Ocean warming around Antarctica has the potential to trigger marine ice-sheet instabilities. It has been suggested that abrupt and irreversible cold-to-warm ocean tipping points may exist, with possible domino effect from ocean to ice-sheet tipping points. A 1/4° ocean model configuration of the Amundsen Sea sector is used to investigate the existence of ocean tipping points, their drivers, and their potential impact on ice-shelf basal melting. We apply idealized atmospheric perturbations of either heat, freshwater or momentum fluxes, and we characterize the key physical processes at play in warm-to-cold and cold-to-warm climate transitions. Relatively weak perturbations of any of these fluxes are able to switch the Amundsen Sea to an intermittent or permanent cold state, i.e., with ocean temperatures close to the surface freezing point and very low ice-shelf melt rate. The transitions are reversible, i.e., cancelling the atmospheric perturbation brings the ocean system back to its unperturbed state within a few decades. All the transitions are primarily driven by changes in surface buoyancy fluxes over the continental shelf, as a direct consequence of the freshwater flux perturbation, or through changes in net sea-ice production resulting from either heat flux perturbations or from changes in sea-ice advection for the momentum flux perturbation. These changes affect the vertical ocean stratification and thereby ice-shelf basal melting. For warmer climate conditions than presently, the surface buoyancy forcing becomes less important as there is a decoupling between the surface and subsurface layers, and ice-shelf melt rates appear less sensitive to climate conditions.
