Southern Ocean ice shelf melting in a warming climate

The Antarctic ice sheet loses mass at its fringes bordering the Southern Ocean. At this boundary, warm circumpolar water can override the continental slope front, reaching the grounding line through submarine glacial troughs and causing high rates of melting at deep ice-shelf bases. The interaction between ocean currents, continental bathymetry, and shelf hydrography is thus likely to influence future rates of ice loss. The evolution of basal loss in a warming climate is presented for ten Antarctic ice shelves, based on the output of two coupled ice–ocean models (BRIOS and FESOM) both forced by the IPCC-SRES E1 and A1B scenario-related atmospheric outputs of the HadCM3 and ECHAM5/MPIOM climate models. Projections of future ice shelf basal melting are similar with regard to the scenarios applied but differ substantially between the climate models used, with the HadCM3 output causing the most significant changes in continental shelf temperatures. All ice shelves face a possible increase in basal melting with the biggest changes occurring at the base of the Filchner-Ronne Ice Shelf. A redirection of the coastal current into the Filchner Trough and underneath the Filchner–Ronne Ice Shelf during the second half of the twenty-first century may lead to increased flow of warm open ocean waters into the deep southern ice-shelf cavity. Here, water temperatures can increase by more than 2 oC boosting average basal melting from 0.2 m/yr, or 82 Gt/yr, to almost 4 m/yr, or 1,600 Gt/yr. The analysis of the results suggests that the changes are caused primarily by the freshening of the shelf water masses and an increase in ocean surface stress in the southeastern Weddell Sea, both due to reduced sea ice formation and a thinning of the formerly consolidated sea-ice cover. A projected further increase of ice loss at the base of the Filchner–Ronne Ice Shelf to 2,500 Gt/yr for the year 2199 is caused by a gradual warming of the deep Weddell Sea in FESOM and does not occur in the regional BRIOS simulation