Interaction between ice shelf and ocean in George VI Sound, Antarctica

George VI Ice Shelf floats on warmer water than any other ice shelf in the Antarctic. Profiles of temperature (T) and salinity (S) taken in the vicinity of the northern ice front show a linear T/S dependence confirming a thermodynamic model of melting in Circumpolar Deep Water and indicate that thermohaline convection is the principal mixing process. Oxygen isotope (δ) profiles demonstrate that the melting ice has a δ value of −20%/°° with respect to Standard Mean Ocean Water (SMOW). An integration of accumulation and isotope data over the ice catchment confirms that this is the mean isotope ratio of present‐day accumulation. Since the basal ice is formed from accumulation over several millennia, it is unlikely that there has been any significant net climatic change in the Antarctic Peninsula over this period. Both summer and long‐term measurements show that currents are weak except at the western margin of the northern ice front where a northward jet conveys some 0.05×106 m3 s−1 of water into Marguerite Bay. This leads to a simple circulation model for the northern part of George VI Sound; Circumpolar Deep Water is advected under the ice shelf at depth, upwells transferring heat which melts the ice and then collects in a northward outflow gathered to the west by Coriolis force. The circulation is driven by the melting process which causes the upwelling of warmer water from greater depths. A salt and energy balance shows that the outflow conveys some 16 km3 yr−1 of ice melt. It is inferred from T/S profiles that the northern circulation penetrates at least 160 km south but not so far as the southern ice front in Ronne Entrance. These geographical limits constrain the basal melt to values between 1.1 and 3.6 m yr−1 A calculation balancing accumulation over the catchment with ice losses from the ice shelf predicts a basal melt of 2.1 m yr−1 If the ice shelf is in equilibrium it alone supplies 53 km3 yr−1 of ice melt or about one‐sixth of the total for Antarctica. Tidal height and current measurements both show a highly suppressed M2 tide and the presence of “shallow water” constituents. A nonlinear ice shelf reponse to tidal forcing is suspected.

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