Seasonal speedup along the western flank of the Greenland Ice Sheet

It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice- bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic- scale view, spanning ice- sheet to outlet- glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups ( 50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller (< 15%). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet- glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice- sheet flow.