- 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 acceleration2, 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 pressure9,10, 11, with observations showing that water under glaciers drains through channels at low pressure or through interconnected cavities at high pressure12, 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 cycles4, 14 and an increase in rain and surface lake drainage events8, 17, 18 rather than an increase in mean melt supply3, 4.
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