The ice sheets of Greenland and Antarctica are losing ice at accelerating rates, much of which is a response to oceanic forcing, especially of the floating ice shelves. Recent observations establish a clear correspondence between the increased delivery of oceanic heat to the ice-sheet margin and increased ice loss. In Antarctica, most of these processes are reasonably well understood but have not been rigorously quantified. In Greenland, an understanding of the processes by which warmer ocean temperatures drive the observed retreat remains elusive. For both ice sheets, multiple challenges remain before the fully coupled ice-ocean-atmosphere models needed for rigorous sea-level projection are available. 

Schematic illustration of the ocean processes influencing ice shelves and outlet glaciers that are described in the main text. Melting beneath Antarctic ice shelves occurs through a combination of three processes. The first occurs where dense, high-salinity shelf water is formed near the ice-shelf front during winter sea-ice growth. Although this water is at the surface freezing point, it can melt ice when it sinks to depths because it is above the local pressure melting point. The second occurs where tidal mixing moves seasonally warmed near-surface ocean water beneath the shelf front. Both of these processes are active for ice shelves with cold cavities. In contrast for warm ice shelf cavities, melting is dominated by the presence of a subsurface, warm water mass (CDW), originating from the Antarctic Circumpolar Current (ACC). Ocean melting of Greenland outlet glaciers is driven by analogous warm waters, namely the IW along the western and southeastern coasts and AW elsewhere. Both of these subsurface water masses originate with the North Atlantic Current (NAC). Where melting occurs, the buoyancy of the resulting melt-water plume produces positive feedback driving further melt (Joughin et al., 2012).

Reference:

Joughin, I., Alley, R. B., and Holland, D. M. (2012). Ice-Sheet Response to Oceanic Forcing

Science, vol. 338, no. 6111, pp.1172–1176. DOI: 10.1126/science.1226481

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Contact person for the above posting: Dr. Alvarinho J. Luis (alvluis@ncaor.org)