Retreat of Thwaites Glacier, West Antarctica, triggered by its neighbours.

The drainage catchments of the neighbouring Thwaites and Pine Island Glaciers, situated in the Amundson Sea Embayment, West Antarctica, contain sufficient ice to raise global mean sea level by a meter. In recent years, significant scientific attention has been given to the potential for sustained retreat of these glaciers as a possible pathway towards widespread deglaciation of the marine-based West Antarctic Ice Sheet. Some recent studies have demonstrated that the Thwaites Ice Shelf provides only limited buttressing to the upstream grounded ice, suggesting limited sensitivity to the melt-driven loss of the ice shelf. We use the BISICLES ice sheet model to perform a series of 1000-year model experiments on the Amundson Sea domain. A synthetic sub-shelf melt rate is selectively applied to the Pine Island, Thwaites and Crosson/Dotson basins or combinations of those basins. We find that over millennial timescales, Thwaites is relatively insensitive to melt-driven thinning of its ice shelf, with its grounding line rapidly restabilising ~60km upstream of its current location. The same melt forcing applied to Pine Island Glacier leads to widespread deglaciation of the Pine Island catchment and significant retreat in the neighbouring Thwaites catchment despite the lack of melting there. Applying melting simultaneously in the Thwaites and Crosson/Dotson basins leads to widespread deglaciation that is much greater than the sum of its parts. This retreat is driven by a feedback between the ice fluxes crossing the basin boundary. We also conduct further experiments to determine the melt rates or additional processes required to trigger retreat of Thwaites Glacier in isolation. The results of our experiments support the suggestion that the Thwaites ice shelf provides limited buttressing, while also demonstrating that Thwaites is still vulnerable to retreat via other pathways.