Abstract
Abstract. Seasonal meltwater lakes on the Greenland Ice Sheet form when surface runoff is temporarily trapped in surface topographic depressions. The development of such lakes affects both the surface energy balance and dynamics of the ice sheet. Although areal extents, depths and lifespan of lakes can be inferred from satellite imagery, such observational studies have a limited temporal resolution. Here, we adopt a modelling-based strategy to estimate the seasonal evolution of surface water storage for the ~ 3600 km2 Paakitsoq region of W. Greenland. We use a high-resolution time-dependent surface mass balance model to calculate surface melt, a supraglacial water routing model to calculate lake filling and a prescribed water-volume-based threshold to predict rapid lake drainage events. This threshold assumes that drainage will occur through a fracture if V = Fa ⋅ H, where V is lake volume, H is the local ice thickness and Fa is the potential fracture area. The model shows good agreement between modelled lake locations and volumes and those observed in nine Landsat 7 ETM images from 2001, 2002 and 2005. We use the model to investigate the lake water volume required to trigger drainage, and the impact that varying this threshold volume has on the proportion of meltwater that is stored in surface lakes and enters the subglacial drainage system. Model performance is maximised with values of Fa between 4000 and 7500 m2. For these thresholds, lakes transiently store < 40% of available meltwater at the beginning of the melt season, decreasing to ~ 5 to 10% by the middle of the melt season; over the course of a melt season, 40 to 50% of total meltwater production enters the subglacial drainage system through moulins at the bottom of drained lakes.
Highlights
IntroductionThe formation of surface meltwater lakes on the surface of the Greenland Ice Sheet (GrIS) (and other Arctic ice masses) during the melt season is a widely observed phenomenon
The formation of surface meltwater lakes on the surface of the Greenland Ice Sheet (GrIS) during the melt season is a widely observed phenomenon
Whilst such studies have allowed the extent and the seasonal evolution of surface lakes to be ascertained for the times when such imagery is available, they are somewhat limited by the fact that lakes are transient features; not all lakes will be observed on any given image, and an image may not capture the maximum extent of any given lake
Summary
The formation of surface meltwater lakes on the surface of the Greenland Ice Sheet (GrIS) (and other Arctic ice masses) during the melt season is a widely observed phenomenon. The storage (and subsequent release) of meltwater in supraglacial lakes is a key control in determining both the timing and rate of delivery of water to the subglacial drainage system. This is important as it is widely accepted that the variability in magnitude and timing of meltwater input to the subglacial drainage system has a greater influence on subglacial water pressures, and ice motion, than the total volume of water input (Schoof, 2010; Bartholomew et al, 2011, 2012; Colgan et al, 2011). Despite numerous studies which compare ice velocity data to lake drainage observations from satellite imagery (e.g. Bartholomew et al, 2010, 2011, 2012; Hoffman et al, 2011; Sole et al, 2011, 2013; Sundal et al, 2011; Cowton et al, 2013; Joughin et al, 2013), there is still uncertainty about how supraglacial lake drainage events affect
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