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James Farquhar - One of the best experts on this subject based on the ideXlab platform.
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early inner solar system origin for anomalous Sulfur Isotopes in differentiated protoplanets
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Michael A Antonelli, Pierre Cartigny, Joost Hoek, Sangtae Kim, Marc Peters, Jabrane Labidi, Richard J Walker, James R Lyons, James FarquharAbstract:Abstract Achondrite meteorites have anomalous enrichments in 33S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying 33S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the 33S anomalies, or of the bulk solar system S-isotope composition. Here, we report well-resolved anomalous 33S depletions in IIIF iron meteorites (<−0.02 per mil), and 33S enrichments in other magmatic iron meteorite groups. The 33S depletions support the idea that differentiated planetesimals inherited Sulfur that was photochemically derived from gases in the early inner solar system (<∼2 AU), and that bulk inner solar system S-isotope composition was chondritic (consistent with IAB iron meteorites, Earth, Moon, and Mars). The range of mass-independent Sulfur isotope compositions may reflect spatial or temporal changes influenced by photochemical processes. A tentative correlation between S Isotopes and Hf-W core segregation ages suggests that the two systems may be influenced by common factors, such as nebular location and volatile content.
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Multiple Sulfur Isotopes fractionations associated with abiotic Sulfur transformations in Yellowstone National Park geothermal springs
Geochemical Transactions, 2014Co-Authors: Alexey Kamyshny, Zahra F Mansaray, Gregory K Druschel, James FarquharAbstract:Background The paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate Sulfur species (zero-valent Sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple Sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent Sulfur. The main goal of this research is to understand multiple Sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, Sulfur cycling. Results Water samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate Sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (
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pathways for neoarchean pyrite formation constrained by mass independent Sulfur Isotopes
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Alexey Kamyshny, James Farquhar, John B Cliff, Aubrey L Zerkle, Simon W Poulton, Mark Claire, David T Adams, Brian HarmsAbstract:It is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the Neoarchean. It is puzzling, therefore, that the Sulfur isotope record of the Neoarchean is characterized by a signal of atmospheric mass-independent chemistry rather than a strong overprint by sulfate reducers. Here, we present a study of the four Sulfur Isotopes obtained using secondary ion MS that seeks to reconcile a number of features seen in the Neoarchean Sulfur isotope record. We suggest that Neoarchean ocean basins had two coexisting, significantly sized Sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record. One of these pools is suggested to be a soluble (sulfate) pool, and the other pool (atmospherically derived elemental Sulfur) is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide. We suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite-forming environments. We also suggest that the existence of a significant nonsulfate pool of reactive Sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record.
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connections between Sulfur cycle evolution Sulfur Isotopes sediments and base metal sulfide deposits
Economic Geology, 2010Co-Authors: James Farquhar, Donald E. Canfield, Nanping Wu, Harry OduroAbstract:Significant links exist between the Sulfur cycle, Sulfur geochemistry of sedimentary systems, and ore deposits over the course of Earth history. A picture emerges of an Archean and Paleoproterozoic stage of the Sulfur cycle that has much lower levels of sulfate (<200 μM ), carries a signal of mass-independent Sulfur, and preserves evidence for temporal and spatial heterogeneity that reflects lower amounts of Sulfur cycling than today. A second stage of ocean chemistry in the Paleoproterozoic, with higher atmospheric oxygen and oceanic sulfate at low millimolar levels, follows this stage. The isotopic record in sedimentary rocks and in sulfide-bearing ore deposits suggests abundant pyrite burial and implies a missing 34S-depleted pool that may have been lost via deep ocean deposition and possibly subduction. Proterozoic ocean chemistry appears to be quite complex. The surface waters of the Proterozoic oceans are believed to have been oxygenated, but geologic evidence from ore deposits and sedimentary rocks supports coexistence of significant sulfidic and nonsulfidic, anoxic, intermediate water and deep-water pools in the Mesoproterozoic. This stage in ocean chemistry ends with the second major global oxidation event in the latest Neoproterozoic (~600 Ma). This event started the transition to more oxygenated intermediate and deep waters, and higher but variable oceanic sulfate concentrations. The event set the scene for the formation in the Phanerozoic of the first significant MVT deposits and possibly is reflected in changes in other sedimentary rock-hosted base metal sulfide deposits.
