Summary
An air-borne radio echo sounding survey was conducted over the Amery Ice Shelf, East Antarctica, in December 2003. Nine transverse profiles were obtained approximately normal to the flow direction, together with one longitudinal profile for a total length of flight lines of about 1000 km. We determined the spatial distribution of the characteristics of the RES signal returned from the ice-water interface at the base of the shelf. The key characteristics are described by the amplitude of the echo and the slope of the leading edge of the returned pulse. For the mass flux we use ice thickness values extracted from our RES data, and velocities derived from InSAR maximum coherence tracking in pairs of Radarsat SAR images, with control provided by surface measurements. We calculate the mass budget for a set of discrete areas bounded by our RES survey lines across the shelf, and flow-lines derived from the velocity field (modified in the across shelf components of the velocity) and from linear flow-features identified in satellite images. Using available estimates of the snow accumulation rate at the upper surface, and assuming the ice thickness and velocity fields are stationary in time, we attribute the mass imbalance within a sub-area to be the result of melt or freeze at the base of the shelf.