \u00b9\u00b2C, slower for \u00b9\u00b3C) for the whole molecule, but it also has one or more side reactions that deplete the reactive \u03b1-APN reservoir by up to 15\u2030. The second hydrolysis step has a 15.4\u2030 normal kinetic isotope effect on the amide (C-1) site of alaninamide, which becomes the carboxyl site of alanine. Other \u03b1-amino acids will likely experience similar nitrogen isotope fractionations between ammonia and their amine sites, and similar carbon isotope fractionations between the carbonyl carbon in reactant aldehydes or ketones and the intermediate \u03b1-aminonitrile, and between cyanide and the carboxyl site. Therefore, these isotope effects allow us to predict the carbon and nitrogen isotopic contents and intramolecular structures of \u03b1-amino acids formed by Strecker synthesis based on their substrates' isotopic compositions, or to infer the isotopic compositions of substrates from which amino acids formed, for example in the case of the amino-acid-rich carbonaceous chondrites. The site-specific C and N isotopic compositions of amino acids formed by Strecker chemistry contrast with those typical of terrestrial biosynthetic amino acids, so these data also provide a means of discriminating between biogenic and abiogenic \u03b1-amino acids.",
"doi": "10.1016/j.gca.2022.01.015",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2022-03-15",
"volume": "321",
"pages": "78-98"
},
{
"id": "authors:htvn3-xbz41",
"collection": "authors",
"collection_id": "htvn3-xbz41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220214-701486900",
"type": "article",
"title": "Practical considerations for amino acid isotope analysis",
"author": [
{
"family_name": "Silverman",
"given_name": "Shaelyn N.",
"clpid": "Silverman-Shaelyn-N"
},
{
"family_name": "Phillips",
"given_name": "Alexandra A.",
"orcid": "0000-0001-5959-5238",
"clpid": "Phillips-Alexandra-A"
},
{
"family_name": "Weiss",
"given_name": "Gabriella M.",
"orcid": "0000-0002-9571-2558",
"clpid": "Weiss-Gabriella-M"
},
{
"family_name": "Wilkes",
"given_name": "Elise B.",
"orcid": "0000-0002-3379-7832",
"clpid": "Wilkes-Elise-B"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Over the last few decades, isotopic analysis of amino acids at the compound- and position-specific levels has been rapidly advancing across diverse fields. As these techniques progress, evaluation of isotopic fractionation associated with sample workup is essential. This critical review of analytical methods through the lens of isotope geochemistry provides a benchmark for researchers across disciplines seeking to make compound- and position-specific amino acid isotope measurements. We focus on preparation, acid hydrolysis, clean-up, derivatization, separation, and C, H, N, and S isotope measurement. Despite substantial customizability across these steps, the following general recommendations should maximize recovery while minimizing isotopic fractionation. Samples should be freeze-dried and stored anoxically at \u2264 \u201320 \u00b0C prior to conventional acid hydrolysis (6N HCl, 110 \u00b0C, 20\u201324 h, anoxic), which suffices for many residues. Both gas and liquid chromatographic (GC and LC, respectively) techniques are well-established and separate about 15 amino acids; LC bypasses the need for derivatization, while GC provides higher sensitivity. When derivatization is needed, n-acetyl and alkoxycarbonyl esters provide the most reproducible C isotope ratios. For compound-specific analyses, online GC\u2013IRMS and LC\u2013IRMS systems offer the easiest workflow, but EA\u2013IRMS enables potential multi-element isotope analysis. Emerging techniques like high-resolution mass spectrometry are also promising for multi-element analysis and recover position-specific isotopic information. Looking forward to the next decade of innovation, isotope geochemists and ecologists can improve amino acid isotope analysis by focusing on streamlining multi-element analysis and standardizing calibration practices across laboratories.",
"doi": "10.1016/j.orggeochem.2021.104345",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2022-02",
"volume": "164",
"pages": "Art. No. 104345"
},
{
"id": "authors:h101r-dvz54",
"collection": "authors",
"collection_id": "h101r-dvz54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220114-12564000",
"type": "article",
"title": "Simultaneous, High-Precision Measurements of \u03b4\u00b2H and \u03b4\u00b9\u00b3C in Nanomole Quantities of Acetate Using Electrospray Ionization-Quadrupole-Orbitrap Mass Spectrometry",
"author": [
{
"family_name": "Mueller",
"given_name": "Elliott P.",
"orcid": "0000-0002-6837-0409",
"clpid": "Mueller-Elliott-P"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Sauer",
"given_name": "Peter E.",
"clpid": "Sauer-Peter-E"
},
{
"family_name": "Weiss",
"given_name": "Gabriella M.",
"orcid": "0000-0002-9571-2558",
"clpid": "Weiss-Gabriella-M"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
}
],
"abstract": "Stable hydrogen isotope compositions (\u00b2H/\u00b9H ratios) have been an invaluable tool for studying biogeochemical processes in nature, but the diversity of molecular targets amenable to such analysis is limited. Here, we demonstrate a new technique for measuring \u03b4\u00b2H of biomolecules via Orbitrap mass spectrometry (MS) using acetate as a model analyte. Acetate was chosen as a target molecule because its production and consumption are central to microbial carbon cycling, yet the mechanisms behind acetate turnover remain poorly understood. \u03b4\u00b2H of acetate could provide a useful constraint on these processes; however, it remains uncharacterized in nature due to analytical challenges. Electrospray ionization (ESI)-Orbitrap MS circumvents these challenges and delivers methyl-specific H-isotope compositions of acetate with nanomole sensitivity, enough to enable analyses of environmental samples. This approach quantifies the methyl-specific \u03b4\u00b2H and molecular-average \u03b4\u00b9\u00b3C of acetate simultaneously while achieving <3 and <0.5\u2030 uncertainty, respectively. Using optimized ionization and Orbitrap parameters, this level of precision is obtained within 15 min using only 15 nmol of acetate. As a demonstration of our analytical approach, we cultured three acetogenic bacteria and found a large \u00b2H-fractionation between acetate and water (>310\u2030 depletion) associated with the Wood\u2013Ljungdahl pathway, while fermentation expressed a muted (\u223c80\u2030) fractionation. With its high precision and sensitivity, Orbitrap MS is a promising tool for investigating these signals in nature after offline purification. Furthermore, the ESI-Orbitrap method presented here could be applied to other molecules amenable to ESI, including central metabolites and sugars, greatly expanding the molecular targets used in hydrogen isotope biogeochemistry.",
"doi": "10.1021/acs.analchem.1c04141",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2022-01-18",
"series_number": "2",
"volume": "94",
"issue": "2",
"pages": "1092-1100"
},
{
"id": "authors:x0qdq-9tb57",
"collection": "authors",
"collection_id": "x0qdq-9tb57",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210811-170707088",
"type": "article",
"title": "Room-level ventilation in schools and universities",
"author": [
{
"family_name": "McNeill",
"given_name": "V. Faye",
"orcid": "0000-0003-0379-6916",
"clpid": "McNeill-V-Faye"
},
{
"family_name": "Corsi",
"given_name": "Richard",
"orcid": "0000-0002-1291-3566",
"clpid": "Corsi-Richard"
},
{
"family_name": "Huffman",
"given_name": "J. Alex",
"orcid": "0000-0002-5363-9516",
"clpid": "Huffman-J-Alex"
},
{
"family_name": "King",
"given_name": "Cathleen",
"orcid": "0000-0003-3147-4834",
"clpid": "King-Cathleen"
},
{
"family_name": "Klein",
"given_name": "Robert",
"clpid": "Klein-Robert"
},
{
"family_name": "Lamore",
"given_name": "Michael",
"clpid": "Lamore-Michael"
},
{
"family_name": "Maeng",
"given_name": "Do Young",
"orcid": "0000-0001-8371-5404",
"clpid": "Maeng-Do-Young"
},
{
"family_name": "Miller",
"given_name": "Shelly L.",
"orcid": "0000-0002-1967-7551",
"clpid": "Miller-Shelly-L"
},
{
"family_name": "Ng",
"given_name": "Nga Lee",
"orcid": "0000-0001-8460-4765",
"clpid": "Ng-Nga-Lee"
},
{
"family_name": "Olsiewski",
"given_name": "Paula",
"orcid": "0000-0001-7014-6126",
"clpid": "Olsiewski-Paula"
},
{
"family_name": "Godri Pollitt",
"given_name": "Krystal J.",
"orcid": "0000-0001-7332-2228",
"clpid": "Godri-Pollitt-Krystal-J"
},
{
"family_name": "Segalman",
"given_name": "Rachel",
"orcid": "0000-0002-4292-5103",
"clpid": "Segalman-Rachel-A"
},
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Squires",
"given_name": "Todd",
"orcid": "0000-0001-6609-9275",
"clpid": "Squires-Todd"
},
{
"family_name": "Westgate",
"given_name": "Sabrina",
"orcid": "0000-0001-7272-2465",
"clpid": "Westgate-Sabrina"
}
],
"abstract": "Ventilation is of primary concern for maintaining healthy indoor air quality and reducing the spread of airborne infectious disease, including COVID-19. In addition to building-level guidelines, increased attention is being placed on room-level ventilation. However, for many universities and schools, ventilation data on a room-by-room basis are not available for classrooms and other key spaces. We present an overview of approaches for measuring ventilation along with their advantages and disadvantages. We also present data from recent case studies for a variety of institutions across the United States, with various building ages, types, locations, and climates, highlighting their commonalities and differences, and examples of the use of this data to support decision making.",
"doi": "10.1016/j.aeaoa.2022.100152",
"pmcid": "PMC8789458",
"issn": "2590-1621",
"publisher": "Elsevier",
"publication": "Atmospheric Environment: X",
"publication_date": "2022-01",
"volume": "13",
"pages": "Art. No. 100152"
},
{
"id": "authors:012te-b6851",
"collection": "authors",
"collection_id": "012te-b6851",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211111-215750456",
"type": "article",
"title": "Methoxyl stable isotopic constraints on the origins and limits of coal-bed methane",
"author": [
{
"family_name": "Lloyd",
"given_name": "M. K.",
"orcid": "0000-0001-9367-2698",
"clpid": "Lloyd-Max-K"
},
{
"family_name": "Trembath-Reichert",
"given_name": "E.",
"orcid": "0000-0002-3979-8676",
"clpid": "Trembath-Reichert-Elizabeth"
},
{
"family_name": "Dawson",
"given_name": "K. S.",
"orcid": "0000-0001-8856-4609",
"clpid": "Dawson-Katherine-S"
},
{
"family_name": "Feakins",
"given_name": "S. J.",
"orcid": "0000-0003-3434-2423",
"clpid": "Feakins-Sarah-J"
},
{
"family_name": "Mastalerz",
"given_name": "M.",
"orcid": "0000-0002-9890-6788",
"clpid": "Mastalerz-Maria"
},
{
"family_name": "Orphan",
"given_name": "V. J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "J. M.",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
}
],
"abstract": "Microbial coal-bed methane is an important economic resource and source of a potent greenhouse gas, but controls on its formation are poorly understood. To test whether the microbial degradability of coal limits microbial methane, we monitored methoxyl group demethylation\u2014a reaction that feeds methanogenesis\u2014in a global sample suite ranging in maturity from wood to bituminous coal. Carbon isotopic compositions of residual methoxyl groups were inconsistent with a thermal reaction, instead implying a substrate-limited biologic process. This suggests that deep biosphere communities participated in transforming plant matter to coal on geologic time scales and that methoxyl abundance influences coal-bed methane yield. Carbon isotopic enrichments resulting from microbial methylotrophy also explain an enigmatic offset in the carbon-13 content of microbial methane from coals and conventional hydrocarbon deposits.",
"doi": "10.1126/science.abg0241",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "2021-11-12",
"series_number": "6569",
"volume": "374",
"issue": "6569",
"pages": "894-897"
},
{
"id": "authors:k1wex-qd335",
"collection": "authors",
"collection_id": "k1wex-qd335",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210817-204334443",
"type": "article",
"title": "Sulfur isotope fractionations constrain the biological cycling of dimethylsulfoniopropionate in the upper ocean",
"author": [
{
"family_name": "Osorio\u2010Rodriguez",
"given_name": "Daniela",
"orcid": "0000-0001-6676-4124",
"clpid": "Osorio\u2010Rodriguez-Daniela"
},
{
"family_name": "Razo-Mejia",
"given_name": "Manuel",
"orcid": "0000-0002-9510-0527",
"clpid": "Razo-Mejia-Manuel"
},
{
"family_name": "Dalleska",
"given_name": "Nathan F.",
"orcid": "0000-0002-2059-1587",
"clpid": "Dalleska-Nathan-F"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"abstract": "The rapid turnover of dimethylsulfoniopropionate (DMSP), likely the most relevant dissolved organic sulfur compound in the surface ocean, makes it pivotal to understand the cycling of organic sulfur. Dimethylsulfoniopropionate is mainly synthesized by phytoplankton, and it can be utilized as carbon and sulfur sources by marine bacteria or cleaved by bacteria or algae to produce the volatile compound dimethylsulfide (DMS), involved in the formation of sulfate aerosols. The fluxes between the consumption (i.e., demethylation) and cleavage pathways are thought to depend on community interactions and their sulfur demand. However, a quantitative assessment of the sulfur partitioning between each of these pathways is still missing. Here, we report for the first time the sulfur isotope fractionations by enzymes involved in DMSP degradation with different catalytic mechanisms, expressed heterologously in Escherichia coli. We show that the residual DMSP from the demethylation pathway is 2.7\u2030 enriched in \u03b4 \u00b3\u2074S relative to the initial DMSP, and that the fractionation factor (\u00b3\u2074\u03b5) of the cleavage pathways varies between \u22121 and \u22129\u2030. The incorporation of these fractionation factors into mass balance calculations constrains the biological fates of DMSP in seawater, supports the notion that demethylation dominates over cleavage in marine environments, and could be used as a proxy for the dominant pathways of degradation of DMSP by marine microbial communities.",
"doi": "10.1002/lno.11901",
"issn": "0024-3590",
"publisher": "American Society of Limnology and Oceanography",
"publication": "Limnology and Oceanography",
"publication_date": "2021-10",
"series_number": "10",
"volume": "66",
"issue": "10",
"pages": "3607-3618"
},
{
"id": "authors:0ztrc-6bd87",
"collection": "authors",
"collection_id": "0ztrc-6bd87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210607-115054814",
"type": "article",
"title": "Duelling narratives of chironomids and pollen explain climate enigmas during The Last Glacial-Interglacial transition in North Island New Zealand",
"author": [
{
"family_name": "Rees",
"given_name": "Andrew B. H.",
"orcid": "0000-0003-4026-7765",
"clpid": "Rees-Andrew-B-H"
},
{
"family_name": "Holt",
"given_name": "Katherine A.",
"clpid": "Holt-Katherine-A"
},
{
"family_name": "Hinojosa",
"given_name": "Jessica L.",
"clpid": "Hinojosa-Jessica-L"
},
{
"family_name": "Newnham",
"given_name": "Rewi M.",
"clpid": "Newnham-Rewi-M"
},
{
"family_name": "Eaves",
"given_name": "Shaun",
"clpid": "Eaves-Shaun"
},
{
"family_name": "Vandergoes",
"given_name": "Marcus J.",
"clpid": "Vandergoes-Marcus-J"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Wilmshurst",
"given_name": "Janet M.",
"clpid": "Wilmshurst-Janet-M"
}
],
"abstract": "The Last Glacial-Interglacial Transition (LGIT) was a dynamic stage of Earth's history, and the difficulty of reconstructing this complex interval may be compounded by divergent proxy records, often collected from the same archive. To overcome this obstacle, we exploit the contrasting biological preferences of chironomids to both summer temperature and degree days (positive) and pollen to both the length of the growing season (positive) and winter duration (negative), recorded by a small lake in the central North Island of New Zealand. The climate proxy records are anchored to shifting zonal boundaries (e.g., southern westerly wind belt) via the hydrogen isotope ratios of leaf wax n-alkanes (\u03b4D_(wax)). These results enable us to interrogate the structure of the LGIT and address two fundamental questions: 1) Is there evidence for Holocene-like temperatures during the early deglacial? and 2) Were early Holocene summers cool? \n\nLake sediment \u03b4D_(wax) values indicate a poleward retreat of the westerlies around 18,000 calibrated years before present (cal kyr BP), signalling the onset of climate amelioration for the region. Remarkably, the independently derived summer and mean annual temperature reconstructions are anti-phased. Chironomid-inferred summer temperatures surpass modern values by 17.5 cal kyr BP, whereas pollen-inferred mean annual temperatures remain supressed. Summers cool from 17.5 to 11 cal kyr BP, when they reach a minimum for the record, while winter and mean annual temperatures simultaneously warm to a maximum. The chironomid record generally traces regional insolation, although an Antarctic template imprints on this trend with declining summer temperatures during the Antarctic Cold Reversal (ACR) and warming during the Younger Dryas (YD). Forest development during the early LGIT, on the other hand, is supressed by cool, dry winters, punctuated by severe frosts, despite being set against a backdrop of overall warming; the successional pattern is best explained by a latitudinal retreat of the westerlies. Our findings underscore the complementarity of multiple bioproxy responses and reveal the importance of seasonal heat and energy distribution during the LGIT.",
"doi": "10.1016/j.quascirev.2021.106997",
"issn": "0277-3791",
"publisher": "Elsevier",
"publication": "Quaternary Science Reviews",
"publication_date": "2021-07-01",
"volume": "263",
"pages": "Art. No. 106997"
},
{
"id": "authors:s4kxf-xh613",
"collection": "authors",
"collection_id": "s4kxf-xh613",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210225-154113785",
"type": "article",
"title": "Microbial succession and dynamics in meromictic Mono Lake, California",
"author": [
{
"family_name": "Phillips",
"given_name": "Alexandra A.",
"orcid": "0000-0001-5959-5238",
"clpid": "Phillips-Alexandra-A"
},
{
"family_name": "Speth",
"given_name": "Daan R.",
"orcid": "0000-0002-2361-5935",
"clpid": "Speth-Daan-R"
},
{
"family_name": "Miller",
"given_name": "Laurence G.",
"orcid": "0000-0002-7807-3475",
"clpid": "Miller-Laurence-G"
},
{
"family_name": "Wang",
"given_name": "Xingchen T.",
"orcid": "0000-0001-5316-789X",
"clpid": "Wang-Xingchen-Tony"
},
{
"family_name": "Wu",
"given_name": "Fenfang",
"orcid": "0000-0003-1134-280X",
"clpid": "Wu-Fenfang"
},
{
"family_name": "Medeiros",
"given_name": "Patricia M.",
"orcid": "0000-0001-6818-2603",
"clpid": "Medeiros-Patricia-M"
},
{
"family_name": "Monteverde",
"given_name": "Danielle R.",
"orcid": "0000-0002-0198-8220",
"clpid": "Monteverde-Danielle-R"
},
{
"family_name": "Osburn",
"given_name": "Magdalena R.",
"orcid": "0000-0001-9180-559X",
"clpid": "Osburn-Magdalena-R"
},
{
"family_name": "Berelson",
"given_name": "William M.",
"orcid": "0000-0002-1526-3802",
"clpid": "Berelson-William-M"
},
{
"family_name": "Betts",
"given_name": "Hannah L.",
"clpid": "Betts-Hannah-L"
},
{
"family_name": "Wijker",
"given_name": "Reto S.",
"orcid": "0000-0001-5104-9849",
"clpid": "Wijker-Reto-S"
},
{
"family_name": "Mullin",
"given_name": "Sean W.",
"orcid": "0000-0002-6225-3279",
"clpid": "Mullin-Sean-W"
},
{
"family_name": "Johnson",
"given_name": "Hope A.",
"orcid": "0000-0001-6721-3340",
"clpid": "Johnson-Hope-A"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Fischer",
"given_name": "Woodward W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"literal": "Geobiology Course 2017"
},
{
"literal": "Geobiology Course 2018"
}
],
"abstract": "Mono Lake is a closed-basin, hypersaline, alkaline lake located in Eastern Sierra Nevada, California, that is dominated by microbial life. This unique ecosystem offers a natural laboratory for probing microbial community responses to environmental change. In 2017, a heavy snowpack and subsequent runoff led Mono Lake to transition from annually mixed (monomictic) to indefinitely stratified (meromictic). We followed microbial succession during this limnological shift, establishing a two-year (2017\u20132018) water-column time series of geochemical and microbiological data. Following meromictic conditions, anoxia persisted below the chemocline and reduced compounds such as sulfide and ammonium increased in concentration from near 0 to ~400 and ~150 \u00b5M, respectively, throughout 2018. We observed significant microbial succession, with trends varying by water depth. In the epilimnion (above the chemocline), aerobic heterotrophs were displaced by phototrophic genera when a large bloom of cyanobacteria appeared in fall 2018. Bacteria in the hypolimnion (below the chemocline) had a delayed, but systematic, response reflecting colonization by sediment \"seed bank\" communities. Phototrophic sulfide-oxidizing bacteria appeared first in summer 2017, followed by microbes associated with anaerobic fermentation in spring 2018, and eventually sulfate-reducing taxa by fall 2018. This slow shift indicated that multi-year meromixis was required to establish a sulfate-reducing community in Mono Lake, although sulfide oxidizers thrive throughout mixing regimes. The abundant green alga Picocystis remained the dominant primary producer during the meromixis event, abundant throughout the water column including in the hypolimnion despite the absence of light and prevalence of sulfide. Our study adds to the growing literature describing microbial resistance and resilience during lake mixing events related to climatic events and environmental change.",
"doi": "10.1111/gbi.12437",
"issn": "1472-4677",
"publisher": "Wiley",
"publication": "Geobiology",
"publication_date": "2021-07",
"series_number": "4",
"volume": "19",
"issue": "4",
"pages": "376-393"
},
{
"id": "authors:s042k-j3m31",
"collection": "authors",
"collection_id": "s042k-j3m31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210322-095354450",
"type": "article",
"title": "Clumped isotope effects of thermogenic methane formation: Insights from pyrolysis of hydrocarbons",
"author": [
{
"family_name": "Dong",
"given_name": "Guannan",
"orcid": "0000-0002-6844-2492",
"clpid": "Dong-Guannan"
},
{
"family_name": "Xie",
"given_name": "Hao",
"orcid": "0000-0001-5656-2035",
"clpid": "Xie-Hao"
},
{
"family_name": "Formolo",
"given_name": "Michael",
"clpid": "Formolo-Michael-J"
},
{
"family_name": "Lawson",
"given_name": "Michael",
"clpid": "Lawson-Michael"
},
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "John",
"orcid": "0000-0001-5768-7593",
"clpid": "Eiler-J-M"
}
],
"abstract": "Methane clumped isotope analysis is a tool used to constrain the formation or equilibration temperatures of methane, or to differentiate methane of thermogenic, microbial or 'abiotic' origins. Geothermometry applications are based on the temperature dependence of relative abundances of multiply-substituted isotopologues in thermodynamic equilibrium, whereas assignments of biogenicity or 'abiogenicity' rely on kinetic isotope effects associated with synthesis, which disturb clumped isotope abundances away from expected equilibrium proportions. However, kinetic processes in thermogenesis or during post-generation storage of thermogenic gas may cause isotopic disequilibrium, confounding thermometry applications or leading to 'false positive' identifications of microbial or abiogenic gases. Non-equilibrated clumped isotope compositions have been observed in thermogenic gases including unconventional oil-associated gases and from coal pyrolysis experiments. The isotopic disequilibria might be caused by kinetic isotope effects expressed during gas migration (including extraction), or by irreversible chemical processes, such as breaking carbon\u2013carbon bonds in an alkyl precursor. In this study, we performed controlled pyrolysis experiments at 400\u202f\u00b0C on n-octadecane (C\u2081\u2088H\u2083\u2088). We characterized the gas chemistry, and compound-specific carbon and hydrogen isotope and methane clumped isotope compositions of the gas products. We found that \u0394\u00b9\u00b3CH\u2083D values (anomalies relative to a stochastic distribution of isotopes) appear to be relatively close to equilibrium at the experimental temperature, whereas \u0394\u00b9\u00b2CH\u2082D\u2082 values are 30\u201340\u2030 lower than expected for equilibrium. The large deficit in \u0394\u00b9\u00b2CH\u2082D\u2082 can be explained by assembling hydrogen atoms affected by two distinct kinetic isotope effects into a methane molecule, previously referred to as a 'combinatorial effect'. We present a kinetic model that describes the full isotopic systematics, including anomalous \u0394\u00b9\u00b2CH\u2082D\u2082 deficits, of pyrolysis product methane. Finally, we propose a model for the isotope signatures of natural thermogenic methane where the non-equilibrium \u0394\u00b9\u00b2CH\u2082D\u2082 composition is a signature of the onset of catagenetic methane production. Our model also describes ways in which this signature disappears as further maturation drives \u0394\u00b9\u00b2CH\u2082D\u2082 to equilibrium through hydrogen exchange. Our findings demonstrate that anomalous depletion in \u0394\u00b9\u00b2CH\u2082D\u2082 is not a unique signature for microbial or putative abiotic methane, and specifically, it can be generated during pyrolytic chemistry.",
"doi": "10.1016/j.gca.2021.03.009",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2021-06-15",
"volume": "303",
"pages": "159-183"
},
{
"id": "authors:s7wm5-a1n81",
"collection": "authors",
"collection_id": "s7wm5-a1n81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201117-132832420",
"type": "article",
"title": "Sulfur isotope analysis of cysteine and methionine via preparatory liquid chromatography and elemental analyzer isotope ratio mass spectrometry",
"author": [
{
"family_name": "Phillips",
"given_name": "Alexandra A.",
"orcid": "0000-0001-5959-5238",
"clpid": "Phillips-Alexandra-A"
},
{
"family_name": "Wu",
"given_name": "Fenfang",
"clpid": "Wu-Fenfang"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Rationale: Sulfur isotope analysis of organic sulfur\u2010containing molecules has previously been hindered by challenging preparatory chemistry and analytical requirements for large sample sizes. The natural\u2010abundance sulfur isotopic compositions of the sulfur\u2010containing amino acids, cysteine and methionine, have therefore not yet been investigated despite potential utility in biomedicine, ecology, oceanography, biogeochemistry, and other fields. \n\nMethods: Cysteine and methionine were subjected to hot acid hydrolysis followed by quantitative oxidation in performic acid to yield cysteic acid and methionine sulfone. These stable, oxidized products were then separated by reversed\u2010phase high\u2010performance liquid chromatography (HPLC) and verified via offline liquid chromatography/mass spectrometry (LC/MS). The sulfur isotope ratios (\u03b4\u00b3\u2074S values) of purified analytes were then measured via combustion elemental analyzer coupled to isotope ratio mass spectrometry (EA/IRMS). The EA was equipped with a temperature\u2010ramped chromatographic column and programmable helium carrier flow rates. \n\nResults: On\u2010column focusing of SO2 in the EA/IRMS system, combined with reduced He carrier flow during elution, greatly improved sensitivity, allowing precise (0.1\u20130.3\u2030 1\u2009s.d.) \u03b4\u00b3\u2074S measurements of 1 to 10\u2009\u03bcg sulfur. We validated that our method for purification of cysteine and methionine was negligibly fractionating using amino acid and protein standards. Proof\u2010of\u2010concept measurements of fish muscle tissue and bacteria demonstrated differences up to 4\u2030 between the \u03b4\u00b3\u2074S values of cysteine and methionine that can be connected to biosynthetic pathways. \n\nConclusions: We have developed a sensitive, precise method for measuring the natural\u2010abundance sulfur isotopic compositions of cysteine and methionine isolated from biological samples. This capability opens up diverse applications of sulfur isotopes in amino acids and proteins, from use as a tracer in organisms and the environment, to fundamental aspects of metabolism and biosynthesis.",
"doi": "10.1002/rcm.9007",
"issn": "0951-4198",
"publisher": "Wiley",
"publication": "Rapid Communications in Mass Spectrometry",
"publication_date": "2021-02-28",
"series_number": "4",
"volume": "35",
"issue": "4",
"pages": "Art. No. e9007"
},
{
"id": "authors:kdaqe-1a852",
"collection": "authors",
"collection_id": "kdaqe-1a852",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200930-131626735",
"type": "article",
"title": "Carbon isotope evidence for the substrates and mechanisms of prebiotic synthesis in the early solar system",
"author": [
{
"family_name": "Chimiak",
"given_name": "L.",
"orcid": "0000-0002-5047-5421",
"clpid": "Chimiak-L"
},
{
"family_name": "Elsila",
"given_name": "J. E.",
"clpid": "Elsila-J-E"
},
{
"family_name": "Dallas",
"given_name": "B.",
"orcid": "0000-0002-1313-3270",
"clpid": "Dallas-B-H"
},
{
"family_name": "Dworkin",
"given_name": "J. P.",
"clpid": "Dworkin-J-P"
},
{
"family_name": "Aponte",
"given_name": "J. C.",
"orcid": "0000-0002-0131-1981",
"clpid": "Aponte-J-C"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "J. M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Meteorites contain prebiotic, bio-relevant organic compounds including amino acids. Their syntheses could result from diverse sources and mechanisms and provide a window on the conditions and materials present in the early solar system. Here we constrain alanine's synthetic history in the Murchison meteorite using site-specific \u00b9\u00b3C/\u00b9\u00b2C measurements, reported relative to the VPDB standard. The \u03b4\u00b9\u00b3C_(VPDB) values of \u221229\u202f\u00b1\u202f10\u2030, 142\u202f\u00b1\u202f20\u2030, and \u221236\u202f\u00b1\u202f20\u2030 for the carboxyl, amine-bound, and methyl carbons, respectively, are consistent with Strecker synthesis of interstellar-medium-derived aldehydes, ammonia, and low-\u03b4\u00b9\u00b3C nebular or interstellar-medium-derived CN. We report experimentally measured isotope effects associated with Strecker synthesis, and use them to constrain the \u03b4\u00b9\u00b3C values of the alanine precursors, which we then use to construct a model that predicts the molecular-average \u03b4\u00b9\u00b3C values of 19 other organic compounds of prebiotic significance found in Murchison if they were made by our proposed synthetic network. Most of these predictions agree with previous measurements, suggesting that interstellar-medium-derived aldehydes and nebular and/or pre-solar CN could have served as substrates for synthesis of a wide range of prebiotic compounds in the early solar system.",
"doi": "10.1016/j.gca.2020.09.026",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2021-01-01",
"volume": "292",
"pages": "188-202"
},
{
"id": "authors:963q0-yj286",
"collection": "authors",
"collection_id": "963q0-yj286",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200928-091727864",
"type": "article",
"title": "Position-specific distribution of hydrogen isotopes in natural propane: Effects of thermal cracking, equilibration and biodegradation",
"author": [
{
"family_name": "Xie",
"given_name": "Hao",
"orcid": "0000-0001-5656-2035",
"clpid": "Xie-Hao"
},
{
"family_name": "Ponton",
"given_name": "Camilo",
"clpid": "Ponton-C"
},
{
"family_name": "Formolo",
"given_name": "Michael J.",
"clpid": "Formolo-M-J"
},
{
"family_name": "Lawson",
"given_name": "Michael",
"orcid": "0000-0003-2743-3773",
"clpid": "Lawson-M"
},
{
"family_name": "Ellis",
"given_name": "Geoffrey S.",
"orcid": "0000-0003-4519-3320",
"clpid": "Ellis-G-S"
},
{
"family_name": "Lewan",
"given_name": "Michael D.",
"clpid": "Lewan-M-D"
},
{
"family_name": "Ferreira",
"given_name": "Alexandre A.",
"clpid": "Ferreira-A-A"
},
{
"family_name": "Morais",
"given_name": "Erica T.",
"clpid": "Morais-E-T"
},
{
"family_name": "Spigolon",
"given_name": "Andre L. D.",
"clpid": "Spigolon-A-L-D"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Intramolecular isotope distributions, including isotope clumping and position specific fractionation, can provide proxies for the formation temperature and formation and destruction pathways of molecules. In this study, we explore the position-specific hydrogen isotope distribution in propane. We analyzed propane samples from 10 different petroleum systems with high-resolution molecular mass spectrometry. Our results show that the hydrogen isotope fractionation between central and terminal positions of natural propanes ranges from \u2212102\u2030 to +205\u2030, a much larger range than that expected for thermodynamic equilibrium at their source and reservoir temperatures (36\u201363\u2030). Based on these findings, we propose that the hydrogen isotope structure of catagenic propane is largely controlled by irreversible processes, expressing kinetic isotope effects (KIEs). Kinetic control on hydrogen isotope composition of the products of thermal cracking is supported by a hydrous pyrolysis experiment using the Woodford Shale as substrate, in which we observed isotopic disequilibrium in the early stage of pyrolysis. We make a more general prediction of KIE signatures associated with kerogen cracking by simulating this chemistry in a kinetic Monte Carlo model for different types of kerogens. In contrast, unconventional shale fluids or hot conventional reservoirs contain propane with an isotopic structure close to equilibrium, presumably reflecting internal and/or heterogeneous exchange during high temperature storage (ca. 100\u2013150 \u00b0C). In relatively cold (<100 \u00b0C) conventional gas accumulations, propane can discharge from its source to a colder reservoir, rapidly enough to preserve disequilibrium signatures even if the source rock thermal maturity is high. These findings imply that long times at elevated temperatures are required to equilibrate the hydrogen isotopic structure of propane in natural gas host rocks and reservoirs. We further defined the kinetics of propane equilibration through hydrogen isotope exchange experiments under hydrous conditions; these experiments show that hydrogen in propane is exchangeable over laboratory timescales when exposed to clay minerals such as kaolinite. This implies rather rapid transfer of propane from sources to cold reservoirs in some of the conventional petroleum systems. Propane is also susceptible to microbial degradation in both oxic and anoxic environments. Biodegradation of propane in the Hadrian and Diana Hoover oil fields (Gulf of Mexico) results in strong increases in central-terminal hydrogen isotope fractionation. This reflects preferential attack on the central position, consistent with previous studies.",
"doi": "10.1016/j.gca.2020.09.009",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2020-12-01",
"volume": "290",
"pages": "235-256"
},
{
"id": "authors:rr89k-60x16",
"collection": "authors",
"collection_id": "rr89k-60x16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200706-145806917",
"type": "article",
"title": "Deposition of sulfate aerosols with positive \u0394\u00b3\u00b3S in the Neoarchean",
"author": [
{
"family_name": "Paris",
"given_name": "Guillaume",
"orcid": "0000-0001-8368-1224",
"clpid": "Paris-G"
},
{
"family_name": "Fischer",
"given_name": "Woodward W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
},
{
"family_name": "Johnson",
"given_name": "Jena E.",
"clpid": "Johnson-J-E"
},
{
"family_name": "Webb",
"given_name": "Samuel M.",
"clpid": "Webb-S-M"
},
{
"family_name": "Present",
"given_name": "Theodore M.",
"orcid": "0000-0002-4747-2174",
"clpid": "Present-T-M"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"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 SO\u2082 molecules. Most interpretations suggest that atmospheric processes generate a reduced S-phase with a positive (\u00b3\u00b3S-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) \u2014 a direct proxy for the isotopic composition of sulfur from seawater sulfate \u2014 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 \u00b3\u00b3S-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.",