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reconstructing earth s surface oxidation across the archean proterozoic transition
Geology, 2009Co-Authors: Harald Strauss, Boswell A. Wing, Alan J Kaufman, Stefan Schroder, Jens Gutzmer, Margaret A Baker, Andrey Bekker, James FarquharAbstract:The Archean-Proterozoic transition is characterized by the widespread deposition of organic-rich shale, sedimentary iron formation, glacial diamictite, and marine carbonates recording profound carbon isotope anomalies, but notably lacks bedded evaporites. All deposits refl ect environmental changes in oceanic and atmospheric redox states, in part associated with Earth’s earliest ice ages. Time-series data for multiple Sulfur Isotopes from carbonateassociated sulfate as well as sulfi des in sediments of the Transvaal Supergroup, South Africa, capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric massindependent Sulfur isotope fractionation. In phase with Sulfur is the earliest recorded positive carbon isotope anomaly, convincingly linking these environmental perturbations to the Great Oxidation Event (ca. 2.3 Ga).
Donald E. Canfield - One of the best experts on this subject based on the ideXlab platform.
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connections between Sulfur cycle evolution Sulfur Isotopes sediments and base metal sulfide deposits
Economic Geology, 2010Co-Authors: James Farquhar, Donald E. Canfield, Nanping Wu, Harry OduroAbstract:Significant links exist between the Sulfur cycle, Sulfur geochemistry of sedimentary systems, and ore deposits over the course of Earth history. A picture emerges of an Archean and Paleoproterozoic stage of the Sulfur cycle that has much lower levels of sulfate (<200 μM ), carries a signal of mass-independent Sulfur, and preserves evidence for temporal and spatial heterogeneity that reflects lower amounts of Sulfur cycling than today. A second stage of ocean chemistry in the Paleoproterozoic, with higher atmospheric oxygen and oceanic sulfate at low millimolar levels, follows this stage. The isotopic record in sedimentary rocks and in sulfide-bearing ore deposits suggests abundant pyrite burial and implies a missing 34S-depleted pool that may have been lost via deep ocean deposition and possibly subduction. Proterozoic ocean chemistry appears to be quite complex. The surface waters of the Proterozoic oceans are believed to have been oxygenated, but geologic evidence from ore deposits and sedimentary rocks supports coexistence of significant sulfidic and nonsulfidic, anoxic, intermediate water and deep-water pools in the Mesoproterozoic. This stage in ocean chemistry ends with the second major global oxidation event in the latest Neoproterozoic (~600 Ma). This event started the transition to more oxygenated intermediate and deep waters, and higher but variable oceanic sulfate concentrations. The event set the scene for the formation in the Phanerozoic of the first significant MVT deposits and possibly is reflected in changes in other sedimentary rock-hosted base metal sulfide deposits.
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fractionation of multiple Sulfur Isotopes during phototrophic oxidation of sulfide and elemental Sulfur by a green Sulfur bacterium
Geochimica et Cosmochimica Acta, 2009Co-Authors: Aubrey L Zerkle, James Farquhar, D Johnston, Raymond P Cox, Donald E. CanfieldAbstract:Abstract We present multiple Sulfur isotope measurements of Sulfur compounds associated with the oxidation of H2S and S0 by the anoxygenic phototrophic S-oxidizing bacterium Chlorobium tepidum. Discrimination between 34S and 32S was +1.8 ± 0.5‰ during the oxidation of H2S to S0, and −1.9 ± 0.8‰ during the oxidation of S0 to SO 4 2 - , consistent with previous studies. The accompanying Δ33S and Δ36S values of sulfide, elemental Sulfur, and sulfate formed during these experiments were very small, less than 0.1‰ for Δ33S and 0.9‰ for Δ36S, supporting mass conservation principles. Examination of these isotope effects within a framework of the metabolic pathways for S oxidation suggests that the observed effects are due to the flow of Sulfur through the metabolisms, rather than abiotic equilibrium isotope exchange alone, as previously suggested. The metabolic network comparison also indicates that these metabolisms work to express some isotope effects (between sulfide, polysulfides, and elemental Sulfur in the periplasm) and suppress others (kinetic isotope effects related to pathways for oxidation of sulfide to sulfate via the same enzymes involved in sulfate reduction acting in reverse). Additionally, utilizing fractionation factors for phototrophic S oxidation calculated from our experiments and for other oxidation processes calculated from the literature (chemotrophic and inorganic S oxidation), we constructed a set of ecosystem-scale Sulfur isotope box models to examine the isotopic consequences of including sulfide oxidation pathways in a model system. These models demonstrate how the small δ34S effects associated with S oxidation combined with large δ34S effects associated with sulfate reduction (by SRP) and Sulfur disproportionation (by SDP) can produce large (and measurable) effects in the Δ33S of Sulfur reservoirs. Specifically, redistribution of material along the pathways for sulfide oxidation diminishes the net isotope effect of SRP and SDP, and can mask the isotopic signal for Sulfur disproportionation if significant recycling of S intermediates occurs. We show that the different sulfide oxidation processes produce different isotopic fields for identical proportions of oxidation, and discuss the ecological implications of these results to interpreting minor S isotope patterns in modern systems and in the geologic record.
