Original Article

The ISME Journal (2014) 8, 2305–2316; doi:10.1038/ismej.2014.59; published online 17 April 2014

Molecular and biogeochemical evidence for methane cycling beneath the western margin of the Greenland Ice Sheet

Markus Dieser1,5,6, Erik L J E Broemsen1,5, Karen A Cameron2,7, Gary M King1, Amanda Achberger1, Kyla Choquette3, Birgit Hagedorn3, Ron Sletten4, Karen Junge2 and Brent C Christner1

  1. 1Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, USA
  2. 2Applied Physics Laboratory, Polar Science Center, University of Washington, Seattle, WA, USA
  3. 3Applied Science Engineering and Technology Laboratory, Environment and Natural Resources Institute, University of Alaska Anchorage, Anchorage, AK, USA
  4. 4Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA

Correspondence: BC Christner, Department of Biological Sciences, Louisiana State University, 202 Life Sciences Building, Baton Rouge, LA 70803, USA. E-mail: xner@lsu.edu

5These authors contributed equally to this work.

6Current address: Center for Biofilm Engineering, Montana State University, 366 EPS Building, Bozeman, MT 59715, USA.

7Current address: Department of Geochemistry, Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen, Denmark.

Received 26 December 2013; Revised 8 March 2014; Accepted 14 March 2014
Advance online publication 17 April 2014

Top

Abstract

Microbial processes that mineralize organic carbon and enhance solute production at the bed of polar ice sheets could be of a magnitude sufficient to affect global elemental cycles. To investigate the biogeochemistry of a polar subglacial microbial ecosystem, we analyzed water discharged during the summer of 2012 and 2013 from Russell Glacier, a land-terminating outlet glacier at the western margin of the Greenland Ice Sheet. The molecular data implied that the most abundant and active component of the subglacial microbial community at these marginal locations were bacteria within the order Methylococcales (59–100% of reverse transcribed (RT)-rRNA sequences). mRNA transcripts of the particulate methane monooxygenase (pmoA) from these taxa were also detected, confirming that methanotrophic bacteria were functional members of this subglacial ecosystem. Dissolved methane ranged between 2.7 and 83μM in the subglacial waters analyzed, and the concentration was inversely correlated with dissolved oxygen while positively correlated with electrical conductivity. Subglacial microbial methane production was supported by δ13C-CH4 values between −64‰ and −62‰ together with the recovery of RT-rRNA sequences that classified within the Methanosarcinales and Methanomicrobiales. Under aerobic conditions, >98% of the methane in the subglacial water was consumed over ~30 days incubation at ~4°C and rates of methane oxidation were estimated at 0.32μM per day. Our results support the occurrence of active methane cycling beneath this region of the Greenland Ice Sheet, where microbial communities poised in oxygenated subglacial drainage channels could serve as significant methane sinks.

Keywords:

Greenland Ice Sheet; methane; methanogenesis; methanotrophy; subglacial aquatic environment