Glaciological and Oceanographic Calculations of the Mass Balance and Oxygen Isotope Ratio of a Melting Ice Shelf

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Abstract
Glaciological estimates of the ice supply to George VI Ice Shelf are obtained by integrating the accumulation over the catchment. The basal melt (or possible shelf thickening) rates for the ice shelf are calculated by balancing the accumulation with calving and melting. We calculate an average equilibrium melt rate for the ice shelf of 2 m a−1. If the ice shelf is in mass balance it alone provides 53 km3a−1melt from its base compared to a total for Antarctica of only 320 km3a−1.The mean oxygen isotope composition of recent accumulation on the catchment is determined by using accumulation and isotope data, supplemented by temperature measurements and a close empirical relationship between isotope ratio and temperature. The catchment has a mean isotope ratio of −20.8‰ relative to SMOW.Oceanographic work has previously shown that the sea-water under the ice shelf at the north of George VI Sound is Warm Deep Water modified by melting ice. The melting ice has an isotope ratio of −20.3‰. The good agreement in isotope ratios suggest that the melting ice is from the catchment and because the basal ice of George VI Ice Shelf represents accumulation over the last few millennia the implication is that there has been no systematic change in the isotope composition of the accumulation during this period. This implies no secular change in either the elevation or the climatic temperature of this part of the ice sheet.