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effect of hydrogen limitation and temperature on the fractionation of Sulfur Isotopes by a deep sea hydrothermal vent sulfate reducing bacterium
Geochimica et Cosmochimica Acta, 2006Co-Authors: Annalouise Reysenbach, Joost Hoek, Kirsten Silvia Habicht, Donald E. CanfieldAbstract:Abstract The fractionation of Sulfur Isotopes by the thermophilic chemolithoautotrophic Thermodesulfatator indicus was explored during sulfate reduction under excess and reduced hydrogen supply, and the full temperature range of growth (40–80 °C). Fractionation of Sulfur Isotopes measured under reduced H2 conditions in a fed-batch culture revealed high fractionations (24–37‰) compared to fractionations produced under excess H2 supply (1–6‰). Higher fractionations correlated with lower sulfate reduction rates. Such high fractionations have never been reported for growth on H2. For temperature-dependant fractionation experiments cell-specific rates of sulfate reduction increased with increasing temperatures to 70 °C after which sulfate-reduction rates rapidly decreased. Fractionations were relatively high at 40 °C and decreased with increasing temperature from 40–60 °C. Above 60 °C, fractionation trends switched and increased again with increasing temperatures. These temperature-dependant fractionation trends have not previously been reported for growth on H2 and are not predicted by a generally accepted fractionation model for sulfate reduction, where fractionations are controlled as a function of temperature, by the balance of the exchange of sulfate across the cell membrane, and enzymatic reduction rates of sulfate. Our results are reproduced with a model where fractionation is controlled by differences in the temperature response of enzyme reaction rates and the exchange of sulfate in and out of the cell.
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biogeochemistry of Sulfur Isotopes
Reviews in Mineralogy & Geochemistry, 2001Co-Authors: Donald E. CanfieldAbstract:Sulfur, with an atomic weight of 32.06, has four stable Isotopes. By far the most abundant is 32S, representing around 95% of the total Sulfur on Earth. The next most abundant isotope is 34S, followed by 33S, and finally 36S is the least abundant contributing only 0.0136% to the total (Table 1⇓). The natural abundances of Sulfur Isotopes, however, vary from these values as a result of biological and inorganic reactions involving the chemical transformation of Sulfur compounds. For thermodynamic reasons, the relative abundance of Sulfur Isotopes can vary between coexisting Sulfur phases. This is because lighter masses partition more of the total bond energy into vibrational rather than translational modes. Bonds with a higher vibrational energy are also more easily broken which is why lighter Isotopes are generally enriched in the reaction products in chemical reactions with associated fractionation. Thus, for a nonreversible chemical reaction, as often occurs in biological systems, independent reactions may be written for the transformation of the light, L, and heavy, H, Isotopes of reactant, A, to product, B (Eqns. 1 and 2). View this table: Table 1. Natural abundance ofstable Sulfur Isotopesa \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[A\_{H}\ {{\rightarrow}\_{}^{k\_{H}}}\ B\_{H}\] \end{document}(1) \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[A\_{L}\ {{\rightarrow}\_{}^{k\_{L}}}\ B\_{L}\] \end{document}(2) Each of these reactions has associated rate constants, kH and kL, and as described above, kH is generally less than kL, yielding an enrichment of the lighter isotope in the product. Fractionations associated with a unidirectional process are referred to as kinetic fractionations. Fractionations can also occur between two chemical species at equilibrium. The basis for equilibrium fractionations is thermodynamic and, as with kinetic fractionations, is related to mass-dependent differences in bond energies between light and heavy Isotopes. The generalized isotope equilibrium between two chemical species is presented in Equation (3). \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[x\ A\_{L}\ +\ y\ B\_{H}\ {\leftrightarrow}\ x\ A\_{H}\ +\ y\ B\_{L}\] \end{document}(3) From Equation (3) an equilibrium constant, Keq, may be …
Alexey Kamyshny - One of the best experts on this subject based on the ideXlab platform.
