Satellite altimetry detection of ice shelf-influenced fast ice

Abstract. The outflow of supercooled Ice Shelf Water from the conjoined Ross and McMurdo ice shelf cavity augments fast ice thickness and forms a thick sub-ice platelet layer in McMurdo Sound. Here, we investigate whether the CryoSat-2 satellite radar altimeter can detect the higher freeboard caused by the thicker fast ice and the buoyant forcing of the sub-ice platelet layer beneath. Freeboards obtained from CryoSat-2 were compared with four years of drill hole measured sea ice freeboard, snow depth, and sea ice and sub-ice platelet layer thicknesses in McMurdo Sound in November of 2011, 2013, 2017 and 2018. The spatial distribution of higher CryoSat-2 freeboard concurred with the distributions of thicker ice shelf-influenced fast ice and the sub-ice platelet layer. The mean CryoSat-2 freeboard was 0.07–0.09 m higher over the main path of supercooled Ice Shelf Water outflow, in the centre of the sound, relative to the west and east. In this central region, the mean CryoSat-2 derived ice thickness was 35 % larger than the mean drill hole measured fast ice thickness. We attribute this overestimate in satellite altimeter obtained ice thickness to the additional buoyant forcing of the sub-ice platelet layer. We demonstrate the capability of CryoSat-2 to detect higher Ice Shelf Water influenced fast ice freeboard in McMurdo Sound and the wider application of this method as a potential tool to identify regions of ice shelf-influenced fast ice elsewhere on the Antarctic coastline.