Coastal Easterly Winds Impact Transport into Antarctic Ice Shelf Cavities

Abstract Intrusions of modified Circumpolar Deep Water (mCDW) onto sections of the Antarctic continental shelf can be steered by troughs and directly enter ice shelf cavities, enhancing ice shelf basal melting. This process-oriented modeling study demonstrates that easterly winds and polynya activity can modify the coastal circulation and interrupt the direct inflow of mCDW from the trough to the ice shelf cavity, so that the flow into the cavity is instead supplied by cooler waters from the ambient continental shelf. The signature of this switched intrusion pathway is a density front at the ice shelf edge, referred to here as the Ice Shelf Edge Front (ISEF), in thermal wind balance with a prominent westward current that redirects the onshore flow of mCDW. We derive an analytical scaling for the strength of the ISEF to confirm that downward Ekman pumping by coastal easterly winds provides the dominant control on the ISEF and therefore heat transport into the ice shelf cavity. Our results emphasize that local interactions between ice, ocean, and atmospheric processes can have major impacts on ice shelf basal melting and the stability of the Antarctic Ice Sheet. Significance Statement To better project the impacts of a changing climate, it is important to understand the physical processes that drive the rapid melting of the West Antarctic ice shelves. The present study demonstrates that strong coastal easterly winds can alter the oceanic circulation at the edge of an ice shelf and interrupt the flow of warmer water from the open ocean into the cavity beneath the ice shelf. This mechanism may explain the reduced melting of West Antarctic ice shelves in recent decades via the intensification of coastal easterly winds. However, because such winds are expected to weaken over the next century, the easing of this mechanism may cause the same ice shelves to become less stable.