"doi": "10.1016/j.gca.2020.06.028",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2020-09-15",
"volume": "285",
"pages": "1-20"
},
{
"id": "authors:dvxxt-w6m43",
"collection": "authors",
"collection_id": "dvxxt-w6m43",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200408-093725679",
"type": "article",
"title": "Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes",
"author": [
{
"family_name": "Douglas",
"given_name": "Peter M. J.",
"orcid": "0000-0002-4282-6615",
"clpid": "Douglas-P-M-J"
},
{
"family_name": "Moguel",
"given_name": "Regina Gonzalez",
"clpid": "Moguel-R-G"
},
{
"family_name": "Anthony",
"given_name": "Katey M. Walter",
"clpid": "Anthony-K-M-W"
},
{
"family_name": "Wik",
"given_name": "Martin",
"orcid": "0000-0003-0368-4623",
"clpid": "Wik-M"
},
{
"family_name": "Crill",
"given_name": "Patrick M.",
"orcid": "0000-0003-1110-3059",
"clpid": "Crill-P-M"
},
{
"family_name": "Dawson",
"given_name": "Katherine S.",
"orcid": "0000-0001-8856-4609",
"clpid": "Dawson-Katherine-S"
},
{
"family_name": "Smith",
"given_name": "Derek A.",
"clpid": "Smith-D-A"
},
{
"family_name": "Yanay",
"given_name": "Ella",
"clpid": "Yanay-E"
},
{
"family_name": "Lloyd",
"given_name": "Max K.",
"orcid": "0000-0001-9367-2698",
"clpid": "Lloyd-M-K"
},
{
"family_name": "Stolper",
"given_name": "Daniel A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "The release of long\u2010stored carbon from thawed permafrost could fuel increased methanogenesis in northern lakes, but it remains unclear whether old carbon substrates released from permafrost are metabolized as rapidly by methanogenic microbial communities as recently produced organic carbon. Here, we apply methane (CH\u2084) clumped isotope (\u0394\u2081\u2088) and \u00b9\u2074C measurements to test whether rates of methanogenesis are related to carbon substrate age. Results from culture experiments indicate that \u0394\u2081\u2088 values are negatively correlated with CH\u2084 production rate. Measurements of ebullition samples from thermokarst lakes in Alaska and glacial lakes in Sweden indicate strong negative correlations between CH\u2084 \u0394\u2081\u2088 and the fraction modern carbon. These correlations imply that CH\u2084 derived from older carbon substrates is produced relatively slowly. Relative rates of methanogenesis, as inferred from \u0394\u2081\u2088 values, are not positively correlated with CH\u2084 flux estimates, highlighting the likely importance of environmental variables other than CH\u2084 production rates in controlling ebullition fluxes.",
"doi": "10.1029/2019gl086756",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "2020-03-28",
"series_number": "6",
"volume": "47",
"issue": "6",
"pages": "Art. No. e2019GL086756"
},
{
"id": "authors:pn7gk-s7w54",
"collection": "authors",
"collection_id": "pn7gk-s7w54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200625-091946833",
"type": "article",
"title": "Cuticular hydrocarbons and the integration of myrmecophile rove beetles into ant colonies",
"author": [
{
"family_name": "Naragon",
"given_name": "T. H.",
"orcid": "0000-0002-5373-4257",
"clpid": "Naragon-Thomas-H"
},
{
"family_name": "Br\u00fcckner",
"given_name": "A. K.",
"orcid": "0000-0002-9184-8562",
"clpid": "Br\u00fcckner-Adrian-K"
},
{
"family_name": "Wijker",
"given_name": "R. S.",
"orcid": "0000-0001-5104-9849",
"clpid": "Wijker-Reto-S"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Parker",
"given_name": "J.",
"orcid": "0000-0001-9598-2454",
"clpid": "Parker-J"
}
],
"abstract": "[no abstract]",
"doi": "10.1093/icb/icaa006",
"issn": "1540-7063",
"publisher": "Oxford University Press",
"publication": "Integrative and Comparative Biology",
"publication_date": "2020-03",
"series_number": "S1",
"volume": "60",
"issue": "S1",
"pages": "E170"
},
{
"id": "authors:z0ev8-vdw04",
"collection": "authors",
"collection_id": "z0ev8-vdw04",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200204-073456000",
"type": "article",
"title": "Stable Isotope Analysis of Intact Oxyanions Using Electrospray Quadrupole-Orbitrap Mass Spectrometry",
"author": [
{
"family_name": "Neubauer",
"given_name": "Cajetan",
"orcid": "0000-0002-5348-5609",
"clpid": "Neubauer-C"
},
{
"family_name": "Cr\u00e9mi\u00e8re",
"given_name": "Antoine",
"orcid": "0000-0001-7382-2097",
"clpid": "Cr\u00e9mi\u00e8re-A"
},
{
"family_name": "Wang",
"given_name": "Xingchen T.",
"orcid": "0000-0001-5316-789X",
"clpid": "Wang-Xingchen-Tony"
},
{
"family_name": "Thiagarajan",
"given_name": "Nivedita",
"clpid": "Thiagarajan-N"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Dalleska",
"given_name": "Nathan F.",
"orcid": "0000-0002-2059-1587",
"clpid": "Dalleska-N-F"
},
{
"family_name": "Turchyn",
"given_name": "Alexandra V.",
"orcid": "0000-0002-9298-2173",
"clpid": "Turchyn-A-V"
},
{
"family_name": "Clegg",
"given_name": "Josephine A.",
"clpid": "Clegg-J-A"
},
{
"family_name": "Moradian",
"given_name": "Annie",
"orcid": "0000-0002-0407-2031",
"clpid": "Moradian-A"
},
{
"family_name": "Sweredoski",
"given_name": "Michael J.",
"orcid": "0000-0003-0878-3831",
"clpid": "Sweredoski-M-J"
},
{
"family_name": "Garbis",
"given_name": "Spiros D.",
"orcid": "0000-0002-1050-0805",
"clpid": "Garbis-S-D"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
}
],
"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\u20132\u2030 for sulfate \u03b4\u00b3\u2074S and \u03b4\u00b9\u2078O and nitrate \u03b4\u00b9\u2075N and \u03b4\u00b9\u2078O, based on in-house and international standards. Less abundant variants such as \u03b4\u00b9\u2077O, \u03b4\u00b3\u00b3S, and \u03b4\u00b3\u2076S, and the \u00b3\u2074S\u2013\u00b9\u2078O \"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 \u00b9\u2078O/\u00b3\u2074S ratios with 0.2\u2030 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.",
"doi": "10.1021/acs.analchem.9b04486",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2020-02-18",
"series_number": "4",
"volume": "92",
"issue": "4",
"pages": "3077-3085"
},
{
"id": "authors:7y1ad-9nq67",
"collection": "authors",
"collection_id": "7y1ad-9nq67",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191203-102139413",
"type": "article",
"title": "Hydrologic change in New Zealand during the last deglaciation linked to reorganization of the Southern Hemisphere westerly winds",
"author": [
{
"family_name": "Hinojosa",
"given_name": "Jessica L.",
"orcid": "0000-0002-8589-102X",
"clpid": "Hinojosa-J-L"
},
{
"family_name": "Moy",
"given_name": "Christopher M.",
"orcid": "0000-0002-2177-5265",
"clpid": "Moy-C-M"
},
{
"family_name": "Vandergoes",
"given_name": "Marcus",
"orcid": "0000-0001-7417-7747",
"clpid": "Vandergoes-M"
},
{
"family_name": "Feakins",
"given_name": "Sarah J.",
"orcid": "0000-0003-3434-2423",
"clpid": "Feakins-S-J"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Millennial\u2010scale climate anomalies punctuating the last deglaciation were expressed differently in the Northern and Southern Hemispheres. While changes in oceanic meridional overturning circulation have been invoked to explain these disparities, the nearly synchronous onset of such events requires atmospheric mediation. Yet the extent and structure of atmospheric reorganization on millennial timescales remains unclear. In particular, the role of the Southern Hemisphere westerly winds (SHWW) and associated storm tracks is poorly constrained, largely due to the paucity of accessible archives of wind behavior. Here we present a new paleohydrologic record from a Lake Hayes, New Zealand (45\u00b0 S) sediment core from ~17\u20109 ka. Using two independent proxies for lake hydrology (Ca/Ti in sediments and \u03b4D values of aquatic plant biomarkers), we find evidence for a wetter Antarctic Cold Reversal (ACR, 14.7\u201013.0 ka) and a drying trend during the Younger Dryas (YD, 12.9\u201011.6 ka) and early Holocene (11.7 ka onward in this record). Comparisons of the Lake Hayes record with other Southern Hemisphere sites indicate coherent atmospheric shifts during the ACR and YD, whereby the former is wetter/cooler and the latter is drier/warmer. The wet/cool phase is associated with a northward shift and/or strengthening of the SHWW, whereas the drier/warmer phase indicates weaker mid\u2010latitude winds. These climatic trends are opposite to the Northern Hemisphere. There is a decoupling of climatic trends between Southern Hemisphere low\u2010 and mid\u2010latitude climates in the early Holocene, which could be explained by several mechanisms, such as the retreat of Antarctic sea ice.",
"doi": "10.1029/2019pa003656",
"issn": "2572-4517",
"publisher": "American Geophysical Union",
"publication": "Paleoceanography and Paleoclimatology",
"publication_date": "2019-12",
"series_number": "12",
"volume": "34",
"issue": "12",
"pages": "2158-2170"
},
{
"id": "authors:1ygjz-h3318",
"collection": "authors",
"collection_id": "1ygjz-h3318",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190531-155520679",
"type": "article",
"title": "\u00b2H/\u00b9H variation in microbial lipids is controlled by NADPH metabolism",
"author": [
{
"family_name": "Wijker",
"given_name": "Reto S.",
"orcid": "0000-0001-5104-9849",
"clpid": "Wijker-Reto-S"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Fuhrer",
"given_name": "Tobias",
"clpid": "Fuhrer-Tobias"
},
{
"family_name": "Phan",
"given_name": "Michelle",
"clpid": "Phan-Michelle"
}
],
"abstract": "The hydrogen-isotopic compositions (\u00b2H/\u00b9H ratios) of lipids in microbial heterotrophs are known to vary enormously, by at least 40% (400\u2030) relative. This is particularly surprising, given that most C-bound H in their lipids appear to derive from the growth medium water, rather than from organic substrates, implying that the isotopic fractionation between lipids and water is itself highly variable. Changes in the lipid/water fractionation are also strongly correlated with the type of energy metabolism operating in the host. Because lipids are well preserved in the geologic record, there is thus significant potential for using lipid ^2H/^1H ratios to decipher the metabolism of uncultured microorganisms in both modern and ancient ecosystems. But despite over a decade of research, the precise mechanisms underlying this isotopic variability remain unclear. Differences in the kinetic isotope effects (KIEs) accompanying NADP+ reduction by dehydrogenases and transhydrogenases have been hypothesized as a plausible mechanism. However, this relationship has been difficult to prove because multiple oxidoreductases affect the NADPH pool simultaneously. Here, we cultured five diverse aerobic heterotrophs, plus five Escherichia coli mutants, and used metabolic flux analysis to show that \u00b2H/\u00b9H fractionations are highly correlated with fluxes through NADP+-reducing and NADPH-balancing reactions. Mass-balance calculations indicate that the full range of \u00b2H/\u00b9H variability in the investigated organisms can be quantitatively explained by varying fluxes, i.e., with constant KIEs for each involved oxidoreductase across all species. This proves that lipid \u00b2H/\u00b9H ratios of heterotrophic microbes are quantitatively related to central metabolism and provides a foundation for interpreting \u00b2H/\u00b9H ratios of environmental lipids and sedimentary hydrocarbons.",
"doi": "10.1073/pnas.1818372116",
"pmcid": "PMC6589753",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2019-06-18",
"series_number": "25",
"volume": "116",
"issue": "25",
"pages": "12173-12182"
},
{
"id": "authors:0ctcx-rxw62",
"collection": "authors",
"collection_id": "0ctcx-rxw62",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190114-132114245",
"type": "article",
"title": "Precise determination of equilibrium sulfur isotope effects during volatilization and deprotonation of dissolved H_2S",
"author": [
{
"family_name": "Sim",
"given_name": "Min Sub",
"orcid": "0000-0002-3491-9002",
"clpid": "Sim-Min-Sub"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"abstract": "Sulfide (H_2S, HS^\u2212, and S^(2\u2212)) 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\u2212)), 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\u2212 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\u00b1\u202f0.5\u202f\u00b0C 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\u2030 and 3.1\u2030 relative to gaseous H_2S and aqueous HS\u2212, respectively. The estimated fractionation between aqueous H_2S and HS^\u2212 lies between two earlier experimental reports, but agrees within the uncertainty of the measurements with a recent theoretical calculation.",
"doi": "10.1016/j.gca.2019.01.016",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2019-03-01",
"volume": "248",
"pages": "242-251"
},
{
"id": "authors:0z9mw-2np97",
"collection": "authors",
"collection_id": "0z9mw-2np97",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190114-083925177",
"type": "article",
"title": "Role of APS reductase in biogeochemical sulfur isotope fractionation",
"author": [
{
"family_name": "Sim",
"given_name": "Min Sub",
"orcid": "0000-0002-3491-9002",
"clpid": "Sim-Min-Sub"
},
{
"family_name": "Ogata",
"given_name": "Hideaki",
"orcid": "0000-0002-2894-2417",
"clpid": "Ogata-Hideaki"
},
{
"family_name": "Lubitz",
"given_name": "Wolfgang",
"orcid": "0000-0001-7059-5327",
"clpid": "Lubitz-Wolfgang"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "McGlynn",
"given_name": "Shawn E.",
"orcid": "0000-0002-8199-7011",
"clpid": "McGlynn-Shawn-E"
}
],
"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\u2030, 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.",
"doi": "10.1038/s41467-018-07878-4",
"pmcid": "PMC6327049",
"issn": "2041-1723",
"publisher": "Nature Publishing Group",
"publication": "Nature Communications",
"publication_date": "2019-01-09",
"volume": "10",
"pages": "Art. No. 44"
},
{
"id": "authors:cce66-3kd70",
"collection": "authors",
"collection_id": "cce66-3kd70",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181003-105017642",
"type": "article",
"title": "Towards measuring growth rates of pathogens during infections by D_2O-labeling lipidomics",
"author": [
{
"family_name": "Neubauer",
"given_name": "Cajetan",
"orcid": "0000-0002-5348-5609",
"clpid": "Neubauer-C"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Booth",
"given_name": "Ian R.",
"clpid": "Booth-I-R"
},
{
"family_name": "Bowen",
"given_name": "Benjamin P.",
"orcid": "0000-0003-1368-3958",
"clpid": "Bowen-B-P"
},
{
"family_name": "Kopf",
"given_name": "Sebastian H.",
"orcid": "0000-0002-2044-0201",
"clpid": "Kopf-S-H"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
},
{
"family_name": "Dalleska",
"given_name": "Nathan F.",
"orcid": "0000-0002-2059-1587",
"clpid": "Dalleska-N-F"
}
],
"abstract": "Rationale: Microbial growth rate is an important physiological parameter that is challenging to measure in situ, partly because microbes grow slowly in many environments. Recently, it has been demonstrated that generation times of S. aureus in cystic fibrosis (CF) infections can be determined by D_2O\u2010labeling of actively synthesized fatty acids. To improve species specificity and allow growth rate monitoring for a greater range of pathogens during the treatment of infections, it is desirable to accurately quantify trace incorporation of deuterium into phospholipids. \n\nMethods: Lipid extracts of D_2O\u2010treated E. coli cultures were measured on liquid chromatography/electrospray ionization mass spectrometry (LC/ESI\u2010MS) instruments equipped with time\u2010of\u2010flight (TOF) and orbitrap mass analyzers, and used for comparison with the analysis of fatty acids by isotope\u2010ratio gas chromatography (GC)/MS. We then developed an approach to enable tracking of lipid labeling, by following the transition from stationary into exponential growth in pure cultures. Lastly, we applied D_2O\u2010labeling lipidomics to clinical samples from CF patients with chronic lung infections. \n\nResults: Lipidomics facilitates deuterium quantification in lipids at levels that are useful for many labeling applications (>0.03 at% D). In the E. coli cultures, labeling dynamics of phospholipids depend largely on their acyl chains and between phospholipids we notice differences that are not obvious from absolute concentrations alone. For example, cyclopropyl\u2010containing lipids reflect the regulation of cyclopropane fatty acid synthase, which is predominantly expressed at the beginning of stationary phase. The deuterium incorporation into a lipid that is specific for S. aureus in CF sputum indicates an average generation time of the pathogen on the order of one cell doubling per day. \n\nConclusions: This study demonstrates how trace level measurement of stable isotopes in intact lipids can be used to quantify lipid metabolism in pure cultures and provides guidelines that enable growth rate measurements in microbiome samples after incubation with a low percentage of D_2O.",
"doi": "10.1002/rcm.8288",
"issn": "0951-4198",
"publisher": "Wiley",
"publication": "Rapid Communications in Mass Spectrometry",
"publication_date": "2018-12-30",
"series_number": "24",
"volume": "32",
"issue": "24",
"pages": "2129-2140"
},
{
"id": "authors:cn4e9-pbm07",
"collection": "authors",
"collection_id": "cn4e9-pbm07",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181004-081517527",
"type": "article",
"title": "Refining the Application of Microbial Lipids as Tracers of Staphylococcus aureus Growth Rates in Cystic Fibrosis Sputum",
"author": [
{
"family_name": "Neubauer",
"given_name": "Cajetan",
"orcid": "0000-0002-5348-5609",
"clpid": "Neubauer-Cajetan"
},
{
"family_name": "Kasi",
"given_name": "Ajay S.",
"orcid": "0000-0003-0435-2807",
"clpid": "Kasi-Ajay-S"
},
{
"family_name": "Grahl",
"given_name": "Nora",
"clpid": "Grahl-Nora"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Kopf",
"given_name": "Sebastian H.",
"orcid": "0000-0002-2044-0201",
"clpid": "Kopf-Sebastian-H"
},
{
"family_name": "Kato",
"given_name": "Roberta M.",
"clpid": "Kato-Roberta-M"
},
{
"family_name": "Hogan",
"given_name": "Deborah A.",
"orcid": "0000-0002-6366-2971",
"clpid": "Hogan-Deborah-A"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "Chronic lung infections in cystic fibrosis (CF) could be treated more effectively if the effects of antimicrobials on pathogens in situ were known. Here, we compared changes in the microbial community composition and pathogen growth rates in longitudinal studies of seven pediatric CF patients undergoing intravenous antibiotic administration during pulmonary exacerbations. The microbial community composition was determined by counting rRNA with NanoString DNA analysis, and growth rates were obtained by incubating CF sputum with heavy water and tracing incorporation of deuterium into two branched-chain (\"anteiso\") fatty acids (a-C_(15:0) and a-C_(17:0)) using gas chromatography-mass spectrometry (GC/MS). Prior to this study, both lipids were thought to be specific for Staphylococcaceae; hence, their isotopic enrichment was interpreted as a growth proxy for Staphylococcus aureus. Our experiments revealed, however, that Prevotella is also a relevant microbial producer of a-C_(17:0) fatty acid in some CF patients; thus, deuterium incorporation into these lipids is better interpreted as a more general pathogen growth rate proxy. Even accounting for a small nonmicrobial background source detected in some patient samples, a-C_(15:0) fatty acid still appears to be a relatively robust proxy for CF pathogens, revealing a median generation time of \u223c1.5 days, similar to prior observations. Contrary to our expectation, pathogen growth rates remained relatively stable throughout exacerbation treatment. We suggest two straightforward \"best practices\" for application of stable-isotope probing to CF sputum metabolites: (i) parallel determination of microbial community composition in CF sputum using culture-independent tools and (ii) assessing background levels of the diagnostic metabolite.",
"doi": "10.1128/jb.00365-18",
"pmcid": "PMC6256016",
"issn": "0021-9193",
"publisher": "American Society for Microbiology",
"publication": "Journal of Bacteriology",
"publication_date": "2018-12",
"series_number": "24",
"volume": "200",
"issue": "24",
"pages": "Art. No. e00365-18"
},
{
"id": "authors:aap75-w8f88",
"collection": "authors",
"collection_id": "aap75-w8f88",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180702-111202770",
"type": "article",
"title": "Position-Specific Hydrogen Isotope Equilibrium in Propane",
"author": [
{
"family_name": "Xie",
"given_name": "Hao",
"clpid": "Xie-Hao"
},
{
"family_name": "Ponton",
"given_name": "Camilo",
"clpid": "Ponton-C"
},
{
"family_name": "Formolo",
"given_name": "Michael J.",
"clpid": "Formolo-M-J"
},
{
"family_name": "Lawson",
"given_name": "Michael",
"clpid": "Lawson-M"
},
{
"family_name": "Peterson",
"given_name": "Brian K.",
"clpid": "Peterson-B-K"
},
{
"family_name": "Lloyd",
"given_name": "Max K.",
"orcid": "0000-0001-9367-2698",
"clpid": "Lloyd-M-K"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Intramolecular isotope distributions can constrain source attribution, mechanisms of formation and destruction, and temperature-time histories of molecules. In this study, we explore the D/H fractionation between central (-CH_2-) and terminal (-CH_3) positions of propane (C_3H_8)- a percent level component of natural gases. The temperature dependenceof position-specific D/H fractionation of propane could potentially work as a geo-thermometer for natural gas systems, and a forensic identifier of specific thermogenic sources of atmospheric or aquatic emissions. Moreover, kinetically controlled departures from temperature dependent equilibrium might constrain mechanisms of thermogenic production, or provide indicators of biological or photochemical destruction. We developed a method to measure position-specific D/H differences of propane with high-resolution gas source mass spectrometry. We performed laboratory exchange experiments to study the exchange ratesfor both terminal and central positions, and used catalysts to drive the hydrogen isotopedistribution of propane to thermodynamic equilibrium. Experimental results demonstrate that D/H exchange between propane and water happens easily in the presence of either Pd catalyst or Ni catalyst. Exchange rates are similar between the two positions catalyzed by Pd. However, the central position exchanges 2.2 times faster than the terminal position in the presence of Ni catalyst. At 200\u202f\u00b0C in the presence of Pd catalyst, the e-folding time of propane-water exchange is 20\u202fdays and of homogeneous exchange (i.e., equilibrium between central and terminal positions) is 28\u202fmin. An equilibrated (bracketed and time-invariant) intramolecular hydrogen isotope distribution was attained for propane at three temperatures, 30\u202f\u00b0C, 100\u202f\u00b0C and 200\u202f\u00b0C; these data serve as an initial experimental calibration of a new position-specific thermometer with a temperature sensitivity of 0.25\u2030 per \u00b0C at 100\u202f\u00b0C. We use this calibration to test the validity of prior published theoretical predictions. Comparison of data with models suggest the most sophisticated of these discrepant models (Webb and Miller, 2014) is most accurate; this conclusion implies that there is a combined experimental and theoretical foundation for an 'absolute reference frame' for position-specific H isotope analysis of propane, following principles previously used for clumped isotope analysis of CO_2, CH_4 and O_2 (Eiler and Schauble, 2004; Yeung et al., 2014; Stolper et al., 2014).",
"doi": "10.1016/j.gca.2018.06.025",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2018-10-01",
"volume": "238",
"pages": "193-207"
},
{
"id": "authors:9f21g-1jt31",
"collection": "authors",
"collection_id": "9f21g-1jt31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180614-093746378",
"type": "article",
"title": "Cenozoic record of \u03b4^(34)S in foraminiferal calcite implies an early Eocene shift to deep-ocean sulfide burial",
"author": [
{
"family_name": "Rennie",
"given_name": "Victoria C. F.",
"clpid": "Rennie-V-C-F"
},
{
"family_name": "Paris",
"given_name": "Guillaume",
"orcid": "0000-0001-8368-1224",
"clpid": "Paris-G"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Abramovich",
"given_name": "Sigal",
"orcid": "0000-0003-3124-1387",
"clpid": "Abramovich-S"
},
{
"family_name": "Turchyn",
"given_name": "Alexandra V.",
"orcid": "0000-0002-9298-2173",
"clpid": "Turchyn-A-V"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"abstract": "Understanding the changes in, and drivers of, isotopic variability of sulfur in seawater sulfate (\u03b4^(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 \u03b4^(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\u2013Palaeogene sea-level changes and tectonic reorganization, occurring as the Himalayan arc first collided with Asia.",
"doi": "10.1038/s41561-018-0200-y",
"issn": "1752-0894",
"publisher": "Nature Publishing Group",
"publication": "Nature Geoscience",
"publication_date": "2018-10",
"series_number": "10",
"volume": "11",
"issue": "10",
"pages": "761-765"
},
{
"id": "authors:v5v9m-xpw15",
"collection": "authors",
"collection_id": "v5v9m-xpw15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171006-091955243",
"type": "article",
"title": "Position-specific ^(13)C distributions within propane from experiments and natural gas samples",
"author": [
{
"family_name": "Piasecki",
"given_name": "Alison",
"clpid": "Piasecki-A"
},
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Lawson",
"given_name": "Michael",
"clpid": "Lawson-M"
},
{
"family_name": "Ferreira",
"given_name": "A. A.",
"clpid": "Ferreira-A-A"
},
{
"family_name": "Santos Neto",
"given_name": "E. V.",
"clpid": "Santos-Neto-E-V"
},
{
"family_name": "Ellis",
"given_name": "Geoffrey S.",
"clpid": "Ellis-G-S"
},
{
"family_name": "Lewan",
"given_name": "Michael D.",
"clpid": "Lewan-M-D"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Site-specific carbon isotope measurements of organic compounds potentially recover information that is lost in a conventional, 'bulk' isotopic analysis. Such measurements are useful because isotopically fractionating processes may have distinct effects at different molecular sites, and thermodynamically equilibrated populations of molecules tend to concentrate heavy isotopes in one molecular site versus another. Most recent studies of site-specific ^(13)C in organics use specialized Nuclear Magnetic Resonance (NMR) techniques or complex chemical degradations prior to mass spectrometric measurements. Herein we present the first application of a new mass spectrometric technique that reconstructs the site-specific carbon isotope composition of propane based on measurements of the ^(13)C/^(12)C ratios of two or more fragment ions that sample different proportions of the terminal and central carbon sites. We apply this method to propane from laboratory experiments and natural gas samples to explore the relationships between site-specific carbon isotope composition, full-molecular \u03b4^(13)C, thermal maturity, and variation in organic matter precursors. Our goal is to advance the understanding of the sources and histories of short-chain alkanes within geologic systems. Our findings suggest that propane varies in its site-specific carbon isotope structure, which is correlated with increasing thermal maturity, first increasing in terminal position \u03b4^(13)C and then increasing in both center and terminal position \u03b4^(13)C. This pattern is observed in both experimental and natural samples, and is plausibly explained by a combination of site-specific, temperature-dependent isotope effects associated with conversion of different precursor molecules (kerogen, bitumen, and/or oil) to propane, differences in site-specific isotopic contents of those precursors, and possibly distillation of reactive components of those precursors with increasing maturity. We hypothesize that the largest changes in site-specific isotopic content of propane occur when bitumen and/or oil replace kerogen as the dominant precursors. If correct, this phenomenon could have significant utility for understanding gas generation in thermogenic petroleum systems.",
"doi": "10.1016/j.gca.2017.09.042",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2018-01-01",
"volume": "220",
"pages": "110-124"
},
{
"id": "authors:arjnf-x4591",
"collection": "authors",
"collection_id": "arjnf-x4591",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170817-141906771",
"type": "article",
"title": "Methane Clumped Isotopes: Progress and Potential for a New Isotopic Tracer",
"author": [
{
"family_name": "Douglas",
"given_name": "Peter M. J.",
"clpid": "Douglas-P-M-J"
},
{
"family_name": "Stolper",
"given_name": "Daniel A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Lawson",
"given_name": "Michael",
"clpid": "Lawson-M"
},
{
"family_name": "Shuai",
"given_name": "Yanhua",
"clpid": "Shuai-Yanhua"
},
{
"family_name": "Bishop",
"given_name": "Andrew",
"clpid": "Bishop-A"
},
{
"family_name": "Podlaha",
"given_name": "Olaf G.",
"clpid": "Podlaha-O-G"
},
{
"family_name": "Ferreira",
"given_name": "Alexandre A.",
"clpid": "Ferreira-A-A"
},
{
"family_name": "Santos Neto",
"given_name": "Eugenio V.",
"clpid": "Santos-Neto-E-V"
},
{
"family_name": "Niemann",
"given_name": "Martin",
"clpid": "Niemann-M"
},
{
"family_name": "Steen",
"given_name": "Arne S.",
"clpid": "Steen-A-S"
},
{
"family_name": "Huang",
"given_name": "Ling",
"clpid": "Huang-Ling"
},
{
"family_name": "Chimiak",
"given_name": "Laura",
"clpid": "Chimiak-L"
},
{
"family_name": "Valentine",
"given_name": "David L.",
"clpid": "Valentine-D-L"
},
{
"family_name": "Fiebig",
"given_name": "Jens",
"clpid": "Fiebig-J"
},
{
"family_name": "Luhmann",
"given_name": "Andrew J.",
"clpid": "Luhmann-A-J"
},
{
"family_name": "Seyfried",
"given_name": "William E., Jr.",
"clpid": "Seyfried-W-E-Jr"
},
{
"family_name": "Etiope",
"given_name": "Giuseppe",
"clpid": "Etiope-G"
},
{
"family_name": "Schoell",
"given_name": "Martin",
"clpid": "Schoell-M"
},
{
"family_name": "Inskeep",
"given_name": "William P.",
"clpid": "Inskeep-W-P"
},
{
"family_name": "Moran",
"given_name": "James J.",
"clpid": "Moran-J-J"
},
{
"family_name": "Kitchen",
"given_name": "Nami",
"clpid": "Kitchen-N-E"
}
],
"abstract": "The isotopic composition of methane is of longstanding geochemical interest, with important implications for understanding petroleum systems, atmospheric greenhouse gas concentrations, the global carbon cycle, and life in extreme environments. Recent analytical developments focusing on multiply substituted isotopologues ('clumped isotopes') are opening a valuable new window into methane geochemistry. When methane forms in internal isotopic equilibrium, clumped isotopes can provide a direct record of formation temperature, making this property particularly valuable for identifying different methane origins. However, it has also become clear that in certain settings methane clumped isotope measurements record kinetic rather than equilibrium isotope effects. Here we present a substantially expanded dataset of methane clumped isotope analyses, and provide a synthesis of the current interpretive framework for this parameter. In general, clumped isotope measurements indicate plausible formation temperatures for abiotic, thermogenic, and microbial methane in many geological environments, which is encouraging for the further development of this measurement as a geothermometer, and as a tracer for the source of natural gas reservoirs and emissions. We also highlight, however, instances where clumped isotope derived temperatures are higher than expected, and discuss possible factors that could distort equilibrium formation temperature signals. In microbial methane from freshwater ecosystems, in particular, clumped isotope values appear to be controlled by kinetic effects, and may ultimately be useful to study methanogen metabolism.",
"doi": "10.1016/j.orggeochem.2017.07.016",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2017-11",
"volume": "113",
"pages": "262-282"
},
{
"id": "authors:xvn3r-yzt81",
"collection": "authors",
"collection_id": "xvn3r-yzt81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170807-134931467",
"type": "article",
"title": "Comparison of three methods for the methylation of aliphatic and aromatic compounds",
"author": [
{
"family_name": "Lee",
"given_name": "Hyejung",
"clpid": "Lee-Hyejung"
},
{
"family_name": "Feakins",
"given_name": "Sarah J.",
"orcid": "0000-0003-3434-2423",
"clpid": "Feakins-S-J"
},
{
"family_name": "Lu",
"given_name": "Zhiyao",
"clpid": "Lu-Zhiyao"
},
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Tierney",
"given_name": "Jessica E.",
"clpid": "Tierney-J-E"
},
{
"family_name": "Williams",
"given_name": "Travis J.",
"clpid": "Williams-T-J"
}
],
"abstract": "Rationale: Methylation protocols commonly call for acidic, hot conditions that are known to promote organic ^1H/^2H exchange in aromatic and aliphatic C\u2014H bonds. Here we tested two such commonly-used methods and compared a third that avoids these acidic conditions, to quantify isotope effects with each method and to directly determine acidic-exchange rates relevant to experimental conditions. \n\nMethods: We compared acidic and non-acidic methylation approaches catalyzed by hydrochloric acid, acetyl chloride and EDCI (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide) / DMAP (4-dimethylaminopyridine) respectively. These were applied to two analytes: phthalic acid (an aromatic) and octacosanoic acid (an aliphatic). We analyzed yield by gas chromatography flame ionization (GC/FID) and hydrogen and carbon isotopic composition by isotope ratio mass spectrometry (GC/IRMS). We quantified the ^1H/^2H exchange rate on dimethyl phthalate under acidic conditions with proton nuclear magnetic resonance (^1H-NMR) measurements. \n\nResults: The \u03b4^2H and \u03b4^(13)C values and yield were equivalent among the three methods for methyl octacosanoate. The two acidic methods resulted in comparable yield and isotopic composition of dimethyl phthalate; however, the non-acidic method resulted in lower \u03b4^2H and \u03b4^(13)C values perhaps due to low yields. Concerns over acid-catalyzed ^1H/^2H exchange are unwarranted as the effect was trivial over a 12-hour reaction time. \n\nConclusions: We find product isolation yield and evaporation to be the main concerns in the accurate determination of isotopic composition. ^1H/^2H exchange reactions are too slow to cause measurable isotope fractionation over the typical duration and reaction conditions used in methylation. Thus, we are able to recommend continued use of acidic catalysts in such methylation reactions for both aliphatic and aromatic compounds.",
"doi": "10.1002/rcm.7947",
"issn": "0951-4198",
"publisher": "Wiley",
"publication": "Rapid Communications in Mass Spectrometry",
"publication_date": "2017-10-15",
"series_number": "19",
"volume": "31",
"issue": "19",
"pages": "1633-1640"
},
{
"id": "authors:6806m-e7r83",
"collection": "authors",
"collection_id": "6806m-e7r83",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171020-085602582",
"type": "article",
"title": "Minimal Influence of [NiFe] Hydrogenase on Hydrogen Isotope Fractionation in H\u2082-Oxidizing Cupriavidus necator",
"author": [
{
"family_name": "Campbell",
"given_name": "Brian J.",
"clpid": "Campbell-Brian-J"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Fox",
"given_name": "Daniel N.",
"clpid": "Fox-Daniel-N"
},
{
"family_name": "Paul",
"given_name": "Blair G.",
"orcid": "0000-0002-5738-5568",
"clpid": "Paul-Blair-G"
},
{
"family_name": "Qin",
"given_name": "Qianhui",
"orcid": "0000-0002-4298-4664",
"clpid": "Qin-Qianhui"
},
{
"family_name": "Kellermann",
"given_name": "Matthias Y.",
"orcid": "0000-0001-5613-7573",
"clpid": "Kellermann-Matthias-Y"
},
{
"family_name": "Valentine",
"given_name": "David L.",
"orcid": "0000-0001-5914-9107",
"clpid": "Valentine-David-L"
}
],
