| Summary: | Recent changes in the flow dynamics and overall geometry of the Greenland Ice Sheet have been concurrent with increased surface melting: the velocity of some outlet glaciers has increased, the ice sheet margins have thinned, and the overall mass of the ice sheet has declined by more than melt alone can account for. A direct linkage between surface melt and ice sheet change is commonly argued but has not been proven. In the proposed work, direct connections between surface melt, the basal hydrological system, and ice motion will be quantified along a flow-line transect of the Greenland Ice Sheet. The region to be studied receives high surface melt, but is located far from the influence of ocean tidewater dynamics. Basal conditions will be directly measured in six boreholes drilled to the bed, with two holes at each of three sites. Surface melt and spatial gradients in ice velocity will be quantified to enable detailed comparison between melt water forcing, basal hydrologic conditions, and ice flow dynamics. Instrumentation at the surface, within the ice, and at the bed will collect data at high time resolution for up to 2 years. Two models will be used to interpret the mechanical and thermal context of the measurements. In turn, the intensive measurement campaign will uniquely constrain the modeling and enable model assessment. This integrated measurement and modeling campaign will be a comprehensive investigation of the role of water in ice sheet motion. This work will support two Ph.D. dissertations and provide field research experiences to at least five students. Several informal education and outreach activities will be supported, including a high proportion of Native American participants.
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