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Basal Drainage System Response to Increasing Surface Melt on the Greenland Ice Sheet

Science  16 Aug 2013:
Vol. 341, Issue 6147, pp. 777-779
DOI: 10.1126/science.1235905

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Draining Through Ice

Water formed by surface melting of the Greenland Ice Sheet is transferred rapidly to the underlying bedrock, but how the water is then dispersed is less clear. This question is important because how the ice-rock interface is lubricated affects how fast the ice sheet moves. Existing conceptual models are based on observations of mountain glaciers, but Meierbachtol et al. (p. 777; see the Perspective by Lüthi) now show that those ideas may not be applicable to the Greenland Ice Sheet. Measuring water pressures in a transect of 23 boreholes revealed that drainage structures differ between the edge, where large melt channels form, and further inland, where more distributed pathways are found.

Abstract

Surface meltwater reaching the bed of the Greenland ice sheet imparts a fundamental control on basal motion. Sliding speed depends on ice/bed coupling, dictated by the configuration and pressure of the hydrologic drainage system. In situ observations in a four-site transect containing 23 boreholes drilled to Greenland’s bed reveal basal water pressures unfavorable to water-draining conduit development extending inland beneath deep ice. This finding is supported by numerical analysis based on realistic ice sheet geometry. Slow meltback of ice walls limits conduit growth, inhibiting their capacity to transport increased discharge. Key aspects of current conceptual models for Greenland basal hydrology, derived primarily from the study of mountain glaciers, appear to be limited to a portion of the ablation zone near the ice sheet margin.

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