Measuring the basal melt rate of Antarctic ice shelves using GPS and phase-sensitive radar observations

Basal melting of Antarctica’s floating ice shelves accounts for between 15 and 35% of the total mass loss from the ice sheet and helps to precondition the shelf waters for deep convection. Despite this pivotal role in ice sheet-ocean interactions, there are only a handful of measurements of actual melting rates. Almost all published figures are of steady state melt rates; that is, the melt rate required to maintain the ice shelf in a state of equilibrium, deduced from the residual of the other mass balance terms. Such observations have obvious limitations, such as the impossibility of determining the role of basal melting in driving ice shelf thinning or retreat. Over the past two Antarctic field seasons we have conducted a series of experiments to measure the actual melt rate at various locations on George VI and Filchner-Ronne ice shelves. The key to our technique is a precise measurement of the ice shelf thinning rate, by phase-sensitive radar. The thinning rate can be partitioned between vertical strain and melting without the need to assume that the ice shelf is in equilibrium, given contemporaneous measurements of the vertical strain rate.

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