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Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments

Li, Chao and Sessions, Alex L. and Kinnaman, Franklin S. and Valentine, David L. (2009) Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments. Geochimica et Cosmochimica Acta, 73 (16). pp. 4803-4823. ISSN 0016-7037.

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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 δD 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 δD values between the two sampling locations, nor with increasing depth for most lipids, indicating that degradation does not influence sedimentary lipid δD values. Second, relatively large differences in δD values among differing molecular structures are observed in all samples. n-Alkyl lipids of probable marine origin have typical δD values between −150 and −200‰, those from terrestrial leaf waxes and aquatic plants range from −80 to −170‰, while petroleum n-alkanes are typically −90 to −150‰. 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‰ or more. At the same time, several other lipids have δD 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.

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Sessions, Alex L.0000-0001-6120-2763
Additional Information:© 2009 Elsevier. Received 16 October 2008; accepted 21 May 2009. Available online 3 June 2009. Associate editor: Josef Werne. We thank Samantha Ying, Timothy Middleton, Daniel Murphy, Molly Redmond, Steven Cheong, John Kessler, Valerie Syverson, Elise Kleeman, Arndt Schimmelmann, Juergen Schieber and Geoff Ravenhill for field and laboratory assistance. Joe Werne, Stefan Schouten, and two anonymous reviewers provided helpful comments and advice. We also acknowledge the scientific party of the BASIN (Biogeochemistry of Anoxic Systems and stable Isotopes in Nature) cruise as well as the Captain and Crew of the R/V New Horizon for a productive cruise. Funding for this study was provided by the National Science Foundation to A.L.S. and D.L.V. (EAR-0311824). Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.gca.2009.05.056.
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Issue or Number:16
Record Number:CaltechAUTHORS:20090808-142503163
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Official Citation:Chao Li, Alex L. Sessions, Franklin S. Kinnaman, David L. Valentine, Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments, Geochimica et Cosmochimica Acta, Volume 73, Issue 16, 15 August 2009, Pages 4803-4823, ISSN 0016-7037, DOI: 10.1016/j.gca.2009.05.056.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14896
Deposited By: George Porter
Deposited On:01 Sep 2009 16:56
Last Modified:03 Oct 2019 00:53

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