Increased Grounding Zone Ice Flux and Dynamic Thinning Creates Vulnerable Regions on George VI Ice Shelf, Antarctic Peninsula

Abstract. George VI Ice Shelf (GVIIS), on the western side of the Antarctic Peninsula, is currently losing mass. Paleo observations suggest that atmospheric and oceanic warming in the early Holocene caused complete loss of the ice shelf, leading to the possibility that modern observed warming can initiate a similar loss. Ice shelf loss is assumed to be, primarily, a direct response to atmospheric and ocean warming through increased hydrofracture and basal melting. Here, however, we consider the hypothesis that increased lubrication of grounded ice is a further contributor to destabilizing the ice shelf, where the lubrication may come from processes such as increased surface meltwater percolating to the base of glaciers or changes in liquid water fluxes across the grounding line. Motivated by the differences in our observation-based strain-induced dynamic thickness change between 2013–2018 along the northern and southern sectors GVIIS which also experiences variable surface melt, we use an ice sheet model to investigate this hypothesis. We find that, as expected, reduced bed friction increases the flow of grounded ice. However, because of the unique ice flow and buttressing features of GVIIS, the increased ice flux across the grounding line also increases compression of the northern GVIIS, which makes it resistant to rifting and hydrofracture. In contrast, the southern GVIIS, which is fed by ice streams sitting on submarine beds, experiences continued divergence. We suggest that the associated strain thinning reduces buttressing of grounded ice, creating a positive feedback of accelerated ice inflow to the southern GVIIS and likely making it more vulnerable to future retreats than the northern sector.