Iron oxides stimulate sulfate-driven anaerobic methane oxidation in seeps

Sivan, Orit and Antler, Gilad and Turchyn, Alexandra V. and Marlow, Jeffrey J. and Orphan, Victoria J. (2014) Iron oxides stimulate sulfate-driven anaerobic methane oxidation in seeps. Proceedings of the National Academy of Sciences, 111 (40). E4139-E4147. DOI 10.1073/pnas.1412269111

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Abstract

Seep sediments are dominated by intensive microbial sulfate reduction coupled to the anaerobic oxidation of methane (AOM). Through geochemical measurements of incubation experiments with methane seep sediments collected from Hydrate Ridge, we provide insight into the role of iron oxides in sulfate-driven AOM. Seep sediments incubated with 13C-labeled methane showed co-occurring sulfate reduction, AOM, and methanogenesis. The isotope fractionation factors for sulfur and oxygen isotopes in sulfate were about 40‰ and 22‰, respectively, reinforcing the difference between microbial sulfate reduction in methane seeps versus other sedimentary environments (for example, sulfur isotope fractionation above 60‰ in sulfate reduction coupled to organic carbon oxidation or in diffusive sedimentary sulfate–methane transition zone). The addition of hematite to these microcosm experiments resulted in significant microbial iron reduction as well as enhancing sulfate-driven AOM. The magnitude of the isotope fractionation of sulfur and oxygen isotopes in sulfate from these incubations was lowered by about 50%, indicating the involvement of iron oxides during sulfate reduction in methane seeps. The similar relative change between the oxygen versus sulfur isotopes of sulfate in all experiments (with and without hematite addition) suggests that oxidized forms of iron, naturally present in the sediment incubations, were involved in sulfate reduction, with hematite addition increasing the sulfate recycling or the activity of sulfur-cycling microorganisms by about 40%. These results highlight a role for natural iron oxides during bacterial sulfate reduction in methane seeps not only as nutrient but also as stimulator of sulfur recycling.

Item Type:	Article
Uncontrolled Keywords:	2014AREP; IA68;
Subjects:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title:	Proceedings of the National Academy of Sciences
Volume:	111
Page Range:	E4139-E4147
Identification Number:	10.1073/pnas.1412269111
Depositing User:	Sarah Humbert
Date Deposited:	24 Nov 2014 17:56
Last Modified:	18 Dec 2014 17:40
URI:	http://eprints.esc.cam.ac.uk/id/eprint/3176

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