On the Multiscale Oceanic Heat Transports Toward the Bases of the Antarctic Ice Shelves

Abstract

The mass balance of the Antarctic Ice Sheet (AIS) is important to global sea-level change. The AIS loses mass mainly through basal melting and subsequent calving of the Antarctic ice shelves. However, the simulated basal melting rates are very uncertain in ice sheet models, partially resulting from the poor understanding of oceanic heat transports. In this article, we review the recent progress in understanding and simulating such heat transports. Regulated by major circulation features, Circumpolar Deep Water (CDW) is much closer to the Bellingshausen–Amundsen Seas and the Cooperation Sea (60°E to 90°E) and the sector further east to 160°E. The ice shelves within these sectors are experiencing enhanced basal melting resulting from tropical forcing and intensified westerlies. Around West Antarctica, the isopycnal structure favors the delivery of CDW across slopes and shelves, while around East Antarctica, the persistent and strong westward Antarctic Slope Current (Front) acts to prevent warm-water intrusion. Both eddies and troughs favor heat transport to the fronts of the ice shelves and even into the cavities. The sharp contrast between the water column thicknesses on both sides of ice shelf fronts blocks the barotropic inflows and can excite topographic Rossby waves. Inside the cavities, the heat fluxes to the bases of the ice shelves are controlled by the cavity geometry, the circulations in the cavities, and the properties of the water masses beneath the ice shelves. Limited direct observations of cavities have promoted the development of various models. To improve basal melting simulations, meltwater plume models have been developed to study meltwater-laden mixed layer dynamics by increasing the vertical resolution, with recent advanced studies considering the vertical structures of frazil ice concentration and velocity. To reduce the uncertainties in the simulated and projected basal mass loss of the Antarctic ice shelves, future efforts should be devoted to improving the bathymetry and cavity geometry, investigating small-scale processes and parameterizing these processes in coupled climate–ice sheet models, and quantifying the feedback from the mass loss of the AIS.

Ice shelf basal channel shape determines channelized ice-ocean interactions

“…Specifically, the turbulent mixing of heat and salt across the ice–ocean boundary layer and across the pycnocline separating GMW and ambient ocean control the melting-induced cooling and freshening and the entrainment-induced warming and salinization, respectively, of the boundary flows. These processes depend intrinsically on resolving the details of the vertical stratification and shear 31 , 32 . This cannot be achieved in depth-integrated plume models, in which physical quantities are assumed to be vertically uniform across the plume and discontinuous at its edges (ref.…”