Climatology and firn processes in the lower accumulation area of the Greenland ice sheet
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
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
Climate Research Environmental Sciences Meteorology and Atmospheric Sciences
IdentifiersURN: urn:nbn:se:uu:diva-284365ISBN: 978-91-554-9571-8OAI: oai:DiVA.org:uu-284365DiVA: diva2:920221
2016-06-10, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:15 (English)
Benn, Douglas, Professor
Pohjola, Veijo, Proffessorvan As, Dirk, Senior researcherPettersson, Rickard, Senior lecturer
ProjectsStability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)Greenland Analogue Project (GAP)
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