| Summary: | The solid earth influences ice sheet dynamics by controlling bedrock deformation and hence surface elevation and grounding line position. These in turn determine surface and basal melt. Ice-sheet models typically include models to compute bedrock deformation with a constant mantle viscosity (or similar parameter), whereas mantle viscosity can vary strongly underneath the ice sheets. Here we use a recently developed model that couples an ice-sheet model (ANICE) to a finite-element based GIA model that includes 3D variations in viscosity derived from seismic measurements. We investigate the effect of mantle viscosity variations on the evolution of the last glacial ice sheets in Antarctica and Greenland. In Antarctica, the main feedback mechanism is the effect of bedrock elevation on local sea level and grounding line position. In particular, uplifting bedrock in marine ice sheets reduces ice sheet loss during deglaciation. Results show a grounding line position that is 500 km more outwards when including 3D variations in mantle viscosity compared to a homogeneous viscosity. In Greenland, the main feedback is the effect of bedrock elevation on the surface elevation and hence surface melt. We show that this feedback mainly manifests in north-west Greenland where the mantle viscosity is above average. The higher mantle viscosity leads to higher ice sheet elevation at last glacial maximum, which leads to less surface melt during deglaciation. The results underline the importance of including 3D viscosity in modeling ice sheet evolution.
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