"abstract": "Fatty acids produced by H\u2082-metabolizing bacteria are sometimes observed to be more D-depleted than those of photoautotrophic organisms, a trait that has been suggested as diagnostic for chemoautotrophic bacteria. The biochemical reasons for such a depletion are not known, but are often assumed to involve the strong D-depletion of H\u2082. Here, we cultivated the bacterium Cupriavidus necator H16 (formerly Ralstonia eutropha H16) under aerobic, H\u2082-consuming, chemoautotrophic conditions and measured the isotopic compositions of its fatty acids. In parallel with the wild type, two mutants of this strain, each lacking one of two key hydrogenase enzymes, were also grown and measured. In all three strains, fractionations between fatty acids and water ranged from -173\u2030 to -235\u2030, and averaged -217\u2030, -196\u2030, and -226\u2030, respectively, for the wild type, SH\u207b mutant, and MBH\u207b mutant. There was a modest increase in \u03b4D as a result of loss of the soluble hydrogenase enzyme. Fractionation curves for all three strains were constructed by growing parallel cultures in waters with \u03b4D_(water) values of approximately -25\u2030, 520\u2030, and 1100\u2030. These curves indicate that at least 90% of the hydrogen in fatty acids is derived from water, not H\u2082. Published details of the biochemistry of the soluble and membrane-bound hydrogenases confirm that these enzymes transfer electrons rather than intact hydride (H\u207b) ions, providing no direct mechanism to connect the isotopic composition of H\u2082 to that of lipids. Multiple lines of evidence thus agree that in this organism, and presumably others like it, environmental H\u2082 plays little or no direct role in controlling lipid \u03b4D values. The observed fractionations must instead result from isotope effects in the reduction of NAD(P)H by reductases with flavin prosthetic groups, which transfer two electrons and acquire H\u207a (or D\u207a) from solution. Parallels to NADPH reduction in photosynthesis may explain why D/H fractionations in C. necator are nearly identical to those in many photoautotrophic algae and bacteria. We conclude that strong D-depletion is not a diagnostic feature of chemoautotrophy.",
"doi": "10.3389/fmicb.2017.01886",
"pmcid": "PMC5649130",
"issn": "1664-302X",
"publisher": "Frontiers Media",
"publication": "Frontiers in Microbiology",
"publication_date": "2017-10-04",
"volume": "8",
"pages": "Art. No. 1886"
},
{
"id": "authors:kaxjq-tkr54",
"collection": "authors",
"collection_id": "kaxjq-tkr54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170227-143517457",
"type": "article",
"title": "Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway",
"author": [
{
"family_name": "Sim",
"given_name": "Min Sub",
"orcid": "0000-0002-3491-9002",
"clpid": "Sim-Min-Sub"
},
{
"family_name": "Paris",
"given_name": "Guillaume",
"orcid": "0000-0001-8368-1224",
"clpid": "Paris-G"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"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\u2030, 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.",
"doi": "10.1016/j.gca.2017.02.024",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2017-06-01",
"volume": "206",
"pages": "57-72"
},
{
"id": "authors:p5vc2-t8s81",
"collection": "authors",
"collection_id": "p5vc2-t8s81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170419-142047535",
"type": "article",
"title": "John M. Hayes 1940-2017. Father of isotopes in modern and ancient biogeochemical processes, biosynthetic carbon and hydrogen isotope fractionation and compound specific isotope analytical techniques",
"author": [
{
"family_name": "Podlaha",
"given_name": "Olaf G.",
"clpid": "Podlaha-O-G"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Freeman",
"given_name": "Katherine",
"orcid": "0000-0002-3350-7671",
"clpid": "Freeman-K-H"
}
],
"abstract": "John Michael Hayes, Professor of chemistry and geology for 26 years at Indiana University (Bloomington) until 1996, then director of the National Ocean Sciences Accelerator Mass Spectrometry facility at Woods Hole Oceanographic Institution and adjunct professor at Harvard University until 2007, died peacefully at his home in Berkeley, California, on February 3rd, 2017.",
"doi": "10.1016/j.orggeochem.2017.04.002",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2017-06",
"volume": "108",
"pages": "113-116"
},
{
"id": "authors:jj2kc-5mv06",
"collection": "authors",
"collection_id": "jj2kc-5mv06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170306-080715333",
"type": "article",
"title": "Rapid Quantification and Isotopic Analysis of Dissolved Sulfur Species",
"author": [
{
"family_name": "Smith",
"given_name": "Derek A.",
"clpid": "Smith-D-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Dalleska",
"given_name": "Nathan",
"orcid": "0000-0002-2059-1587",
"clpid": "Dalleska-N-F"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
}
],
"abstract": "Rationale: Dissolved sulfur species are of significant interest, both as important substrates for microbial activities and as key intermediaries in biogeochemical cycles. Species of intermediate oxidation state such as sulfite, thiosulfate, and thiols are of particular interest but are notoriously difficult to analyze, because of low concentrations and rapid oxidation during storage and analysis. \n\nMethods: Dissolved sulfur species are reacted with monobromobimane which yields a fluorescent bimane derivative that is stable to oxidation. Separation by Ultra-Performance Liquid Chromatography (UPLC) on a C18 column yields baseline resolution of analytes in under 5 minutes. Fluorescence detection (380 nm excitation, 480 nm emission) provides highly selective and sensitive quantitation, and Time of Flight Mass Spectrometry (TOF-MS) is used to quantify isotopic abundance, providing the ability to detect stable isotope tracers (either ^(33)S or ^(34)S). \n\nResults: Sulfite, thiosulfate, methanethiol, and bisulfide were quantified with on-column detection limits of picomoles (\u03bcM concentrations). Other sulfur species with unshared electrons are also amenable to analysis. TOF-MS detection of ^(34)S enrichment was accurate and precise to within 0.6% (relative) when sample and standard had similar isotope ratios, and was able to detect enrichments as small as 0.01 atom%. Accuracy was validated by comparison to isotope-ratio mass spectrometry. Four example applications are provided to demonstrate the utility of this method. \n\nConclusions: Derivatization of aqueous sulfur species with bromobimane is easily accomplished in the field, and protects analytes from oxidation during storage. UPLC separation with fluorescence detection provides low \u03bcM detection limits. Using a high-resolution TOF-MS, accurate detection of as little as 0.01% ^(34)S label incorporation into multiple species is feasible. This provides a useful new analytical window into microbial sulfur cycling.",
"doi": "10.1002/rcm.7846",
"issn": "0951-4198",
"publisher": "Wiley",
"publication": "Rapid Communications in Mass Spectrometry",
"publication_date": "2017-05-15",
"series_number": "9",
"volume": "31",
"issue": "9",
"pages": "791-803"
},
{
"id": "authors:6zbed-hjz55",
"collection": "authors",
"collection_id": "6zbed-hjz55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170410-073940373",
"type": "article",
"title": "Paleoecology and paleoceanography of the Athel silicilyte, Ediacaran-Cambrian boundary, Sultanate of Oman",
"author": [
{
"family_name": "Stolper",
"given_name": "D. A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Love",
"given_name": "G. D.",
"orcid": "0000-0002-6516-014X",
"clpid": "Love-G-D"
},
{
"family_name": "Bates",
"given_name": "S.",
"clpid": "Bates-S"
},
{
"family_name": "Lyons",
"given_name": "T. W.",
"clpid": "Lyons-T-W"
},
{
"family_name": "Young",
"given_name": "E.",
"clpid": "Young-E"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Grotzinger",
"given_name": "J. P.",
"orcid": "0000-0001-9324-1257",
"clpid": "Grotzinger-J-P"
}
],
"abstract": "The Athel silicilyte is an enigmatic, hundreds of meters thick, finely laminated quartz deposit, in which silica precipitated in deep water (>~100\u2013200 m) at the Ediacaran\u2013Cambrian boundary in the South Oman Salt Basin. In contrast, Meso-Neoproterozoic sinks for marine silica were dominantly restricted to peritidal settings. The silicilyte is known to contain sterane biomarkers for demosponges, which today are benthic, obligately aerobic organisms. However, the basin has previously been described as permanently sulfidic and time-equivalent shallow-water carbonate platform and evaporitic facies lack silica. The Athel silicilyte thus represents a unique and poorly understood depositional system with implications for late Ediacaran marine chemistry and paleoecology. To address these issues, we made petrographic observations, analyzed biomarkers in the solvent-extractable bitumen, and measured whole-rock iron speciation and oxygen and silicon isotopes. These data indicate that the silicilyte is a distinct rock type both in its sedimentology and geochemistry and in the original biology present as compared to other facies from the same time period in Oman. The depositional environment of the silicilyte, as compared to the bounding shales, appears to have been more reducing at depth in sediments and possibly bottom waters with a significantly different biological community contributing to the preserved biomarkers. We propose a conceptual model for this system in which deeper, nutrient-rich waters mixed with surface seawater via episodic mixing, which stimulated primary production. The silica nucleated on this organic matter and then sank to the seafloor, forming the silicilyte in a sediment-starved system. We propose that the silicilyte may represent a type of environment that existed elsewhere during the Neoproterozoic. These environments may have represented an important locus for silica removal from the oceans.",
"doi": "10.1111/gbi.12236",
"issn": "1472-4677",
"publisher": "Blackwell Publishing",
"publication": "Geobiology",
"publication_date": "2017-05",
"series_number": "3",
"volume": "15",
"issue": "3",
"pages": "401-426"
},
{
"id": "authors:vetve-xm298",
"collection": "authors",
"collection_id": "vetve-xm298",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160714-073258113",
"type": "article",
"title": "Rapid Organic Matter Sulfurization in Sinking Particles from the Cariaco Basin Water Column",
"author": [
{
"family_name": "Raven",
"given_name": "Morgan Reed",
"clpid": "Raven-M-R"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Thunell",
"given_name": "Robert C.",
"clpid": "Thunell-R-C"
}
],
"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.",
"doi": "10.1016/j.gca.2016.06.030",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2016-10-01",
"volume": "190",
"pages": "175-190"
},
{
"id": "authors:jw7me-bx388",
"collection": "authors",
"collection_id": "jw7me-bx388",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160705-133851635",
"type": "article",
"title": "Prediction of equilibrium distributions of isotopologues for methane, ethane and propane using density functional theory",
"author": [
{
"family_name": "Piasecki",
"given_name": "Alison",
"clpid": "Piasecki-A"
},
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Peterson",
"given_name": "Brian",
"clpid": "Peterson-B"
},
{
"family_name": "Eiler",
"given_name": "John",
"clpid": "Eiler-J-M"
}
],
"abstract": "Many previous studies have examined abundances of deuterium (D) and ^(13)C within small organic molecules. Recent advances in analytical instrumentation add the abilities to measure site-specific and multiply substituted isotopologues of natural organics. Here we perform first-principles calculations of the equilibrium distributions of ^(13)C and D in the volatile alkanes (including both single and multiple substitutions), as a guide to the interpretation of current measurements and as a basis for anticipating isotope effects that might be examined with future analytical techniques. The models we present illustrate several common themes of the isotopic structures of the small alkanes, including; temperature dependent enrichment of clumped isotope species, with amplitudes in the order D\u2013D > ^(13)C\u2013D > ^(13)C\u2013^(13)C; similarity in strength of such clumped isotope effects between different molecules (e.g., ^(13)C\u2013D clumping is \u223c5\u2030 enriched at 300 K in methane, ethane and propane); a \u223c10\u00d7 contrast between the amplitudes of stronger adjacent substitution of two heavy isotopes vs. weaker non-adjacent substitution; temperature-dependent site-specific fractionation of D and ^(13)C into interior positions of molecules relative to terminal methyl groups; and a relatively simple additive effect to the overall amplitude of enrichment when clumped and site specific effects combine in the same isotopologue. We suggest that the most promising tools suggested by our results are isotopic thermometers based on site-specific distribution of deuterium, which exhibits strong (\u223c100\u2030), highly temperature dependent fractionation between methyl groups and methylene carbon positions in propane (and likely other larger n-alkanes).",
"doi": "10.1016/j.gca.2016.06.003",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2016-10-01",
"volume": "190",
"pages": "1-12"
},
{
"id": "authors:wrgca-5wy37",
"collection": "authors",
"collection_id": "wrgca-5wy37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161014-072012938",
"type": "article",
"title": "Plant-wax D/H ratios in the southern European Alps record multiple aspects of climate variability",
"author": [
{
"family_name": "Wirth",
"given_name": "Stefanie B.",
"clpid": "Wirth-S-B"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "We present a Younger Dryas\u2013Holocene record of the hydrogen isotopic composition of sedimentary plant waxes (\u03b4D_(wax)) from the southern European Alps (Lake Ghirla, N-Italy) to investigate its sensitivity to climatic forcing variations in this mid-latitude region (45\u00b0N). \n\nA modern altitudinal transect of \u03b4D values of river water and leaf waxes in the Lake Ghirla catchment is used to test present-day climate sensitivity of \u03b4D_(wax). While we find that altitudinal effects on \u03b4D_(wax) are minor at our study site, temperature, precipitation amount, and evapotranspiration all appear to influence \u03b4D_(wax) to varying extents. \n\nIn the lake-sediment record, \u03b4D_(wax) values vary between \u2212134 and \u2212180\u2030 over the past 13 kyr. The long-term Holocene pattern of \u03b4D_(wax) parallels the trend of decreasing temperature and is thus likely forced by the decline of northern hemisphere summer insolation. Shorter-term fluctuations, in contrast, may reflect both temperature and moisture-source changes. During the cool Younger Dryas and Little Ice Age (LIA) periods we observe unexpectedly high \u03b4D_(wax) values relative to those before and after. We suggest that a change towards a more D-enriched moisture source is required during these intervals. In fact, a shift from northern N-Atlantic to southern N-Atlantic/western Mediterranean Sea sources would be consistent with a southward migration of the Westerlies with climate cooling. Prominent \u03b4D_(wax) fluctuations in the early and middle Holocene are negative and potentially associated with temperature declines. In the late Holocene (<4 kyr BP), excursions are partly positive (as for the LIA) suggesting a stronger influence of moisture-source changes on \u03b4D_(wax) variation. In addition to isotopic fractionations of the hydrological cycle, changes in vegetation composition, in the length of the growing season, and in snowfall amount provide additional potential sources of variability, although we cannot yet quantitatively assess these in the paleo-record. We conclude that while our \u03b4D_(wax) record from the Alps does contain climatic information, it is a complicated record that would require additional constraints to be robustly interpreted. This also has important implications for other water-isotope-based proxy records of precipitation and hydro-climate from this region, such as cave speleothems.",
"doi": "10.1016/j.quascirev.2016.07.020",
"issn": "0277-3791",
"publisher": "Elsevier",
"publication": "Quaternary Science Reviews",
"publication_date": "2016-09-15",
"volume": "148",
"pages": "176-191"
},
{
"id": "authors:svwx9-frb17",
"collection": "authors",
"collection_id": "svwx9-frb17",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160610-151828176",
"type": "article",
"title": "Analysis of the site-specific carbon isotope composition of propane by gas source isotope ratio mass spectrometer",
"author": [
{
"family_name": "Piasecki",
"given_name": "Alison",
"clpid": "Piasecki-A"
},
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Lawson",
"given_name": "Michael",
"clpid": "Lawson-M"
},
{
"family_name": "Ferreira",
"given_name": "A. A.",
"clpid": "Ferreira-A-A"
},
{
"family_name": "Santos Neto",
"given_name": "E. V.",
"clpid": "Santos-Neto-E-V"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Site-specific isotope ratio measurements potentially provide valuable information about the formation and degradation of complex molecules\u2014information that is lost in conventional bulk isotopic measurements. Here we discuss the background and possible applications of such measurements, and present a technique for studying the site-specific carbon isotope composition of propane at natural abundance based on mass spectrometric analysis of the intact propane molecule and its fragment ions. We demonstrate the feasibility of this approach through measurements of mixtures of natural propane and propane synthesized with site-specific^(13)C enrichment, and we document the limits of precision of our technique. We show that mass balance calculations of the bulk \u03b4^(13)C of propane based on our site-specific measurements is generally consistent with independent constraints on bulk \u03b4^(13)C. We further demonstrate the accuracy of the technique, and illustrate one of its simpler applications by documenting the site-specific carbon isotope signature associated with gas phase diffusion of propane, confirming that our measurements conform to the predictions of the kinetic theory of gases. This method can be applied to propane samples of moderate size (tens of micromoles) isolated from natural gases. Thus, it provides a means of studying the site-specific stable isotope systematics of propane at natural isotope abundances on sample sizes that are readily recovered from many natural environments. This method may also serve as a model for future techniques that apply high-resolution mass spectrometry to study the site-specific isotopic distributions of larger organic molecules, with potential applications to biosynthesis, forensics and other geochemical subjects.",
"doi": "10.1016/j.gca.2016.04.048",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2016-09-01",
"volume": "188",
"pages": "58-72"
},
{
"id": "authors:b4c3m-gmt65",
"collection": "authors",
"collection_id": "b4c3m-gmt65",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160610-103423261",
"type": "article",
"title": "Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues",
"author": [
{
"family_name": "Douglas",
"given_name": "P. M. J.",
"clpid": "Douglas-P-M-J"
},
{
"family_name": "Stolper",
"given_name": "D. A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Smith",
"given_name": "D. A.",
"clpid": "Smith-D-A"
},
{
"family_name": "Anthony",
"given_name": "K. M. Walter",
"clpid": "Anthony-K-M-W"
},
{
"family_name": "Paull",
"given_name": "C. K.",
"clpid": "Paull-C-K"
},
{
"family_name": "Dallimore",
"given_name": "S.",
"clpid": "Dallimore-S"
},
{
"family_name": "Wik",
"given_name": "M.",
"clpid": "Wik-M"
},
{
"family_name": "Crill",
"given_name": "P. M.",
"clpid": "Crill-P-M"
},
{
"family_name": "Winterdahl",
"given_name": "M.",
"clpid": "Winterdahl-M"
},
{
"family_name": "Eiler",
"given_name": "J. M.",
"clpid": "Eiler-J-M"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Methane is a potent greenhouse gas, and there are concerns that its natural emissions from the Arctic could act as a substantial positive feedback to anthropogenic global warming. Determining the sources of methane emissions and the biogeochemical processes controlling them is important for understanding present and future Arctic contributions to atmospheric methane budgets. Here we apply measurements of multiply-substituted isotopologues, or clumped isotopes, of methane as a new tool to identify the origins of ebullitive fluxes in Alaska, Sweden and the Arctic Ocean. When methane forms in isotopic equilibrium, clumped isotope measurements indicate the formation temperature. In some microbial methane, however, non-equilibrium isotope effects, probably related to the kinetics of methanogenesis, lead to low clumped isotope values. We identify four categories of emissions in the studied samples: thermogenic methane, deep subsurface or marine microbial methane formed in isotopic equilibrium, freshwater microbial methane with non-equilibrium clumped isotope values, and mixtures of deep and shallow methane (i.e., combinations of the first three end members). Mixing between deep and shallow methane sources produces a non-linear variation in clumped isotope values with mixing proportion that provides new constraints for the formation environment of the mixing end-members. Analyses of microbial methane emitted from lakes, as well as a methanol-consuming methanogen pure culture, support the hypothesis that non-equilibrium clumped isotope values are controlled, in part, by kinetic isotope effects induced during enzymatic reactions involved in methanogenesis. Our results indicate that these kinetic isotope effects vary widely in microbial methane produced in Arctic lake sediments, with non-equilibrium \u0394_18 values spanning a range of more than 5\u2030.",
"doi": "10.1016/j.gca.2016.05.031",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2016-09-01",
"volume": "188",
"pages": "163-188"
},
{
"id": "authors:vgkw3-45b53",
"collection": "authors",
"collection_id": "vgkw3-45b53",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160915-075013877",
"type": "article",
"title": "Study of thermochemical sulfate reduction mechanism using compound specific sulfur isotope analysis",
"author": [
{
"family_name": "Meshoulam",
"given_name": "Alexander",
"clpid": "Meshoulam-A"
},
{
"family_name": "Ellis",
"given_name": "Geoffrey S.",
"clpid": "Ellis-G-S"
},
{
"family_name": "Ahmad",
"given_name": "Ward Said",
"clpid": "Ahmad-W-S"
},
{
"family_name": "Deev",
"given_name": "Andrei",
"clpid": "Deev-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Tang",
"given_name": "Yongchun",
"clpid": "Tang-Yongchun"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Liu",
"given_name": "Jinzhong",
"clpid": "Liu-Jinzhong"
},
{
"family_name": "Gilhooly",
"given_name": "William P., III",
"clpid": "Gilhooly-W-P-III"
},
{
"family_name": "Aizenshtat",
"given_name": "Zeev",
"clpid": "Aizenshtat-Z"
},
{
"family_name": "Amrani",
"given_name": "Alon",
"clpid": "Amrani-A"
}
],
"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\u2030 for H_2S and as much as 22.2\u2030 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 (\u223c17\u2030).\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 \u03b4^(34)S values obtained from bulk phases such as H2S, oil, and sulfate minerals, and provide important mechanistic details about the overall TSR process.",
"doi": "10.1016/j.gca.2016.05.026",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2016-09-01",
"volume": "188",
"pages": "73-92"
},
{
"id": "authors:vn9n3-gjs76",
"collection": "authors",
"collection_id": "vn9n3-gjs76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160822-080815250",
"type": "article",
"title": "Fractionation of Hydrogen Isotopes by Sulfate- and Nitrate-Reducing Bacteria",
"author": [
{
"family_name": "Osburn",
"given_name": "Magdalena R.",
"orcid": "0000-0001-9180-559X",
"clpid": "Osburn-M-R"
},
{
"family_name": "Dawson",
"given_name": "Katherine S.",
"orcid": "0000-0001-8856-4609",
"clpid": "Dawson-Katherine-S"
},
{
"family_name": "Fogel",
"given_name": "Marilyn L.",
"clpid": "Fogel-M-L"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Hydrogen atoms from water and food are incorporated into biomass during cellular metabolism and biosynthesis, fractionating the isotopes of hydrogen\u2014protium and deuterium\u2014that are recorded in biomolecules. While these fractionations are often relatively constant in plants, large variations in the magnitude of fractionation are observed for many heterotrophic microbes utilizing different central metabolic pathways. The correlation between metabolism and lipid \u03b4^2H provides a potential basis for reconstructing environmental and ecological parameters, but the calibration dataset has thus far been limited mainly to aerobes. Here we report on the hydrogen isotopic fractionations of lipids produced by nitrate-respiring and sulfate-reducing bacteria. We observe only small differences in fractionation between oxygen- and nitrate-respiring growth conditions, with a typical pattern of variation between substrates that is broadly consistent with previously described trends. In contrast, fractionation by sulfate-reducing bacteria does not vary significantly between different substrates, even when autotrophic and heterotrophic growth conditions are compared. This result is in marked contrast to previously published observations and has significant implications for the interpretation of environmental hydrogen isotope data. We evaluate these trends in light of metabolic gene content of each strain, growth rate, and potential flux and reservoir-size effects of cellular hydrogen, but find no single variable that can account for the differences between nitrate- and sulfate-respiring bacteria. The emerging picture of bacterial hydrogen isotope fractionation is therefore more complex than the simple correspondence between \u03b4^2H and metabolic pathway previously understood from aerobes. Despite the complexity, the large signals and rich variability of observed lipid \u03b4^2H suggest much potential as an environmental recorder of metabolism.",
"doi": "10.3389/fmicb.2016.01166",
"pmcid": "PMC4969296",
"issn": "1664-302X",
"publisher": "Frontiers Research Foundation",
"publication": "Frontiers in Microbiology",
"publication_date": "2016-08-02",
"volume": "7",
"pages": "Art. No. 1166"
},
{
"id": "authors:x96x8-4vt90",
"collection": "authors",
"collection_id": "x96x8-4vt90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160510-131537800",
"type": "article",
"title": "Sedimentary pyrite \u03b4^(34)S differs from porewater sulfide in Santa Barbara Basin: proposed role of organic sulfur",
"author": [
{
"family_name": "Raven",
"given_name": "Morgan Reed",
"clpid": "Raven-M-R"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Fischer",
"given_name": "Woodward W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"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 (\u2211H_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 \u223c30\u2030 more ^(34)S-depleted than coexisting \u2211H_2S in porewater. S^0 has the same strongly ^(34)S-depleted composition as pyrite where it forms near the sediment\u2013water interface, though not at depth. This pattern is not easily explained by conventional hypotheses in which sedimentary pyrite derives from abiotic reactions with porewater \u2211H_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 \u2211H_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 \u03b4^(34)S values would then reflect the balance between microbial sulfide formation and the abundance of exchangeable OS. Both OS and pyrite \u03b434S records thus have the potential to provide valuable information about biogeochemical cycles and redox structure in sedimentary paleoenvironments.",
"doi": "10.1016/j.gca.2016.04.037",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2016-08-01",
"volume": "186",
"pages": "120-134"
},
{
"id": "authors:1zraz-cc163",
"collection": "authors",
"collection_id": "1zraz-cc163",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160610-155812845",
"type": "article",
"title": "The stable hydrogen isotopic composition of sedimentary plant waxes as quantitative proxy for rainfall in the West African Sahel",
"author": [
{
"family_name": "Niedermeyer",
"given_name": "Eva M.",
"clpid": "Niedermeyer-E-M"
},
{
"family_name": "Forrest",
"given_name": "Matthew",
"clpid": "Forrest-M"
},
{
"family_name": "Beckmann",
"given_name": "Britta",
"clpid": "Beckmann-B"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Mulch",
"given_name": "Andreas",
"clpid": "Mulch-A"
},
{
"family_name": "Schefu\u00df",
"given_name": "Enno",
"clpid": "Schefu\u00df-E"
}
],
"abstract": "Various studies have demonstrated that the stable hydrogen isotopic composition (\u03b4D) of terrestrial leaf waxes tracks that of precipitation (\u03b4D_(precip)) both spatially across climate gradients and over a range of different timescales. Yet, reconstructed estimates of \u03b4D_(precip) and corresponding rainfall typically remain largely qualitative, due mainly to uncertainties in plant ecosystem net fractionation, relative humidity, and the stability of the amount effect through time. Here we present \u03b4D values of the C_(31) n-alkane (\u03b4D_(wax)) from a marine sediment core offshore the Northwest (NW) African Sahel covering the past 100 years and overlapping with the instrumental record of rainfall. We use this record to investigate whether accurate, quantitative estimates of past rainfall can be derived from our \u03b4D_(wax) time series. We infer the composition of vegetation (C_3/C_4) within the continental catchment area by analysis of the stable carbon isotopic composition of the same compounds (\u03b4^(13)C_(wax)), calculated a net ecosystem fractionation factor, and corrected the \u03b4D_(wax) time series accordingly to derive \u03b4D_(precip). Using the present-day relationship between \u03b4D_(precip) and the amount of precipitation in the tropics, we derive quantitative estimates of past precipitation amounts. Our data show that (a) vegetation composition can be inferred from \u03b4^(13)C_(wax), (b) the calculated net ecosystem fractionation represents a reasonable estimate, and (c) estimated total amounts of rainfall based on \u03b4D_(wax) correspond to instrumental records of rainfall. Our study has important implications for future studies aiming to reconstruct rainfall based on \u03b4D_(wax); the combined data presented here demonstrate that it is feasible to infer absolute rainfall amounts from sedimentary \u03b4D_(wax) in tandem with \u03b4^(13)C_(wax) in specific depositional settings.",
"doi": "10.1016/j.gca.2016.03.034",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2016-07-01",
"volume": "184",
"pages": "55-70"
},
{
"id": "authors:ecvc5-1vg84",
"collection": "authors",
"collection_id": "ecvc5-1vg84",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160328-081725938",
"type": "article",
"title": "Factors Controlling the Deuterium Contents of Sedimentary Hydrocarbons",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "The hydrogen isotopic compositions of sedimentary hydrocarbon molecules are now being used to address a range of scientific questions, from paleoclimate to environmental reconstruction to understanding of petroleum systems. Here I review the environmental, biological, and physical/chemical factors that influence the H isotopic compositions of sedimentary hydrocarbons. A hierarchy of four main controls can be recognized: i) the composition of environmental water that serves as ultimate hydrogen source to the biosphere ii) physiologic and metabolic processes in organisms that fix water hydrogen into organic molecules, iii) hydrogen exchange processes that alter D/H ratios slowly over time under geologic conditions, and iv) kinetic fractionations that arise during the thermal conversion of sedimentary organic matter to liquid hydrocarbons. Variations in the terrestrial hydrologic cycle, and in biologic fractionations, create lipids with \u03b4D values spanning a huge range, and carrying abundant information about source organisms and environments. This information is gradually lost over geologic timescales due to hydrogen exchange, although the rates of this process appear to vary by orders of magnitude in clastic versus carbonate sediments. The H isotopes of hydrocarbons in many sediments of low to moderate thermal maturity may only be partially exchanged. Finally, additional kinetic fractionations are imposed during thermal cracking to generate mobile hydrocarbons. The \u03b4D values of sedimentary hydrocarbons are thus concluded to generally reflect a complicated combination of processes. Although it is tempting to view this as a failure of the isotopic record, there are numerous opportunities for understanding environment, diagenetic, and catagenetic processes if we can learn to quantitatively disentangle the competing fractionations.",
"doi": "10.1016/j.orggeochem.2016.02.012",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2016-06",
"volume": "96",
"pages": "43-64"
},
{
"id": "authors:ctqd2-qq437",
"collection": "authors",
"collection_id": "ctqd2-qq437",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160425-101439840",
"type": "article",
"title": "Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, n-Alkanes, Fatty Acid Methyl Esters, Glycines, L-Valines, Polyethylenes, and Oils",
"author": [
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Qi",
"given_name": "Haiping",
"clpid": "Qi-Haiping"
},
{
"family_name": "Coplen",
"given_name": "Tyler B.",
"clpid": "Coplen-T-B"
},
{
"family_name": "Brand",
"given_name": "Willi A.",
"clpid": "Brand-W-A"
},
{
"family_name": "Fong",
"given_name": "Jon",
"clpid": "Fong-Jon"
},
{
"family_name": "Meier-Augenstein",
"given_name": "Wolfram",
"clpid": "Meier-Augenstein-W"
},
{
"family_name": "Kemp",
"given_name": "Helen F.",
"clpid": "Kemp-H-F"
},
{
"family_name": "Toman",
"given_name": "Blaza",
"clpid": "Toman-B"
},
{
"family_name": "Ackermann",
"given_name": "Annika",
"clpid": "Ackermann-A"
},
{
"family_name": "Assonov",
"given_name": "Sergey",
"clpid": "Assonov-S"
},
{
"family_name": "Aerts-Bijma",
"given_name": "Anita T.",
"clpid": "Aerts-Bijma-A-T"
},
{
"family_name": "Brejcha",
"given_name": "Ramona",
"clpid": "Brejcha-R"
},
{
"family_name": "Chikaraishi",
"given_name": "Yoshito",
"clpid": "Chikaraishi-Yoshito"
},
{
"family_name": "Darwish",
"given_name": "Tamim",
"clpid": "Darwish-T"
},
{
"family_name": "Elsner",
"given_name": "Martin",
"clpid": "Elsner-M"
},
{
"family_name": "Gehre",
"given_name": "Matthias",
"clpid": "Gehre-M"
},
{
"family_name": "Geilmann",
"given_name": "Heike",
"clpid": "Geilmann-H"
},
{
"family_name": "Gr\u00f6ning",
"given_name": "Manfred",
"clpid": "Gr\u00f6ning-M"
},
{
"family_name": "H\u00e9lie",
"given_name": "Jean-Fran\u00e7ois",
"clpid": "H\u00e9lie-J-F"
},
{
"family_name": "Herrero-Mart\u00edn",
"given_name": "Sara",
"clpid": "Herrero-Mart\u00edn-S"
},
{
"family_name": "Meijer",
"given_name": "Harro A. J.",
"clpid": "Meijer-H-A-J"
},
{
"family_name": "Sauer",
"given_name": "Peter E.",
"clpid": "Sauer-P-E"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Werner",
"given_name": "Roland A.",
"clpid": "Werner-R-A"
}
],
"abstract": "An international project developed, quality-tested, and determined isotope\u2212\u03b4 values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope\u2212\u03b4 scales. The RMs span a range of \u03b4^2H_(VSMOW-SLAP) values from \u2212210.8 to +397.0 mUr or \u2030, for \u03b4^(13)C_(VPDB-LSVEC) from \u221240.81 to +0.49 mUr and for \u03b4^(15)N_(Air) from \u22125.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C_(16) n-alkanes, n-C_(20)-fatty acid methyl esters (FAMEs), glycines, and L-valines, together with polyethylene powder and string, one n-C_(17)-FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a ^2H-enriched vacuum oil. A total of 11 laboratories from 7 countries used multiple analytical approaches and instrumentation for 2-point isotopic normalization against international primary measurement standards. The use of reference waters in silver tubes allowed direct normalization of \u03b42H values of organic materials against isotopic reference waters following the principle of identical treatment. Bayesian statistical analysis yielded the mean values reported here. New RMs are numbered from USGS61 through USGS78, in addition to NBS 22a. Because of exchangeable hydrogen, amino acid RMs currently are recommended only for carbon- and nitrogen-isotope measurements. Some amino acids contain ^(13)C and carbon-bound organic ^2H-enrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies.",
"doi": "10.1021/acs.analchem.5b04392",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2016-04-19",
"series_number": "8",
"volume": "88",
"issue": "8",
"pages": "4294-4302"
},
{
"id": "authors:jd362-19531",
"collection": "authors",
"collection_id": "jd362-19531",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160301-075335319",
