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Carbon isotope equilibration during sulphate-limited anaerobic oxidation of methane

Nature Geoscience

By:
, , , , , , , ,
DOI: 10.1038/ngeo2069

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Abstract

Collectively, marine sediments comprise the largest reservoir of methane on Earth. The flux of methane from the sea bed to the overlying water column is mitigated by the sulphate-dependent anaerobic oxidation of methane by marine microbes within a discrete sedimentary horizon termed the sulphate–methane transition zone. According to conventional isotope systematics, the biological consumption of methane leaves a residue of methane enriched in 13C (refs 1–3). However, in many instances the methane within sulphate–methane transition zones is depleted in 13C, consistent with the production of methane, and interpreted as evidence for the intertwined anaerobic oxidation and production of methane4–6. Here, we report results from experiments in which we incubated cultures of microbial methane consumers with methane and low levels of sulphate, and monitored the stable isotope composition of the methane and dissolved inorganic carbon pools over time. Residual methane became progressively enriched in 13C at sulphate concentrations above 0.5 mM, and progressively depleted in 13C below this threshold. We attribute the shift to 13C depletion during the anaerobic oxidation of methane at low sulphate concentrations to the microbially mediated carbon isotope equilibration between methane and carbon dioxide. We suggest that this isotopic e ect could help to explain the 13C-depletion of methane in subseafloor sulphate–methane transition zones.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Carbon isotope equilibration during sulphate-limited anaerobic oxidation of methane
Series title:
Nature Geoscience
DOI:
10.1038/ngeo2069
Year Published:
2013
Language:
English
Contributing office(s):
Woods Hole Coastal and Marine Science Center
Description:
4 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article