Collaborative Research: Disentangling runoff- and Terminus-driven Velocity Variations of Fast Flowing Outlet Glaciers

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Ice loss from the polar ice sheets is the largest anticipated contribution to global mean-sea-level rise in the coming century. A fundamental control on the rate of ice loss is how fast ice flows from ice sheet interiors out to the edges. In the interior of the Greenland Ice Sheet, ice flow responds to liquid water (“runoff") input, which affects how the ice slides over the bedrock beneath. At ocean-terminating "outlet glaciers” around the edges of Greenland, ice flows into the ocean with speed that varies by season. That strong seasonal variation makes it more difficult to determine the extent to which liquid water input is affecting the flow speed. Identifying the relative strength of ocean-driven versus melt-driven ice flow variations is essential for computer models used to forecast future ice loss. It has been difficult to assess those factors in a consistent way because they operate over multiple time scales, thus requiring different methods of observation that could not be directly compared.This proposal seeks to address three key motivating questions: (Q1) How does runoff affect outlet glacier flow over timescales of hours to years?; (Q2) How does glacier geometry affect the response to runoff?; and (Q3) How do runoff- and terminus-driven velocity variations interact? To address these questions, the PIs will combine new field observations at a large marine-terminating outlet glacier with newly available satellite data from multiple sources, using recently developed methods for flexible time series analysis. Multivariate statistical analysis and idealized numerical model experiments will test hypothesized feedbacks between runoff-driven and terminus-driven changes, as well as connect the observational work to more general settings. The PIs will develop open-source software that allows other researchers to replicate their analysis for remote-sensing and in situ data obtained on any glacier. Museum professionals on the team will coordinate with the PIs to develop a special exhibit on the drivers of Arctic glacier change; after initial installation at the University of Alaska Museum of the North, the exhibit will be made available to tour other Arctic museums.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.