Abstract
ABSTRACTIncreased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the subglacial environment. However, spatial patterns of surface input and partitioning of meltwater between different pathways to the base remain poorly understood. To further our understanding of surface drainage, we apply a supraglacial hydrology model to the Paakitsoq region, West Greenland for three contrasting melt seasons. During an average melt season, crevasses drain ~47% of surface runoff, lake hydrofracture drains ~3% during the hydrofracturing events themselves, while the subsequent surface-to-bed connections drain ~21% and moulins outside of lake basins drain ~15%. Lake hydrofracture forms the primary drainage pathway at higher elevations (above ~850 m) while crevasses drain a significant proportion of meltwater at lower elevations. During the two higher intensity melt seasons, model results show an increase (~5 and ~6% of total surface runoff) in the proportion of runoff drained above ~1300 m relative to the melt season of average intensity. The potential for interannual changes in meltwater partitioning could have implications for how the dynamics of the ice sheet respond to ongoing changes in meltwater production.
Highlights
The Greenland ice sheet (GrIS) has experienced elevated rates of melt since the 1990s
We apply the updated model to the Paakitsoq region of western Greenland over three melt seasons with contrasting melt intensities, incorporating moulins identified from high resolution satellite imagery, and crevassed areas determined from surface stresses derived from mean winter velocities
We divide the volume entering the englacial system through hydrofracturing into two components, the water that is in a lake when hydrofracture occurs, and subsequent drainage into the moulin that results from hydrofracture
Summary
The Greenland ice sheet (GrIS) has experienced elevated rates of melt since the 1990s (van den Broeke and others, 2009; Fettweis and others, 2011, 2013). In addition to driving surface mass loss, observations and modelling suggest that higher rates of surface melting may lead to dynamic changes of the ice sheet (Hewitt, 2013; Doyle and others, 2014; Moon and others, 2014; Tedstone and others, 2015; Van De Wal and others, 2015). Correlations between the summer melt season and increased summer ice velocities indicate that surface meltwater entering the subglacial system modulates water pressures, influencing ice velocities through changes in basal drag (Zwally and others, 2002; Bartholomew and others, 2011; Joughin and others, 2013; Fitzpatrick and others, 2013; Moon and others, 2014). Recent modelling studies of the subglacial hydrological system report that the temporal variability of meltwater input (Schoof, 2010; Hewitt, 2013) is an important control on basal drag. Water draining into the englacial system can be trapped in crevasses, leading to modest increases in ice velocities due to cryohydrologic warming of the ice sheet (Van Der Veen and others, 2011; Phillips and others, 2013; Lüthi and others, 2015; Harrington and others, 2015; Poinar and others, 2016)
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