Aquatic habitats beneath ice masses contain active microbial ecosystems capable of cycling important greenhouse gases, such as methane (CH4). A large methane reservoir is thought to exist beneath the West Antarctic Ice Sheet, but its quantity, source and ultimate fate are poorly understood. For instance, O2 supplied by basal melting should result in conditions favourable for aerobic methane oxidation. Here we use measurements of methane concentrations and stable isotope compositions along with genomic analyses to assess the sources and cycling of methane in Subglacial Lake Whillans (SLW) in West Antarctica. We show that sub-ice-sheet methane is produced through the biological reduction of CO2 using H2. This methane pool is subsequently consumed by aerobic, bacterial methane oxidation at the SLW sediment–water interface. Bacterial oxidation consumes >99% of the methane and represents a significant methane sink, and source of biomass carbon and metabolic energy to the surficial SLW sediments. We conclude that aerobic methanotrophy may mitigate the release of methane to the atmosphere upon subglacial water drainage to ice sheet margins and during periods of deglaciation.
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This study was funded by National Science Foundation – Division of Polar Programs grants (0838933, 1346250, 1439774 to J.C.P.; 0838941 to B.C.C.) awarded as part of the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project. We thank the WISSARD Science Team (see http://wissard.org for the full list of team members) for their assistance in expedition planning and with collecting and processing samples. Partial support was provided by graduate fellowships from the NSF-IGERT Program (0654336), Montana Space Grant Consortium and NSF-Center for Dark Energy Biosphere Investigations (A.B.M.); a dissertation grant from the American Association of University Women (T.J.V.-M.); a NSF-Graduate Research Fellowship (A.M.A.); and a Sêr Cymru National Research Network for Low Carbon, Energy and the Environment Grant from the Welsh Government and Higher Education Funding Council for Wales (A.C.M.). We thank R. Scherer and R. Powell for sediment cores. B.B. Jørgensen, M. A. Lever and S. Nielsen provided support and assistance with DNA extraction and pmoA/mcrA amplification. Logistics were conducted by the 139th Expeditionary Airlift Squadron of the New York Air National Guard, Kenn Borek Air, and Antarctic Support Contractor, managed by Lockheed-Martin. Hot-water drill support was provided by University of Nebraska-Lincoln and directed by F. Rack and D. Duling (chief driller). D. Blythe, J. Burnett, C. Carpenter, D. Gibson, J. Lemery, A. Melby and G. Roberts provided drill support at SLW. This is C-DEBI contribution #371.
The authors declare no competing financial interests.
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Michaud, A., Dore, J., Achberger, A. et al. Microbial oxidation as a methane sink beneath the West Antarctic Ice Sheet. Nature Geosci 10, 582–586 (2017). https://doi.org/10.1038/ngeo2992
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