Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, Southwest Greenland

摘要

Meltwater delivered to the bed of the Greenland Ice Sheet is a driver ofvariable ice-motion through changes in effective pressure and enhanced basallubrication. Ice surface velocities have been shown to respond rapidly bothto meltwater production at the surface and to drainage of supraglaciallakes, suggesting efficient transfer of meltwater from the supraglacial tosubglacial hydrological systems. Although considerable effort is currentlybeing directed towards improved modelling of the controlling surface andbasal processes, modelling the temporal and spatial evolution of thetransfer of melt to the bed has received less attention. Here we present theresults of spatially distributed modelling for prediction of moulins andlake drainages on the Leverett Glacier in Southwest Greenland. The model isrun for the 2009 and 2010 ablation seasons, and for future increased meltscenarios. The temporal pattern of modelled lake drainages are qualitativelycomparable with those documented from analyses of repeat satellite imagery.The modelled timings and locations of delivery of meltwater to the bed alsomatch well with observed temporal and spatial patterns of ice surface speed-ups. This is particularly true for the lower catchment (<1000 m a.s.l.)where both the model and observations indicate that the developmentof moulins is the main mechanism for the transfer of surface meltwater tothe bed. At higher elevations (e.g. 1250–1500 m a.s.l.) the development anddrainage of supraglacial lakes becomes increasingly important. At thesehigher elevations, the delay between modelled melt generation and subsequentdelivery of melt to the bed matches the observed delay between the peak airtemperatures and subsequent velocity speed-ups, while the instantaneoustransfer of melt to the bed in a control simulation does not. Although bothmoulins and lake drainages are predicted to increase in number for futurewarmer climate scenarios, the lake drainages play an increasingly importantrole in both expanding the area over which melt accesses the bed and inenabling a greater proportion of surface melt to reach the bed.