Ice sheets are currently ignored in global methane budgets1,2. Although ice sheets have been proposed to contain large reserves of methane that may contribute to a rise in atmospheric methane concentration if released during periods of rapid ice retreat3,4, no data exist on the current methane footprint of ice sheets. Here we find that subglacially produced methane is rapidly driven to the ice margin by the efficient drainage system of a subglacial catchment of the Greenland ice sheet. We report the continuous export of methane-supersaturated waters (CH4(aq)) from the ice-sheet bed during the melt season. Pulses of high CH4(aq) concentration coincide with supraglacially forced subglacial flushing events, confirming a subglacial source and highlighting the influence of melt on methane export. Sustained methane fluxes over the melt season are indicative of subglacial methane reserves that exceed methane export, with an estimated 6.3 tonnes (discharge-weighted mean; range from 2.4 to 11 tonnes) of CH4(aq) transported laterally from the ice-sheet bed. Stable-isotope analyses reveal a microbial origin for methane, probably from a mixture of inorganic and ancient organic carbon buried beneath the ice. We show that subglacial hydrology is crucial for controlling methane fluxes from the ice sheet, with efficient drainage limiting the extent of methane oxidation5 to about 17 per cent of methane exported. Atmospheric evasion is the main methane sink once runoff reaches the ice margin, with estimated diffusive fluxes (4.4 to 28 millimoles of CH4 per square metre per day) rivalling that of major world rivers6. Overall, our results indicate that ice sheets overlie extensive, biologically active methanogenic wetlands and that high rates of methane export to the atmosphere can occur via efficient subglacial drainage pathways. Our findings suggest that such environments have been previously underappreciated and should be considered in Earth's methane budget.

Department of Earth Sciences University of Toronto Toronto Ontario Canada

Department of Ecology Faculty of Science Charles University Prague Czechia

Department of Environmental Sciences Aarhus University Roskilde Denmark

Department of Geoscience Environment and Society Université Libre de Bruxelles Brussels Belgium

German Research Centre for Geosciences GFZ Potsdam Germany

Kongsberg Maritime Contros GmbH Kiel Germany

National High Magnetic Field Lab and Earth Ocean and Atmospheric Sciences Florida State University Tallahassee FL USA

National Oceanography Centre Southampton UK

School of Earth and Ocean Sciences Cardiff University Cardiff UK

School of Geographical Sciences University of Bristol Bristol UK

School of Natural and Environmental Sciences Newcastle University Newcastle UK

Citace poskytuje Crossref.org

Methylotrophic Communities Associated with a Greenland Ice Sheet Methane Release Hotspot

Catchment characteristics and seasonality control the composition of microbial assemblages exported from three outlet glaciers of the Greenland Ice Sheet

Storage and export of microbial biomass across the western Greenland Ice Sheet

Enhanced trace element mobilization by Earth's ice sheets

Patterns in Microbial Assemblages Exported From the Meltwater of Arctic and Sub-Arctic Glaciers

Silicon isotopes in Arctic and sub-Arctic glacial meltwaters: the role of subglacial weathering in the silicon cycle