Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage

The increased amounts of meltwater generated in warmer years might be expected to act as lubrication between moving glaciers or ice sheets and the bedrock below, thereby increasing the velocity of the moving body of ice. But apparently not — satellite observations of ice velocity in Greenland now provide empirical support for a recent theoretical prediction (http://go.nature.com/v7WSps) that the development of efficient subglacial drainage associated with high meltwater input can, in fact, reduce the ice velocity. Data from six major glaciers on the Greenland Ice Sheet show that, although the initial ice speedup was similar in all six years of the study, the glacier experienced a dramatic late summer slow-down during the warm years when more melt water was produced.