Summary: | Glacial isostatic adjustment (GIA) represents an important negative feedback on ice-sheet dynamics. The magnitude and time scale of GIA primarily depend on the upper mantle viscosity and the lithosphere thickness. These parameters have been found to vary strongly over the Antarctic continent, showing ranges of 10^18 - 10^23 Pa s for the viscosity and 30 - 250 km for the lithospheric thickness. Recent studies show that capturing these spatial dependencies are of significant importance for the long-term evolution of the Antarctic Ice Sheet (AIS). However, 3D GIA models are computationally expensive and sometimes require an iterative coupling for the ice sheet and the solid-Earth solutions to converge. As a consequence, their use remains limited, potentially leading to errors in the simulated ice-sheet response and associated sea-level rise projections. Here, we propose to tackle this problem by generalising the work of Bueler et al. (2007) and Coulon et al. (2021). FastIsostasy allows for an explicit accounting of the effects of spatially heterogeneous viscosity and lithospheric thicknesses and is computationally very efficient.
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