Cold Ocean Cavity and Weak Basal Melting of the Sorsdal Ice Shelf Revealed by Surveys Using Autonomous Platforms

Basal melting of ice shelves is inherently difficult to quantify through direct observations, yet it is a critical factor controlling Antarctic mass balance and global sea-level rise. While much research attention is paid to larger ice shelves and those experiencing the most rapid change, many smaller, unstudied ice shelves offer valuable insights. Here, we investigate the oceanographic conditions and melting beneath the Sorsdal ice shelf, East Antarctica. We present results from the 2018/2019 Sorsdal deployment of the University of Tasmania's autonomous underwater vehiclenupiri muka. Oceanography adjacent to and beneath the ice shelf front shows a cold and relatively saline environment dominated by Winter Water and Dense Shelf Water, while bathymetry measurements show a deep (similar to 1,200 m) trough running into the ice shelf cavity. Two multiyear deployments of Autonomous Phase-sensitive Radar Echo Sounders on the surface of the ice shelf show weak melt rates (average of 1.6 and 2.3 m yr(-1)) with low temporal variability. These observations are supported by numerical ocean model and satellite estimates of melting. We speculate that the presence of a similar to 825 m thick (350 m to at least 1,175 m) homogeneous layer of cold, dense water blocks access from warmer waters that intrude into Prydz Bay from offshore, resulting in weak melt rates. However, the newly identified trough means that the ice shelf is vulnerable to any decrease in polynya activity that allows warm water to enter the cavity. This could lead to increased basal melting and mass loss through this sector of Antarctica.