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  Sulfur and oxygen isotope fractionation during sulfate reduction coupled to anaerobic oxidation of methane is dependent on methane concentration

Deusner, C., Holler, T., Arnold, G., Bernasconi, S., Formolo, M., & Brunner, B. (2014). Sulfur and oxygen isotope fractionation during sulfate reduction coupled to anaerobic oxidation of methane is dependent on methane concentration. Earth and Planetary Science Letters, 399, 61-73.

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 Creators:
Deusner, C.1, Author           
Holler, T.1, Author           
Arnold, G.2, Author           
Bernasconi, S., Author
Formolo, M.2, Author           
Brunner, B.2, Author           
Affiliations:
1Department of Microbiology, Max Planck Institute for Marine Microbiology, Max Planck Society, ou_2481695              
2Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Max Planck Society, ou_2481693              

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 Abstract: Isotope signatures of sulfur compounds are key tools for studying sulfur cycling in the modern environment and throughout earth's history. However, for meaningful interpretations, the isotope effects of the processes involved must be known. Sulfate reduction coupled to the anaerobic oxidation of methane (AOM-SR) plays a pivotal role in sedimentary sulfur cycling and is the main process responsible for the consumption of methane in marine sediments - thereby efficiently limiting the escape of this potent greenhouse gas from the seabed to the overlying water column and atmosphere. In contrast to classical dissimilatory sulfate reduction (DSR), where sulfur and oxygen isotope effects have been measured in culture studies and a wide range of isotope effects has been observed, the sulfur and oxygen isotope effects by AOM-SR are unknown. This gap in knowledge severely hampers the interpretation of sulfur cycling in methane-bearing sediments, especially because, unlike DSR which is carried out by a single organism, AOM-SR is presumably catalyzed by consortia of archaea and bacteria that both contribute to the reduction of sulfate to sulfide. We studied sulfur and oxygen isotope effects by AOM-SR at various aqueous methane concentrations from 1.4 +/- 0.6 mM up to 58.8 +/- 10.5 mM in continuous incubation at steady state. Changes in the concentration of methane induced strong changes in sulfur isotope enrichment (epsilon S-34) and oxygen isotope exchange between water and sulfate relative to sulfate reduction (theta(o)), as well as sulfate reduction rates (SRR). Smallest delta S-34 (21.9 +/- 1.9 parts per thousand) and theta(o) (0.5 +/- 0.2) as well as highest SRR were observed for the highest methane concentration, whereas highest epsilon S-34 (67.3 +/- 26.1 parts per thousand) and theta(o) (2.5 +/- 1.5) and lowest SRR were reached at low methane concentration. Our results show that epsilon S-34, theta(o) and SRR during AOM-SR are very sensitive to methane concentration and thus also correlate with energy yield. In sulfate-methane transition zones, AOM-SR is likely to induce very large sulfur isotope fractionation between sulfate and sulfide (i.e. >60 parts per thousand) and will drive the oxygen isotope composition of sulfate towards the sulfate-water oxygen isotope equilibrium value. Sulfur isotope fractionation by AOM-SR at gas seeps, where methane fluxes are high, will be much smaller (i.e. 20 to 40 parts per thousand). (C) 2014 Elsevier B.V. All rights reserved.

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Language(s): eng - English
 Dates: 2014-08-01
 Publication Status: Issued
 Pages: 13
 Publishing info: -
 Table of Contents: -
 Rev. Type: Internal
 Identifiers: eDoc: 700652
ISI: 000338620200007
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Title: Earth and Planetary Science Letters
  Other : Earth Planet. Sci. Lett.
Source Genre: Journal
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Publ. Info: Amsterdam : Elsevier
Pages: - Volume / Issue: 399 Sequence Number: - Start / End Page: 61 - 73 Identifier: ISSN: 0012-821X
CoNE: https://pure.mpg.de/cone/journals/resource/954925395406