Donglai Yang, Kristin Poinar , Sophie Nowicki, Beata Csatho

Outlet glaciers in Greenland are undergoing retreat and diffusive thinning in response to external forcings, but the rates and magnitudes of these responses differ from glacier to glacier for unclear reasons. We test how changes in ice overburden pressure and basal lubrication affect diffusive thinning rates and their spatial patterns by conducting numerical experiments over various idealized Greenland-like glacier domains. We find that ~10 km frontal retreat over a decade can produce sustained thinning rates as large as 16 m/a due to ice overburden pressure changes, at outlet glaciers with high basal drag (> 60 kPa) and lateral resistive stress (> 70 kPa). Localized basal lubrication perturbations induce upstream thinning and downstream thickening up to 12 m/a; the duration of the lubrication forcing generally has a greater effect than its intensity on induced thickness changes. Lastly, episodic grounding line retreats over a rough bed produce a stepped timeseries of thinning broadly consistent with observations of dynamic elevation change on multiple Greenland glaciers. Our findings highlight the importance of local stress state changes on the spatial variation of thinning, and the critical role of grounding line position -- not ice front position -- in the total thinning over a glacier domain.