Reversibility experiments of present-day Antarctic grounding lines: the short-term perspective

The stability of the grounding lines of Antarctica is a fundamental question in glaciology, because current grounding lines in some locations are at the edge of large marine basins, and have been hypothesized to potentially undergo irreversible retreat in response to climate change. This could have global consequences and raise sea levels by several metres. If the Antarctic grounding lines in their current configuration are close to being unstable, a small change in external forcing, e.g. a reduction in ice shelf buttressing resulting from an increase in ice shelf melt rates, would lead to continued retreat of the grounding line due to the marine ice sheet instability hypothesis, even after the melt perturbation is reverted. Alternatively, if the system state reverts to its previous value after the perturbation is removed, we can consider the current grounding line positions to be reversible. 

Here, we initialise the ice sheets models Úa and Elmer/Ice to closely replicate the current configuration of the Antarctic Ice Sheet, in particular, the current position of the grounding lines. Under control conditions, state fluxes and ice volume changes are forced to be in balance. Using these quasi-steady state ice sheet configurations, we apply a small amplitude perturbation in ice shelf melt rates by imposing an increase for 20 years in the far-field ocean temperature. After 20 years the melt rate perturbation is returned to zero, and model simulations are continued for a further 80-year recovery period. During this recovery period we examine the trend in ice flux and grounding line position, i.e. do they tend towards their previous values, or do they move further away from their initial state? Our results suggest that the global grounding line around Antarctica begins to reverse to its former state after the perturbation is removed. However, we find the reversibility and response times of grounding lines to a small perturbation in ice shelf buttressing varies between individual basins across the ice sheet.

This work is part of the TiPACCs project and complements an overview presentation on the reversibility of present-day Antarctic grounding lines (EGU22-5176) as well as a presentation exploring long-term reversibility experiments (EGU22-7885).