Regime shift of Filchner-Ronne Ice Shelf cavity remains reversible

The cavity underneath the second largest ice shelf in Antarctica, the Filchner-Ronne Ice Shelf, could flip under strong climate warming from its current 'cold' state into a 'warm' state (Hellmer et al., 2012). Numerical models show that this regime shift occurs relatively abrupt, within a decade, with sub-shelf melt rates increasing 21-fold (Naughten et al., 2021). The increase in melting will reduce the ice shelfs buttressing capacity, thereby driving grounded ice loss, and a contribution to sea-level rise. Moreover, changes in sub-shelf melting, and the cavity geometry, in turn, can influence the ocean circulation, creating feedbacks that only emerge when considering the ice and ocean systems together. It is unclear, how these feedbacks influence the regime shift and subsequent evolution of the system, as well as a potential reversibility of the cavity. Here we run regional, numerical simulations of the coupled ice sheet and ocean system to investigate the role of ice-ocean feedbacks on the ocean regime shift, its reversibility, and the impact on ice sheet dynamics. We find that while sub-shelf melt rates increase only half as much as in the coupled system due to the geometric changes, the feedbacks do not influence a reversibility of the regime shift that we find in our simulations. Importantly, the reversal occurs more gradual than the 'cold' to 'warm' flip, and meanwhile the ice sheet continues losing ice and retreating. Our results imply that melt rate projections are ideally conducted in a coupled system, however, the regime shift and reversal of Filchner-Ronne cavity appears to be controlled by local atmospheric conditions, and is not qualitatively influenced by ice-ocean feedbacks.