Abstract
AbstractWe present ice velocities from a land‐terminating transect extending >115 km into the western Greenland Ice Sheet during three contrasting melt years (2009–2011) to determine whether enhanced melting accelerates dynamic mass loss. We find no significant correlation between surface melt and annual ice flow. There is however a positive correlation between melt and summer ice displacement, but a negative correlation with winter displacement. This response is consistent with hydro‐dynamic coupling; enhanced summer ice flow results from longer periods of increasing surface melting and greater duration ice surface to bed connections, while reduced winter motion is explicable by drainage of high basal water pressure regions by larger more extensive subglacial channels. Despite mean interannual surface melt variability of up to 70%, mean annual ice velocities changed by <7.5%. Increased summer melting thereby preconditions the ice‐bed interface for reduced winter motion resulting in limited dynamic sensitivity to interannual variations in surface melting.
Highlights
[2] Meltwater generated at the surface of the Greenland Ice Sheet (GrIS) drains through the ice into the subglacial hydraulic system and influences rates of basal motion by altering effective pressure at the ice-bed interface, defined as ice overburden minus subglacial water pressure
[3] In response to sustained inputs of surface meltwater, theory and data suggest that subglacial drainage systems develop from hydraulically inefficient structures into efficient channels, which operate at lower pressures for a given discharge [Kamb, 1987; Röthlisberger, 1972; Schoof, 2010, Cowton et al, 2013], thereby reducing the lubrication effect of further meltwater inputs
National Centers for Environmental Prediction/ National Center for Atmospheric Research reanalysis data show that May–August 1000 mb temperature anomalies in SOLE ET AL.: INTERANNUAL GREENLAND ICE FLOW CHANGES
Summary
[2] Meltwater generated at the surface of the Greenland Ice Sheet (GrIS) drains through the ice into the subglacial hydraulic system and influences rates of basal motion by altering effective pressure at the ice-bed interface, defined as ice overburden minus subglacial water pressure. [3] In response to sustained inputs of surface meltwater, theory and data suggest that subglacial drainage systems develop from hydraulically inefficient structures into efficient channels, which operate at lower pressures for a given discharge [Kamb, 1987; Röthlisberger, 1972; Schoof, 2010, Cowton et al, 2013], thereby reducing the lubrication effect of further meltwater inputs This reasoning can explain why GrIS ice velocities in late summer are lower than those in early summer [Bartholomew et al, 2010; Sundal et al, 2011]. Recent theoretical [Pimentel and Flowers, 2011; Schoof, 2010], remote sensing, and field [Sundal et al, 2011; Van de Wal et al, 2008] studies have proposed that marginal ice will flow more slowly in higher melt years since subglacial channelization will occur more quickly in response to increased inputs of meltwater, thereby reducing the dynamic sensitivity of the GrIS to climate warming. The dynamic behavior of the whole ablation zone in different melt seasons and the resulting impact on annual ice motion remain uncertain
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