Modelling the evolution of Thwaites Glacier over the 20th century

Thwaites Glacier is rapidly evolving and could make large sea-level contributions in the coming centuries, making it essential to understand the drivers of the ongoing ice loss. Sediment core analysis suggests that Thwaites Glacier was in a relatively quasi-steady state for millennia before its western pinning point ungrounded in the 1940s. We use the MITgcm-WAVI coupled ocean-ice sheet model to create example quasi-steady pre-1940s configurations for Thwaites Glacier, including a most plausible pre-1940s state, finding that healing the damaged ice shelf is necessary to achieve this. Next, we trigger ice retreat and highlight key processes as the model evolves into the present-day configuration, including ice damage, pinning-point ungrounding driven by ocean melting, and ice piracy between eastern and western Thwaites Glacier. By conducting reversibility experiments during the retreat, we find that multiple quasi-steady ice-sheet states are possible under the same ocean forcing, demonstrating the importance of feedbacks and possible tipping points in the system. Either ice damage or increased ocean forcing can eliminate these quasi-steady states, prompting retreat, as observed today.