Transition to a much warmer climate for the global ocean and Antarctic Ice Sheet coupled system, and its reversibility

Abstract. In Antarctica, two plausible tipping points have been suggested: an ocean tipping point involving a cold-to-warm transition of ice shelf cavities, and an ice sheet tipping point associated with the marine ice sheet instability. This study explores the existence of such tipping points at the scale of Antarctica, using a coupled ocean–ice-sheet model. We first apply and then remove an abrupt perturbation to the ocean, instantaneously switching the atmospheric forcing to high-end 23rd century conditions, which shifts all ice shelf cavities of Antarctica to warm conditions. Our findings reveal that Antarctic continental shelf waters rapidly warm, leading to a regime shift with increased ice shelf melt rates, significant ice shelf thinning, and retreat of ice sheet grounding lines. The ocean conditions reverse over a few years when the atmospheric perturbation ceases, while the ice sheet’s response is much slower. Some regions of East Antarctica show signs of ice sheet reversibility over several centuries. In contrast, we identify 14 ice streams, primarily in the Ross, Amundsen, Filchner, Ronne, and Dronning Maud Land basins, that still undergo irreversible retreat several centuries after the removal of the perturbation.