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Greenland meltwater storage in firn limited by near-surface ice formation


Machguth, Horst; MacFerrin, Mike; van As, Dirk; Box, Jason E; Charalampidis, Charalampos; Colgan, William; Fausto, Robert S; Meijer, Harro A J; Mosley-Thompson, Ellen; van de Wal, Roderik S W (2016). Greenland meltwater storage in firn limited by near-surface ice formation. Nature Climate Change, 6(4):390-393.

Abstract

Approximately half of Greenland’s current annual mass loss is attributed to runoff from surface melt1. At higher elevations, however, melt does not necessarily equal runoff, because meltwater can refreeze in the porous near-surface snow and firn2. Two recent studies suggest that all3 or most3, 4 of Greenland’s firn pore space is available for meltwater storage, making the firn an important buffer against contribution to sea level rise for decades to come3. Here, we employ in situ observations and historical legacy data to demonstrate that surface runoff begins to dominate over meltwater storage well before firn pore space has been completely filled. Our observations frame the recent exceptional melt summers in 2010 and 2012 (refs 5,6), revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (more than ~1,900 m above sea level), firn has undergone substantial densification, while at lower elevations, where melt is most abundant, porous firn has lost most of its capability to retain meltwater. Here, the formation of near-surface ice layers renders deep pore space difficult to access, forcing meltwater to enter an efficient7 surface discharge system and intensifying ice sheet mass loss earlier than previously suggested3.

Abstract

Approximately half of Greenland’s current annual mass loss is attributed to runoff from surface melt1. At higher elevations, however, melt does not necessarily equal runoff, because meltwater can refreeze in the porous near-surface snow and firn2. Two recent studies suggest that all3 or most3, 4 of Greenland’s firn pore space is available for meltwater storage, making the firn an important buffer against contribution to sea level rise for decades to come3. Here, we employ in situ observations and historical legacy data to demonstrate that surface runoff begins to dominate over meltwater storage well before firn pore space has been completely filled. Our observations frame the recent exceptional melt summers in 2010 and 2012 (refs 5,6), revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (more than ~1,900 m above sea level), firn has undergone substantial densification, while at lower elevations, where melt is most abundant, porous firn has lost most of its capability to retain meltwater. Here, the formation of near-surface ice layers renders deep pore space difficult to access, forcing meltwater to enter an efficient7 surface discharge system and intensifying ice sheet mass loss earlier than previously suggested3.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Language:English
Date:2016
Deposited On:19 Sep 2016 12:57
Last Modified:08 Dec 2017 20:24
Publisher:Nature Publishing Group
ISSN:1758-678X
Publisher DOI:https://doi.org/10.1038/nclimate2899

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