"type": "article",
"title": "Measuring the in situ carbon isotopic composition of distinct marine plankton populations sorted by flow cytometry",
"author": [
{
"family_name": "Hansman",
"given_name": "Roberta L.",
"clpid": "Hansman-R-L"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "The carbon isotope ratio (\u03b4^(13)C value) of marine particulates is a potentially useful tracer for elucidating pathways of carbon flow in the marine environment. Different species of phytoplankton vary in fractionation vs. CO_2 by up to 24\u2030 in laboratory cultures under varying nutrient and growth conditions, a signal that should propagate through the microbial food web. However, such contrasts have been difficult to confirm in field measurements due to analytical limitations. Here, we combine fluorescence-activated cell sorting (FACS) with a specialized micro-combustion interface and isotope-ratio mass spectrometry (SWiM-IRMS) to provide some of the first direct measurements of whole-cell \u03b4^(13)C values for specific phytoplankton populations in the wild. For three samples collected off Scripps Pier in 2010\u20132011, Synechococcus averages \u03b4^(13)C values of \u221225.7\u2009\u00b1\u20092.0\u2030, Prochlorococcus averages \u221223.0\u2009\u00b1\u20091.3, and diatoms average \u221220.8\u2009\u00b1\u20091.7\u2030. Diatoms were \u223c3\u2030 enriched in ^(13)C when measured during a bloom (March 2011) as compared with mid-summer (July 2010). Sorted particles thought to represent living heterotrophic bacteria averaged \u221225.4\u2009\u00b1\u20092.5\u2030, whereas total filterable particles averaged \u221219.6\u2009\u00b1\u20091.0\u2030, indicating a strong similarity to diatom biomass. These variations demonstrate that in situ differences in \u03b4^(13)C among different populations of particles can be exploited to follow carbon flow through successive trophic levels, and throughout organic matter remineralization, sinking, and preservation.",
"doi": "10.1002/lom3.10073",
"issn": "1541-5856",
"publisher": "American Society for Limnology and Oceanography",
"publication": "Limnology and Oceanography: Methods",
"publication_date": "2016-02",
"series_number": "2",
"volume": "14",
"issue": "2",
"pages": "87-99"
},
{
"id": "authors:f77p5-wfy55",
"collection": "authors",
"collection_id": "f77p5-wfy55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160104-065151473",
"type": "article",
"title": "Trace incorporation of heavy water reveals slow and heterogeneous pathogen growth rates in cystic fibrosis sputum",
"author": [
{
"family_name": "Kopf",
"given_name": "Sebastian H.",
"orcid": "0000-0002-2044-0201",
"clpid": "Kopf-Sebastian-H"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Cowley",
"given_name": "Elise S.",
"clpid": "Cowley-Elise-S"
},
{
"family_name": "Reyes",
"given_name": "Carmen",
"clpid": "Reyes-Carmen"
},
{
"family_name": "Van Sambeek",
"given_name": "Lindsey",
"orcid": "0000-0002-7206-7410",
"clpid": "Van-Sambeek-Lindsey"
},
{
"family_name": "Hu",
"given_name": "Yang",
"clpid": "Hu-Yang"
},
{
"family_name": "Orphan",
"given_name": "Victoria J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
},
{
"family_name": "Kato",
"given_name": "Roberta M.",
"clpid": "Kato-Roberta-M"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "Effective treatment for chronic infections is undermined by a significant gap in understanding of the physiological state of pathogens at the site of infection. Chronic pulmonary infections are responsible for the morbidity and mortality of millions of immunocompromised individuals worldwide, yet drugs that are successful in laboratory culture are far less effective against pathogen populations persisting in vivo. Laboratory models, upon which preclinical development of new drugs is based, can only replicate host conditions when we understand the metabolic state of the pathogens and the degree of heterogeneity within the population. In this study, we measured the anabolic activity of the pathogen Staphylococcus aureus directly in the sputum of pediatric patients with cystic fibrosis (CF), by combining the high sensitivity of isotope ratio mass spectrometry with a heavy water labeling approach to capture the full range of in situ growth rates. Our results reveal S. aureus generation times with a median of 2.1 d, with extensive growth rate heterogeneity at the single-cell level. These growth rates are far below the detection limit of previous estimates of CF pathogen growth rates, and the rates are slowest in acutely sick patients undergoing pulmonary exacerbations; nevertheless, they are accessible to experimental replication within laboratory models. Treatment regimens that include specific antibiotics (vancomycin, piperacillin/tazobactam, tobramycin) further appear to correlate with slow growth of S. aureus on average, but follow-up longitudinal studies must be performed to determine whether this effect holds for individual patients.",
"doi": "10.1073/pnas.1512057112",
"pmcid": "PMC4720290",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2016-01-12",
"series_number": "2",
"volume": "113",
"issue": "2",
"pages": "E110-E116"
},
{
"id": "authors:dsv28-1q023",
"collection": "authors",
"collection_id": "dsv28-1q023",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150914-125155730",
"type": "article",
"title": "Route to Renewable PET: Reaction Pathways and Energetics of Diels\u2013Alder and Dehydrative Aromatization Reactions Between Ethylene and Biomass-Derived Furans Catalyzed by Lewis Acid Molecular Sieves",
"author": [
{
"family_name": "Pacheco",
"given_name": "Joshua J.",
"clpid": "Pacheco-J-J"
},
{
"family_name": "Labinger",
"given_name": "Jay A.",
"orcid": "0000-0002-1942-9232",
"clpid": "Labinger-J-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Davis",
"given_name": "Mark E.",
"orcid": "0000-0001-8294-1477",
"clpid": "Davis-M-E"
}
],
"abstract": "Silica molecular sieves that have the zeolite beta topology and contain framework Lewis acid centers (e.g., Zr-\u03b2, Sn-\u03b2) are useful catalysts in the Diels\u2013Alder and dehydrative aromatization reactions between ethylene and various renewable furans for the production of biobased terephthalic acid precursors. Here, the main side products in the synthesis of methyl 4-(methoxymethyl)benzene carboxylate that are obtained by reacting ethylene with methyl 5-(methoxymethyl)-furan-2-carboxylate are identified, and an overall reaction pathway is proposed. Madon\u2013Boudart experiments using Zr-\u03b2 samples of varying Si/Zr ratios clearly indicate that there are no transport limitations to the rate of reaction for the synthesis of p-xylene from 2,5-dimethylfuran and ethylene and strongly suggest no mass transport limitations in the synthesis of methyl p-toluate from methyl 5-methyl-2-furoate and ethylene. Measured apparent activation energies for these reaction-limited systems are small (<10.5 kcal/mol), suggesting that apparent activation energies are derived from a collection of parameters and are not true activation energies for a single chemical step. In addition, 13C kinetic isotope effects (KIE) in the synthesis of MMBC and MPT measured by gas chromatography/isotope-ratio mass spectrometry in reactant-depletion experiments support the Madon\u2013Boudart result that these systems are not transport-limited and the KIE values agree with those previously reported for Diels\u2013Alder cycloadditions.",
"doi": "10.1021/acscatal.5b01309",
"issn": "2155-5435",
"publisher": "American Chemical Society",
"publication": "ACS Catalysis",
"publication_date": "2015-10",
"series_number": "10",
"volume": "5",
"issue": "10",
"pages": "5904-5913"
},
{
"id": "authors:5hr5k-xzg86",
"collection": "authors",
"collection_id": "5hr5k-xzg86",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150504-103056372",
"type": "article",
"title": "Lipid remodeling in Rhodopseudomonas palustris TIE-1 upon loss of hopanoids and hopanoid methylation",
"author": [
{
"family_name": "Neubauer",
"given_name": "C.",
"orcid": "0000-0002-5348-5609",
"clpid": "Neubauer-C"
},
{
"family_name": "Dalleska",
"given_name": "N. F.",
"orcid": "0000-0002-2059-1587",
"clpid": "Dalleska-N-F"
},
{
"family_name": "Cowley",
"given_name": "E. S.",
"clpid": "Cowley-E-S"
},
{
"family_name": "Shikuma",
"given_name": "N. J.",
"orcid": "0000-0001-5518-5020",
"clpid": "Shikuma-Nicholas-J"
},
{
"family_name": "Wu",
"given_name": "C.-H.",
"clpid": "Wu-C-H"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Newman",
"given_name": "D. K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "The sedimentary record of molecular fossils (biomarkers) can potentially provide important insights into the composition of ancient organisms; however, it only captures a small portion of their original lipid content. To interpret what remains, it is important to consider the potential for functional overlap between different lipids in living cells, and how the presence of one type might impact the abundance of another. Hopanoids are a diverse class of steroid analogs made by bacteria and found in soils, sediments, and sedimentary rocks. Here, we examine the trade-off between hopanoid production and that of other membrane lipids. We compare lipidomes of the metabolically versatile \u03b1-proteobacterium Rhodopseudomonas palustris TIE-1 and two hopanoid mutants, detecting native hopanoids simultaneously with other types of polar lipids by electrospray ionization mass spectrometry. In all strains, the phospholipids contain high levels of unsaturated fatty acids (often >80 %). The degree to which unsaturated fatty acids are modified to cyclopropyl fatty acids varies by phospholipid class. Deletion of the capacity for hopanoid production is accompanied by substantive changes to the lipidome, including a several-fold rise of cardiolipins. Deletion of the ability to make methylated hopanoids has a more subtle effect; however, under photoautotrophic growth conditions, tetrahymanols are upregulated twofold. Together, these results illustrate that the 'lipid fingerprint' produced by a micro-organism can vary depending on the growth condition or loss of single genes, reminding us that the absence of a biomarker does not necessarily imply the absence of a particular source organism.",
"doi": "10.1111/gbi.12143",
"issn": "1472-4677",
"publisher": "Wiley-Blackwell",
"publication": "Geobiology",
"publication_date": "2015-09",
"series_number": "5",
"volume": "13",
"issue": "5",
"pages": "443-453"
},
{
"id": "authors:9zqqt-kvn93",
"collection": "authors",
"collection_id": "9zqqt-kvn93",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150505-105030332",
"type": "article",
"title": "Metabolic associations with archaea drive shifts in hydrogen isotope fractionation in sulfate-reducing bacterial lipids in cocultures and methane seeps",
"author": [
{
"family_name": "Dawson",
"given_name": "K. S.",
"orcid": "0000-0001-8856-4609",
"clpid": "Dawson-Katherine-S"
},
{
"family_name": "Osburn",
"given_name": "M. R.",
"orcid": "0000-0001-9180-559X",
"clpid": "Osburn-M-R"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Orphan",
"given_name": "V. J.",
"orcid": "0000-0002-5374-6178",
"clpid": "Orphan-V-J"
}
],
"abstract": "Correlation between hydrogen isotope fractionation in fatty acids and carbon metabolism in pure cultures of bacteria indicates the potential of biomarker D/H analysis as a tool for diagnosing carbon substrate usage in environmental samples. However, most environments, in particular anaerobic habitats, are built from metabolic networks of micro-organisms rather than a single organism. The effect of these networks on D/H of lipids has not been explored and may complicate the interpretation of these analyses. Syntrophy represents an extreme example of metabolic interdependence. Here, we analyzed the effect of metabolic interactions on the D/H biosignatures of sulfate-reducing bacteria (SRB) using both laboratory maintained cocultures of the methanogen Methanosarcina acetivorans and the SRB Desulfococcus multivorans in addition to environmental samples harboring uncultured syntrophic consortia of anaerobic methane-oxidizing archaea (ANME) and sulfate-reducing Deltaproteobacteria (SRB) recovered from deep-sea methane seeps. Consistent with previously reported trends, we observed a ~80\u2030 range in hydrogen isotope fractionation (\u03b5_(lipid\u2013water)) for D. multivorans grown under different carbon assimilation conditions, with more D-enriched values associated with heterotrophic growth. In contrast, for cocultures of D. multivorans with M. acetivorans, we observed a reduced range of \u03b5_(lipid\u2013water) values (~36\u2030) across substrates with shifts of up to 61\u2030 compared to monocultures. Sediment cores from methane seep settings in Hydrate Ridge (offshore Oregon, USA) showed similar D-enrichment in diagnostic SRB fatty acids coinciding with peaks in ANME/SRB consortia concentration suggesting that metabolic associations are connected to the observed shifts in \u03b5_(lipid\u2013water) values.",
"doi": "10.1111/gbi.12140",
"issn": "1472-4677",
"publisher": "Wiley-Blackwell",
"publication": "Geobiology",
"publication_date": "2015-09",
"series_number": "5",
"volume": "13",
"issue": "5",
"pages": "462-477"
},
{
"id": "authors:wc761-4ny75",
"collection": "authors",
"collection_id": "wc761-4ny75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150427-094456620",
"type": "article",
"title": "Distinguishing and understanding thermogenic and biogenic sources of methane using multiply substituted isotopologues",
"author": [
{
"family_name": "Stolper",
"given_name": "D. A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Martini",
"given_name": "A. M.",
"clpid": "Martini-A-M"
},
{
"family_name": "Clog",
"given_name": "M.",
"clpid": "Clog-M"
},
{
"family_name": "Douglas",
"given_name": "P. M.",
"clpid": "Douglas-P-M"
},
{
"family_name": "Shusta",
"given_name": "S. S.",
"clpid": "Shusta-S-S"
},
{
"family_name": "Valentine",
"given_name": "D. L.",
"clpid": "Valentine-D-L"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "J. M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Sources of methane to sedimentary environments are commonly identified and quantified using the stable-isotopic compositions of methane. The methane \"clumped-isotope geothermometer\", based on the measurement of multiply substituted methane isotopologues (^(13)CH_3D and ^(12)CH_2D_2), shows promise in adding new constraints to the sources and formational environments of both biogenic and thermogenic methane. However, questions remain about how this geothermometer behaves in systems with mixtures of biogenic and thermogenic gases and different biogenic environments. We have applied the methane clumped-isotope thermometer to a mixed biogenic-thermogenic system (Antrim Shale, USA) and to biogenic gas from gas seeps (Santa Barbara and Santa Monica Basin, USA), a pond on the Caltech campus, and methanogens grown in pure-culture. We demonstrate that clumped-isotope based temperatures add new quantitative constraints to the relative amounts of biogenic vs. thermogenic gases in the Antrim Shale indicating a larger proportion (\u223c50%) of thermogenic gas in the system than previously thought. Additionally, we find that the clumped-isotope temperature of biogenic methane appears related to the environmental settings in which the gas forms. In systems where methane generation rates appear to be slow (e.g., the Antrim Shale and gas seeps), microbial methane forms in or near both internal isotopic equilibrium and hydrogen-isotope equilibrium with environmental waters. In systems where methane forms rapidly, microbial methane is neither in internal isotopic equilibrium nor hydrogen-isotope equilibrium with environmental waters. A quantitative model of microbial methanogenesis that incorporates isotopes is proposed to explain these results.",
"doi": "10.1016/j.gca.2015.04.015",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2015-07-15",
"volume": "161",
"pages": "219-247"
},
{
"id": "authors:m95d3-tpr25",
"collection": "authors",
"collection_id": "m95d3-tpr25",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150126-083217317",
"type": "article",
"title": "Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments",
"author": [
{
"family_name": "Raven",
"given_name": "Morgan Reed",
"clpid": "Raven-M-R"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Werne",
"given_name": "Josef P.",
"clpid": "Werne-J-P"
},
{
"family_name": "Lyons",
"given_name": "Timothy W.",
"clpid": "Lyons-T-W"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"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 \u2013 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.",
"doi": "10.1016/j.orggeochem.2015.01.002",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2015-03",
"volume": "80",
"pages": "53-59"
},
{
"id": "authors:stw8e-e1j09",
"collection": "authors",
"collection_id": "stw8e-e1j09",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150116-101740001",
"type": "article",
"title": "Planning Considerations Related to the Organic Contamination of Martian Samples and Implications for the Mars 2020 Rover",
"author": [
{
"family_name": "Summons",
"given_name": "R. E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Allwood",
"given_name": "A. C.",
"clpid": "Allwood-A-C"
},
{
"family_name": "Barton",
"given_name": "H. A.",
"clpid": "Barton-H-A"
},
{
"family_name": "Beaty",
"given_name": "D. W.",
"clpid": "Beaty-D-W"
},
{
"family_name": "Blakkolb",
"given_name": "B.",
"clpid": "Blakkolb-B"
},
{
"family_name": "Canham",
"given_name": "J.",
"clpid": "Canham-J"
},
{
"family_name": "Clark",
"given_name": "B. C.",
"orcid": "0000-0002-5546-8757",
"clpid": "Clark-B-C"
},
{
"family_name": "Dworkin",
"given_name": "J. P.",
"clpid": "Dworkin-J-P"
},
{
"family_name": "Lin",
"given_name": "Y.",
"clpid": "Lin-Y"
},
{
"family_name": "Mathies",
"given_name": "R.",
"clpid": "Mathies-R"
},
{
"family_name": "Milkovich",
"given_name": "S. M.",
"clpid": "Milkovich-S-M"
},
{
"family_name": "Steele",
"given_name": "A.",
"clpid": "Steele-A-D"
}
],
"abstract": "Data gathered during recent NASA missions to\nMars, particularly by the Rovers Spirit, Opportunity,\nand Curiosity, have provided important insights into the\npast history and habitability of the Red Planet. The Mars\nscience community, via input through the National Research\nCouncil (NRC) Planetary Science Decadal Survey\nCommittee, also identified the prime importance of a Mars\nsample return (MSR) mission to further exploration of\nthe Red Planet. In response, the Mars 2020 Mission (Mars\n2020) Science Definition Team (SDT) (Mustard et al.,\n2013) was chartered by the NASA Mars Exploration Program\nto formulate a new rover mission that would take\nconcrete steps toward an eventual sample return. The SDT\nrecommended that the 2020 rover should select and cache\nscientifically compelling samples for possible return to\nEarth. They also noted that organic contamination of the\nsamples was a significant and complex issue that should be\nindependently investigated by a future committee. Accordingly,\nNASA chartered the Mars 2020 Organic Contamination\nPanel (OCP).",
"doi": "10.1089/ast.2014.1244",
"issn": "1531-1074",
"publisher": "Mary Ann Liebert",
"publication": "Astrobiology",
"publication_date": "2014-12",
"series_number": "12",
"volume": "14",
"issue": "12",
"pages": "969-1027"
},
{
"id": "authors:jccjk-4kp68",
"collection": "authors",
"collection_id": "jccjk-4kp68",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141009-162752745",
"type": "article",
"title": "Sulfate was a trace constituent of Archean seawater",
"author": [
{
"family_name": "Crowe",
"given_name": "Sean A.",
"clpid": "Crowe-S-A"
},
{
"family_name": "Paris",
"given_name": "Guillaume",
"orcid": "0000-0001-8368-1224",
"clpid": "Paris-G"
},
{
"family_name": "Katsev",
"given_name": "Sergei",
"clpid": "Katsev-S"
},
{
"family_name": "Jones",
"given_name": "CarriAyne",
"clpid": "Jones-C"
},
{
"family_name": "Kim",
"given_name": "Sang-Tae",
"clpid": "Kim-Sang-Tae"
},
{
"family_name": "Zerkle",
"given_name": "Aubrey L.",
"clpid": "Zerkle-A-L"
},
{
"family_name": "Nomosatryo",
"given_name": "Sulung",
"clpid": "Nomosatryo-S"
},
{
"family_name": "Fowle",
"given_name": "David A.",
"clpid": "Fowle-D-A"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Farquhar",
"given_name": "James",
"clpid": "Farquhar-J"
},
{
"family_name": "Canfield",
"given_name": "Donald E.",
"clpid": "Canfield-D-E"
}
],
"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 \u03b4^(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.",
"doi": "10.1126/science.1258966",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "2014-11-07",
"series_number": "6210",
"volume": "346",
"issue": "6210",
"pages": "735-739"
},
{
"id": "authors:ycesk-4hw39",
"collection": "authors",
"collection_id": "ycesk-4hw39",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141009-161941084",
"type": "article",
"title": "Neoarchean carbonate-associated sulfate records positive \u0394\u00b3\u00b3S anomalies",
"author": [
{
"family_name": "Paris",
"given_name": "G.",
"orcid": "0000-0001-8368-1224",
"clpid": "Paris-G"
},
{
"family_name": "Adkins",
"given_name": "J. F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Webb",
"given_name": "S. M.",
"clpid": "Webb-S-M"
},
{
"family_name": "Fischer",
"given_name": "W. W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
}
],
"abstract": "Mass-independent fractionation of sulfur isotopes (reported as \u0394\u00b3\u00b3S) 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 \u0394\u00b3\u00b3S 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 \u0394\u00b3\u00b3S signatures. We report unexpected, large, widespread positive \u0394\u00b3\u00b3S 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 \u0394\u00b3\u00b3S from sulfur mass-independent fractionation in the Neoarchean atmosphere.",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "2014-11-07",
"series_number": "6410",
"volume": "346",
"issue": "6410",
"pages": "739-741"
},
{
"id": "authors:zhtz2-vat37",
"collection": "authors",
"collection_id": "zhtz2-vat37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140623-092251695",
"type": "article",
"title": "Hydroclimate of the western Indo-Pacific Warm Pool during the past 24,000 years",
"author": [
{
"family_name": "Niedermeyer",
"given_name": "Eva M.",
"clpid": "Niedermeyer-E-M"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Feakins",
"given_name": "Sarah J.",
"orcid": "0000-0003-3434-2423",
"clpid": "Feakins-S-J"
},
{
"family_name": "Mohtadi",
"given_name": "Mahyar",
"clpid": "Mohtadi-M"
}
],
"abstract": "The Indo-Pacific Warm Pool (IPWP) is a key site for the global hydrologic cycle, and modern observations indicate that both the Indian Ocean Zonal Mode (IOZM) and the El Ni\u00f1o Southern Oscillation exert strong influence on its regional hydrologic characteristics. Detailed insight into the natural range of IPWP dynamics and underlying climate mechanisms is, however, limited by the spatial and temporal coverage of climate data. In particular, long-term (multimillennial) precipitation patterns of the western IPWP, a key location for IOZM dynamics, are poorly understood. To help rectify this, we have reconstructed rainfall changes over Northwest Sumatra (western IPWP, Indian Ocean) throughout the past 24,000 y based on the stable hydrogen and carbon isotopic compositions (\u03b4D and \u03b4^(13)C, respectively) of terrestrial plant waxes. As a general feature of western IPWP hydrology, our data suggest similar rainfall amounts during the Last Glacial Maximum and the Holocene, contradicting previous claims that precipitation increased across the IPWP in response to deglacial changes in sea level and/or the position of the Intertropical Convergence Zone. We attribute this discrepancy to regional differences in topography and different responses to glacioeustatically forced changes in coastline position within the continental IPWP. During the Holocene, our data indicate considerable variations in rainfall amount. Comparison of our isotope time series to paleoclimate records from the Indian Ocean realm reveals previously unrecognized fluctuations of the Indian Ocean precipitation dipole during the Holocene, indicating that oscillations of the IOZM mean state have been a constituent of western IPWP rainfall over the past ten thousand years.",
"doi": "10.1073/pnas.1323585111",
"pmcid": "PMC4084490",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2014-07-01",
"series_number": "26",
"volume": "111",
"issue": "26",
"pages": "9402-9406"
},
{
"id": "authors:5anv7-8x934",
"collection": "authors",
"collection_id": "5anv7-8x934",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140604-103128643",
"type": "article",
"title": "Formation temperatures of thermogenic and biogenic methane",
"author": [
{
"family_name": "Stolper",
"given_name": "D. A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Lawson",
"given_name": "M.",
"clpid": "Lawson-M"
},
{
"family_name": "Davis",
"given_name": "C. L.",
"clpid": "Davis-C-L"
},
{
"family_name": "Ferreira",
"given_name": "A. A.",
"clpid": "Ferreira-A-A"
},
{
"family_name": "Santos Neto",
"given_name": "E. V.",
"clpid": "Santos-Neto-E-V"
},
{
"family_name": "Ellis",
"given_name": "G. S.",
"clpid": "Ellis-G-S"
},
{
"family_name": "Lewan",
"given_name": "M. D.",
"clpid": "Lewan-M-D"
},
{
"family_name": "Martini",
"given_name": "A. M.",
"clpid": "Martini-A-M"
},
{
"family_name": "Tang",
"given_name": "Y.",
"clpid": "Tang-Y"
},
{
"family_name": "Schoell",
"given_name": "M.",
"clpid": "Schoell-M"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "J. M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Methane is an important greenhouse gas and energy resource generated dominantly by methanogens at low temperatures and through the breakdown of organic molecules at high temperatures. However, methane-formation temperatures in nature are often poorly constrained. We measured formation temperatures of thermogenic and biogenic methane using a \"clumped isotope\" technique. Thermogenic gases yield formation temperatures between 157\u00b0 and 221\u00b0C, within the nominal gas window, and biogenic gases yield formation temperatures consistent with their comparatively lower-temperature formational environments (<50\u00b0C). In systems where gases have migrated and other proxies for gas-generation temperature yield ambiguous results, methane clumped-isotope temperatures distinguish among and allow for independent tests of possible gas-formation models.",
"doi": "10.1126/science.1254509",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "2014-06-27",
"series_number": "6191",
"volume": "344",
"issue": "6191",
"pages": "1500-1503"
},
{
"id": "authors:je510-12g80",
"collection": "authors",
"collection_id": "je510-12g80",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140627-090728672",
"type": "article",
"title": "Experimental determination of carbonate-associated sulfate \u03b4^(34)S in planktonic foraminifera shells",
"author": [
{
"family_name": "Paris",
"given_name": "Guillaume",
"orcid": "0000-0001-8368-1224",
"clpid": "Paris-G"
},
{
"family_name": "Fehrenbacher",
"given_name": "Jennifer S.",
"clpid": "Fehrenbacher-J-S"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Spero",
"given_name": "Howard J.",
"clpid": "Spero-H-J"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"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 (\u03b4^(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 \u03b4^(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 \u03b4^(13)C, \u03b4^(18)O, and \u03b4^(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 \u03b4^(34)S values approaching 0.1\u2030 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 \u03b4^(34)S calibration for future applications to the fossil record. Our new method uses <650 \u03bcg of carbonate (\u223c15 shells) per analysis. The results show that S isotopes are fractionated consistently by \u22121\u2030 between seawater and O. universa tests. We also demonstrate that O. universa faithfully records the [SO^(2\u2212)_(4)]/[Ca^(2+)] ratio of the seawater in which it grew.",
"doi": "10.1002/2014GC005295",
"issn": "1525-2027",
"publisher": "American Geophysical Union",
"publication": "Geochemistry, Geophysics, Geosystems",
"publication_date": "2014-04",
"series_number": "4",
"volume": "15",
"issue": "4",
"pages": "1452-1461"
},
{
"id": "authors:4j2za-44r54",
"collection": "authors",
"collection_id": "4j2za-44r54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140407-105009295",
"type": "article",
"title": "Diverse capacity for 2-methylhopanoid production correlates with a specific ecological niche",
"author": [
{
"family_name": "Ricci",
"given_name": "Jessica N.",
"clpid": "Ricci-J-N"
},
{
"family_name": "Coleman",
"given_name": "Maureen L.",
"clpid": "Coleman-M-L"
},
{
"family_name": "Welander",
"given_name": "Paul V.",
"clpid": "Welander-P-V"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Spear",
"given_name": "John R.",
"orcid": "0000-0002-4664-7438",
"clpid": "Spear-J-R"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "Molecular fossils of 2-methylhopanoids are prominent biomarkers in modern and ancient sediments that have been used as proxies for cyanobacteria and their main metabolism, oxygenic photosynthesis. However, substantial culture and genomic-based evidence now indicates that organisms other than cyanobacteria can make 2-methylhopanoids. Because few data directly address which organisms produce 2-methylhopanoids in the environment, we used metagenomic and clone library methods to determine the environmental diversity of hpnP, the gene encoding the C-2 hopanoid methylase. Here we show that hpnP copies from alphaproteobacteria and as yet uncultured organisms are found in diverse modern environments, including some modern habitats representative of those preserved in the rock record. In contrast, cyanobacterial hpnP genes are rarer and tend to be localized to specific habitats. To move beyond understanding the taxonomic distribution of environmental 2-methylhopanoid producers, we asked whether hpnP presence might track with particular variables. We found hpnP to be significantly correlated with organisms, metabolisms and environments known to support plant\u2013microbe interactions (P-value<10^\u22126); in addition, we observed diverse hpnP types in closely packed microbial communities from other environments, including stromatolites, hot springs and hypersaline microbial mats. The common features of these niches indicate that 2-methylhopanoids are enriched in sessile microbial communities inhabiting environments low in oxygen and fixed nitrogen with high osmolarity. Our results support the earlier conclusion that 2-methylhopanoids are not reliable biomarkers for cyanobacteria or any other taxonomic group, and raise the new hypothesis that, instead, they are indicators of a specific environmental niche.",
"doi": "10.1038/ismej.2013.191",
"pmcid": "PMC3930323",
"issn": "1751-7362",
"publisher": "Nature Publishing Group",
"publication": "ISME Journal",
"publication_date": "2014-03",
"series_number": "3",
"volume": "8",
"issue": "3",
"pages": "675-684"
},
{
"id": "authors:0bm16-t2075",
"collection": "authors",
"collection_id": "0bm16-t2075",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140211-095212681",
"type": "article",
"title": "Combined ^(13)C\u2013D and D\u2013D clumping in methane: Methods and preliminary results",
"author": [
{
"family_name": "Stolper",
"given_name": "D. A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Ferreira",
"given_name": "A. A.",
"clpid": "Ferreira-A-A"
},
{
"family_name": "Santos Neto",
"given_name": "E. V.",
"clpid": "Santos-Neto-E-V"
},
{
"family_name": "Schimmelmann",
"given_name": "A.",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Shusta",
"given_name": "S. S.",
"clpid": "Shusta-S-S"
},
{
"family_name": "Valentine",
"given_name": "D. L.",
"clpid": "Valentine-D-L"
},
{
"family_name": "Eiler",
"given_name": "J. M.",
"clpid": "Eiler-J-M"
}
],
"contributor": [
{
"family_name": "Farquhar",
"given_name": "James",
"clpid": "Farquhar-J"
}
],
"abstract": "The stable isotopic composition of methane (e.g., \u03b4D and \u03b4^(13)C values) is often used as a tracer for its sources and sinks. Conventional \u03b4D and \u03b4^(13)C measurements represent the average isotope ratios of all ten isotopologues of methane, though they are effectively controlled by the relative abundances of the three most abundant species: (^12)CH_4, (^13)CH_4, and (^12)CH_3D. The precise relative abundances of the other seven isotopologues remains largely unexplored because these species contain multiple rare isotopes and are thus rare themselves. These multiply substituted (or 'clumped') isotopologues each have their own distinctive chemical and physical properties, which could provide additional constraints on the geochemistry of methane. This work focuses on quantifying the abundances of two rare isotopologues, (^13)CH_3D and (^12)CH_2D_2, of methane in order to assess their utility as a window into methane's geochemistry. Specifically, we seek to assess whether clumped isotope distributions might be useful to quantify the temperature at which methane formed and/or equilibrated. To this end, we report the first highly precise combined measurements of the relative abundances of (^13)CH_3D and (^12)CH_2D_2 at natural abundances (i.e., unlabeled) via the high-resolution magnetic-sector mass spectrometry of intact methane. We calibrate the use of these measurements as a geothermometer using both theory and experiment, and apply this geothermometer to representative natural samples. The method yields accurate average (i.e., bulk) isotopic ratios based on comparison with conventional techniques. We demonstrate the accuracy and precision of measurements of (^13)CH_3D and (^12)CH_2D_2 through analyses of methane driven to high temperature (> 200 \u00b0C) equilibrium in the laboratory. Application of this thermometer to natural samples yields apparent temperatures consistent with their known formation environments and appears to distinguish between biogenic and thermogenic methane.",
"doi": "10.1016/j.gca.2013.10.045",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2014-02-01",
"volume": "126",
"pages": "169-191"
},
{
"id": "authors:7hnw0-46t70",
"collection": "authors",
"collection_id": "7hnw0-46t70",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140206-114311185",
"type": "article",
"title": "Probing the Subcellular Localization of Hopanoid Lipids in Bacteria Using NanoSIMS",
"author": [
{
"family_name": "Doughty",
"given_name": "David M.",
"clpid": "Doughty-D-M"
},
{
"family_name": "Dieterle",
"given_name": "Michael",
"clpid": "Dieterle-M"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Fischer",
"given_name": "Woodward W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "The organization of lipids within biological membranes is poorly understood. Some studies have suggested lipids group\ninto microdomains within cells, but the evidence remains controversial due to non-native imaging techniques. A recently developed NanoSIMS technique indicated that sphingolipids group into microdomains within membranes of human fibroblast cells. We extended this NanoSIMS approach to study the localization of hopanoid lipids in bacterial cells by developing a stable isotope labeling method to directly detect subcellular localization of specific lipids in bacteria with ca. 60 nm resolution. Because of the relatively small size of bacterial cells and the relative abundance of hopanoid lipids in membranes, we employed a primary ^2H-label to maximize our limit of detection. This approach permitted the analysis of multiple stable isotope labels within the same sample, enabling visualization of subcellular lipid microdomains within different cell types using a secondary label to mark the growing end of the cell. Using this technique, we demonstrate subcellular localization of hopanoid lipids within alpha-proteobacterial and cyanobacterial cells. Further, we provide evidence of hopanoid lipid domains in between cells of the filamentous cyanobacterium Nostoc punctiforme. More broadly, our method provides a means to image lipid microdomains in a wide range of cell types and test hypotheses for their functions in membranes.",
"doi": "10.1371/journal.pone.0084455",
"pmcid": "PMC3883690",
"issn": "1932-6203",
"publisher": "Public Library of Science",
"publication": "PLoS ONE",
"publication_date": "2014-01",
"series_number": "1",
"volume": "9",
"issue": "1",
"pages": "Art. No. e84455"
