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

 

26 April 2010

 

Accepted

 

25 October 2010

 

Published online

 

08 December 2010

Ice-sheet acceleration driven by melt supply variability

• Christian Schoof

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 acceleration^{2, 3, 4, 5, 6} 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 pressure^9,10, 11, with observations showing that water under glaciers drains through channels at low pressure or through interconnected cavities at high pressure^{12, 13, 14, 15}. 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 cycles^4, 14 and an increase in rain and surface lake drainage events^8, 17, 18 rather than an increase in mean melt supply^3, 4.

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