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Greenland meltwater storage in firn limited by near-surface ice formation
Department of Geography, University of Zurich.ORCID iD: 0000-0001-5924-0998
Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado at Boulder.ORCID iD: 0000-0001-8157-7159
Geological Survey of Denmark and Greenland (GEUS).ORCID iD: 0000-0002-6553-8982
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS). (Ice, Climate and Environment)ORCID iD: 0000-0003-0853-697X
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2016 (English)In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 6, no 4, 390-393 p.Article in journal, Letter (Refereed) PublishedText
Abstract [en]

Approximately half of Greenland's current annual mass loss is attributed to runoff from surface melt. At higher elevations, however, melt does not necessarily equal runoff, because meltwater can refreeze in the porous near-surface snow and firn. Two recent studies suggest that all or most 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 come. 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, revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (more than similar to 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 efficient surface discharge system and intensifying ice sheet mass loss earlier than previously suggested.

Place, publisher, year, edition, pages
2016. Vol. 6, no 4, 390-393 p.
Keyword [en]
Greenland, ice sheet, refreezing, percolation, melt, firn
National Category
Climate Research
URN: urn:nbn:se:uu:diva-280716DOI: 10.1038/nclimate2899ISI: 000373060000016OAI: oai:DiVA.org:uu-280716DiVA: diva2:911845
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)
Available from: 2016-03-14 Created: 2016-03-14 Last updated: 2016-06-15
In thesis
1. Climatology and firn processes in the lower accumulation area of the Greenland ice sheet
Open this publication in new window or tab >>Climatology and firn processes in the lower accumulation area of the Greenland ice sheet
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Greenland ice sheet is the largest Northern Hemisphere store of fresh water, and it is responding rapidly to the warming climate. In situ observations document the changing ice sheet properties in the lower accumulation area, Southwest Greenland. Firn densities from 1840 meters above sea level retrieved in May 2012 revealed the existence of a 5.5-meter-thick, near-surface ice layer in response to the recent increased melt and refreezing in firn. As a consequence, vertical meltwater percolation in the extreme summer 2012 was inefficient, resulting in surface runoff. Meltwater percolated and refroze at six meters depth only after the end of the melt season. This prolonged autumn refreezing under the newly accumulated snowpack resulted in unprecedented firn warming with temperature at ten meters depth increased by more than four degrees Celsius. Simulations confirm that meltwater reached nine meters depth at most. The refrozen meltwater was estimated at 0.23 meters water equivalent, amounting to 25 % of the total 2012 ablation.

A surface energy balance model was used to evaluate the seasonal and interannual variability of all surface energy fluxes at that elevation in the years 2009 to 2013. Due to the meltwater presence at the surface in 2012, the summer-averaged albedo was significantly reduced (0.71 in 2012; typically 0.78). A sensitivity analysis revealed that 71 % of the subsequent additional solar radiation in 2012 was used for melt, corresponding to 36 % of the total 2012 surface lowering. This interplay between melt and firn properties highlights that the lower accumulation area of the Greenland ice sheet will be responding rapidly in a warming climate.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 81 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1372
climate change, Greenland ice sheet, accumulation area, automatic weather stations, surface energy balance, melt–albedo feedback, surface mass budget, snow, firn, meltwater, percolation, refreezing, runoff
National Category
Climate Research Environmental Sciences Meteorology and Atmospheric Sciences
urn:nbn:se:uu:diva-284365 (URN)978-91-554-9571-8 (ISBN)
Public defence
2016-06-10, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:15 (English)
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)Greenland Analogue Project (GAP)
Available from: 2016-05-20 Created: 2016-04-17 Last updated: 2016-06-15

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