Ocean cavity regime shift reversed West Antarctic grounding line retreat in the late Holocene

Abstract Holocene climate variations were relatively modest compared to the preceding deglaciation and anthropogenic climate change. Yet recent geologic evidence suggests that the grounding line of the Siple Coast of the West Antarctic Ice Sheet (WAIS) retreated hundreds of kilometers beyond its present position during the middle to late Holocene (7.5 to 2.0 ka) and readvanced within the past 2.0 ka. The extent to which these substantial ice sheet changes were driven by climatic or non-climatic processes is debated. The inferred retreat and readvance have been attributed to both changing rates of isostatic rebound and regional climate change. We test these two hypotheses using a proxy-informed ensemble of ice sheet model simulations with varying ocean thermal forcing, global glacioisostatic adjustment (GIA) model simulations, and coupled ice sheet-GIA simulations that consider the interactions between these two processes. Our results indicate that a regime shift from a warm to cold ocean cavity due to increased polynya efficiency in the Late Holocene is the most likely cause of this past grounding line migration. This implies that the Siple Coast grounding line is sensitive to future changes in the Ross Sea polynya and sub-ice shelf ocean circulation.