},
{
"id": "authors:rh38k-he859",
"collection": "authors",
"collection_id": "rh38k-he859",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130909-081720156",
"type": "article",
"title": "Lipid biomarkers in ooids from different locations and ages: evidence for a common bacterial flora",
"author": [
{
"family_name": "Summons",
"given_name": "R. E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Bird",
"given_name": "L. R.",
"orcid": "0000-0002-6034-9533",
"clpid": "Bird-L-R"
},
{
"family_name": "Gillespie",
"given_name": "A. L.",
"clpid": "Gillespie-A-L"
},
{
"family_name": "Pruss",
"given_name": "S. B.",
"clpid": "Pruss-S-B"
},
{
"family_name": "Roberts",
"given_name": "M.",
"clpid": "Roberts-M"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Ooids are one of the common constituents of ancient carbonate rocks, yet the role that microbial communities may or may not play in their formation remains unresolved. To search for evidence of microbial activity in modern and Holocene ooids, samples collected from intertidal waters, beaches and outcrops in the Bahamas and in Shark Bay in Western Australia were examined for their contents of lipid biomarkers. Modern samples from Cat and Andros islands in the Bahamas and from Carbla Beach in Hamelin Pool, Western Australia, showed abundant and notably similar distributions of hydrocarbons, fatty acids (FAs) and alcohols. A large fraction of these lipids were bound into the carbonate matrix and only released on acid dissolution, which suggests that these lipids were being incorporated continuously during ooid growth. The distributions of hydrocarbons, and their disparate carbon isotopic signatures, were consistent with mixed input from cyanobacteria together with small and variable amounts of vascular plant leaf wax [C_(27)\u2013C_(35); \u03b4^(13)C \u221225 to \u221232\u2030Vienna Pee Dee Belemnite (VPDB)]. The FAs comprised a complex mixture of C_(12)\u2013C_(18) normal and branched short-chain compounds with the predominant straight-chain components attributable to bacteria and/or cyanobacteria. Branched FA, especially 10-MeC_(16) and 10-MeC_(17), together with the prevalence of elemental sulfur in the extracts, indicate an origin from sulfate-reducing bacteria. The iso- and anteiso-FA were quite variable in their ^(13)C contents suggesting that they come from organisms with diverse physiologies. Hydrogen isotopic compositions provide further insight into this issue. FAs in each sample show disparate \u03b4D values consistent with inputs from autotrophs and heterotrophs. The most enigmatic lipid assemblage is an homologous series of long-chain (C_(24)\u2013C_(32)) FA with pronounced even carbon number preference. Typically, such long-chain FA are thought to come from land plant leaf wax, but in this case, their ^(13)C-enriched isotopic signatures compared to co-occurring n-alkanes (e.g., Hamelin Pool TLE FA C_(24)\u2013C_(32); \u03b4^(13)C \u221220 to \u221224.2\u2030 VPDB; TLE n-alkanes \u03b4^(13)C \u221224.1 to \u221226.2 \u2212\u2030VPDB) indicate a microbial origin, possibly sulfate-reducing bacteria. Lastly, we identified homohopanoic acid and bishomohopanol as the primary degradation products of bacterial hopanoids. The distributions of lipids isolated from Holocene oolites from the Rice Bay Formation of Cat Island, Bahamas were very similar to the beach ooids described above and, in total, these modern and fossil biomarker data lead us to hypothesize that ooids are colonized by a defined microbial community and that these microbes possibly mediate calcification.",
"doi": "10.1111/gbi.12047",
"issn": "1472-4677",
"publisher": "Blackwell Publishing",
"publication": "Geobiology",
"publication_date": "2013-09",
"series_number": "5",
"volume": "11",
"issue": "5",
"pages": "420-436"
},
{
"id": "authors:eb3xb-5ya12",
"collection": "authors",
"collection_id": "eb3xb-5ya12",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130917-102929781",
"type": "article",
"title": "Carbon isotopes and lipid biomarkers from organic-rich facies of the Shuram Formation, Sultanate of Oman",
"author": [
{
"family_name": "Lee",
"given_name": "C.",
"clpid": "Lee-C"
},
{
"family_name": "Fike",
"given_name": "D. A.",
"orcid": "0000-0003-2848-0328",
"clpid": "Fike-D-A"
},
{
"family_name": "Love",
"given_name": "G. D.",
"orcid": "0000-0002-6516-014X",
"clpid": "Love-G-D"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Grotzinger",
"given_name": "J. P.",
"orcid": "0000-0001-9324-1257",
"clpid": "Grotzinger-J-P"
},
{
"family_name": "Summons",
"given_name": "R. E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Fischer",
"given_name": "W. W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
}
],
"abstract": "The largest recorded carbon isotopic excursion in Earth history is observed globally in carbonate rocks of middle Ediacaran age. Known from the Sultanate of Oman as the 'Shuram excursion', this event records a dramatic, systematic shift in \u03b4^(13)C_(carbonate) values to ca. \u221212\u2030. Attempts to explain the nature, magnitude and origin of this excursion include (i) a primary signal resulting from the protracted oxidation of a large dissolved organic carbon reservoir in seawater, release of methane from sediment-hosted clathrates, or water column stratification; and (ii) a secondary signal from diagenetic processes. The compositions and isotope ratios of organic carbon phases during the excursion are critical to evaluating these ideas; however, previous work has focused on localities that are low in organic carbon, hindering straightforward interpretation of the observed time-series trends. We report carbon isotope data from bulk organic carbon, extracted bitumen and kerogen, in addition to lipid biomarker data, from a subsurface well drilled on the eastern flank of the South Oman Salt Basin, Sultanate of Oman. This section captures Nafun Group strata through the Ediacaran\u2013Cambrian boundary in the Ara Group and includes an organic-rich, deeper-water facies of the Shuram Formation. Despite the high organic matter contents, the carbon isotopic compositions of carbonates \u2013 which record a negative \u03b4^(13)C isotope excursion similar in shape and magnitude to sections elsewhere in Oman \u2013 do not covary with those of organic phases (bulk TOC, bitumen and kerogen). Paired inorganic and organic \u03b4^(13)C data only display coupled behaviour during the latter part of the excursion's recovery. Furthermore, lipid biomarker data reveal that organic matter composition and source inputs varied stratigraphically, reflecting biological community shifts in non-migrated, syngenetic organic matter deposited during this interval.",
"doi": "10.1111/gbi.12045",
"issn": "1472-4677",
"publisher": "Blackwell Publishing",
"publication": "Geobiology",
"publication_date": "2013-09",
"series_number": "5",
"volume": "11",
"issue": "5",
"pages": "406-419"
},
{
"id": "authors:webwp-azt77",
"collection": "authors",
"collection_id": "webwp-azt77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141013-144432495",
"type": "article",
"title": "Carbon Isotope and Lipid Biomarker Stratigraphy from Organic-Rich Strata Through the Neoproterozoic Shuram Excursion in South Oman",
"author": [
{
"family_name": "Lee",
"given_name": "C.",
"clpid": "Lee-C"
},
{
"family_name": "Fike",
"given_name": "D. A.",
"orcid": "0000-0003-2848-0328",
"clpid": "Fike-D-A"
},
{
"family_name": "Love",
"given_name": "G. D.",
"orcid": "0000-0002-6516-014X",
"clpid": "Love-G-D"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Grotzinger",
"given_name": "J. P.",
"orcid": "0000-0001-9324-1257",
"clpid": "Grotzinger-J-P"
},
{
"family_name": "Summons",
"given_name": "R. E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Fischer",
"given_name": "W. W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
}
],
"abstract": "The regulation of oxygen levels in Earth's atmosphere and\noceans is inextricably linked to the carbon cycle. Carbon\nisotope ratios of carbonate and sedimentary organic matter\nprovide first order insights into the operation of the carbon cycle in the geologic past. During the Ediacaran period, the ~580 Ma 'Shuram Excursion' (SE) records a dramatic, systematic shift in \u03b4^(13)C_(carbonate) values to as low as c\u0251. -12\u2030, lasting potentially millions to tens of millions of years in duration and constitutes the largest carbon isotope excursion known in the record [1]. The extremely negative carbon isotope values in carbonate challenges our understanding of the ancient carbon cycle and is difficult to rationalise via uniform carbon cycle principles. Several hypotheses have been developed to explain this behaviour, all of which make different predictions for the abundance, structure, and isotopic\ncomposition of organic carbon through the excursion. For a direct test of these ideas, we report paired organic and inorganic stable carbon isotope ratios in addition to detailed lipid biomarker stratigraphic records from a subsurface well drilled on the eastern flank of the South Oman Salt Basin, Sultanate of Oman. This well captures thermally immature and organic-rich Nafun Group strata traversing the SE, yielding variable but primary biomarker characteristics typical of Neoproterozoic rocks from this region. Despite the high organic matter contents, the carbon isotopic compositions of carbonates do not covary with those of organic phases. Furthermore, lipid biomarker data reveal that organic matter composition and source inputs varied stratigraphically, reflecting biological community shifts in non-migrated, syngenetic organic matter deposited during this interval. Together these observations imply that carbonateorganic isotopic decoupling during the SE is not a result of mixing of fossil or exogenous carbon sources (either DOC, detrital, or migrated) with syngenetic organic matter.",
"doi": "10.1180/minmag.2013.077.5.12",
"issn": "0026-461X",
"publisher": "Mineralogical Society",
"publication": "Mineralogical Magazine",
"publication_date": "2013-07",
"series_number": "5",
"volume": "77",
"issue": "5",
"pages": "1565"
},
{
"id": "authors:b44pf-kyr02",
"collection": "authors",
"collection_id": "b44pf-kyr02",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130509-110734434",
"type": "article",
"title": "Geochemistry and geobiology of a present-day\n serpentinization site in California: The Cedars",
"author": [
{
"family_name": "Morrill",
"given_name": "Penny L.",
"clpid": "Morrill-P-L"
},
{
"family_name": "Kuenen",
"given_name": "J. Gijs",
"clpid": "Kuenen-J-G"
},
{
"family_name": "Johnson",
"given_name": "Orion J.",
"clpid": "Johnson-O-J"
},
{
"family_name": "Suzuki",
"given_name": "Shino",
"clpid": "Suzuki-Shino"
},
{
"family_name": "Rietze",
"given_name": "Amanda",
"clpid": "Rietze-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Fogel",
"given_name": "Marilyn L.",
"clpid": "Fogel-M-L"
},
{
"family_name": "Nealson",
"given_name": "Kenneth H.",
"orcid": "0000-0001-5189-3732",
"clpid": "Nealson-K-H"
}
],
"abstract": "Ultra-basic (pH 11\u201312) reducing (\u2212656 to \u2212585 mV) groundwater springs discharging from serpentinized peridotite of The Cedars, CA, were investigated for their geochemistry and geobiology. The spring waters investigated were of meteoric origin; however, geochemical modeling suggests that there were two sources of groundwater, a shallow source with sufficient contact with The Cedars' peridotite body to be altered geochemically by serpentinization, and a deeper groundwater source that not only flows through the peridotite body but was also in contact with the marine sediments of the Franciscan Subduction Complex (FSC) below the peridotite body. We propose that the groundwater discharging from lower elevations (GPS1 and CS1) reflect the geochemistry of the deeper groundwater in contact with FSC, while groundwaters discharging from springs at higher elevations (NS1 and BSC) were a mixture of the shallow peridotite-only groundwater and the deeper groundwater that has been in contact with the FSC. Cell densities of suspended microbes within these waters were extremely low. In the NS1 and BSC spring fluids, cell densities ranged from 10^2 to 10^3 cells/ml, while suspended cells at GPS were lower than 10 cells/mL. However, glass slides incubated in the BSC and GPS1 springs for 2\u20133 weeks were colonized by cells with densities ranging from 10^6 to 10^7 cells/cm^2 attached to their surfaces. All of the springs were very low (\u2a7d1 \u03bcM) in several essential elements and electron acceptors (e.g. nitrate/ammonium, sulfate, and phosphate) required for (microbial) growth, which is not uncommon at sites of continental serpentinization. Gases rich in N_2, H_2, and CH_4 were exsolving from the springs. The stable carbon isotope value (\u03b4^(13)C_(CH4) = \u221268 \u00b1 0.6\u2030) and the CH_4/C_(2+) (>10^3) of methane and other gaseous hydrocarbons exsolving from NS1 were typical of microbially sourced methane, whereas the isotope values and the CH_4/C_(2+) of BSC and CS1 springs were more enriched in ^(13)C and had CH_4/C_(2+) < 10^3, suggesting a mixture of microbial and non-microbial methane. The concentrations of aromatic compounds, and ethane, propane, iso- and n-butane were well described by simple physical mixing between the aromatic- and alkane-poor, shallow groundwater and the relatively aromatic, and alkane-rich groundwater that flows through both the peridotite and the FSC suggesting that these aromatic and alkane compounds originated in the deeper FSC groundwater and are not produced in the shallow peridotite-only groundwater. The aromatic compounds most probably originated from the diagenesis/degradation of organic matter in the marine sediments below the peridotite body, while the gaseous alkanes may have multiple sources including thermal degradation of the organic matter in the marine sediments below the peridotite body and possibly by abiogenic reactions occurring within the peridotite body. This geochemical study demonstrates the complexity of The Cedars, and the possible sources of hydrocarbons at continental sites of serpentinization.",
"doi": "10.1016/j.gca.2013.01.043",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2013-05-15",
"volume": "109",
"pages": "222-240"
},
{
"id": "authors:xva1p-pdz42",
"collection": "authors",
"collection_id": "xva1p-pdz42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130801-142621209",
"type": "article",
"title": "MC-ICP-MS measurement of \u03b4^(34)S and \u0394^(33)S in small amounts of dissolved sulfate",
"author": [
{
"family_name": "Paris",
"given_name": "Guillaume",
"orcid": "0000-0001-8368-1224",
"clpid": "Paris-G"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Subhas",
"given_name": "Adam V.",
"orcid": "0000-0002-7688-6624",
"clpid": "Subhas-A-V"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"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 \u03b4^(34)S values of natural samples with a typical reproducibility of 0.08\u20130.15\u2030 (2sd) on 5 to 40 nmol sulfur introduced into the instrument. We applied this method to two seawater profiles, using 25 \u03bcl of sample (700 nmol of sulfate). The average \u03b4^(34)S_(VCDT) value is 20.97 \u00b1 0.10\u2030 (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\u20130.3\u2030 (2sd) is achieved on the measurement of mass independent fractionations (\u0394^(33)S). This is the first time such precision has been achieved on samples of this size.",
"doi": "10.1016/j.chemgeo.2013.02.022",
"issn": "0009-2541",
"publisher": "Elsevier",
"publication": "Chemical Geology",
"publication_date": "2013-05-08",
"volume": "345",
"pages": "50-61"
},
{
"id": "authors:tv9a3-z4q22",
"collection": "authors",
"collection_id": "tv9a3-z4q22",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130409-104413706",
"type": "article",
"title": "Equilibrium ^2H/^1H fractionation in organic molecules: III. Cyclic ketones and hydrocarbons",
"author": [
{
"family_name": "Wang",
"given_name": "Ying",
"clpid": "Wang-Ying"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Nielsen",
"given_name": "Robert J.",
"orcid": "0000-0002-7962-0186",
"clpid": "Nielsen-R-J"
},
{
"family_name": "Goddard",
"given_name": "William A., III",
"orcid": "0000-0003-0097-5716",
"clpid": "Goddard-W-A-III"
}
],
"abstract": "Quantitative interpretation of stable hydrogen isotope ratios (^2H/^1H) in organic compounds is greatly aided by knowledge of the relevant equilibrium fractionation factors (\u03b5_(eq)). Previous efforts have combined experimental measurements and hybrid Density Functional Theory (DFT) calculations to accurately predict equilibrium fractionations in linear (acyclic) organic molecules ( Wang et al., 2009a and Wang et al., 2009b), but the calibration produced by that study is not applicable to cyclic compounds. Here we report experimental measurements of equilibrium ^2H/^1H fractionation in six cyclic ketones, and use those data to evaluate DFT calculations of fractionation in diverse monocyclic and polycyclic compounds commonly found in sedimentary organic matter and petroleum. At 25, 50, and 75 \u00b0C, the experimentally measured \u03b5_(eq) values for secondary and tertiary H_\u03b1 in isotopic equilibrium with water are in the ranges of \u2212130\u2030 to \u2212150\u2030 and +10\u2030 to \u221240\u2030 respectively. Measured data are similar to DFT calculations of \u03b5eq for axial H_\u03b1 but not equatorial H_\u03b1. In tertiary C_\u03b1 positions with methyl substituents, this can be understood as a result of the methyl group forcing H_\u03b1 atoms into a dominantly axial position. For secondary C_\u03b1 positions containing both axial and equatorial H_\u03b1 atoms, we propose that axial H_\u03b1 exchanges with water significantly faster than the equatorial H_\u03b1 does, due to the hyperconjugation-stabilized transition state. Interconversion of axial and equatorial positions via ring flipping is much faster than isotopic exchange at either position, and as a result the steady-state isotopic composition of both H's is strongly weighted toward that of axial H_\u03b1. Based on comparison with measured \u03b5_(eq) values, a total uncertainty of 10\u201330\u2030 remains for theoretical \u03b5_(eq) values.\nUsing DFT, we systematically estimated the \u03b5_(eq) values for individual H positions in various cyclic structures. By summing over all individual H positions, the molecular equilibrium fractionation was estimated to be \u221275\u2030 to \u221295\u2030 for steroids, \u221290\u2030 to \u2212105\u2030 for hopanoids, and \u221265\u2030 to \u2212100\u2030 for typical cycloparaffins between 0 and 100 \u00b0C relative to water. These are distinct from the typical biosynthetic fractionations of \u2212150\u2030 to \u2212300\u2030, but are similar to equilibrium fractionations for linear hydrocarbons (Wang et al., 2009b). Thus post-burial H exchange will generally remove the \u223c50\u2013100\u2030 biosynthetic fractionations between cyclic isoprenoid and n-alkyl lipid molecules, which can be used to evaluate the extent of H exchange in sedimentary organic matter and oils.",
"doi": "10.1016/j.gca.2013.01.001",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2013-04-15",
"volume": "107",
"pages": "82-95"
},
{
"id": "authors:zfsjt-6m593",
"collection": "authors",
"collection_id": "zfsjt-6m593",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130503-154036933",
"type": "article",
"title": "Identification and quantification of polyfunctionalized hopanoids by high temperature gas chromatography\u2013mass spectrometry",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Zhang",
"given_name": "Lichun",
"clpid": "Zhang-Lichun"
},
{
"family_name": "Welander",
"given_name": "Paula V.",
"clpid": "Welander-P-V"
},
{
"family_name": "Doughty",
"given_name": "David",
"clpid": "Doughty-D-M"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "Hopanoids are triterpenoids produced mainly by bacteria, are ubiquitous in the environment, and have many important applications as biological markers. A wide variety of related hopanoid structures exists, many of which are polyfunctionalized. These modifications render the hopanoids too involatile for conventional gas chromatography (GC) separation, so require either laborious oxidative cleavage of the functional groups or specialized high temperature (HT) columns. Here we describe the systematic evaluation and optimization of a HT\u2013GC method for the analysis of polyfunctionalized hopanoids and their methylated homologs. Total lipid extracts are derivatized with acetic anhydride and no further treatment or workup is required. We show that acid or base hydrolysis to remove di- and triacylglycerides leads to degradation of several BHP structures. DB-XLB type columns can elute hopanoids up to bacteriohopanetetrol at 350 \u00b0C, with baseline separation of all 2-methyl/desmethyl homologs. DB-5HT type columns can additionally elute bacteriohopaneaminotriol and bacteriohopaneaminotetrol, but do not fully separate 2-methyl/desmethyl homologs. The method gave 2- to 7-fold higher recovery of hopanoids than oxidative cleavage and can provide accurate quantification of all analytes including 2-methyl hopanoids. By comparing data from mass spectra with those from a flame ionization detector, we show that the mass spectromet (MS) response factors for different hopanoids using either total ion counts or m/z 191 vary substantially. Similarly, 2-methyl ratios estimated from selected-ion data are lower than those from FID by 10\u201330% for most hopanoids, but higher by ca. 10% for bacteriohopanetetrol. Mass spectra for a broad suite of hopanoids, including 2-methyl homologs, from Rhodopseudomonas palustris are presented, together with the tentative assignment of several new hopanoid degradation products.",
"doi": "10.1016/j.orggeochem.2012.12.009",
"pmcid": "PMC3780965",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2013-03",
"volume": "56",
"pages": "120-130"
},
{
"id": "authors:t7cet-6he05",
"collection": "authors",
"collection_id": "t7cet-6he05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130315-093157570",
"type": "article",
"title": "A high-resolution gas-source isotope ratio mass spectrometer",
"author": [
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
},
{
"family_name": "Clog",
"given_name": "Matthieu",
"clpid": "Clog-M"
},
{
"family_name": "Magyar",
"given_name": "Paul",
"clpid": "Magyar-P"
},
{
"family_name": "Piasecki",
"given_name": "Alison",
"clpid": "Piasecki-A"
},
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Stolper",
"given_name": "Daniel",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Deerberg",
"given_name": "Michael",
"clpid": "Deerberg-M"
},
{
"family_name": "Schlueter",
"given_name": "Hans-Juergen",
"clpid": "Schlueter-H-J"
},
{
"family_name": "Schwieters",
"given_name": "Johannes",
"clpid": "Schwieters-J"
}
],
"abstract": "We describe a new high-resolution, multi-collector gas source mass spectrometer designed for isotopic analysis of volatile and semi-volatile molecules: the Thermo Scientific MAT253-Ultra, a prototype double-focusing isotope ratio mass spectrometer installed in the Caltech laboratories for stable isotope geochemistry. This instrument achieves mass resolving power of up to \u223c27,000 (M/\u0394M) and can analyze diverse gases and semi-volatile compounds using a conventional dual inlet and/or a carrier gas. It has a multi-collector array comprised of 7 detector positions with adjustable spacing, all of which can register ions through an SEM or Faraday cup and spanning up to a 10^(13) range in signal strength. Abundance sensitivity in the He mass range is as good as 10^(\u221212), and precision commonly approaches the counting statistics limit down to 0.1\u2030 (SEM) or 0.01\u2030 (Faraday) for a range of analytes. This instrument permits resolution of isobaric interferences arising from both contaminants and multiple isotopologues of an analyte that share a cardinal mass, enabling direct isotopic analysis of molecules with complex mass spectra such as hydrocarbons. This ability should enable the measurement of position-specific isotopic compositions, including multiple substitutions, by comparing isotope ratios of molecular ions with those of daughter fragment ions (assuming products of recombination and other source reactions are recognized and corrected for). The combination of high mass resolution with stable multicollection will provide a wide range of potential new tools for isotope geochemistry, including (but not limited to): singly and multiply substituted methane and larger hydrocarbons; position-specific ^(13)C analysis of propane and larger hydrocarbons; precise analysis of ^(17)O/^(16)O and ^(18)O/^(16)O on fragment ions from CO_2 and other molecules; analysis of a variety of N_2O isotopologues (including ^(18)O, ^(17)O, position-specific ^(15)N, and various 'clumped' species); and high precision and abundance sensitivity noble gas analyses. These capabilities greatly extend the scope of stable isotope variations that can be utilized for problems in forensics, environmental geochemistry, biochemistry, and Earth and planetary sciences.",
"doi": "10.1016/j.ijms.2012.10.014",
"issn": "1387-3806",
"publisher": "Elsevier",
"publication": "International Journal of Mass Spectrometry",
"publication_date": "2013-02-01",
"volume": "335",
"pages": "45-56"
},
{
"id": "authors:j18z6-30g67",
"collection": "authors",
"collection_id": "j18z6-30g67",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130807-141851016",
"type": "article",
"title": "Measurement of intact methane isotopologues, including ^(13)CH_3D",
"author": [
{
"family_name": "Stolper",
"given_name": "Daniel A.",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "Methane (CH_4) is both a significant greenhouse gas and\nresource. Its present and past cycling can be studied through\nmeasurements of concentration and/or bulk isotopic ratios (^(13)C/^(12)C,\nD/H, and ^(14)C/^(12)C). Currently, isotope ratios are measured by mass\nspectrometric analysis of H_2 and CO_2 produced from CH_4, or by\nspectroscopy of CH_4. However, the interpretation of bulk isotopic\nvariations of CH_4 are often equivocal, necessitating additional\ntracers.",
"issn": "0026-461X",
"publisher": "Mineralogical Society",
"publication": "Mineralogical Magazine",
"publication_date": "2012-11",
"series_number": "6",
"volume": "76",
"issue": "6",
"pages": "2413"
},
{
"id": "authors:x5xs2-6bw26",
"collection": "authors",
"collection_id": "x5xs2-6bw26",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130807-094904824",
"type": "article",
"title": "The MAT-253 Ultra \u2014 a novel high-resolution, multi-collector gas source mass spectrometer",
"author": [
{
"family_name": "Eiler",
"given_name": "John",
"clpid": "Eiler-J-M"
},
{
"family_name": "Clog",
"given_name": "Matthieu",
"clpid": "Clog-M"
},
{
"family_name": "Deerberg",
"given_name": "Michael",
"clpid": "Deerberg-M"
},
{
"family_name": "Magyar",
"given_name": "Paul",
"clpid": "Magyar-P"
},
{
"family_name": "Piasecki",
"given_name": "Alison",
"clpid": "Piasecki-A"
},
{
"family_name": "Schlueter",
"given_name": "Hans-Juergen",
"clpid": "Schlueter-H-J"
},
{
"family_name": "Schwieters",
"given_name": "Johannes",
"clpid": "Schwieters-J"
},
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Stolper",
"given_name": "Daniel",
"orcid": "0000-0003-3299-3177",
"clpid": "Stolper-D-A"
},
{
"family_name": "Thiagarajan",
"given_name": "Nivedita",
"clpid": "Thiagarajan-N"
}
],
"abstract": "We present the design, performance and representative applications of the MAT 253 Ultra \u2013 the first prototype of a new class of high-resolution gas source isotope ratio mass\nspectrometers.",
"issn": "0026-461X",
"publisher": "Mineralogical Society",
"publication": "Mineralogical Magazine",
"publication_date": "2012-11",
"series_number": "6",
"volume": "76",
"issue": "6",
"pages": "1680"
},
{
"id": "authors:sn974-7j006",
"collection": "authors",
"collection_id": "sn974-7j006",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121116-131754394",
"type": "article",
"title": "^2H/^1H ratio of hopanes, tricyclic and tetracyclic terpanes in oils and source rocks from the Potiguar Basin, Brazil",
"author": [
{
"family_name": "Ferreira",
"given_name": "Alexandre A.",
"clpid": "Ferreira-A-A"
},
{
"family_name": "Santos Neto",
"given_name": "Eugenio V.",
"clpid": "Santos-Neto-E-V"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Aquino Neto",
"given_name": "Francisco R.",
"clpid": "Aquino-Neto-F-R"
}
],
"abstract": "We report the hydrogen isotope ratio ^2H/^1H (expressed as \u03b4^2H values) of 8 selected hopanes, tricyclic and tetracyclic terpanes from oils and source rocks in the Potiguar Basin, and of associated formation water. Hopanes ranged in \u03b4^2H value from \u221279\u2030 to \u2212142\u2030, whereas tri- and tetracyclic terpanes (TTTs) ranged from \u2212137\u2030 to \u2212225\u2030. Formation water \u03b4^2H values ranged from \u221223\u2030 to \u221232\u2030. The most significant pattern in the data is the systematic ^2H enrichment of hopanes relative to TTTs, by an average of 45\u2030 in oils and 78\u2030 in source rock extracts. The hopanes appear close to hydrogen isotopic equilibrium with coeval formation water, whereas TTTs are significantly more ^2H depleted. Given the similarities in structure between the two compound classes, it is unlikely that hopanes would be exchanged completely while the others would not. More likely, both classes have undergone a limited extent of exchange, but with the hopanes being biosynthesized with \u03b4^2H values closer to equilibrium. Our data suggest that at least some primary environmental and/or biotic information can be retained in the \u03b4^2H values of biomarkers in oils and extracts, and is not completely obscured by hydrogen exchange.",
"doi": "10.1016/j.orggeochem.2012.07.007",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2012-10",
"volume": "51",
"pages": "13-16"
},
{
"id": "authors:b7xj3-7h603",
"collection": "authors",
"collection_id": "b7xj3-7h603",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121022-122410675",
"type": "article",
"title": "Sulfur isotopes of organic matter preserved in 3.45-billion-year-old stromatolites reveal microbial metabolism",
"author": [
{
"family_name": "Bontognali",
"given_name": "Tomaso R. R.",
"clpid": "Bontognali-T-R-R"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Allwood",
"given_name": "Abigail C.",
"clpid": "Allwood-A-C"
},
{
"family_name": "Fischer",
"given_name": "Woodward W.",
"orcid": "0000-0002-8836-3054",
"clpid": "Fischer-W-W"
},
{
"family_name": "Grotzinger",
"given_name": "John P.",
"orcid": "0000-0001-9324-1257",
"clpid": "Grotzinger-J-P"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Eiler",
"given_name": "John M.",
"clpid": "Eiler-J-M"
}
],
"abstract": "The 3.45-billion-year-old Strelley Pool Formation of Western Australia preserves stromatolites that are considered among the oldest evidence for life on Earth. In places of exceptional preservation, these stromatolites contain laminae rich in organic carbon, interpreted\nas the fossil remains of ancient microbial mats. To better\nunderstand the biogeochemistry of these rocks, we performed\nmicroscale in situ sulfur isotope measurements of the preserved organic sulfur, including both \u0394^(33)S and \u03b4^(34)S_(CDT). This approach allows us to tie physiological inference from isotope ratios directly to fossil biomass, providing a means to understand sulfur metabolism\nthat is complimentary to, and independent from, inorganic\nproxies (e.g., pyrite). \u0394^(33)S values of the kerogen reveal mass-anomalous fractionations expected of the Archean sulfur cycle, whereas \u03b4^(34)S_(CDT) values show large fractionations at very small spatial scales, including values below \u221215\u2030. We interpret these isotopic\npatterns as recording the process of sulfurization of organic matter by H_2S in heterogeneous mat pore-waters influenced by respiratory S metabolism. Positive \u0394^(33)S anomalies suggest that disproportionation of elemental sulfur would have been a prominent microbial process in these communities.",
"doi": "10.1073/pnas.1207491109",
"pmcid": "PMC3458326",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2012-09-18",
"series_number": "38",
"volume": "109",
"issue": "38",
"pages": "15146-15151"
},
{
"id": "authors:1sk6p-s7142",
"collection": "authors",
"collection_id": "1sk6p-s7142",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120509-102449517",
"type": "article",
"title": "The sulfur-isotopic compositions of benzothiophenes and dibenzothiophenes as a proxy for thermochemical sulfate reduction",
"author": [
{
"family_name": "Amrani",
"given_name": "Alon",
"clpid": "Amrani-A"
},
{
"family_name": "Deev",
"given_name": "Andrei",
"clpid": "Deev-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Tang",
"given_name": "Yongchun",
"clpid": "Tang-Yongchun"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
},
{
"family_name": "Hill",
"given_name": "Ronald J.",
"clpid": "Hill-R-J"
},
{
"family_name": "Moldowan",
"given_name": "J. Michael",
"clpid": "Moldowan-J-M"
},
{
"family_name": "Wei",
"given_name": "Zhibin",
"clpid": "Wei-Zhibin"
}
],
"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 \u223c50\u2030 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 \u03b4^(34)S values of BTs are close to those of sulfate-bearing evaporites of the Smackover Fm., whereas the \u03b4^(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 \u03b4^(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 \u03b4^(34)S, preserving their original \u03b4^(34)S values longer than do BTs because of their greater thermal stability and slow rate of formation. We propose that comparison of the \u03b4^(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.",
"doi": "10.1016/j.gca.2012.01.023",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2012-05-01",
"volume": "84",
"pages": "152-164"
},
{
"id": "authors:y91c2-69s27",
"collection": "authors",
"collection_id": "y91c2-69s27",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121114-072328879",
"type": "article",
"title": "Molecular Paleohydrology: Interpreting the Hydrogen-Isotopic Composition of Lipid Biomarkers from Photosynthesizing Organisms",
"author": [
{
"family_name": "Sachse",
"given_name": "Dirk",
"clpid": "Sachse-D"
},
{
"family_name": "Billault",
"given_name": "Isabelle",
"clpid": "Billault-I"
},
{
"family_name": "Bowen",
"given_name": "Gabriel K.",
"clpid": "Bowen-G-K"
},
{
"family_name": "Chikaraishi",
"given_name": "Yoshiro",
"clpid": "Chikaraishi-Yoshiro"
},
{
"family_name": "Dawson",
"given_name": "Todd E.",
"clpid": "Dawson-T-E"
},
{
"family_name": "Feakins",
"given_name": "Sarah J.",
"orcid": "0000-0003-3434-2423",
"clpid": "Feakins-S-J"
},
{
"family_name": "Freeman",
"given_name": "Katherine H.",
"orcid": "0000-0002-3350-7671",
"clpid": "Freeman-K-H"
},
{
"family_name": "Magill",
"given_name": "Clayton R.",
"clpid": "Magill-C-R"
},
{
"family_name": "McInerney",
"given_name": "Francesca A.",
"clpid": "McInerney-F-A"
},
{
"family_name": "Van der Meer",
"given_name": "Marcel T. J.",
"clpid": "Van-der-Meer-M-T-J"
},
{
"family_name": "Polissar",
"given_name": "Pratigya",
"clpid": "Polissar-P"
},
{
"family_name": "Robins",
"given_name": "Richard J.",
"clpid": "Robins-R-J"
},
{
"family_name": "Sachs",
"given_name": "Julian P.",
"clpid": "Sachs-J-P"
},
{
"family_name": "Schmidt",
"given_name": "Hans-Ludwig",
"clpid": "Schmidt-H-L"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "White",
"given_name": "James W. C.",
"clpid": "White-J-W-C"
},
{
"family_name": "West",
"given_name": "Jason B.",
"clpid": "West-J-B"
},
{
"family_name": "Kahmen",
"given_name": "Ansgar",
"clpid": "Kahmen-A"
}
],
"abstract": "Hydrogen-isotopic abundances of lipid biomarkers are emerging as important proxies in the study of ancient environments and ecosystems. A decade ago, pioneering studies made use of new analytical methods and demonstrated that the hydrogen-isotopic composition of individual lipids from aquatic and terrestrial organisms can be related to the composition of their growth (i.e., environmental) water. Subsequently, compound-specific deuterium/hydrogen (D/H) ratios of sedimentary biomarkers have been increasingly used as paleohydrological proxies over a range of geological timescales. Isotopic fractionation observed between hydrogen in environmental water and hydrogen in lipids, however, is sensitive to biochemical, physiological, and environmental influences on the composition of hydrogen available for biosynthesis in cells. Here we review the factors and processes that are known to influence the hydrogen-isotopic compositions of lipids\u2014especially n-alkanes\u2014from photosynthesizing organisms, and we provide a framework for interpreting their D/H ratios from ancient sediments and identify future research opportunities.",
