Reinforced ridges in Thwaites Glacier yield insights into resolution requirements for coupled ice sheet and solid Earth models

Abstract. Grounding line retreat in the Amundsen Sea Embayment (ASE) is expected to drive the largest Antarctic contribution to sea-level rise over the coming centuries. In this region, low mantle viscosity accelerates the solid Earth's viscoelastic response to ice mass loss, leading to a stabilizing feedback via bedrock uplift and local sea-level fall: effects governed by gravitation, rotation, and deformation (GRD) processes. These stabilizing effects can be enhanced by the presence of ridges and confinements, which have been identified in ASE but can only be represented by using high model resolutions. Here, we investigate how coupled ice sheet–GRD simulations respond to (i) ice sheet model resolution, (ii) GRD spatial resolution, and (iii) the coupling interval between the two systems. We consider two model setups with distinct mesh structures, surface mass balance (SMB) forcings, and basal melt parametrizations. Our findings underscore the importance of feedback mechanisms at kilometer scales and decadal to sub-decadal timescales. Resolving bedrock topography at 2 km instead of 1 km raises the projected sea level by 7.1 % in 2100 and lowers it by 18.8 % in 2350. In our most conservative setup, we find that bedrock uplift delays grounding line retreat by up to 30 years on ridges located 34 and 75 km upstream of Thwaites Glacier's current grounding line. This mechanism plays a key role in reducing Thwaites' sea-level contribution by up to 53.1 % in 2350. These findings underscore the critical need to reduce uncertainties in bedrock topography.