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Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments

Raven, Morgan Reed and Adkins, Jess F. and Werne, Josef P. and Lyons, Timothy W. and Sessions, Alex L. (2015) Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments. Organic Geochemistry, 80 . pp. 53-59. ISSN 0146-6380.

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Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are ^(34)S-enriched relative to coexisting sulfide, and experiments have produced ^(34)S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography – inductively coupled plasma mass spectrometry, to measure the compound-specific sulfur isotopic compositions of volatile organosulfur compounds over a 6 m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in ^(34)S relative to coexisting kerogen and porewater sulfide. We hypothesize that this ^(34)S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon-sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary pore water. The ^(34)S-depleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.

Item Type:Article
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Adkins, Jess F.0000-0002-3174-5190
Sessions, Alex L.0000-0001-6120-2763
Additional Information:© 2015 Elsevier B.V. Received Date: 13 February 2014; Revised Date: 22 December 2014; Accepted Date: 7 January 2015; Available online 14 January 2015. We thank N. Dalleska and G. Paris at Caltech for significant analytical assistance, and J. Rae, A. Amrani, C. Marotta and A. Subhas for helpful advice. We also thank two anonymous reviewers, whose comments significantly improved the manuscript. Financial support was provided by the National Science Foundation through award EAR-1024919 to A.L.S. and J.F.A. The research is also funded in part by the Gordon and Betty Moore Foundation through Grant GBMF#3306 to A.L.S.
Funding AgencyGrant Number
Gordon and Betty Moore Foundation3306
Subject Keywords:sulfur isotopes, organosulfur compounds, sediment diagenesis, kerogen, Cariaco Basin
Record Number:CaltechAUTHORS:20150126-083217317
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Official Citation:Morgan Reed Raven, Jess F. Adkins, Josef P. Werne, Timothy W. Lyons, Alex L. Sessions, Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments, Organic Geochemistry, Volume 80, March 2015, Pages 53-59, ISSN 0146-6380, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54056
Deposited By: Tony Diaz
Deposited On:26 Jan 2015 17:18
Last Modified:24 Feb 2020 10:30

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