Identifying thresholds of ocean-induced Antarctic ice loss through idealized ice-sheet model simulations

The Antarctic Ice Sheet is currently losing mass through ocean induced melting at the underside of its large ice shelves. In the future, ice shelf cavities could switch from a ‘’cold” to a “warm” state, following a distinct increase in ocean temperatures e.g. by a redirection of coastal currents allowing warm circumpolar waters to access Antarctic grounding lines. With the ice-sheet model PISM, we delineate potential thresholds, at which the Antarctic Ice Sheet could experience ocean-induced non-linear ice loss. To this end, we apply circum-Antarctic ocean temperature perturbations of 1 to 5 K for different durations, ranging from tens to hundreds of years, and analyze the ice-sheet evolution after reversing the forcing over centennial to millennial timescales. Additionally, we perform ice-sheet simulations in which we slowly ramp up our forcing over similar timescales. Using these idealized overshoot scenarios, we analyze when and where critical thresholds that lead to large-scale, irreversible grounding line retreat are crossed.  We assess uncertainties of these thresholds by analysing the initial state uncertainty as well as parametric and structural uncertainties.