Abstract
Abstract. Supraglacial lakes play an important role in establishing hydrological connections that allow lubricating seasonal meltwater to reach the base of the Greenland Ice Sheet. Here we use new surface velocity observations to examine the influence of supraglacial lake drainages and surface melt rate on ice flow. We find large, spatially extensive speedups concurrent with times of lake drainage, showing that lakes play a key role in modulating regional ice flow. While surface meltwater is supplied to the bed via a geographically sparse network of moulins, the observed ice-flow enhancement suggests that this meltwater spreads widely over the ice-sheet bed. We also find that the complex spatial pattern of speedup is strongly determined by the combined influence of bed and surface topography on subglacial water flow. Thus, modeling of ice-sheet basal hydrology likely will require knowledge of bed topography resolved at scales (sub-kilometer) far finer than existing data (several km).
Highlights
Summer surface meltwater descends through hundreds of meters of glacial ice (Das et al, 2008; Doyle et al, 2013) to lubricate the base of the Greenland Ice Sheet, seasonally enhancing ice flow (Zwally et al, 2002)
As earlier results suggest (Das et al, 2008; Alley et al, 2005; van der Veen, 2007; Krawczynski et al, 2009; Doyle et al, 2013), our observations indicate that supraglacial lakes play an important role in the seasonal ice dynamics by providing reservoirs of water that facilitate hydrofracture, and influence the timing of when surface meltwater first reaches much of the bed
The TerraSAR-X data reveal a complex spatiotemporal evolution of ice flow throughout the summer melt season, with the timing of lake drainage determining when much of the widespread seasonal speedup occurs
Summary
Summer surface meltwater descends through hundreds of meters of glacial ice (Das et al, 2008; Doyle et al, 2013) to lubricate the base of the Greenland Ice Sheet, seasonally enhancing ice flow (Zwally et al, 2002). While this enhancement does not account for recent large increases in mean-annual ice-flow speed (Joughin et al, 2008), it may become more important in controlling Greenland’s contribution to sea level in the coming decades to centuries as marine-terminating outlet glaciers retreat from their deep troughs (Parizek and Alley, 2004). Joughin et al.: Influence of ice-sheet geometry and supraglacial lakes
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