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Wednesday, December 8, 2010

Christian Schoof, Nature 468 (2010), "Ice-sheet acceleration driven by melt supply variability" (re: Greenland)

Nature
468,
 
803–806
 
(09 December 2010)
 
doi:10.1038/nature09618

Received
 
 
Accepted
 
 
Published online
 


Ice-sheet acceleration driven by melt supply variability


Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia V6T 1Z4, Canada

Abstract

Increased ice velocities in Greenland1 are contributing significantly to eustatic sea level rise. Faster ice flow has been associated with ice–ocean interactions in water-terminating outlet glaciers2 and with increased surface meltwater supply to the ice-sheet bed inland. Observed correlations between surface melt and ice acceleration23456 have raised the possibility of a positive feedback in which surface melting and accelerated dynamic thinning reinforce one another7, suggesting that overall warming could lead to accelerated mass loss. Here I show that it is not simply mean surface melt4but an increase in water input variability8 that drives faster ice flow. Glacier sliding responds to melt indirectly through changes in basal water pressure9,1011, with observations showing that water under glaciers drains through channels at low pressure or through interconnected cavities at high pressure12131415. Using a model that captures the dynamic switching12between channel and cavity drainage modes, I show that channelization and glacier deceleration rather than acceleration occur above a critical rate of water flow. Higher rates of steady water supply can therefore suppress rather than enhance dynamic thinning16, indicating that the melt/dynamic thinning feedback is not universally operational. Short-term increases in water input are, however, accommodated by the drainage system through temporary spikes in water pressure. It is these spikes that lead to ice acceleration, which is therefore driven by strong diurnal melt cycles414 and an increase in rain and surface lake drainage events81718 rather than an increase in mean melt supply34.

Link:  http://www.nature.com/nature/journal/v468/n7325/full/nature09618.html

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