"doi": "10.1146/annurev-earth-042711-105535",
"issn": "0084-6597",
"publisher": "Annual Reviews",
"publication": "Annual Review of Earth and Planetary Sciences",
"publication_date": "2012-05",
"volume": "40",
"pages": "221-249"
},
{
"id": "authors:prr8s-y3373",
"collection": "authors",
"collection_id": "prr8s-y3373",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111128-101611198",
"type": "article",
"title": "The RND-family transporter, HpnN, is required for hopanoid localization to the outer membrane of Rhodopseudomonas palustris TIE-1",
"author": [
{
"family_name": "Doughty",
"given_name": "David M.",
"clpid": "Doughty-D-M"
},
{
"family_name": "Coleman",
"given_name": "Maureen L.",
"clpid": "Coleman-M-L"
},
{
"family_name": "Hunter",
"given_name": "Ryan C.",
"orcid": "0000-0003-3841-1676",
"clpid": "Hunter-Ryan-C"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "Rhodopseudomonas palustris TIE-1 is a Gram-negative bacterium that produces structurally diverse hopanoid lipids that are similar to eukaryotic steroids. Its genome encodes several homologues to proteins involved in eukaryotic steroid trafficking. In this study, we explored the possibility that two of these proteins are involved\nin intracellular hopanoid transport. R. palustris has a sophisticated membrane system comprising outer, cytoplasmic, and inner cytoplasmic membranes. It also divides asymmetrically, producing a mother and swarmer cell. We deleted genes encoding two putative hopanoid transporters that belong to the resistance\u2013nodulation\u2013\ncell division superfamily. Phenotypic analyses revealed that\none of these putative transporters (HpnN) is essential for the movement of hopanoids from the cytoplasmic to the outer membrane, whereas the other (Rpal_4267) plays a minor role. C30 hopanoids, such as diploptene, are evenly distributed between mother and swarmer cells, whereas hpnN is required for the C35 hopanoid, bacteriohopanetetrol, to remain localized to the mother cell type. Mutant cells lacking HpnN grow like the WT at 30 \u00b0C but slower at 38 \u00b0C. Following cell division at 38 \u00b0C, the \u0394hpnN cells remain\nconnected by their cell wall, forming long filaments. This phenotype may be attributed to hopanoid mislocalization because a double mutant deficient in both hopanoid biosynthesis and transport does not form filaments. However, the lack of hopanoids severely compromises cell growth at higher temperatures more generally. Because hopanoid mutants only manifest a strong phenotype under\ncertain conditions, R. palustris is an attractive model organism in which to study their transport and function.",
"doi": "10.1073/pnas.1104209108",
"pmcid": "PMC3215060",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2011-11-08",
"series_number": "45",
"volume": "108",
"issue": "45",
"pages": "E1045-E1051"
},
{
"id": "authors:p7yb9-5re62",
"collection": "authors",
"collection_id": "p7yb9-5re62",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111006-104756740",
"type": "article",
"title": "Tracing iron-fueled microbial carbon production within the hydrothermal plume at the Loihi seamount",
"author": [
{
"family_name": "Bennett",
"given_name": "Sarah A.",
"clpid": "Bennett-S-A"
},
{
"family_name": "Hansman",
"given_name": "Roberta L.",
"clpid": "Hansman-R-L"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Nakamura",
"given_name": "Ko-ichi",
"clpid": "Nakamura-Ko-ichi"
},
{
"family_name": "Edwards",
"given_name": "Katrina J.",
"clpid": "Edwards-K-J"
}
],
"abstract": "The Loihi hydrothermal plume provides an opportunity to investigate iron (Fe) oxidation and microbial processes in a system that is truly Fe dominated and distinct from mid-ocean ridge spreading centers. The lack of hydrogen sulfide within the Loihi hydrothermal fluids and the presence of an oxygen minimum zone at this submarine volcano's summit, results in a prolonged presence of reduced Fe within the dispersing non-buoyant plume. In this study, we have investigated the potential for microbial carbon fixation within the Loihi plume. We sampled for both particulate and dissolved organic carbon in hydrothermal fluids, microbial mats growing around vents, and the dispersing plume, and carried out stable carbon isotope analysis on the particulate fraction. The \u03b4^(13)C values of the microbial mats ranged from \u221223\u2030 to \u221228\u2030, and are distinct from those of deep-ocean particulate organic carbon (POC). The mats and hydrothermal fluids were also elevated in dissolved organic carbon (DOC) compared to background seawater. Within the hydrothermal plume, DOC and POC concentrations were elevated and the isotopic composition of POC within the plume suggests mixing between background seawater POC and a ^(13)C-depleted hydrothermal component. The combination of both DOC and POC increasing in the dispersing plume that cannot solely be the result of entrainment and DOC adsorption, provides strong evidence for in-situ microbial productivity by chemolithoautotrophs, including a likelihood for iron-oxidizing microorganisms.",
"doi": "10.1016/j.gca.2011.06.039",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2011-10-01",
"series_number": "19",
"volume": "75",
"issue": "19",
"pages": "5526-5539"
},
{
"id": "authors:dfefb-a6b34",
"collection": "authors",
"collection_id": "dfefb-a6b34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110930-080341629",
"type": "article",
"title": "Hydrogen-isotopic variability in fatty acids from Yellowstone National Park hot spring microbial communities",
"author": [
{
"family_name": "Osburn",
"given_name": "Magdalena R.",
"orcid": "0000-0001-9180-559X",
"clpid": "Osburn-M-R"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Pepe-Ranney",
"given_name": "Charles",
"clpid": "Pepe-Ranney-C"
},
{
"family_name": "Spear",
"given_name": "John R.",
"orcid": "0000-0002-4664-7438",
"clpid": "Spear-J-R"
}
],
"abstract": "We report the abundances and hydrogen-isotopic compositions (D/H ratios) of fatty acids extracted from hot-spring microbial mats in Yellowstone National Park. The terrestrial hydrothermal environment provides a useful system for studying D/H fractionations because the numerous microbial communities in and around the springs are visually distinct, separable, and less complex than those in many other aquatic environments. D/H fractionations between lipids and water ranged from \u2212374\u2030 to +41\u2030 and showed systematic variations between different types of microbial communities. Lipids produced by chemoautotrophic hyperthermophilic bacteria, such as icosenoic acid (20:1), generally exhibited the largest and most variable fractionations from water (\u2212374\u2030 to \u2212165\u2030). This was in contrast to lipids characteristic of heterotrophs, such as branched, odd chain-length fatty acids, which had the smallest fractionations (\u2212163\u2030 to +41\u2030). Mats dominated by photoautotrophs exhibited intermediate fractionations similar in magnitude to those expressed by higher plants. These data support the hypothesis that variations in lipid D/H are strongly influenced by central metabolic pathways. Shifts in the isotopic compositions of individual fatty acids across known ecological boundaries show that the isotopic signature of specific metabolisms can be recognized in modern environmental samples, and potentially recorded in ancient ones. Considering all sampled springs, the total range in D/H ratios is similar to that observed in marine sediments, suggesting that the trends observed here are not exclusive to the hydrothermal environment.",
"doi": "10.1016/j.gca.2011.05.038",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2011-09-01",
"series_number": "17",
"volume": "75",
"issue": "17",
"pages": "4830-4845"
},
{
"id": "authors:hajtr-z1g95",
"collection": "authors",
"collection_id": "hajtr-z1g95",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110328-093422251",
"type": "article",
"title": "D/H variation in terrestrial lipids from Santa Barbara Basin over the past 1400 years: A preliminary assessment of paleoclimatic relevance",
"author": [
{
"family_name": "Li",
"given_name": "Chao",
"clpid": "Li-Chao"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Valentine",
"given_name": "David L.",
"clpid": "Valentine-D-L"
},
{
"family_name": "Thiagarajan",
"given_name": "Nivedita",
"clpid": "Thiagarajan-N"
}
],
"abstract": "We analyzed D/H ratios of common terrestrial leaf wax lipids in a 1400 year sediment core from the Santa Barbara Basin (SBB) to test whether they accurately record terrestrial climate in Southern California. The D/H ratios of long chain n-alkanes vary substantially with depth, but are poorly correlated with other terrestrial climate proxies. Interference from fossil hydrocarbons may be at least partly responsible. Long chain n-alkanoic acids exhibit nearly constant downcore D/H ratio values. This constancy in the face of known climatic shifts presumably reflects a substantial residence time for leaf wax compounds in terrestrial soil and/or on the basin flanks. Alternatively, the isotopic composition of meteoric waters in Southern California may not covary with climate, particularly aridity. However, the \u03b4D values of n_(-C22) and n_(-C24) fatty acids, commonly attributed to terrestrial aquatic sources, are partially correlated with Southern California winter Palmer Drought Severity Index, a tree ring-based climatic proxy (R^2 0.25; p < 0.01) on\nmulti-centennial scales with an inferred ca. 215 year time lag. The improved correlation of these biomarkers\ncan be explained by the fact that they are not stored in terrestrial soil nor are subject to interference\nfrom fossil hydrocarbons. Our study indicates that the SBB is unlikely to preserve high resolution\nleaf wax D/H records that can serve as quantitative paleoclimate proxies, though some qualitative information\nmay be retained. More generally, the sources of lipids in marginal marine basins need to be carefully evaluated prior to attempting paleoclimate reconstruction based on the leaf wax D/H proxy.",
"doi": "10.1016/j.orggeochem.2010.09.011",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2011-01",
"series_number": "1",
"volume": "42",
"issue": "1",
"pages": "15-24"
},
{
"id": "authors:hz2bw-68d47",
"collection": "authors",
"collection_id": "hz2bw-68d47",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110222-130709748",
"type": "article",
"title": "Crassulacean acid metabolism influences D/H ratio of leaf wax in succulent plants",
"author": [
{
"family_name": "Feakins",
"given_name": "Sarah J.",
"orcid": "0000-0003-3434-2423",
"clpid": "Feakins-S-J"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "This study sought to characterize hydrogen isotopic fractionation during biosynthesis of leaf wax n-alkanes in succulent plants capable of crassulacean acid metabolism (CAM). The metabolic and physiological features of CAM represent crucial strategies for survival in hot and dry climates and have been hypothesized to impact hydrogen isotope fractionation. We measured the stable carbon and hydrogen isotopic compositions (\u03b4^(13)C and \u03b4D, respectively) of individual n-alkanes in 20 species of succulent plants from a global collection of the Huntington Botanical Gardens, San Marino, California. Greenhouse conditions and irrigation with water of constant \u03b4D value enabled determination of interspecies differences in net D/H fractionation between source water and leaf wax products. Carbon isotope ratios provide constraints on the extent of CAM vs. C3 photosynthesis and indicate a wide range of CAM use, with \u03b4^(13)C values ranging from \u221233.01\u2030 to \u221218.54\u2030 (C_(27)\u2013C_(33) n-alkanes) and \u221226.66\u2030 to \u221217.64\u2030 (bulk tissue). Despite the controlled growth environment, we observed ca. 90\u2030 interspecies range in \u03b4D values from \u2212193\u2030 to \u2212107\u2030. A positive correlation between \u03b4^(13)C_(bulk) and \u03b4D_(C31) values with R^2 = 0.60 (\u03b4^(13)C_(C31) and \u03b4D_(C31) values with R^2 = 0.41) implicates a metabolic isotope effect as the dominant cause of interspecies variation in the hydrogen isotopic composition of leaf wax n-alkanes in CAM-intermediate plants.",
"doi": "10.1016/j.orggeochem.2010.09.007",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2010-12",
"series_number": "12",
"volume": "41",
"issue": "12",
"pages": "1269-1276"
},
{
"id": "authors:ams5s-cg161",
"collection": "authors",
"collection_id": "ams5s-cg161",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101209-121741039",
"type": "article",
"title": "Orbital- and millennial-scale changes in the hydrologic cycle and vegetation in the western African Sahel: insights from individual plant wax \u03b4D and \u03b4^(13)C",
"author": [
{
"family_name": "Niedermeyer",
"given_name": "Eva M.",
"clpid": "Niedermeyer-E-M"
},
{
"family_name": "Schefu\u00df",
"given_name": "Enno",
"clpid": "Schefu\u00df-E"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Mulitza",
"given_name": "Stefan",
"clpid": "Mulitza-S"
},
{
"family_name": "Mollenhauer",
"given_name": "Gesine",
"clpid": "Mollenhauer-G"
},
{
"family_name": "Schulz",
"given_name": "Michael",
"clpid": "Schulz-M"
},
{
"family_name": "Wefer",
"given_name": "Gerold",
"clpid": "Wefer-G"
}
],
"abstract": "To reconstruct variability of the West African monsoon and associated vegetation changes on precessional and millennial time scales, we analyzed a marine sediment core from the continental slope off Senegal spanning the past 44,000 years (44 ka). We used the stable hydrogen isotopic composition (\u03b4D) of individual terrestrial plant wax n-alkanes as a proxy for past rainfall variability. The abundance and stable carbon isotopic composition (\u03b4^(13)C) of the same compounds were analyzed to assess changes in vegetation composition (C_(3)/C_(4) plants) and density. The \u03b4D record reveals two wet periods that coincide with local maximum summer insolation from 38 to 28 ka and 15 to 4 ka and that are separated by a less wet period during minimum summer insolation. Our data indicate that rainfall intensity during the rainy season throughout both wet humid periods was similar, whereas the length of the rainy season was presumably shorter during the last glacial than during the Holocene. Additional dry intervals are identified that coincide with North Atlantic Heinrich stadials and the Younger Dryas interval, indicating that the West African monsoon over tropical northwest Africa is linked to both insolation forcing and high-latitude climate variability. The \u03b4^(13)C record indicates that vegetation of the western Sahel was consistently dominated by C_4 plants during the past 44 ka, whereas C_(3)-type vegetation increased during the Holocene. Moreover, we observe a gradual ending of the Holocene humid period together with unchanging ratio of C_3 to C_4 plants, indicating that an abrupt aridification due to vegetation feedbacks is not a general characteristic of this time interval.",
"doi": "10.1016/j.quascirev.2010.06.039",
"issn": "0277-3791",
"publisher": "Elsevier",
"publication": "Quaternary Science Reviews",
"publication_date": "2010-11",
"series_number": "23-24",
"volume": "29",
"issue": "23-24",
"pages": "2996-3005"
},
{
"id": "authors:64m8j-f8t94",
"collection": "authors",
"collection_id": "64m8j-f8t94",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101022-131749813",
"type": "article",
"title": "Identification of Novel Methane-, Ethane-, and Propane-Oxidizing Bacteria at Marine Hydrocarbon Seeps by Stable Isotope Probing",
"author": [
{
"family_name": "Redmond",
"given_name": "Molly C.",
"clpid": "Redmond-M-C"
},
{
"family_name": "Valentine",
"given_name": "David L.",
"clpid": "Valentine-D-L"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Marine hydrocarbon seeps supply oil and gas to microorganisms in sediments and overlying water. We used stable isotope probing (SIP) to identify aerobic bacteria oxidizing gaseous hydrocarbons in surface sediment from the Coal Oil Point seep field located offshore of Santa Barbara, California. After incubating sediment with ^(13)C-labeled methane, ethane, or propane, we confirmed the incorporation of ^(13)C into fatty acids and DNA. Terminal restriction fragment length polymorphism (T-RFLP) analysis and sequencing of the 16S rRNA and particulate methane monooxygenase (pmoA) genes in ^(13)C-DNA revealed groups of microbes not previously thought to contribute to methane, ethane, or propane oxidation. First, ^(13)C methane was primarily assimilated by Gammaproteobacteria species from the family Methylococcaceae, Gammaproteobacteria related to Methylophaga, and Betaproteobacteria from the family Methylophilaceae. Species of the latter two genera have not been previously shown to oxidize methane and may have been cross-feeding on methanol, but species of both genera were heavily labeled after just 3 days. pmoA sequences were affiliated with species of Methylococcaceae, but most were not closely related to cultured methanotrophs. Second, ^(13)C ethane was consumed by members of a novel group of Methylococcaceae. Growth with ethane as the major carbon source has not previously been observed in members of the Methylococcaceae; a highly divergent pmoA-like gene detected in the ^(13)C-labeled DNA may encode an ethane monooxygenase. Third, ^(13)C propane was consumed by members of a group of unclassified Gammaproteobacteria species not previously linked to propane oxidation. This study identifies several bacterial lineages as participants in the oxidation of gaseous hydrocarbons in marine seeps and supports the idea of an alternate function for some pmoA-like genes.",
"doi": "10.1128/AEM.00271-10",
"pmcid": "PMC2950463",
"issn": "0099-2240",
"publisher": "American Society for Microbiology",
"publication": "Applied and Environmental Microbiology",
"publication_date": "2010-10",
"series_number": "19",
"volume": "76",
"issue": "19",
"pages": "6412-6422"
},
{
"id": "authors:e56gn-feq14",
"collection": "authors",
"collection_id": "e56gn-feq14",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140623-100201451",
"type": "article",
"title": "Influence of water on D/H ratios of n-alkanes from hydrous pyrolysis of source rocks with kerogen types I, II, IIS and III",
"author": [
{
"family_name": "Gao",
"given_name": "L.",
"clpid": "Gao-L"
},
{
"family_name": "Schimmelmann",
"given_name": "A.",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Wang",
"given_name": "Y.",
"clpid": "Wang-Y"
},
{
"family_name": "Mastalerz",
"given_name": "M.",
"clpid": "Masterlerz-M"
}
],
"abstract": "Compound-specific D/H ratios of n-alkanes in soils and\nimmature source rocks can be used to help constrain\npaleoenvironmental and paleoclimatic conditions. With\nincreasing thermal maturity, however, the isotopic\ncomposition of primary biogenic n-alkanes can be altered both by isotopic exchange and the production of thermogenic nalkanes via cracking of sedimentary organic matter.",
"doi": "10.1016/j.gca.2010.04.032",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2010-06",
"series_number": "12",
"volume": "74",
"issue": "12",
"pages": "A318-A318"
},
{
"id": "authors:2fjqd-hm415",
"collection": "authors",
"collection_id": "2fjqd-hm415",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140623-103125636",
"type": "article",
"title": "The importance of metabolism for lipid D/H ratios",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Zhang",
"given_name": "Xinning",
"clpid": "Zhang-Xinning"
},
{
"family_name": "Gillespie",
"given_name": "Aimee L.",
"clpid": "Gillespie-A-L"
}
],
"abstract": "Recent work on factors controlling hydrogen-isotopic\nfractionations in lipids has yielded two rather surprising\nobservations. The first is that the net D/H fractionation\nbetween growth water and synthesized lipids (\u0454_(w/l)) can change substantially as a function of environmental salinity.",
"doi": "10.1016/j.gca.2010.04.045",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2010-06",
"series_number": "12",
"volume": "74",
"issue": "12",
"pages": "A936-A936"
},
{
"id": "authors:n0ee3-8ax91",
"collection": "authors",
"collection_id": "n0ee3-8ax91",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100601-111422016",
"type": "article",
"title": "Identification of a methylase required for 2-methylhopanoid production and implications for the interpretation of sedimentary hopanes",
"author": [
{
"family_name": "Welander",
"given_name": "Paula V.",
"clpid": "Welander-P-V"
},
{
"family_name": "Coleman",
"given_name": "Maureen L.",
"clpid": "Coleman-M-L"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "The rise of atmospheric oxygen has driven environmental change and biological evolution throughout much of Earth's history and was enabled by the evolution of oxygenic photosynthesis in the cyanobacteria. Dating this metabolic innovation using inorganic proxies from sedimentary rocks has been difficult and one important approach has been to study the distributions of fossil lipids, such as steranes and 2-methylhopanes, as biomarkers for this process. 2-methylhopanes arise from degradation of 2-methylbacteriohopanepolyols (2-MeBHPs), lipids thought to be synthesized primarily by cyanobacteria. The discovery that 2-MeBHPs are produced by an anoxygenic phototroph, however, challenged both their taxonomic link with cyanobacteria and their functional link with oxygenic photosynthesis. Here, we identify a radical SAM methylase encoded by the hpnP gene that is required for methylation at the C-2 position in hopanoids. This gene is found in several, but not all, cyanobacteria and also in \u03b1 -proteobacteria and acidobacteria. Thus, one cannot extrapolate from the presence of 2-methylhopanes alone, in modern environments or ancient sedimentary rocks, to a particular taxonomic group or metabolism. To understand the origin of this gene, we reconstructed the evolutionary history of HpnP. HpnP proteins from cyanobacteria, Methylobacterium species, and other \u03b1-proteobacteria form distinct phylogenetic clusters, but the branching order of these clades could not be confidently resolved. Hence,it is unclear whether HpnP, and 2-methylhopanoids, originated first in the cyanobacteria. In summary, existing evidence does not support the use of 2-methylhopanes as biomarkers for oxygenic photosynthesis.",
"doi": "10.1073/pnas.0912949107",
"pmcid": "PMC2889317",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2010-05-11",
"series_number": "19",
"volume": "107",
"issue": "19",
"pages": "8537-8542"
},
{
"id": "authors:zpced-cma33",
"collection": "authors",
"collection_id": "zpced-cma33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100412-095415054",
"type": "article",
"title": "A Stratified Redox Model for the Ediacaran Ocean",
"author": [
{
"family_name": "Li",
"given_name": "Chao",
"clpid": "Li-Chao"
},
{
"family_name": "Love",
"given_name": "Gordon D.",
"orcid": "0000-0002-6516-014X",
"clpid": "Love-G-D"
},
{
"family_name": "Lyons",
"given_name": "Timothy W.",
"clpid": "Lyons-T-W"
},
{
"family_name": "Fike",
"given_name": "David A.",
"orcid": "0000-0003-2848-0328",
"clpid": "Fike-D-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Chu",
"given_name": "Xuelei",
"clpid": "Chu-Xuelei"
}
],
"abstract": "The Ediacaran Period (635 to 542 million years ago) was a time of fundamental environmental and evolutionary change, culminating in the first appearance of macroscopic animals. Here, we present a detailed spatial and temporal record of Ediacaran ocean chemistry for the Doushantuo Formation in the Nanhua Basin, South China. We find evidence for a metastable zone of euxinic (anoxic and sulfidic) waters impinging on the continental shelf and sandwiched within ferruginous [Fe(II)-enriched] deep waters. A stratified ocean with coeval oxic, sulfidic, and ferruginous zones, favored by overall low oceanic sulfate concentrations, was maintained dynamically throughout the Ediacaran Period. Our model reconciles seemingly conflicting geochemical redox conditions proposed previously for Ediacaran deep oceans and helps to explain the patchy temporal record of early metazoan fossils.",
"doi": "10.1126/science.1182369",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "2010-04-02",
"series_number": "5974",
"volume": "328",
"issue": "5974",
"pages": "80-83"
},
{
"id": "authors:rcqpx-a8k20",
"collection": "authors",
"collection_id": "rcqpx-a8k20",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100406-110940817",
"type": "article",
"title": "Controls on the D/H ratios of plant leaf waxes in an arid ecosystem",
"author": [
{
"family_name": "Feakins",
"given_name": "Sarah J.",
"orcid": "0000-0003-3434-2423",
"clpid": "Feakins-S-J"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "The extent to which leaf water D-enrichment (transpiration) and soil water D-enrichment (evaporation) affect the D/H ratio of plant leaf waxes remains a contentious issue, with important implications for paleohydrologic reconstructions. In this study we measure \u03b4D values of precipitation (\u03b4D_p), groundwater (\u03b4D_(gw)), plant xylem water (\u03b4D_(xw)) and leaf water (\u03b4D_(lw)) to understand their impact on the \u03b4D values of plant leaf wax n-alkanes (\u03b4D_(wax)) in an arid ecosystem. Our survey includes multiple species at four sites across an aridity gradient (80\u201330% relative humidity) in southern California.\n\nWe find that many species take up groundwater or precipitation without significant fractionation. D-enriched soil water is a minor source even in species known to perform and utilize waters from hydraulic lift, such as Larrea tridentata (+10\u2030). Measurements of leaf water isotopic composition demonstrate that transpiration is an important mechanism for D-enrichment of leaf waters (+74 \u00b1 20\u2030, 1\u03c3), resulting in the smallest net fractionation yet reported between source water and leaf waxes (L. tridentata \u221241\u2030; multi-species mean value is \u221294 \u00b1 21\u2030, 1\u03c3). We find little change in leaf water D-enrichment or net fractionation across the climatic gradient sampled by our study, suggesting that a net fractionation of ca. \u221290\u2030 may be appropriate for paleohydrologic reconstructions in semi-arid to arid environments. Large interspecies offsets in net fractionations (1\u03c3 = 21\u2030) are potentially troublesome, given the observed floristic diversity and the likelihood of species assemblage changes with climate shifts.",
"doi": "10.1016/j.gca.2010.01.016",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2010-04-01",
"series_number": "7",
"volume": "74",
"issue": "7",
"pages": "2128-2141"
},
{
"id": "authors:r0hjr-caz34",
"collection": "authors",
"collection_id": "r0hjr-caz34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100127-113130226",
"type": "article",
"title": "Equilibrium ^2H/^1H fractionations in organic molecules: I. Experimental calibration of ab initio calculations",
"author": [
{
"family_name": "Wang",
"given_name": "Ying",
"clpid": "Wang-Ying-Min"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Nielsen",
"given_name": "Robert J.",
"orcid": "0000-0002-7962-0186",
"clpid": "Nielsen-R-J"
},
{
"family_name": "Goddard",
"given_name": "William A., III",
"orcid": "0000-0003-0097-5716",
"clpid": "Goddard-W-A-III"
}
],
"abstract": "Carbon-bound hydrogen in sedimentary organic matter can undergo exchange over geologic timescales, altering its isotopic composition. Studies investigating the natural abundance distribution of ^1H and ^2H in such molecules must account for this exchange, which in turn requires quantitative knowledge regarding the endpoint of exchange, i.e., the equilibrium isotopic fractionation factor (\u03b1_(eq)). To date, relevant data have been lacking for molecules larger than methane. Here we describe an experimental method to measure \u03b1_(eq) for C-bound H positions adjacent to carbonyl group (H_\u03b1) in ketones. H at these positions equilibrates on a timescale of days as a result of keto-enol tautomerism, allowing equilibrium ^2H/^1H distributions to be indirectly measured. Molecular vibrations for the same ketone molecules are then computed using Density Functional Theory at the B3LYP/6-311G** level and used to calculate \u03b1_(eq) values for H_\u03b1. Comparison of experimental and computational results for six different straight and branched ketones yields a temperature-dependent linear calibration curve with slope = 1.081\u22120.00376T and intercept = 8.404\u22120.387T, where T is temperature in degrees Celsius. Since the dominant systematic error in the calculation (omission of anharmonicity) is of the same size for ketones and C-bound H in most other linear compounds, we propose that this calibration can be applied to analogous calculations for a wide variety of organic molecules with linear carbon skeletons for temperatures below 100 \u00b0C. In a companion paper (Wang et al., 2009) we use this new calibration dataset to calculate the temperature-dependent equilibrium isotopic fractionation factors for a range of linear hydrocarbons, alcohols, ethers, ketones, esters and acids.",
"doi": "10.1016/j.gca.2009.08.019",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2009-12-01",
"series_number": "23",
"volume": "73",
"issue": "23",
"pages": "7060-7075"
},
{
"id": "authors:5z0e3-sbf04",
"collection": "authors",
"collection_id": "5z0e3-sbf04",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100127-143515017",
"type": "article",
"title": "Equilibrium ^2H/^1H fractionations in organic molecules. II: Linear alkanes, alkenes, ketones, carboxylic acids, esters, alcohols and ethers",
"author": [
{
"family_name": "Wang",
"given_name": "Ying Min",
"clpid": "Wang-Ying-Min"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Nielsen",
"given_name": "Robert J.",
"orcid": "0000-0002-7962-0186",
"clpid": "Nielsen-R-J"
},
{
"family_name": "Goddard",
"given_name": "William A., III",
"orcid": "0000-0003-0097-5716",
"clpid": "Goddard-W-A-III"
}
],
"abstract": "Equilibrium ^2H/^1H fractionation factors (\u03b1_(eq)) for various H positions in alkanes, alkenes, ketones, carboxylic acids, esters, alcohols, and ethers were calculated between 0 and 100 \u00b0C using vibrational frequencies from ab initio QM calculations (B3LYP/6-311G**). Results were then corrected using a temperature-dependent linear calibration curve based on experimental data for H_\u03b1 in ketones (Wang et al., 2009). The total uncertainty in reported \u03b1_(eq) values is estimated at 10\u201320\u2030. The effects of functional groups were found to increase the value of \u03b1_(eq) for H next to electron-donating groups, e.g. -OR, -OH or -O(CO)R, and to decrease the value of \u03b1_(eq) for H next to electron-withdrawing groups, e.g. -(C=O)R or -(C=O)OR. Smaller but significant functional group effects are also observed for H_\u03b2 and sometimes H_\u03b3. By summing over individual H positions, we estimate the equilibrium fractionation relative to water to be \u221290\u2030 to \u221270\u2030 for n-alkanes and around \u2212100\u2030 for pristane and phytane. The temperature dependence of these fractionations is very weak between 0 and 100 \u00b0C. Our estimates of \u03b1_(eq) agree well with field data for thermally mature hydrocarbons (\u03b4^2H values between \u221280\u2030 and \u2212110\u2030 relative to water). Therefore the observed \u03b42H increase of individual hydrocarbons and the disappearance of the biosynthetic \u03b4^2H offset between n-alkyl and linear isoprenoid lipids during maturation of organic matter can be confidently attributed to H exchange towards an equilibrium state. Our results also indicate that many n-alkyl lipids are biosynthesized with \u03b4^2H values that are close to equilibrium with water. In these cases, constant down-core \u03b4^2H values for n-alkyl lipids cannot be reliably used to infer a lack of isotopic exchange.",
"doi": "10.1016/j.gca.2009.08.018",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2009-12-01",
"series_number": "23",
"volume": "73",
"issue": "23",
"pages": "7076-7086"
},
{
"id": "authors:p5vc5-78680",
"collection": "authors",
"collection_id": "p5vc5-78680",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100614-153741613",
"type": "article",
"title": "Compound-Specific \u03b4^(34)S Analysis of Volatile Organics by Coupled GC/Multicollector-ICPMS",
"author": [
{
"family_name": "Amrani",
"given_name": "Alon",
"clpid": "Amrani-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Adkins",
"given_name": "Jess F.",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"abstract": "We have developed a highly sensitive and robust method for the analysis of \u03b4^(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\u2212sample bracketing with peaks of SF6 reference gas. The precision of measured \u03b4^(34)S values approaches 0.1\u2030 for analytes containing >40 pmol S and is better than 0.5\u2030 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\u2030. 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 \u03b4^(34)S and demonstrate the robustness and precision of the method in complex environmental samples.",
"doi": "10.1021/ac9016538",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2009-11-01",
"series_number": "21",
"volume": "81",
"issue": "21",
"pages": "9027-9034"
},
{
"id": "authors:f15dd-28x07",
"collection": "authors",
"collection_id": "f15dd-28x07",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091223-095612383",
"type": "article",
"title": "Raman spectroscopy and biomarker analysis reveal multiple carbon inputs to a Precambrian glacial sediment",
"author": [
{
"family_name": "Marshall",
"given_name": "Alison Olcott",
"clpid": "Marshall-A-O"
},
{
"family_name": "Corsetti",
"given_name": "Frank A.",
"clpid": "Corsetti-F-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Marshall",
"given_name": "Craig P.",
"clpid": "Marshall-C-P"
}
],
"abstract": "Extractable biomarkers can help elucidate the environment and biota of ancient glaciations, although the method must be applied with care, as glacial sediments have a potential for incorporation of older detrital carbon. In Phanerozoic glacial sediments, the distinct elemental, molecular and isotopic compositions of the terrestrial and marine biomass allow discrimination between primary marine and redeposited terrestrial organic matter. However, as the Proterozoic biosphere was largely microbial and marine, biomarker and isotopic analyses are insufficient for distinguishing primary organic matter from secondary reworked organic matter. Here, we report the combined application of Raman spectroscopy and biomarker analysis to Precambrian glacial sediments, which, together, allows discrimination between mixed pools of organic carbon and provides a promising new approach for rapidly screening Precambrian sediments for immature organic matter amenable to biomarker analysis.",
"doi": "10.1016/j.orggeochem.2009.08.006",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2009-11",
"series_number": "11",
"volume": "40",
"issue": "11",
"pages": "1115-1123"
},
{
"id": "authors:tv52g-bzj52",
"collection": "authors",
"collection_id": "tv52g-bzj52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091002-105243373",
"type": "article",
"title": "Hopanoids Play a Role in Membrane Integrity and pH Homeostasis in Rhodopseudomonas palustris TIE-1",
"author": [
{
"family_name": "Welander",
"given_name": "Paula V.",
"clpid": "Welander-P-V"
},
{
"family_name": "Hunter",
"given_name": "Ryan C.",
"orcid": "0000-0003-3841-1676",
"clpid": "Hunter-Ryan-C"
},
{
"family_name": "Zhang",
"given_name": "Lichun",
