Abstract
Abstract. This study uses data from six on-ice weather stations, calibrated MODIS-derived albedo and proglacial river gauging measurements to drive and validate an energy balance model. We aim to quantify the record-setting positive temperature anomaly in 2010 and its effect on mass balance and runoff from the Kangerlussuaq sector of the Greenland ice sheet. In 2010, the average temperature was 4.9 °C (2.7 standard deviations) above the 1974–2010 average in Kangerlussuaq. High temperatures were also observed over the ice sheet, with the magnitude of the positive anomaly increasing with altitude, particularly in August. Simultaneously, surface albedo was anomalously low in 2010, predominantly in the upper ablation zone. The low albedo was caused by high ablation, which in turn profited from high temperatures and low winter snowfall. Surface energy balance calculations show that the largest melt excess (∼170%) occurred in the upper ablation zone (above 1000 m), where higher temperatures and lower albedo contributed equally to the melt anomaly. At lower elevations the melt excess can be attributed to high atmospheric temperatures alone. In total, we calculate that 6.6 ± 1.0 km3 of surface meltwater ran off the ice sheet in the Kangerlussuaq catchment in 2010, exceeding the reference year 2009 (based on atmospheric temperature measurements) by ∼150%. During future warm episodes we can expect a melt response of at least the same magnitude, unless a larger wintertime snow accumulation delays and moderates the melt-albedo feedback. Due to the hypsometry of the ice sheet, yielding an increasing surface area with elevation, meltwater runoff will be further amplified by increases in melt forcings such as atmospheric heat.
Highlights
Greenland stores nearly three million cubic kilometres of ice, a large potential contribution to sea level rise
The low albedo was caused by high ablation, which in turn profited from high temperatures and low winter snowfall
Half of recent Greenland ice sheet mass loss can be attributed to increases in surface melt (Van den Broeke et al, 2009), which reaffirms the importance of surface mass balance (SMB) monitoring
Summary
Greenland stores nearly three million cubic kilometres of ice, a large potential contribution to sea level rise. Whereas the retreat and thinning of numerous marine-terminating glaciers has not been limited to recent years (Csatho et al, 2008), the acceleration of many major outlets and consequent increase in iceberg discharge is, and has become a significant component of the overall net mass loss in the last decade (Rignot and Kanagaratnam, 2006; Howat et al, 2011). Large sections of the land-terminating ice sheet margin are known to be subject to thinning (Pritchard et al, 2009), as a direct and potentially indirect consequence of increasing surface melt. Half of recent Greenland ice sheet mass loss can be attributed to increases in surface melt (Van den Broeke et al, 2009), which reaffirms the importance of surface mass balance (SMB) monitoring
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