Simulating the impact of an AMOC weakening on the Antarctic Ice Sheet using a coupled climate and ice-sheet model

Abstract. Climate model studies show that a shutdown of the Atlantic Meridional Overturning Circulation (AMOC) reduces northward heat transport into the North Atlantic, which causes an accumulation of heat in the sub-tropical Southern Ocean. The Antarctic Ice Sheet meanwhile has been shown to be particularly susceptible to temperature changes in ocean water flowing into the cavities of its grounded ice shelves. How AMOC-induced modulation of inter-hemispheric heat transport could influence the present-day state of the Antarctic Ice Sheet via a southward propagation of warm anomalies is little studied. As both, the AMOC as well as the West Antarctic Ice Sheet, are classified as climate tipping points, which can trigger irreversible changes in the Earth System, it is highly relevant how both systems interact with each other.

In this study, we simulate for the first time a shutdown of the AMOC in a global climate model interactively coupled to an ice-sheet model for Antarctica. In line with previous studies, an AMOC shutdown causes increased sea-surface temperatures in the Southern Hemisphere along with a small shift in the mid-latitude westerlies. However, Southern Ocean subsurface temperatures, which drive basal melt in Antarctica, do not change in most regions along the Antarctic margin for the first eight centuries post AMOC shutdown. Therefore, we do not find a change in the total Antarctic Ice volume in this time span. At later times, this is followed by a shift towards stronger Ross Sea convection, causing negative subsurface temperature anomalies of −1.4 °C on average. This cooling decreases basal melt in Antarctica, however increased calving balances the ice mass change. Even though our coupling approach strongly simplifies eddy mass and heat fluxes in the Southern Ocean, and does not resolve flows within ice-shelf cavities, our approach is an important first step to systematically investigate Earth-system stability in coupled climate–ice-sheet models.