Basal Melting Variability of the Ross Ice Shelf From Mixing Ratios of Simulated Water Masses (1993–2018) and Potential Climatic Drivers

Several water masses circulate under the Ross Ice Shelf (RIS), the largest ice shelf in Antarctica, each causing basal melting with a specific spatio-temporal pattern. To investigate these patterns and their variability, we applied a mixing ratio analysis to simulated water masses from a new numerical ocean model of the Ross Sea. The simulation, which was run over 26 years (1993–2018) and which includes the RIS cavity, shows good agreement with seaborne and mooring observations. The total RIS basal melt rate is 90 Gt/yr on average, and is caused mostly by High Salinity Shelf Water (HSSW) (68%), which enters the western portion of the RIS cavity. In the eastern RIS, relatively warm modified Circumpolar Deep Water (mCDW) intrudes below a small portion of the RIS front, causing 25% of the total melting. Mainly near the Ross Island region, Antarctic Surface Water (AASW) is advected under the RIS, causing a small percentage (7%) of melting. A strong seasonal cycle is present in basal melting for all water masses. Melting by HSSW is stronger in winter, when salinification due to sea ice production is larger. By contrast, in the summer, reduced density gradients along the RIS front allow stronger intrusions of mCDW and AASW. Interannual variability is large for mCDW and AASW. Melting caused by HSSW shows decadal variability, mostly related to the salinity of HSSW, which is impacted by sea ice import from the Amundsen Sea and sea ice production in local polynyas, both potentially affected by Pacific teleconnections.