On the sensitivity of the Antarctic Ice Shelves to a Warming Ocean

The underside of ice streams flowing from the Antarctic continent typically melt into the ocean where they cross the grounding line and begin to float as ice shelves and ice tongues. Melting is governed by the transport of ocean heat and by the seawater freezing point dependence on pressure. The resulting melt water participates in the ventilation of the deepest parts of the ocean. Here, we calculated bottom melt rates of > 25 of the largest glaciers in Antarctica, combining satellite radar interferometry with other data, and compared the results with thermal forcing from the ocean. Melt rates are calculated close to grounding lines of deep-draft glaciers because discharge of continetal ice is principally controlled by these glaciers, and because these regions are the locus of high bottom melting. The bottom melt rates ranges from < 4m/yr to > 40 m/yr. The wide range of values is consistent with limited prior studies, and stems from different groudning line drafts and sea water temperatures. The melting rate is postively correlated with thermal forcing, increasing by 1 meter per year for each 0.1° rise in ocean temperature. Those results have important consequences for modelling studies of the evolution of Antarctica in a warming climate and for the analysis of observations of cryospheric changes from satellites: 1) the inferred rates are much higher than used in modelling studies, which often assume melting to be uniform over the entire ice shelf area, and henceforth underestimate the impact of thermal forcing of the ocean on the ice sheet evolution; 2) The potential impact of bottom melting on short-term ice sheet stability is greatest in regions where deep water has access to glacier grounding lines, e.g. the south-east Pacific-west Antarctic Sector, but also sectors of East Antarctica; 3) Ocean temperature seaward of Antarctica's continental shelf break have risen 0.2° over recent decades, enough to account for the rapid thinning of ice shelves in the western Amundsen sea, which may play an essential role in the observed flow acceleration and mass loss of their nourishing glaciers. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory and at the University of Columbia, under a contract with the Cryospheric Science Program of the National Aeronautics and Space Administration.