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multiple Sulfur Isotopes fractionations associated with abiotic Sulfur transformations in yellowstone national park geothermal springs
Geochemical Transactions, 2014Co-Authors: Alexey Kamyshny, Zahra F Mansaray, Gregory K Druschel, James FarquhaAbstract:The paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate Sulfur species (zero-valent Sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple Sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent Sulfur. The main goal of this research is to understand multiple Sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, Sulfur cycling. Water samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate Sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (<6 μmol L-1) in the pools with low pH due to fast disproportionation of thiosulfate. In the pools with higher pH, the concentration of thiosulfate varies, depending on different geochemical pathways of thiosulfate formation. The δ34S values of sulfate in four systems were close to those calculated using a mixing line of the model based on dilution and boiling of a deep hot parent water body. In two pools δ34S values of sulfate varied significantly from the values calculated from this model. Sulfur isotope fractionation between ZVS and hydrogen sulfide was close to zero at pH < 4. At higher pH zero-valent Sulfur is slightly heavier than hydrogen sulfide due to equilibration in the rhombic Sulfur–polysulfide – hydrogen sulfide system. Triple Sulfur isotope (32S, 33S, 34S) fractionation patterns in waters of hydrothermal pools are more consistent with redox processes involving intermediate Sulfur species than with bacterial sulfate reduction. Small but resolved differences in ∆33S among species and between pools are observed. The variation of sulfate isotopic composition, the origin of differences in isotopic composition of sulfide and zero–valent Sulfur, as well as differences in ∆33S of sulfide and sulfate are likely due to a complex network of abiotic redox reactions, including disproportionation pathways.
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Multiple Sulfur Isotopes fractionations associated with abiotic Sulfur transformations in Yellowstone National Park geothermal springs
Geochemical Transactions, 2014Co-Authors: Alexey Kamyshny, Zahra F Mansaray, Gregory K Druschel, James FarquharAbstract:Background The paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate Sulfur species (zero-valent Sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple Sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent Sulfur. The main goal of this research is to understand multiple Sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, Sulfur cycling. Results Water samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate Sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (
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pathways for neoarchean pyrite formation constrained by mass independent Sulfur Isotopes
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Alexey Kamyshny, James Farquhar, John B Cliff, Aubrey L Zerkle, Simon W Poulton, Mark Claire, David T Adams, Brian HarmsAbstract:It is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the Neoarchean. It is puzzling, therefore, that the Sulfur isotope record of the Neoarchean is characterized by a signal of atmospheric mass-independent chemistry rather than a strong overprint by sulfate reducers. Here, we present a study of the four Sulfur Isotopes obtained using secondary ion MS that seeks to reconcile a number of features seen in the Neoarchean Sulfur isotope record. We suggest that Neoarchean ocean basins had two coexisting, significantly sized Sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record. One of these pools is suggested to be a soluble (sulfate) pool, and the other pool (atmospherically derived elemental Sulfur) is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide. We suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite-forming environments. We also suggest that the existence of a significant nonsulfate pool of reactive Sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record.
Boswell A. Wing - One of the best experts on this subject based on the ideXlab platform.
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reconstructing earth s surface oxidation across the archean proterozoic transition
Geology, 2009Co-Authors: Harald Strauss, Boswell A. Wing, Alan J Kaufman, Stefan Schroder, Jens Gutzmer, Margaret A Baker, Andrey Bekker, James FarquharAbstract:The Archean-Proterozoic transition is characterized by the widespread deposition of organic-rich shale, sedimentary iron formation, glacial diamictite, and marine carbonates recording profound carbon isotope anomalies, but notably lacks bedded evaporites. All deposits refl ect environmental changes in oceanic and atmospheric redox states, in part associated with Earth’s earliest ice ages. Time-series data for multiple Sulfur Isotopes from carbonateassociated sulfate as well as sulfi des in sediments of the Transvaal Supergroup, South Africa, capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric massindependent Sulfur isotope fractionation. In phase with Sulfur is the earliest recorded positive carbon isotope anomaly, convincingly linking these environmental perturbations to the Great Oxidation Event (ca. 2.3 Ga).
