Geometric controls on the inland extent of dynamic thinning for Greenland Ice Sheet outlet glaciers




Felikson, Denis

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The Greenland Ice Sheet has been losing mass at an accelerating rate since 2003, in part due to changes in ice sheet dynamics. As ocean-terminating outlet glaciers retreat, they initiate thinning that diffuses inland, causing dynamic mass loss from the ice sheet interior. Although outlet glaciers have undergone widespread retreat during the last two decades, the inland extent of thinning and, thus, the mass loss is heterogeneous between glacier catchments. There remains a lack of a unifying explanation of the cause of this heterogeneity and accurately projecting the sea-level rise contribution from the ice sheet requires improvement in our understanding of what controls the upstream diffusion of thinning, initiated by terminus retreat. In this dissertation, I use observations and modeling to identify limits to the upstream diffusion of dynamic thinning for ocean-terminating glaciers draining the Greenland Ice Sheet. I start by using diffusive-kinematic wave theory to describe the evolution of thinning and I calibrate a metric that identifies how far upstream a thinning perturbation can diffuse from glacier termini. This metric is calculable from the observed glacier bed and surface topography and I use it to predict inland thinning limits for the majority of Greenland's outlet glaciers. I find that inland thinning limits often coincide with subglacial knickpoints in bed topography. These are steep reaches of the bed that are located at the transition between the portion of the bed that is below sea level and the upstream portion that is above sea level. I use the predicted thinning limits to help identify individual glaciers that have the largest potential to contribute to sea-level rise in the coming century. Finally, I use higher-order numerical modeling to validate the predicted thinning limits from the first-order kinematic wave model, and to investigate the timing and magnitude of glacier mass loss over the coming century. I find that glaciers that have small ice fluxes but are susceptible to thin far into the interior of the ice sheet have the potential to contribute as much to sea-level rise as their higher-flux counterparts. These lower-flux glaciers are often not discussed in literature but will be significant contributors to sea-level rise by 2100.


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