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Greenland melt drives continuous export of methane from the ice-sheet bed

Greenland melt drives continuous export of methane from the ice-sheet bed
Greenland melt drives continuous export of methane from the ice-sheet bed
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.
0028-0836
73-77
Lamarche-gagnon, Guillaume
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Wadham, Jemma L.
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Sherwood Lollar, Barbara
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Arndt, Sandra
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Fietzek, Peer
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Beaton, Alexander D.
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Tedstone, Andrew J.
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Telling, Jon
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Bagshaw, Elizabeth A.
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Hawkings, Jon R.
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Kohler, Tyler J.
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Zarsky, Jakub D.
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Mowlem, Matthew C.
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Anesio, Alexandre M.
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Stibal, Marek
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Lamarche-gagnon, Guillaume
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Wadham, Jemma L.
fccc19ee-c691-4f95-bbfd-41f4d4f32c57
Sherwood Lollar, Barbara
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Arndt, Sandra
5d9779dd-3ff4-4521-9276-e2255e725782
Fietzek, Peer
96006f83-9f7d-46df-adb4-33501ff24124
Beaton, Alexander D.
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Tedstone, Andrew J.
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Telling, Jon
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Bagshaw, Elizabeth A.
d34b716f-8162-4788-81a8-03146d5528ed
Hawkings, Jon R.
6010d694-7b3f-4a03-921e-eb2c8cfd54d3
Kohler, Tyler J.
49cd9259-0327-4c52-b4f2-149b5e347ed5
Zarsky, Jakub D.
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Mowlem, Matthew C.
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Anesio, Alexandre M.
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Stibal, Marek
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Lamarche-gagnon, Guillaume, Wadham, Jemma L., Sherwood Lollar, Barbara, Arndt, Sandra, Fietzek, Peer, Beaton, Alexander D., Tedstone, Andrew J., Telling, Jon, Bagshaw, Elizabeth A., Hawkings, Jon R., Kohler, Tyler J., Zarsky, Jakub D., Mowlem, Matthew C., Anesio, Alexandre M. and Stibal, Marek (2019) Greenland melt drives continuous export of methane from the ice-sheet bed. Nature, 565 (7737), 73-77. (doi:10.1038/s41586-018-0800-0).

Record type: Article

Abstract

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.

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Accepted/In Press date: 8 November 2018
e-pub ahead of print date: 2 January 2019

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Local EPrints ID: 428062
URI: https://eprints.soton.ac.uk/id/eprint/428062
ISSN: 0028-0836
PURE UUID: e8c7a4c0-d539-4aef-87f4-1de993ea1b37

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Date deposited: 07 Feb 2019 17:30
Last modified: 13 Mar 2019 17:37

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