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implications of conservation of mass effects on mass dependent isotope fractionations influence of network structure on Sulfur isotope phase space of dissimilatory sulfate reduction
Geochimica et Cosmochimica Acta, 2007Co-Authors: James Farquhar, David T Johnston, Boswell A. WingAbstract:This paper presents worked solutions for the fractionations of all four stable Sulfur Isotopes ( 32 S, 33 S, 34 S, and 36 S) in several models of the sulfate reduction metabolism. We describe methods for obtaining solutions and how the predictions made by these solutions define different compositional fields (phase space) that can be used to gain new insights into Sulfur metabolisms, specifically with respect to understanding the structure of and fractionations associated with the network of reactions that describe the transformations of Sulfur within the cell. We show how this treatment can be used to evaluate data from experiments with dissimilatory sulfate reducers and to suggest that the expression of fractionations by the metabolic process is largely limited by the fraction of sulfate that is lost from the cell, and that the variation in observed fractionations reflects differences in the proportion of Sulfur intermediates that are reoxidized to sulfate. This analysis provides a line of support for this assertion that depends only on the Sulfur isotopic fractionations between sulfate and sulfide. This analysis also indicates that internal fractionations are consistent with a relationship given by 33 a =( 34 a) h where a is the fractionation factor (e.g.,
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multiple Sulfur Isotopes and the evolution of the atmosphere
Earth and Planetary Science Letters, 2003Co-Authors: James Farquhar, Boswell A. WingAbstract:Abstract Interest in multiple Sulfur isotope analyses has been fueled by recent reports of mass-independent Sulfur isotope signatures in the geologic record. A non-zero multiple isotopic signature of Sulfur (Δ33S and Δ36S) is produced primarily through photochemical reactions, and it is an almost perfect tracer of the source of Sulfur. Once the signature is passed on to a given Sulfur reservoir, it will be preserved unless there is addition of Sulfur with a different Δ33S or Δ36S. In the geological record, this signature has been used to study the evolution of the Earth’s atmosphere and to trace movement of Sulfur through geological systems early in Earth’s history. Recently, small but significant mass-independent signatures have been reported for some younger samples, raising the possibility of additional applications of multiple isotope studies. The purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous, but not uncommon isotopic signatures.
Joost Hoek - One of the best experts on this subject based on the ideXlab platform.
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early inner solar system origin for anomalous Sulfur Isotopes in differentiated protoplanets
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Michael A Antonelli, Pierre Cartigny, Joost Hoek, Sangtae Kim, Marc Peters, Jabrane Labidi, Richard J Walker, James R Lyons, James FarquharAbstract:Abstract Achondrite meteorites have anomalous enrichments in 33S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying 33S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the 33S anomalies, or of the bulk solar system S-isotope composition. Here, we report well-resolved anomalous 33S depletions in IIIF iron meteorites (<−0.02 per mil), and 33S enrichments in other magmatic iron meteorite groups. The 33S depletions support the idea that differentiated planetesimals inherited Sulfur that was photochemically derived from gases in the early inner solar system (<∼2 AU), and that bulk inner solar system S-isotope composition was chondritic (consistent with IAB iron meteorites, Earth, Moon, and Mars). The range of mass-independent Sulfur isotope compositions may reflect spatial or temporal changes influenced by photochemical processes. A tentative correlation between S Isotopes and Hf-W core segregation ages suggests that the two systems may be influenced by common factors, such as nebular location and volatile content.
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effect of hydrogen limitation and temperature on the fractionation of Sulfur Isotopes by a deep sea hydrothermal vent sulfate reducing bacterium
Geochimica et Cosmochimica Acta, 2006Co-Authors: Annalouise Reysenbach, Joost Hoek, Kirsten Silvia Habicht, Donald E. CanfieldAbstract:Abstract The fractionation of Sulfur Isotopes by the thermophilic chemolithoautotrophic Thermodesulfatator indicus was explored during sulfate reduction under excess and reduced hydrogen supply, and the full temperature range of growth (40–80 °C). Fractionation of Sulfur Isotopes measured under reduced H2 conditions in a fed-batch culture revealed high fractionations (24–37‰) compared to fractionations produced under excess H2 supply (1–6‰). Higher fractionations correlated with lower sulfate reduction rates. Such high fractionations have never been reported for growth on H2. For temperature-dependant fractionation experiments cell-specific rates of sulfate reduction increased with increasing temperatures to 70 °C after which sulfate-reduction rates rapidly decreased. Fractionations were relatively high at 40 °C and decreased with increasing temperature from 40–60 °C. Above 60 °C, fractionation trends switched and increased again with increasing temperatures. These temperature-dependant fractionation trends have not previously been reported for growth on H2 and are not predicted by a generally accepted fractionation model for sulfate reduction, where fractionations are controlled as a function of temperature, by the balance of the exchange of sulfate across the cell membrane, and enzymatic reduction rates of sulfate. Our results are reproduced with a model where fractionation is controlled by differences in the temperature response of enzyme reaction rates and the exchange of sulfate in and out of the cell.
