Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet

摘要

We present four years (August 2003–August 2007) of surface mass balance datafrom the ablation zone of the west Greenland ice sheet along the 67° Nlatitude circle. Sonic height rangers and automatic weather stationscontinuously measured accumulation/ablation and near-surface climate atdistances of 6, 38 and 88 km from the ice sheet margin at elevations of 490,1020 and 1520 m a.s.l. Using a melt model and reasonable assumptions aboutsnow density and percolation characteristics, these data are used toquantify the partitioning of energy and mass fluxes during melt episodes.The lowest site receives very little winter accumulation, and ice melting isnearly continuous in June, July and August. Due to the lack of snowaccumulation, little refreezing occurs and virtually all melt energy isinvested in runoff. Higher up the ice sheet, the ice sheet surface freezesup during the night, making summer melting intermittent. At the intermediatesite, refreezing in snow consumes about 10% of the melt energy,increasing to 40% at the highest site. The sum of these effects is thattotal melt and runoff increase exponentially towards the ice sheet margin,each time doubling between the stations. At the two lower sites, we estimatethat radiation penetration causes 20–30% of the ice melt to occur belowthe surface.