"clpid": "Zhang-Lichun"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "Sedimentary hopanes are pentacyclic triterpenoids that serve as biomarker proxies for bacteria and certain bacterial metabolisms, such as oxygenic photosynthesis and aerobic methanotrophy. Their parent molecules, the bacteriohopanepolyols (BHPs), have been hypothesized to be the bacterial equivalent of sterols. However, the actual function of BHPs in bacterial cells is poorly understood. Here, we report the physiological study of a mutant in Rhodopseudomonas palustris TIE-1 that is unable to produce any hopanoids. The deletion of the gene encoding the squalene-hopene cyclase protein (Shc), which cyclizes squalene to the basic hopene structure, resulted in a strain that no longer produced any polycyclic triterpenoids. This strain was able to grow chemoheterotrophically, photoheterotrophically, and photoautotrophically, demonstrating that hopanoids are not required for growth under normal conditions. A severe growth defect, as well as significant morphological damage, was observed when cells were grown under acidic and alkaline conditions. Although minimal changes in shc transcript expression were observed under certain conditions of pH shock, the total amount of hopanoid production was unaffected; however, the abundance of methylated hopanoids significantly increased. This suggests that hopanoids may play an indirect role in pH homeostasis, with certain hopanoid derivatives being of particular importance.",
"doi": "10.1128/JB.00460-09",
"pmcid": "PMC2747905",
"issn": "0021-9193",
"publisher": "American Society for Microbiology",
"publication": "Journal of Bacteriology",
"publication_date": "2009-10",
"series_number": "19",
"volume": "191",
"issue": "19",
"pages": "6145-6156"
},
{
"id": "authors:stvz1-4jb60",
"collection": "authors",
"collection_id": "stvz1-4jb60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090808-142503163",
"type": "article",
"title": "Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments",
"author": [
{
"family_name": "Li",
"given_name": "Chao",
"clpid": "Li-Chao"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Kinnaman",
"given_name": "Franklin S.",
"clpid": "Kinnaman-F-S"
},
{
"family_name": "Valentine",
"given_name": "David L.",
"clpid": "Valentine-D-L"
}
],
"abstract": "We conducted an extensive survey of hydrogen-isotopic compositions (D/H ratios) of diverse sedimentary lipids from the Santa Barbara Basin (SBB), offshore southern California. The main goal of this survey was to assess the diversity of D/H ratios in lipids from marine sediments, in order to provide a more detailed understanding of relevant biological and geochemical factors impacting lipid isotopic variability. A total of 1182 individual \u03b4D values are reported from two stations in SBB, one located in the suboxic basin depocenter and the other on the fully oxic flank of the basin. Sediments collected from the basin depocenter span a depth of not, vert, similar2.5 m and reach the methanogenic zone. Lipids that were analyzed include n-alkanes, n-alkanols and alkenols, short- and long-chain fatty acids, linear isoprenoids, steroids, and hopanoids, and exhibit several systematic patterns. First, there are no significant differences in \u03b4D values between the two sampling locations, nor with increasing depth for most lipids, indicating that degradation does not influence sedimentary lipid \u03b4D values. Second, relatively large differences in \u03b4D values among differing molecular structures are observed in all samples. n-Alkyl lipids of probable marine origin have typical \u03b4D values between \u2212150 and \u2212200\u2030, those from terrestrial leaf waxes and aquatic plants range from \u221280 to \u2212170\u2030, while petroleum n-alkanes are typically \u221290 to \u2212150\u2030. Third, lipids inferred to derive from bacteria (branched fatty acids and hopanols) living at the sediment surface or in the water column tend to be D-enriched relative to similar algal products by 30\u2030 or more. At the same time, several other lipids have \u03b4D values that decrease strongly with depth, presumably as a result of in situ production by anaerobic bacteria. This dichotomy in isotopic compositions of bacterial lipids is inconsistent with a nearly constant D/H fractionation during lipid biosynthesis, and likely reflects significant variations associated with metabolism.",
"doi": "10.1016/j.gca.2009.05.056",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2009-08-15",
"series_number": "16",
"volume": "73",
"issue": "16",
"pages": "4803-4823"
},
{
"id": "authors:38gwe-c0y47",
"collection": "authors",
"collection_id": "38gwe-c0y47",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090817-144809554",
"type": "article",
"title": "Large D/H variations in bacterial lipids reflect central metabolic pathways",
"author": [
{
"family_name": "Zhang",
"given_name": "Xinning",
"clpid": "Zhang-Xinning"
},
{
"family_name": "Gillespie",
"given_name": "Aimee L.",
"clpid": "Gillespie-A-L"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Large hydrogen-isotopic (D/H) fractionations between lipids and growth water have been observed in most organisms studied to date. These fractionations are generally attributed to isotope effects in the biosynthesis of lipids, and are frequently assumed to be approximately constant for the purpose of reconstructing climatic variables. Here, we report D/H fractionations between lipids and water in 4 cultured members of the phylum Proteobacteria, and show that they can vary by up to 500\u2030 in a single organism. The variation cannot be attributed to lipid biosynthesis as there is no significant change in these pathways between cultures, nor can it be attributed to changing substrate D/H ratios. More importantly, lipid/water D/H fractionations vary systematically with metabolism: chemoautotrophic growth (approximately \u2212200 to \u2212400\u2030), photoautotrophic growth (\u2212150 to \u2212250\u2030), heterotrophic growth on sugars (0 to \u2212150\u2030), and heterotrophic growth on TCA-cycle precursors and intermediates (\u221250 to +200\u2030) all yield different fractionations. We hypothesize that the D/H ratios of lipids are controlled largely by those of NADPH used for biosynthesis, rather than by isotope effects within the lipid biosynthetic pathway itself. Our results suggest that different central metabolic pathways yield NADPH\u2014and indirectly lipids\u2014with characteristic isotopic compositions. If so, lipid \u03b4D values could become an important biogeochemical tool for linking lipids to energy metabolism, and would yield information that is highly complementary to that provided by ^(13)C about pathways of carbon fixation.",
"doi": "10.1073/pnas.0903030106",
"pmcid": "PMC2722351",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2009-08-04",
"series_number": "31",
"volume": "106",
"issue": "31",
"pages": "12580-12586"
},
{
"id": "authors:2gcg4-reg90",
"collection": "authors",
"collection_id": "2gcg4-reg90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090817-144818780",
"type": "article",
"title": "The Continuing Puzzle of the Great Oxidation Event",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Doughty",
"given_name": "David M.",
"clpid": "Doughty-D-M"
},
{
"family_name": "Welander",
"given_name": "Paula V.",
"clpid": "Welander-P-V"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "The rise of atmospheric O_2 was a milestone in the history of life. Although O_2 itself is not a climate-active gas, its appearance would have removed a methane greenhouse present on the early Earth and potentially led to dramatic cooling. Moreover, by fundamentally altering the biogeochemical cycles of C, N, S and Fe, its rise first in the atmosphere and later in the oceans would also have had important indirect effects on Earth's climate. Here, we summarize major lines of evidence from the geological literature that pertain to when and how O_2 first appeared in significant amounts in the atmosphere. On the early Earth, atmospheric O_2 would initially have been very low, probably <10^(\u22125) of the present atmospheric level. Around 2.45 billion years ago, atmospheric O_2 rose suddenly in what is now termed the Great Oxidation Event. While the rise of oxygen has been the subject of considerable attention by Earth scientists, several important aspects of this problem remain unresolved. Our goal in this review is to provide a short summary of the current state of the field, and make the case that future progress towards solving the riddle of oxygen will benefit greatly from the involvement of molecular biologists.",
"doi": "10.1016/j.cub.2009.05.054",
"issn": "0960-9822",
"publisher": "Cell Press",
"publication": "Current Biology",
"publication_date": "2009-07-28",
"series_number": "14",
"volume": "19",
"issue": "14",
"pages": "R567-R574"
},
{
"id": "authors:8bsvd-bfp37",
"collection": "authors",
"collection_id": "8bsvd-bfp37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-132120521",
"type": "article",
"title": "A geochemical redox model for Ediacaran ocean chemistry in Nanhua Basin, South China",
"author": [
{
"family_name": "Li",
"given_name": "Chao",
"clpid": "Li-Chao"
},
{
"family_name": "Love",
"given_name": "Gordon D.",
"orcid": "0000-0002-6516-014X",
"clpid": "Love-G-D"
},
{
"family_name": "Lyons",
"given_name": "Timothy W.",
"clpid": "Lyons-T-W"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Fike",
"given_name": "David A.",
"orcid": "0000-0003-2848-0328",
"clpid": "Fike-D-A"
},
{
"family_name": "Chu",
"given_name": "Xuelei",
"clpid": "Chu-Xuelei"
}
],
"abstract": "A detailed spatial and temporal record of Ediacaran\nmarine biogeochemistry has been compiled for the\nDoushantuo Formation (635-551 Myr) in South China at four\noutcrop sections in the Nanhua Basin, encompassing a shelfto-\nbasinal paleoenvironmental transect.",
"doi": "10.1016/j.gca.2009.05.010",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2009-06",
"series_number": "S13",
"volume": "73",
"issue": "S13",
"pages": "A750"
},
{
"id": "authors:aykqf-0ch63",
"collection": "authors",
"collection_id": "aykqf-0ch63",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090722-153238411",
"type": "article",
"title": "Hydrogen isotopic fractionation in lipid biosynthesis by H_2-consuming Desulfobacterium autotrophicum",
"author": [
{
"family_name": "Campbell",
"given_name": "Brian J.",
"clpid": "Campbell-B-J"
},
{
"family_name": "Li",
"given_name": "Chao",
"clpid": "Li-Chao"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Valentine",
"given_name": "David L.",
"clpid": "Valentine-D-L"
}
],
"abstract": "We report hydrogen isotopic fractionations between water and fatty acids of the sulfate-reducing bacterium Desulfobacterium autotrophicum. Pure cultures were grown in waters with deuterium (D) contents that were systematically varied near the level of natural abundance (\u221237\u2030 \u2264 \u03b4D \u2264 993\u2030). H_2 of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H_2, and specific fatty acids were measured by isotope-ratio mass spectrometry. The results demonstrate that D. autotrophicum catalyzes hydrogen isotopic exchange between water and H_2, and this reaction is conclusively shown to approach isotopic equilibrium. In addition, variation in the D/H ratio of growth water accounts for all variation in the hydrogen isotopic composition of fatty acids. The D/H ratios of fatty acids from cultures grown on H_2/CO_2 are compared with those from a separate set of cultures grown on D-enriched formate, an alternative electron donor. This comparison rules out H_2 as a significant source of fatty acid hydrogen. Grown on either H_2/CO_2 or formate, D. autotrophicum produces fatty acids in which all hydrogen originates from water. For specific fatty acids, biosynthetic fractionation factors are mostly in the range 0.60 \u2264 \u03b1FA\u2013water \u2264 0.70; the 18:0 fatty acid exhibits a lower fractionation factor of 0.52. The data show that \u03b1FA_\u2013water generally increases with length of the carbon chain from C_14 to C_17 among both saturated and unsaturated fatty acids. These results indicate a net fractionation associated with fatty acid biosynthesis in D. autotrophicum that is slightly smaller than in another H_2-consuming bacterium (Sporomusa sp.), but much greater than in most photoautotrophs.",
"doi": "10.1016/j.gca.2009.02.034",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2009-05-15",
"series_number": "10",
"volume": "73",
"issue": "10",
"pages": "2744-2757"
},
{
"id": "authors:n6rsp-17245",
"collection": "authors",
"collection_id": "n6rsp-17245",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090727-142530506",
"type": "article",
"title": "Simplified batch equilibration for D/H determination of non-exchangeable hydrogen in solid organic material",
"author": [
{
"family_name": "Sauer",
"given_name": "Peter E.",
"clpid": "Sauer-P-E"
},
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Topalov",
"given_name": "Katarina",
"clpid": "Topalov-K"
}
],
"abstract": "Hydrogen isotopic analysis of organic materials has been widely applied in studies of paleoclimate, animal migration, forensics, food and flavor authentication, and the origin and diagenesis of organic matter. Hydrogen bound to carbon (C-H) generally retains isotopic information about the water present during organic matter synthesis and associated biosynthetic fractionations, but hydrogen bound to other elements (O, S, or N) can readily exchange with atmospheric water vapor and reflects recent exposure to water or vapor. These two pools must be separated to obtain meaningful information from isotope ratios of organic materials. Previously published analytical methods either replace exchangeable H chemically or control its isotopic composition, usually by equilibration with water or waters of known isotopic composition. In addition, the fraction of H that is exchangeable can vary among samples and is itself of scientific interest. Here we report an improved and automated double-equilibration approach. \nSamples are loaded in a 50-position autosampler carousel in an air-tight aluminum equilibration chamber. Water vapor of known isotopic composition is pumped through the chamber at 115\u00b0C for at least 6 h. After flushing with dry N_2 and being cooled, the carousel is rapidly transferred from the equilibration chamber to a He-purged autosampler attached to a pyrolysis elemental analyzer connected to an isotope ratio mass spectrometer. By equilibrating two aliquots of each sample with two isotopically distinct waters, it is possible to calculate both (1) the D/H ratio of non-exchangeable H, and (2) the fraction of H that is exchangeable. Relative to previous double-equilibration techniques, this approach offers significant reductions in sample size and labor by allowing simultaneous equilibration of several tens of samples.",
"doi": "10.1002/rcm.3954",
"issn": "0951-4198",
"publisher": "Wiley",
"publication": "Rapid Communications in Mass Spectrometry",
"publication_date": "2009-04",
"series_number": "7",
"volume": "23",
"issue": "7",
"pages": "949-956"
},
{
"id": "authors:w5rtf-ga080",
"collection": "authors",
"collection_id": "w5rtf-ga080",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:WANac08",
"type": "article",
"title": "Memory Effects in Compound-Specific D/H Analysis by Gas Chromatography/Pyrolysis/Isotope-Ratio Mass Spectrometry",
"author": [
{
"family_name": "Wang",
"given_name": "Ying",
"clpid": "Wang-Ying"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Compound-specific analyses of lipid D/H ratios often encounter ranges of 300\u2030 or more, and experiments using D-enriched water to study fractionations often extend the range up to 1000\u2030. Here we show that for such large dynamic ranges in D/H ratio, isotopic \"memory\" between adjacent peaks can be significant. Memory effects have not been previously reported for GC/P/IRMS systems but can have a significant impact on many measurements, even those exploring only natural-abundance variations in D/H. To quantitatively evaluate these effects, we synthesized two series of organic standards with \u03b4D values varying from \u2212230 to +800\u2030. We then analyzed chromatograms in which analyte \u03b4D values, retention times, or relative abundances were independently varied. For two sequential GC peaks, isotopic memory is measured to be typically 2\u22124% of the difference in \u03b4D values between the two. Roughly half of this effect can be attributed to unknown processes within the GC itself, and the other half to surface adsorption processes in the pyrolytic conversion of analytes to H2. Isotopic memory increases with decreasing time separation between peaks, with decreasing analyte abundance, and with increasing age of pyrolysis reactors. A simple numerical model that simulates dynamic adsorption of H2 on pyrolytic carbon can reproduce many aspects of the experimental data, suggesting that this is likely to be an important mechanism in isotopic memory. Several steps to mitigate memory effects in routine analyses are suggested.",
"doi": "10.1021/ac801170v",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2008-12-01",
"series_number": "23",
"volume": "80",
"issue": "23",
"pages": "9162-9170"
},
{
"id": "authors:ak3qg-82x59",
"collection": "authors",
"collection_id": "ak3qg-82x59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-124754729",
"type": "article",
"title": "Development of coupled GC/ICPMS for analysis of \u03b4^(34)S in individual organic compounds",
"author": [
{
"family_name": "Amrani",
"given_name": "Alon",
"clpid": "Amrani-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Adkins",
"given_name": "Jess",
"orcid": "0000-0002-3174-5190",
"clpid": "Adkins-J-F"
}
],
"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.",
"doi": "10.1016/j.gca.2008.05.004",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2008-07",
"series_number": "12",
"volume": "72",
"issue": "12",
"pages": "A20"
},
{
"id": "authors:wn7aa-c3508",
"collection": "authors",
"collection_id": "wn7aa-c3508",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-131455663",
"type": "article",
"title": "Variations in D/H fractionation associated with microbial heterotrophy",
"author": [
{
"family_name": "Zhang",
"given_name": "Xinning",
"clpid": "Zhang-Xinning"
},
{
"family_name": "Sessions",
"given_name": "A.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Compound-specific D/H measurements are emerging as a useful tool for paleoclimatology, chemical oceanography, biogeochemistry, and geobiology.",
"doi": "10.1016/j.gca.2008.05.028",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2008-07",
"series_number": "S12",
"volume": "72",
"issue": "S12",
"pages": "A1089"
},
{
"id": "authors:826s2-ezt65",
"collection": "authors",
"collection_id": "826s2-ezt65",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-125936342",
"type": "article",
"title": "Equilibrium D/H fractionation of carbon-bound hydrogen",
"author": [
{
"family_name": "Wang",
"given_name": "Ying",
"clpid": "Wang-Ying"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "As sedimentary organic matter (SOM) thermally matures, \u03b4D values of individual hydrocarbons increase steadily while biosynthetic offsets between linear and isoprenoid lipids steadily disappear.",
"doi": "10.1016/j.gca.2008.05.025",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2008-07",
"series_number": "S12",
"volume": "72",
"issue": "S12",
"pages": "A1003"
},
{
"id": "authors:72ng1-pxk20",
"collection": "authors",
"collection_id": "72ng1-pxk20",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100708-075607498",
"type": "article",
"title": "D/H ratios of fatty acids from marine particulate organic matter in the California Borderland Basins",
"author": [
{
"family_name": "Jones",
"given_name": "Ashley A.",
"clpid": "Jones-A-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Campbell",
"given_name": "Brian J.",
"clpid": "Campbell-B-J"
},
{
"family_name": "Li",
"given_name": "Chao",
"clpid": "Li-Chao"
},
{
"family_name": "Valentine",
"given_name": "David L.",
"clpid": "Valentine-D-L"
}
],
"abstract": "We report the molecular and hydrogen\u2013isotopic compositions of fatty acids extracted from suspended particulate organic matter (POM) and surface sediments at three stations off the southern California coast: Santa Barbara Basin, Santa Monica Basin, and the Gulf of Santa Catalina. Values of \u03b4D for individual fatty acids ranged from \u2212237\u2030 to \u221273\u2030 in POM and from \u2212216\u2030 to \u2212124\u2030 in sediments. For most fatty acids, there are no significant differences in \u03b4D between sampling locations, with depth at each location, or between POM and sediments. Two fatty acids of likely bacterial origin (i-15:0, 15:0) are strongly D enriched in all samples, while a third (cyc-17:0) is not. The origins of that enrichment are uncertain, and could reflect either an anomalous D/H fractionation in certain marine bacteria, or a significant terrestrial source for those fatty acids, or both. In surface POM and sediments, even carbon numbered fatty acids become slightly D enriched as chain length increases. This isotopic ordering is similar to that observed in living organisms, and is presumably biosynthetic in origin. In contrast, all POM samples from below the mixed layer show a consistent pattern of D depletion with increasing chain length. The order of D enrichment in these fatty acids is well correlated with their solubility, and may be caused by fractionations accompanying dissolution or degradation by microbes.",
"doi": "10.1016/j.orggeochem.2007.11.001",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2008-05",
"series_number": "5",
"volume": "39",
"issue": "5",
"pages": "485-500"
},
{
"id": "authors:ynvq5-smv57",
"collection": "authors",
"collection_id": "ynvq5-smv57",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:PEAaem08",
"type": "article",
"title": "Quantifying microbial utilization of petroleum hydrocarbons in salt-marsh sediments using the ^(13)C content of bacterial rRNA",
"author": [
{
"family_name": "Pearson",
"given_name": "Ann",
"orcid": "0000-0003-2785-8405",
"clpid": "Pearson-A"
},
{
"family_name": "Kraunz",
"given_name": "Kimberly S.",
"clpid": "Kraunz-K-S"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Dekas",
"given_name": "Anne E.",
"orcid": "0000-0001-9548-8413",
"clpid": "Dekas-A-E"
},
{
"family_name": "Leavitt",
"given_name": "William R.",
"clpid": "Leavitt-W-R"
},
{
"family_name": "Edwards",
"given_name": "Katrina J.",
"clpid": "Edwards-K-J"
}
],
"abstract": "Natural remediation of oil spills is catalyzed by complex microbial consortia. Here we take a whole-community approach to investigate bacterial incorporation of petroleum hydrocarbons from a simulated oil spill. We utilized the natural difference in carbon-isotopic abundance between a salt marsh ecosystem supported by the ^(13)C-enriched C4 grass, Spartina alterniflora, and the ^(13)C-depleted composition of petroleum to monitor changes in the ^(13)C content of biomass. Magnetic-bead capture methods for the selective recovery of bacterial RNA were used to monitor the ^(13)C content of bacterial biomass during a two-week experiment. The data show that by the end of the experiment, up to 26% of bacterial biomass derived from consumption of the freshly-spilled oil. The results contrast with the inertness of a nearby relict spill, which occurred in 1969 in West Falmouth, MA. Sequences of 16S rRNA genes from our experimental samples also were consistent with previous reports suggesting the importance of {gamma}- and {delta}-Proteobacteria and Firmicutes in the remineralization of hydrocarbons. The magnetic-bead capture approach makes it possible to quantify uptake of petroleum hydrocarbons by microbes in-situ. Although employed here at the Domain level, RNA-capture procedures can be highly specific. The same strategy could be used with genus-level specificity, something which is not currently possible using the ^(13)C content of biomarker lipids.",
"doi": "10.1128/AEM.01014-07",
"pmcid": "PMC2258585",
"issn": "0099-2240",
"publisher": "American Society for Microbiology",
"publication": "Applied and Environmental Microbiology",
"publication_date": "2008-02-15",
"series_number": "4",
"volume": "74",
"issue": "4",
"pages": "1157-1166"
},
{
"id": "authors:7e4th-d5711",
"collection": "authors",
"collection_id": "7e4th-d5711",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:RASpnas07",
"type": "article",
"title": "Biosynthesis of 2-methylbacteriohopanepolyols by an anoxygenic phototroph",
"author": [
{
"family_name": "Rashby",
"given_name": "Sky E.",
"clpid": "Rashby-S-E"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Newman",
"given_name": "Dianne K.",
"orcid": "0000-0003-1647-1918",
"clpid": "Newman-D-K"
}
],
"abstract": "Sedimentary 2-methyhopanes have been used as biomarker proxies for cyanobacteria, the only known bacterial clade capable of oxygenic photosynthesis and the only group of organisms found thus far to produce abundant 2-methylbacteriohopanepolyols (2-MeBHPs). Here, we report the identification of significant quantities of 2-MeBHP in two strains of the anoxygenic phototroph Rhodopseudomonas palustris. Biosynthesis of 2-MeBHP can occur in the absence of O2, deriving the C-2 methyl group from methionine. The relative abundance of 2-MeBHP varies considerably with culture conditions, ranging from 13.3% of total bacteriohopanepolyol (BHP) to trace levels of methylation. Analysis of intact BHPs reveals the presence of methylated bacteriohopane-32,33,34,35-tetrol but no detectable methylation of 35-aminobacteriohopane-32,33,34-triol. Our results demonstrate that an anoxygenic photoautotroph is capable of generating 2-MeBHPs and show that the potential origins of sedimentary 2-methylhopanoids are more diverse than previously thought.",
"doi": "10.1073/pnas.0704912104",
"pmcid": "PMC1986619",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2007-09-18",
"series_number": "38",
"volume": "104",
"issue": "38",
"pages": "15099-15014"
},
{
"id": "authors:xwqtt-qc784",
"collection": "authors",
"collection_id": "xwqtt-qc784",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-122718400",
"type": "article",
"title": "Carbonate concretions as a window to the evolving chemistry of the early ocean and atmosphere",
"author": [
{
"family_name": "Lyons",
"given_name": "T.",
"clpid": "Lyons-T-T"
},
{
"family_name": "Raiswell",
"given_name": "R.",
"clpid": "Raiswell-R"
},
{
"family_name": "Robinson",
"given_name": "A.",
"clpid": "Robinson-A"
},
{
"family_name": "Scott",
"given_name": "C.",
"clpid": "Scott-C"
},
{
"family_name": "Chu",
"given_name": "X.",
"clpid": "Chu-X"
},
{
"family_name": "Li",
"given_name": "C.",
"clpid": "Li-C"
},
{
"family_name": "Love",
"given_name": "G.",
"orcid": "0000-0002-6516-014X",
"clpid": "Love-G-D"
},
{
"family_name": "Sessions",
"given_name": "A.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Gill",
"given_name": "B.",
"clpid": "Gill-B"
}
],
"abstract": "Ellipsoidal calcium carbonate concretions with diameters ranging up to meter-scale are common in organic-rich shales throughout the Phanerozoic. These features arise through early (pre-compactional), highly localized cementation.",
"doi": "10.1016/j.gca.2007.06.020",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2007-08-01",
"series_number": "S15",
"volume": "71",
"issue": "S15",
"pages": "A606"
},
{
"id": "authors:e4b79-hyx10",
"collection": "authors",
"collection_id": "e4b79-hyx10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130610-111937609",
"type": "article",
"title": "Carbon-isotopic analysis of microbial cells sorted by flow cytometry",
"author": [
{
"family_name": "Eek",
"given_name": "K. M.",
"clpid": "Eek-K-M"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Lies",
"given_name": "D. P.",
"clpid": "Lies-D-P"
}
],
"abstract": "One of the outstanding current problems in both geobiology and environmental microbiology is the quantitative analysis of in situ microbial metabolic activities. Techniques capable of such analysis would have wide application, from quantifying natural rates of biogeochemical cycling to identifying the metabolic activity of uncultured organisms. We describe here a method that represents one step towards that goal, namely the high-precision measurement of ^(13)C in specific populations of microbial cells that are purified by fluorescence-activated cell sorting (FACS). Sorted cells are concentrated on a Teflon membrane filter, and their ^(13)C content is measured by coupling an isotope ratio mass spectrometer (IRMS) with a home-built spooling wire microcombustion (SWiM) apparatus. The combined instrumentation provides measurements of \u03b4^(13)C in whole cells with precision better than 0.2\u2030 for samples containing as little as 25 ng of carbon. When losses associated with sample handling are taken into account, isotopic analyses require sorting roughly 10^4 eukaryotic or 10^7 bacterial cells per sample. Coupled with ^(13)C-labelled substrate additions, this approach has the potential to directly quantify uptake of metabolites in specific populations of sorted cells. The high precision afforded by SWiM-IRMS also permits useful studies of natural abundance variations in ^(13)C. The approach is equally applicable to specific populations of cells sorted from multicellular organisms.",
"doi": "10.1111/j.1472-4669.2006.00094.x",
"issn": "1472-4677",
"publisher": "Blackwell Publishing",
"publication": "Geobiology",
"publication_date": "2007-03",
"series_number": "1",
"volume": "5",
"issue": "1",
"pages": "85-95"
},
{
"id": "authors:fdmgk-p3s20",
"collection": "authors",
"collection_id": "fdmgk-p3s20",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-150029707",
"type": "article",
"title": "Equilibrium D/H fractionation of organic hydrogen",
"author": [
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Wang",
"given_name": "Y.",
"clpid": "Wang-Y"
}
],
"abstract": "Interpretations of D/H data from ancient organic molecules\nmust generally address the possibility of isotopic exchange with ambient water. A lack of systematic changes in dD of organic molecules with age is commonly used to infer the lack of exchange, as are large differences in the D/H ratios of organic molecule and water.",
"doi": "10.1016/j.gca.2006.06.1059",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2006-08",
"series_number": "S18",
"volume": "70",
"issue": "S18",
"pages": "A572"
},
{
"id": "authors:6ejkq-t9080",
"collection": "authors",
"collection_id": "6ejkq-t9080",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-142024179",
"type": "article",
"title": "Biogeochemistry of neoproterozoic low latitude glaciations",
"author": [
{
"family_name": "Olcott",
"given_name": "A. N.",
"clpid": "Olcott-A-N"
},
{
"family_name": "Li",
"given_name": "C.",
"clpid": "Li-C"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Corsetti",
"given_name": "F. A.",
"clpid": "Corsetti-F-A"
},
{
"family_name": "Peng",
"given_name": "P.",
"clpid": "Peng-P"
}
],
"abstract": "The Neoproterozoic (c.a. 1000\u2013540 Ma) was a time of great\nchange. Eukaryotes radiated through the ocean, while metazoans originated and diversified. The rock record preserves multiple negative excursions of over 15% in the carbonate ^(13)C/^(12)C, at least three of which are associated with global low-latitude glaciations.",
"doi": "10.1016/j.gca.2006.06.918",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2006-08",
"series_number": "18",
"volume": "70",
"issue": "18",
"pages": "A456"
},
{
"id": "authors:53a5r-gaw21",
"collection": "authors",
"collection_id": "53a5r-gaw21",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140624-160528233",
"type": "article",
"title": "Multi-isotopic constraints on the origin and fate of n-alkyl lipids in recent sediments",
"author": [
{
"family_name": "Eglinton",
"given_name": "T. I.",
"clpid": "Eglinton-T-I"
},
{
"family_name": "Ohkouchi",
"given_name": "N.",
"clpid": "Ohkouchi-N"
},
{
"family_name": "Drenzek",
"given_name": "N.",
"clpid": "Drenzek-N"
},
{
"family_name": "Dickens",
"given_name": "A.",
"clpid": "Dickens-A"
},
{
"family_name": "Mollenhauer",
"given_name": "G.",
"clpid": "Mollenhauer-G"
},
{
"family_name": "Schefuss",
"given_name": "E.",
"clpid": "Schefuss-E"
},
{
"family_name": "Sessions",
"given_name": "A.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Montlucon",
"given_name": "D.",
"clpid": "Montlucon-D"
},
{
"family_name": "Sylva",
"given_name": "S.",
"clpid": "Sylva-S"
},
{
"family_name": "Hayes",
"given_name": "J. M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "Recent analytical advances now make it feasible to determine multiple isotopic characteristics of individual organic compounds within complex mixtures. In particular, hydrogen isotopic compositions and radiocarbon contents can now be readily determined to complement information derived from stable carbon isotopic analysis. When used in concert, these lines of geochemical information can yield important new insights into the origins and histories of the biomarker compounds, and lead to new and refined interpretation of molecular proxy records of paleoenvironmental variability.\n\nWe present multi-isotopic data on n-alkyl lipids isolated from a range of recent aquatic sediments in order to demonstrate both the complexity of geochemical signals preserved in environmental matices, and the utility of multi-isotopic information in constraining inputs. In particular, we focus on long-chain lipids derived from terrestrial and marine precursors. Marked radiocarbon age and stable isotopic variability is apparent, even within closely related homologous series of compounds recovered from the same sample. Based on multi-isotope characteristics, we interpret these variations in terms of differences in source versus reactivity of individual organic compounds, and discuss implications for interpretation of the sedimentary record.",
"doi": "10.1016/j.gca.2006.06.1378",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2006-08",
"series_number": "18",
"volume": "70",
"issue": "18",
"pages": "A156"
},
{
"id": "authors:3ccmr-a7m90",
"collection": "authors",
"collection_id": "3ccmr-a7m90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-152551075",
"type": "article",
"title": "Carbon and hydrogen isotopic analysis of hydrocarbons from the South Oman Salt Basin",
"author": [
{
"family_name": "Summons",
"given_name": "R. E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Grosjean",
"given_name": "E.",
"clpid": "Grosjean-Emmanuelle"
},
{
"family_name": "Love",
"given_name": "G. D.",
"orcid": "0000-0002-6516-014X",
"clpid": "Love-G-D"
},
{
"family_name": "Colonero",
"given_name": "C. L. K.",
"clpid": "Colonero-C-L-K"
},
{
"family_name": "Sylva",
"given_name": "S.",
"clpid": "Sylva-S-P"
},
{
"family_name": "Hayes",
"given_name": "J. M.",
"clpid": "Hayes-J-M"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "The ^(13)C and ^2H contents of sedimentary hydrocarbons are\ncontrolled by multiple factors including the isotopic contents of the inorganic carbon and ambient water, the isotopic fractionations imposed by the enzymes of C and H assimilation and biosynthesis, and processes that take place during diagenesis and catagenesis.",
"doi": "10.1016/j.gca.2006.06.1160",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2006-08",
"series_number": "S18",
"volume": "70",
"issue": "S18",
"pages": "A625"
},
{
"id": "authors:xzjpd-fze33",
"collection": "authors",
"collection_id": "xzjpd-fze33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130604-110627696",
"type": "article",
"title": "Isotope-ratio detection for gas chromatography",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Instrumentation and methods exist for highly precise analyses of the stable-isotopic composition of organic compounds separated by GC. The general approach combines a conventional GC, a chemical reaction interface, and a specialized isotope-ratio mass spectrometer (IRMS). Most existing GC hardware and methods are amenable to isotope-ratio detection. The interface continuously and quantitatively converts all organic matter, including column bleed, to a common molecular form for isotopic measurement. C and N are analyzed as CO_2 and N_2, respectively, derived from combustion of analytes. H and O are analyzed as H_2 and CO produced by pyrolysis/reduction. IRMS instruments are optimized to provide intense, highly stable ion beams, with extremely high precision realized via a system of differential measurements in which ion currents for all major isotopologs are simultaneously monitored. Calibration to an internationally recognized scale is achieved through comparison of closely spaced sample and standard peaks. Such systems are capable of measuring ^(13)C/^(12)C ratios with a precision approaching 0.1\u2030 (for values reported in the standard delta notation), four orders of magnitude better than that typically achieved by conventional \"organic\" mass spectrometers. Detection limits to achieve this level of precision are typically <1 nmol C (roughly 10 ng of a typical hydrocarbon) injected on-column. Achievable precision and detection limits are correspondingly higher for N, O, and H, in that order.",
"doi": "10.1002/jssc.200600002",
"issn": "1615-9306",
