Timescales for Ice Shelf Collapse and MISI Initiation in the Filchner-Ronne Sector

The Filchner-Ronne sector of Antarctica contains a number of deep-bedded ice streams and glaciers potentially vulnerable to the Marine Ice Sheet Instability (MISI).  Previous work has shown that, in a warming climate, the ocean circulation in the cavity underneath the Filchner-Ronne Ice Shelf (FRIS) could switch from its present cold state to an alternate warm mode, in which intrusions of Circumpolar Deep Water (CDW) cause high basal melt rates near the deep grounding lines of potentially vulnerable glaciers.  However, less work has been done on modeling the response of the ice sheet and ice shelf system to such a mode switch in the cavity circulation.  Here, we use the Ice-sheet and Sea-level System Model (ISSM) to simulate the response of the Filchner-Ronne sector of Antarctica over multi-centennial timescales to changes in basal melt rate caused by a mode switch in the cavity circulation.  We force ISSM with both melt rates directly calculated by the cavity-resolving Finite-Element Sea ice-Ocean Model (FESOM) and with parameterized melt rate forcing derived from CMIP6 global models.  We find that parameterized melt rates in high-emissions scenarios cause rapid grounding line retreat at almost all of the major glaciers and ice streams feeding the FRIS beginning in the 22nd century, followed by ice shelf collapse and rapid sea level rise in the 23rd.  Using FESOM simulated melt rates the destabilization of the FRIS sector proceeds more slowly. During the 22nd century retreat is concentrated in specific ice streams, reflecting the more heterogeneous distribution of melt rate in the ocean model as opposed to the parameterized forcing.  In the 23rd century retreat becomes more widespread, culminating in ice shelf collapse and rapid sea level rise in the 24th and 25th centuries.