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The Carbon-Sulfur Link in the Remineralization of Organic Carbon in Surface Sediments

Published version
Peer-reviewed

Type

Article

Change log

Authors

Bradbury, HJ 
Turchyn, AV 
Bateson, A 
Antler, G 
Fotherby, A 

Abstract

jats:pHere we present the carbon isotopic composition of dissolved inorganic carbon (DIC) and the sulfur isotopic composition of sulfate, along with changes in sulfate concentrations, of the pore fluid collected from a series of sediment cores located along a depth transect on the Iberian Margin. We use these data to explore the coupling of microbial sulfate reduction (MSR) to organic carbon oxidation in the uppermost (up to nine meters) sediment. We argue that the combined use of the carbon and sulfur isotopic composition, of DIC and sulfate respectively, in sedimentary pore fluids, viewed through a δjats:sup13</jats:sup>Cjats:subDIC</jats:sub> vs. δjats:sup34</jats:sup>Sjats:subSO4</jats:sub> cross plot, reveals significant insight into the nature of carbon-sulfur coupling in marine sedimentary pore fluids on continental margins. Our data show systemic changes in the carbon and sulfur isotopic composition of DIC and sulfate (respectively) where, at all sites, the carbon isotopic composition of the DIC decreases before the sulfur isotopic composition of sulfate increases. We compare our results to global data and show that this behavior persists over a range of sediment types, locations and water depths. We use a reactive-transport model to show how changes in the amount of DIC in seawater, the carbon isotopic composition of organic matter, the amount of organic carbon oxidation by early diagenetic reactions, and the presence and source of methane influence the carbon and sulfur isotopic composition of sedimentary pore fluids and the shape of the δjats:sup13</jats:sup>Cjats:subDIC</jats:sub> vs. δjats:sup34</jats:sup>Sjats:subSO4</jats:sub> cross plot. The δjats:sup13</jats:sup>C of the DIC released during sulfate reduction and sulfate-driven anaerobic oxidation of methane is a major control on the minimum δjats:sup13</jats:sup>Cjats:subDIC</jats:sub> value in the δjats:sup13</jats:sup>Cjats:subDIC</jats:sub> vs. δjats:sup34</jats:sup>Sjats:subSO4</jats:sub> cross plot, with the δjats:sup13</jats:sup>C of the organic carbon being important during both MSR and combined sulfate reduction, sulfate-driven AOM and methanogenesis.</jats:p>

Description

Keywords

carbon isotopes, sulfur isotopes, early diagenesis, microbial sulfate reduction, methanotrophy and methanogenesis, reactive transport modeling

Journal Title

Frontiers in Earth Science

Conference Name

Journal ISSN

2296-6463
2296-6463

Volume Title

9

Publisher

Frontiers Media SA
Sponsorship
Natural Environment Research Council (NE/J00653X/1)
European Research Council (307582)
Natural Environment Research Council (NE/R013519/1)