Changing surface–atmosphere energy exchange and refreezing capacity of the lower accumulation area, West Greenland
- 1Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350 Copenhagen K, Denmark
- 2Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden
- 3Institute for Marine and Atmospheric research (IMAU), Utrecht University, P.O. Box 80005, 3508TA Utrecht, the Netherlands
- 4Department of Earth and Space Sciences and Engineering, York University, 4700 Keele Street, M3J 1P3, Toronto, Canada
- 5Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, UK
- 6Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology, University of Tromsø, Dramsveien 201, 9037 Tromsø, Norway
- 7Cooperative Institute for Research in Environmental Sciences (CIRES), 216 UCB, University of Colorado Boulder, Boulder, CO 80309, USA
- 8Arctic Technology Centre (ARTEK), Technical University of Denmark, Brovej, byg. 118, 2800 Kgs. Lyngby, Denmark
Abstract. We present 5 years (2009–2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l. – above sea level) of the Greenland ice sheet in the Kangerlussuaq region. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater run-off. The observed run-off was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals an anomalously low 2012 summer-averaged albedo of 0.71 (typically ~ 0.78), as meltwater was present at the ice sheet surface. Consequently, during the 2012 melt season, the ice sheet surface absorbed 28 % (213 MJ m−2) more solar radiation than the average of all other years.
A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity analysis reveals that 71 % of the additional solar radiation in 2012 was used for melt, corresponding to 36 % (0.64 m) of the 2012 surface lowering. The remaining 64 % (1.14 m) of surface lowering resulted from high atmospheric temperatures, up to a +2.6 °C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt–albedo feedback.
Longer time series of SMB, regional temperature, and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year, with the lowest albedo, at this elevation on record. The warm conditions of recent years have resulted in enhanced melt and reduction of the refreezing capacity in the lower accumulation area. If high temperatures continue, the current lower accumulation area will turn into a region with superimposed ice in coming years.