Quantitative estimates of velocity sensitivity to surface melt variations at a large Greenland outlet glacier
12 pages, 10 figures. The flow speed of Greenland outlet glaciers is governed by several factors, the relative importance of which is poorly understood. The delivery of surface-generated meltwater to the bed of alpine glaciers has been shown to influence glacier flow speed when the volume of water i...
| Published in: | Journal of Glaciology |
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| Main Authors: | , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
International Glaciological Society
2011
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| Subjects: | |
| Online Access: | http://hdl.handle.net/10261/53313 https://doi.org/10.3189/002214311797409785 |
| Summary: | 12 pages, 10 figures. The flow speed of Greenland outlet glaciers is governed by several factors, the relative importance of which is poorly understood. The delivery of surface-generated meltwater to the bed of alpine glaciers has been shown to influence glacier flow speed when the volume of water is sufficient to increase basal fluid pressure and hence basal lubrication. While this effect has also been demonstrated on the Greenland ice-sheet margin, little is known about the influence of surface melting on the large, marine-terminating outlet glaciers that drain the ice sheet. We use a validated model of meltwater input and GPS-derived surface velocities to quantify the sensitivity of glacier flow speed to changes in surface melt at Helheim Glacier during two summer seasons (2007-08). Our observations span ∼55 days near the middle of each melt season. We find that relative changes in glacier speed due to meltwater input are small, with variations of ∼45% in melt producing changes in velocity of ∼2-4%. These velocity variations are, however, of similar absolute magnitude to those observed at smaller glaciers and on the ice-sheet margin. We find that the glacier's sensitivity to variations in meltwater input decreases approximately exponentially with distance from the calving front. Sensitivity to melt varies with time, but generally increases as the melt season progresses. We interpret the time-varying sensitivity of glacier flow to meltwater input as resulting from changes in subglacial hydraulic routing caused by the changing volume of meltwater input. The Helheim 2007 and 2008 project was supported by the Gary Comer Science and Education Foundation, the US National Science Foundation, the Danish Commission for Scientific Research in Greenland (KVUG), the Spanish Ministry of Science and Innovation (MICINN), the Geological Survey of Denmark and Greenland (GEUS), Geocenter Copenhagen, the Danish National Space Center, NASA, the Lamont–Doherty Climate Center, and the Dan and Betty Churchill Exploration Fund. ... |
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