"publisher": "Wiley",
"publication": "Journal of Separation Science",
"publication_date": "2006-08",
"series_number": "12",
"volume": "29",
"issue": "12",
"pages": "1946-1961"
},
{
"id": "authors:wtte3-dvm61",
"collection": "authors",
"collection_id": "wtte3-dvm61",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:SCHIareps06",
"type": "article",
"title": "Hydrogen isotopic (D/H) composition of organic matter during diagenesis and thermal maturation",
"author": [
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Mastalerz",
"given_name": "Maria",
"clpid": "Masterlerz-M"
}
],
"abstract": "Changes in the D/H ratio of sedimentary organic matter (SOM) during thermal maturation have been difficult to interpret because the effects of hydrogen exchange and kinetic fractionations are confounded in natural samples. Recent analytical developments have significantly improved our understanding of the responsible mechanisms. In this paper, we review experimental and field data that document a progressive increase in the D/H ratio of most organic hydrogen at the bulk and molecular levels, and suggest that the transfer of hydrogen from water to organic matter is the most important mechanism leading to those changes. SOM and water in natural petroleum systems approach a pseudoequilibrium D/H fractionation of about \u221280 to \u2212110\u2030. D/H ratios of organic hydrogen can preserve quantitative information about paleoclimate throughout diagenesis, and some qualitative information through catagenesis.",
"doi": "10.1146/annurev.earth.34.031405.125011",
"issn": "0084-6597",
"publisher": "Annual Reviews",
"publication": "Annual Review of Earth and Planetary Sciences",
"publication_date": "2006-05-30",
"volume": "34",
"pages": "501-533"
},
{
"id": "authors:n67zf-q1f19",
"collection": "authors",
"collection_id": "n67zf-q1f19",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130604-073316335",
"type": "article",
"title": "Seasonal changes in D/H fractionation accompanying lipid biosynthesis in Spartina alterniflora",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "To investigate potential variability in the biosynthetic fractionation of hydrogen isotopes between environmental water and plant lipids, the cord grass Spartina alterniflora was sampled from a single location in a coastal marsh over a period of 16 months. Values of \u03b4D for a variety of lipids were measured by gas chromatography/pyrolysis/isotope ratio mass spectrometry. S. alterniflora grows partially submerged in seawater, so it has a virtually unlimited supply of water with nearly unvarying isotopic composition. Temporal changes in the \u03b4D values of lipids can thus be interpreted as representing mainly variations in biosynthetic fractionation. Fatty acids, n-alkanes, and phytol extracted from S. alterniflora have nearly constant \u03b4D values from \u223cOctober through May, but exhibit marked decreases of up to 40\u2030 during summer months. These shifts in lipid \u03b4D values are interpreted as representing a change in the source of organic substrates, principally acetate, used for their biosynthesis. Lower summertime \u03b4D values for lipids are consistent with an increasing reliance on current photosynthate as feedstock for biosynthesis, whereas stored carbohydrate reserves are utilized more extensively during other times of the year. Regardless of the specific mechanism, the data emphasize that overall fractionations between water and plant lipids depend on biological as well as environmental variables, and that the biosynthetic fractionation is not necessarily constant even for a single plant. Because lipids such as fatty acids are present in all cells and turn over on timescales of weeks to months, measurements of \u03b4D values in fatty acids may also provide useful constraints for distinguishing biologic versus environmental controls on cellulose \u03b4D values in trees.",
"doi": "10.1016/j.gca.2006.02.003",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2006-05-01",
"series_number": "9",
"volume": "70",
"issue": "9",
"pages": "2153-2162"
},
{
"id": "authors:hhv5z-9ee12",
"collection": "authors",
"collection_id": "hhv5z-9ee12",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130626-100413215",
"type": "article",
"title": "Biomarker Evidence for Photosynthesis During Neoproterozoic Glaciation",
"author": [
{
"family_name": "Olcott",
"given_name": "Alison N.",
"clpid": "Olcott-A-N"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Corsetti",
"given_name": "Frank A.",
"clpid": "Corsetti-F-A"
},
{
"family_name": "Kaufman",
"given_name": "Alan J.",
"clpid": "Kaufman-A-J"
},
{
"family_name": "de Oliviera",
"given_name": "Tolentino Flavio",
"clpid": "de-Oliviera-T-F"
}
],
"abstract": "Laterally extensive black shales were deposited on the S\u00e3o Francisco craton in southeastern Brazil during low-latitude Neoproterozoic glaciation \u223c740 to 700 million years ago. These rocks contain up to 3.0 weight % organic carbon, which we interpret as representing the preserved record of abundant marine primary productivity from glacial times. Extractable biomarkers reflect a complex and productive microbial ecosystem, including both phototrophic bacteria and eukaryotes, living in a stratified ocean with thin or absent sea ice, oxic surface waters, and euxinic conditions within the photic zone. Such an environment provides important constraints for parts of the \"Snowball Earth\" hypothesis.",
"doi": "10.1126/science.1115769",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "2005-10-21",
"series_number": "5747",
"volume": "310",
"issue": "5747",
"pages": "471-474"
},
{
"id": "authors:dxpr9-p5491",
"collection": "authors",
"collection_id": "dxpr9-p5491",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130605-151425113",
"type": "article",
"title": "Moving-Wire Device for Carbon Isotopic Analyses of Nanogram Quantities of Nonvolatile Organic Carbon",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Sylva",
"given_name": "Sean P.",
"clpid": "Sylva-S-P"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "We describe a moving-wire analyzer for measuring ^(13)C in dissolved, involatile organic materials. Liquid samples are first deposited and dried on a continuously spooling nickel wire. The residual sample is then combusted as the wire moves through a furnace, and the evolved CO_2 is analyzed by continuous-flow isotope ratio mass spectrometry. A typical analysis requires 1 \u03bcL of sample solution and produces a CO_2 peak ~5 s wide. The system can measure \"bulk\" \u03b4^(13)C values of ~10 nmol of organic carbon with precision better than 0.2\u2030. For samples containing 1 nmol of C, precision is ~1\u2030. Precision and sensitivity are limited mainly by background noise derived from carbon within the wire. Instrument conditions minimizing that background are discussed in detail. Accuracy is better than 0.5\u2030 for nearly all dissolved analytes tested, including lipids, proteins, nucleic acids, sugars, halocarbons, and hydrocarbons. The sensitivity demonstrated here for 13C measurements represents a ~1000-fold improvement relative to existing elemental analyzers and should allow the use of many new preparative techniques for collecting and purifying nonvolatile biochemicals for isotopic analysis.",
"doi": "10.1021/ac051251z",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2005-10-15",
"series_number": "20",
"volume": "77",
"issue": "20",
"pages": "6519-6527"
},
{
"id": "authors:47szn-63m10",
"collection": "authors",
"collection_id": "47szn-63m10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-133459039",
"type": "article",
"title": "Controls on the D/H composition of individual petroleum hydrocarbons",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Compound-specific D/H measurements are increasingly used to study petroleum systems. Thus far, it has been unclear how such measurements should be used to maximum advantage.",
"doi": "10.1016/j.gca.2005.03.031",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2005-05-15",
"series_number": "S10",
"volume": "69",
"issue": "S10",
"pages": "A500"
},
{
"id": "authors:a2r4g-r7680",
"collection": "authors",
"collection_id": "a2r4g-r7680",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130723-112638988",
"type": "article",
"title": "Calculation of hydrogen isotopic fractionations in biogeochemical systems",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "Hydrogen-isotopic data are often interpreted using mathematical approximations originally intended for other isotopes. One of the most common, apparent in literature over the last several decades, assumes that delta values of reactants and products are separated by a constant fractionation factor: \u03b4_p = \u03b4_r + \u03b5_(p/r). Because of the large fractionations that affect hydrogen isotopes, such approximations can lead to substantial errors. Here we review and develop general equations for isotopic mass balances that include the differential fractionation of each component in a mixture and discuss their use in three geochemical applications. For the fractionation of a single component, the reactant and product are related by \u03b4_p = \u03b1_(p/r)\u03b4_r + \u03b5_(p/r), where \u03b1 and \u03b5 refer to the same fractionation. Regression of \u03b4_p on \u03b4_r should give equivalent fractionations based on the intercept and slope, but this has not generally been recognized in studies of D/H fractionation. In a mixture of two components, each of which is fractionated during mixing, there is no unique solution for the three unknown variables (two fractionation factors and the elemental mixing ratio of the two hydrogen sources). The flow of H from CH_4 and H_2O to bacterial lipids in the metabolism of Methylococcus capsulatus provides an example of such a case. Data and conclusions from an earlier study of that system (Sessions et al., 2002) are reexamined here. Several constraints on the variables are available based on plausible ranges for fractionation factors. A possible refinement to current experimental procedures is the measurement of three different isotopes, which would allow unique determination of all variables.",
"doi": "10.1016/j.gca.2004.08.005",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2005-02-01",
"series_number": "3",
"volume": "69",
"issue": "3",
"pages": "593-597"
},
{
"id": "authors:1n53g-hwe04",
"collection": "authors",
"collection_id": "1n53g-hwe04",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130604-074054886",
"type": "article",
"title": "Phylogenetically specific separation of rRNA from prokaryotes for isotopic analysis",
"author": [
{
"family_name": "Pearson",
"given_name": "Ann",
"orcid": "0000-0003-2785-8405",
"clpid": "Pearson-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Edwards",
"given_name": "Katrina J.",
"clpid": "Edwards-K-J"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "A wealth of genetic sequence information is available publicly and can be used to support investigations in organic geochemistry. Here, we present a new method to separate ribosomal RNA in order to use this rRNA as a \"biomarker\" for molecular isotopic studies. The primary goal is to obtain pure fractions that reflect selected phylogenetic groups. We demonstrate the ability to separate rRNA of a target organism from RNA representing a mixture of species. In this approach, an oligonucleotide probe containing a poly-d(GGGT) tail is hybridized to RNA in solution. Simultaneously, an aliquot of oligo-dT paramagnetic beads is hybridized to an oligonucleotide made of poly-d(CCCA) with a poly-dA tail. The two solutions are combined and a high-affinity GCAT complex is formed. The magnetic beads are captured and re-suspended in fresh solution. Careful determination of the melting temperatures of all three hybrids permits melting of the captured rRNA while leaving the majority of the oligonucleotides bound to the beads. Authenticity of the captured product is determined by reverse-transcriptase (RT)-PCR on a sub-sample; the remainder is washed, re-suspended in H_2O, and saved for subsequent isotopic analysis.",
"doi": "10.1016/j.marchem.2004.06.032",
"issn": "0304-4203",
"publisher": "Elsevier",
"publication": "Marine Chemistry",
"publication_date": "2004-12-01",
"series_number": "1-4",
"volume": "92",
"issue": "1-4",
"pages": "295-306"
},
{
"id": "authors:j35h7-cgy31",
"collection": "authors",
"collection_id": "j35h7-cgy31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MCDggg04",
"type": "article",
"title": "Rapid analysis of 13C in plant-wax n-alkanes for reconstruction of terrestrial vegetation signals from aquatic sediments",
"author": [
{
"family_name": "McDuffee",
"given_name": "Kelsey E.",
"clpid": "McDuffee-K-E"
},
{
"family_name": "Eglinton",
"given_name": "Timothy I.",
"clpid": "Eglinton-T-I"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Sylva",
"given_name": "Sean",
"clpid": "Sylva-S"
},
{
"family_name": "Wagner",
"given_name": "Thomas",
"clpid": "Wagner-T"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "Long-chain, odd-carbon-numbered C25 to C35 n-alkanes are characteristic components of epicuticular waxes produced by terrestrial higher plants. They are delivered to aquatic systems via eolian and fluvial transport and are preserved in underlying sediments. The isotopic compositions of these products can serve as records of past vegetation. We have developed a rapid method for stable carbon isotopic analyses of total plant-wax n-alkanes using a novel, moving-wire system coupled to an isotope-ratio mass spectrometer (MW-irMS). The n-alkane fractions are prepared from sediment samples by (1) saponification and extraction with organic solvents, (2) chromatographic separation using silica gel, (3) isolation of straight-chain carbon skeletons using a zeolite molecular sieve, and (4) oxidation and removal of unsaturated hydrocarbons with RuO4. Short-chain n-alkanes of nonvascular plant origin (",
"doi": "10.1029/2004GC000772",
"issn": "1525-2027",
"publisher": "American Geophysical Union",
"publication": "Geochemistry, Geophysics, Geosystems",
"publication_date": "2004-10-15",
"series_number": "10",
"volume": "5",
"issue": "10",
"pages": "Art. No. 2004GC000772"
},
{
"id": "authors:sawr6-hxk24",
"collection": "authors",
"collection_id": "sawr6-hxk24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131106-113151972",
"type": "article",
"title": "D/H ratios in terrestrially sourced petroleum systems",
"author": [
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Boreham",
"given_name": "Christopher J.",
"clpid": "Boreham-C-J"
},
{
"family_name": "Edwards",
"given_name": "Dianne S.",
"clpid": "Edwards-D-S"
},
{
"family_name": "Logan",
"given_name": "Graham A.",
"clpid": "Logan-G-A"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
}
],
"abstract": "D/H ratios of terrestrially-sourced whole oils and their respective saturated, aromatic, and polar fractions, individual n-alkanes, formation waters and non-exchangeable hydrogen in kerogen were measured in potential source rocks from seven Australian petroleum basins. Data for 75 oils and condensates, their sub-fractions and 52 kerogens indicate that oil sub-fractions have \u03b4D values comparable to \u03b4D_(oil), with a \u0394\u03b4D offset (\u03b4D_(kerogen)\u2212\u03b4D_(oil)) averaging ca. 23\u2030. The weighted-average \u03b4D of individual n-alkanes is usually identical to \u03b4D_(oil) and \u03b4D_(saturate). A trend of increasing \u03b4D with n-alkane chain length in most oils causes individual n-alkanes from an oil to vary in \u03b4D by 30\u2030 or more. A modest correlation between \u03b4D for aromatic sub-fractions and formation waters indicates that about 50% of aromatic C-bound H has exchanged with water. In contrast, \u03b4D_(oil) and \u03b4D_(saturated) show no evidence for H-exchange with formation water under reservoir conditions at temperatures up to 150 \u00b0C. Acyclic isoprenoids and n-alkanes show essentially indistinguishable \u03b4D, indicating that primary isotopic differences from biosynthesis have been erased. Overall, extensive exchange of C-bound H in petroleum with other hydrogen is apparent, but seems to have affected most hydrocarbons only during their chemical genesis from precursor molecules. Our isotopic findings from terrestrially-sourced oils should be qualitatively relevant for marine oils as well.",
"doi": "10.1016/j.orggeochem.2004.05.006",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "2004-10",
"series_number": "10",
"volume": "35",
"issue": "10",
"pages": "1169-1195"
},
{
"id": "authors:yz935-5td85",
"collection": "authors",
"collection_id": "yz935-5td85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130612-105641499",
"type": "article",
"title": "A gas ion source for continuous-flow AMS",
"author": [
{
"family_name": "Schneider",
"given_name": "R. J.",
"clpid": "Schneider-R-J"
},
{
"family_name": "Kim",
"given_name": "S.-W",
"clpid": "Kim-S-W"
},
{
"family_name": "von Reden",
"given_name": "K. F.",
"clpid": "von-Reden-K-F"
},
{
"family_name": "Hayes",
"given_name": "J. M.",
"clpid": "Hayes-J-M"
},
{
"family_name": "Wills",
"given_name": "J. S. C",
"clpid": "Wills-J-S-C"
},
{
"family_name": "Griffin",
"given_name": "V. S.",
"clpid": "Griffin-V-S"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Sylva",
"given_name": "S.",
"clpid": "Sylva-S"
}
],
"abstract": "The first gas-fed ion source for radiocarbon AMS applications (without sputtering) has been operated at the Woods\nHole NOSAMS Facility. A three-year, off-line test program resulted in positive carbon ion currents up to 1 mA and\nnegative ion currents up to 80 \u00b5A. Recently, the compact, permanent-magnet microwave plasma ion source and\nmagnesium vapor charge-exchange canal were coupled to the recombinator injector of the 2.5 MV Tandetron. When\nthe ion source was operated on CO_2 at a flow rate of about 200 \u00b51 per minute, negative carbon ion beams up to 20 \u00b5A\nwere obtained, at an energy of 35 keV. Radiocarbon measurements were performed on standard reference gases and the\ndynamic response to square-wave pulses of gas was determined. Time constants in the ion source are less than 1 s, which\nshould allow analysis of chromatographic peaks of CO_2 with very little broadening. A combustion device has been\nconstructed to generate CO_2 for direct injection into the source. Argon carrier gas is used to buffer the pressure at one\natmosphere in the sample gas injector. A dedicated ion-beam injector, with higher angular acceptance and higher\ntransmitted currents, is being constructed for the AMS system.",
"doi": "10.1016/j.nimb.2004.04.031",
"issn": "0168-583X",
"publisher": "Elsevier",
"publication": "Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms",
"publication_date": "2004-08",
"volume": "223",
"pages": "149-154"
},
{
"id": "authors:jpz3w-02q91",
"collection": "authors",
"collection_id": "jpz3w-02q91",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131120-101920612",
"type": "article",
"title": "Hydrogen isotope fractionation during H_2/CO_2 acetogenesis: hydrogen utilization efficiency and the origin of lipid-bound hydrogen",
"author": [
{
"family_name": "Valentine",
"given_name": "D. L.",
"clpid": "Valentine-D-L"
},
{
"family_name": "Sessions",
"given_name": "A. L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Tyler",
"given_name": "S. C.",
"clpid": "Tyler-S-C"
},
{
"family_name": "Chidthaisong",
"given_name": "A.",
"clpid": "Chidthaisong-A"
}
],
"abstract": "Hydrogen metabolism was studied in the anaerobic bacterium, Sporomusa sp. strain DMG 58, by measuring natural abundance levels of deuterium in H_2, H_(2)O, and individual fatty acids during acetogenic growth on H_2/CO_2. Four cultures were grown, each in medium with a distinct hydrogen-isotopic composition (\u03b4D-H_(2)O). The \u03b4D value of H_2 was quantified in the residual gas exiting the growth chambers and found to decrease concurrently with net H_2 consumption, indicating rapid isotope exchange between H_2 and H_(2)O. An isotopic mass balance was used to constrain the efficiency with which H_2 was activated by the cell and the reducing equivalents catabolized, which we term the H_2 utilization efficiency. Results indicate that H_2 utilization efficiency in these cultures is less than 20% during the growth phase, and less than 2% after the growth phase. The gross rate of cellular H_2 activation was similar in the growth phase and afterward. Biomass harvested at the end of each experiment was used to analyse the D/H of individual membrane lipids. Values of \u03b4D were highly correlated between lipids and water (\u03b4D-lipids = 0.59 \u00d7 \u03b4D-water \u2013 381\u2030; R2 = 0.995), indicating the source of lipid hydrogen is in isotopic equilibrium with water. Results are consistent with two possibilities: (i) water is the sole source of hydrogen to lipids, and the fractionation during biosynthesis is significantly larger than previously observed (\u03b1 = 0.59), or (ii) hydrogen from H_2 is incorporated into lipids, but only after reaching isotopic equilibrium with H_(2)O. Fatty acids were strongly depleted in deuterium relative to all other organisms studied thus far, and such large depletions may prove useful as biomarkers for studying H_2 cycling in anoxic environments as well as in the geological record.",
"doi": "10.1111/j.1472-4677.2004.00030.x",
"issn": "1472-4677",
"publisher": "Blackwell Publishing",
"publication": "Geobiology",
"publication_date": "2004-07",
"series_number": "3",
"volume": "2",
"issue": "3",
"pages": "179-188"
},
{
"id": "authors:3tpd4-kb393",
"collection": "authors",
"collection_id": "3tpd4-kb393",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130626-103329702",
"type": "article",
"title": "Isotopic exchange of carbon-bound hydrogen over geologic timescales",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Sylva",
"given_name": "Sean P.",
"clpid": "Sylva-S-P"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "The increasing popularity of compound-specific hydrogen isotope (D/H) analyses for investigating sedimentary organic matter raises numerous questions about the exchange of carbon-bound hydrogen over geologic timescales. Important questions include the rates of isotopic exchange, methods for diagnosing exchange in ancient samples, and the isotopic consequences of that exchange. This article provides a review of relevant literature data along with new data from several pilot studies to investigate such issues. Published experimental estimates of exchange rates between organic hydrogen and water indicate that at warm temperatures (50\u2013100\u00b0C) exchange likely occurs on timescales of 10^4 to 10^8 yr. Incubation experiments using organic compounds and D-enriched water, combined with compound-specific D/H analyses, provide a new and highly sensitive method for measuring exchange at low temperatures. Comparison of \u03b4D values for isoprenoid and n-alkyl carbon skeletons in sedimentary organic matter provides no evidence for exchange in young (<1 Ma), cool sediments, but strong evidence for exchange in ancient (>350 Ma) rocks. Specific rates of exchange are probably influenced by the nature and abundance of organic matter, pore-water chemistry, the presence of catalytic mineral surfaces, and perhaps even enzymatic activity.\nEstimates of equilibrium fractionation factors between organic H and water indicate that typical lipids will be depleted in D relative to water by \u223c75 to 140\u2030 at equilibrium (30\u00b0C). Thus large differences in \u03b4D between organic molecules and water cannot be unambiguously interpreted as evidence against hydrogen exchange. A better approach may be to use changes in stereochemistry as a proxy for hydrogen exchange. For example, estimated rates of H exchange in pristane are similar to predicted rates for stereochemical inversion in steranes and hopanes. The isotopic consequences of this exchange remain in question. Incubations of cholestene with D_2O indicate that the number of D atoms incorporated during structural rearrangements can be far less than the number of C-H bonds that are broken. Sample calculations indicate that, for steranes in immature sediments, the D/H ratio imparted by biosynthesis may be largely preserved in spite of significant structural changes.",
"doi": "10.1016/j.gca.2003.06.004",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2004-04-01",
"series_number": "7",
"volume": "68",
"issue": "7",
"pages": "1545-1559"
},
{
"id": "authors:ngpxt-9ct55",
"collection": "authors",
"collection_id": "ngpxt-9ct55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130626-112758754",
"type": "article",
"title": "Hydrogen isotope fractionation in lipids of the methane-oxidizing bacterium Methylococcus capsulatus",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Jahnke",
"given_name": "Linda L.",
"clpid": "Jahnke-L-L"
},
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "Hydrogen isotopic compositions of individual lipids from Methylococcus capsulatus, an aerobic, methane-oxidizing bacterium, were analyzed by hydrogen isotope-ratio-monitoring gas chromatography\u2013mass spectrometry (GC-MS). The purposes of the study were to measure isotopic fractionation factors between methane, water, and lipids and to examine the biochemical processes that determine the hydrogen isotopic composition of lipids. M. capsulatus was grown in six replicate cultures in which the \u03b4D values of methane and water were varied independently. Measurement of concomitant changes in \u03b4D values of lipids allowed estimation of the proportion of hydrogen derived from each source and the isotopic fractionation associated with the utilization of each source.\nAll lipids examined, including fatty acids, sterols, and hopanols, derived 31.4 \u00b1 1.7% of their hydrogen from methane. This was apparently true whether the cultures were harvested during exponential or stationary phase. Examination of the relevant biochemical pathways indicates that no hydrogen is transferred directly (with C-H bonds intact) from methane to lipids. Accordingly, we hypothesize that all methane H is oxidized to H_2O, which then serves as the H source for all biosynthesis, and that a balance between diffusion of oxygen and water across cell membranes controls the concentration of methane-derived H_2O at 31%. Values for \u03b1_(l/w), the isotopic fractionation between lipids and water, were 0.95 for fatty acids and 0.85 for isoprenoid lipids. These fractionations are significantly smaller than those measured in higher plants and algae. Values for \u03b1_(l/m), the isotopic fractionation between lipids and methane, were 0.94 for fatty acids and 0.79 for isoprenoid lipids. Based on these results, we predict that methanotrophs living in seawater and consuming methane with typical \u03b4D values will produce fatty acids with \u03b4D between \u221250 and \u2212170\u2030, and sterols and hopanols with \u03b4D between \u2212150 and \u2212270\u2030.",
"doi": "10.1016/S0016-7037(02)00981-X",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2002-11-15",
"series_number": "22",
"volume": "66",
"issue": "22",
"pages": "3955-3969"
},
{
"id": "authors:79fjc-9bs76",
"collection": "authors",
"collection_id": "79fjc-9bs76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150107-075007866",
"type": "article",
"title": "Hydrogen isotopic compositions of petroleum hydrocarbons",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Summons",
"given_name": "Roger E.",
"orcid": "0000-0002-7144-8537",
"clpid": "Summons-R-E"
},
{
"family_name": "Boreham",
"given_name": "Chris J.",
"clpid": "Boreham-C-J"
},
{
"family_name": "Logan",
"given_name": "Graham A.",
"clpid": "Logan-G-A"
},
{
"family_name": "Hope",
"given_name": "Janet M.",
"clpid": "Hope-J-M"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "To examine the processes which influence D/H ratios of\npetroleum, we measured \u03b4D of bulk oils, saturated, aromatic,\nand polar oil fractions, individual n-alkanes, formation waters\nand kerogen from source rocks. These data provide new\ninsights into the H-isotopic variability of petroleum.",
"doi": "10.1016/S0016-7037(02)01012-8",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2002-08-15",
"series_number": "15A",
"volume": "66",
"issue": "15A",
"pages": "A697"
},
{
"id": "authors:kqcmm-mpt18",
"collection": "authors",
"collection_id": "kqcmm-mpt18",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130604-075847754",
"type": "article",
"title": "Correction of H_3^+ Contributions in Hydrogen Isotope Ratio Monitoring Mass Spectrometry",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Burgoyne",
"given_name": "Thomas W.",
"clpid": "Burgoyne-T-W"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "Two fundamentally different approaches, termed \"pointwise\" and \"peakwise,\" are currently used to correct hydrogen isotope ratio monitoring data for the presence of H_3^+ ion contributions. Consideration of the underlying assumptions shows that the peakwise approach is valid only for peaks with the same functional shape and only when background signals do not vary. The pointwise correction is much more versatile and can be used even when peak shapes and sizes, as well as background signals, vary significantly. It is not exact and is limited in accuracy by (1) the signal-broadening effects of electronic time constants, (2) the analog-to-digital conversion frequency, and (3) the highest frequency of the sample signal. To minimize errors for typical gas chromatographic signals, time constants of <500 ms and analog-to-digital sampling intervals of \u2264250 ms are needed. Errors are further minimized by matching sample and standard peaks in both amplitude and D/H ratio. Using the pointwise algorithm, we demonstrate that a series of 14 homologous n-alkanes varying in concentration over a 5-fold range can be analyzed with a mean precision of 2.3\u2030 and no systematic errors.",
"doi": "10.1021/ac000489e",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2001-01-15",
"series_number": "2",
"volume": "73",
"issue": "2",
"pages": "192-199"
},
{
"id": "authors:zxq7v-ada23",
"collection": "authors",
"collection_id": "zxq7v-ada23",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130711-103723469",
"type": "article",
"title": "Determination of the H_3 Factor in Hydrogen Isotope Ratio Monitoring Mass Spectrometry",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Burgoyne",
"given_name": "Thomas W.",
"clpid": "Burgoyne-T-W"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "The H_3 factor, K, is a parameter required in high precision,\nmass spectrometric analyses of hydrogen isotopic\nabundances. When H_2 is used as the sample gas,\nR* = R - Ki_2, where R* is the true HD/H_2 ratio, R is the\nobserved (mass 3)/(mass 2) ion-current ratio, and i_2 is\nthe ion current at mass 2. Four different methods for the\ndetermination of K were defined and tested under conditions\ncharacteristic of isotope ratio monitoring systems.\nThree of these were peak-based. The fourth employed\nsteady flows of H_2 from a conventional inlet system.\nResults obtained using the latter method were more\nprecise (standard deviation of K = 0.1 versus ~0.6 ppm\nmV^(-1) for the peak-based methods). However, use of the\nresulting values of K for correction of isotope ratio\nmonitoring GC/MS results led to systematic errors as\nlarge as 9\u2030, whereas use of the peak-based values led\nto no systematic errors. Values of K were only weakly\ndependent on the pressure of He, declining ~5% for each\n10-fold increase in P_(He). Small variations in partial pressures\nof H_2O and CH_4, potential contaminants under\nisotope ratio monitoring conditions, had no significant\neffect on values of K.",
"doi": "10.1021/ac000488m",
"issn": "0003-2700",
"publisher": "American Chemical Society",
"publication": "Analytical Chemistry",
"publication_date": "2001-01-15",
"series_number": "2",
"volume": "73",
"issue": "2",
"pages": "200-207"
},
{
"id": "authors:7qmxp-w3m65",
"collection": "authors",
"collection_id": "7qmxp-w3m65",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130612-092001113",
"type": "article",
"title": "Compound-specific D/H ratios of lipid biomarkers from sediments as a proxy for environmental and climatic conditions",
"author": [
{
"family_name": "Sauer",
"given_name": "Peter E.",
"clpid": "Sauer-P-E"
},
{
"family_name": "Eglinton",
"given_name": "Timothy I.",
"clpid": "Eglinton-T-I"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
},
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
}
],
"abstract": "Hydrogen isotope ratios (D/H) of lipid biomarkers extracted from aquatic sediments were\nmeasured to determine whether they can be used as a proxy for D/H of environmental water. Values of \u03b4D\nwere determined by using a recently developed isotope-ratio-monitoring gas chromatograph-mass spectrometer\nsystem (irmGCMS) and were confirmed by conventional hydrogen isotopic measurements (i.e., combustion\nfollowed by reduction) on individual compounds isolated by preparative capillary gas chromatography.\nDiverse lipids (alkanes, n-alkanols, sterols, and pentacyclic triterpenols) were analyzed to examine hydrogenisotopic\ncontrols on lipids of varying origin and biosynthetic pathway. For algal sterols (24-methylcholest-\n3\u03b2-ol, 24-ethylcholest-5,22-dien-3\u03b2-ol, and 4,23,24-trimethylcholesterol, or dinosterol), the fractionation\nbetween sedimentary lipids and environmental water was -201 \u00b1 10\u2030 and was similar in both marine and\nfreshwater sites. In a sediment from a small lake in a forested catchment, triterpenols from terrestrial sources\nwere enriched in D by 30\u2030 relative to algal sterols. Apparent fractionation factors for n-alkyl lipids were\nsmaller than those of triterpenols and were more variable, probably reflecting multiple sources for these\ncompounds. We conclude that hydrogen-isotopic analyses of algal sterols provide a viable means of\nreconstructing D/H of environmental waters. Results are less ambiguous than reconstructions based on\nanalyses of kerogen or other operationally defined organic matter fractions.",
"doi": "10.1016/S0016-7037(00)00520-2",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2001-01",
"series_number": "2",
"volume": "65",
"issue": "2",
"pages": "213-222"
},
{
"id": "authors:0bsw7-6cz17",
"collection": "authors",
"collection_id": "0bsw7-6cz17",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130604-081443883",
"type": "article",
"title": "Fractionation of hydrogen isotopes in lipid biosynthesis",
"author": [
{
"family_name": "Sessions",
"given_name": "Alex L.",
"orcid": "0000-0001-6120-2763",
"clpid": "Sessions-A-L"
},
{
"family_name": "Burgoyne",
"given_name": "Thomas W.",
"clpid": "Burgoyne-T-W"
},
{
"family_name": "Schimmelmann",
"given_name": "Arndt",
"orcid": "0000-0003-4648-5253",
"clpid": "Schimmelmann-A"
},
{
"family_name": "Hayes",
"given_name": "John M.",
"clpid": "Hayes-J-M"
}
],
"abstract": "Isotopic compositions of carbon-bound hydrogen in individual compounds from eight different organisms were measured using isotope-ratio-monitoring gas chromatography\u2013mass spectrometry. This technique is capable of measuring D/H ratios at natural abundance in individual lipids yielding as little as 20 nmol of H_2, and is applicable to a wide range of compounds including hydrocarbons, sterols, and fatty acids. The hydrogen isotopic compositions of lipids are controlled by three factors: isotopic compositions of biosynthetic precursors, fractionation and exchange accompanying biosynthesis, and hydrogenation during biosynthesis. \u03b4D values of lipids from the eight organisms examined here suggest that all three processes are important for controlling natural variations in isotopic abundance. n-Alkyl lipids are depleted in D relative to growth water by 113\u2013262\u2030, while polyisoprenoid lipids are depleted in D relative to growth water by 142\u2013376\u2030. Isotopic variations within compound classes (e.g., n-alkanes) are usually less than \u223c50\u2030, but variations as large as 150\u2030 are observed among isoprenoid lipids from a single organism. Phytol is consistently depleted in D by up to 50\u2030 relative to other isoprenoid lipids. Inferred isotopic fractionations between cellular water and lipids are greater than those indicated by previous studies.",
"doi": "10.1016/S0146-6380(99)00094-7",
"issn": "0146-6380",
"publisher": "Elsevier",
"publication": "Organic Geochemistry",
"publication_date": "1999-09",
"series_number": "9",
"volume": "30",
"issue": "9",
"pages": "1193-1200"
}
]