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Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark. (Ice, Climate and Environment)ORCID iD: 0000-0003-0853-697X
Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.ORCID iD: 0000-0002-6553-8982
Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.; York Univ, Dept Earth & Space Sci & Engn, 4700 Keele St, Toronto, ON M3J 1P3, Canada.ORCID iD: 0000-0001-6334-1660
Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.
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2016 (English)In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 57, no 72, 1-10 p., 6000021Article in journal (Refereed) Published
Abstract [en]

We present in situ firn temperatures from the extreme 2012 melt season in the southwestern lower accumulation area of the Greenland ice sheet. The upper 2.5 m of snow and firn was temperate during the melt season, when vertical meltwater percolation was inefficient due to a c. 5.5 m thick ice layer underlying the temperate firn. Meltwater percolation and refreezing beneath 2.5 m depth only occurred after the melt season. Deviations from temperatures predicted by pure conductivity suggest that meltwater refroze in discrete bands at depths of 2.0–2.5, 5.0–6.0 and 8.0–9.0 m. While we find no indication of meltwater percolation below 9 m depth or complete filling of pore volume above, firn at 10 and 15 m depth was respectively 4.2–4.5 degrees C and 1.7 degrees C higher than in a conductivity-only simulation. Even though meltwater percolation in 2012 was inefficient, firn between 2 and 15 m depth the following winter was on average 4.7 degrees C warmer due to meltwater refreezing. Our observations also suggest that the 2012 firn conditions were preconditioned by two warm summers and ice layer formation in 2010 and 2011. Overall, firn temperatures during the years 2009–13 increased by 0.6 degrees C.

Place, publisher, year, edition, pages
2016. Vol. 57, no 72, 1-10 p., 6000021
Keyword [en]
Greenland ice sheet, accumulation area, firn, percolation, refreezing, superimposed ice
National Category
Climate Research
Identifiers
URN: urn:nbn:se:uu:diva-284357DOI: 10.1017/aog.2016.2ISI: 000385592800002OAI: oai:DiVA.org:uu-284357DiVA: diva2:920213
Projects
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitiring of the Greenland Ice Sheet (PROMICE)Greenland Analogue Project (GAP)
Available from: 2016-04-17 Created: 2016-04-17 Last updated: 2016-11-23Bibliographically approved
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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1372
Keyword
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
Identifiers
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)
Opponent
Supervisors
Projects
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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