Role of off‐shelf to on‐shelf transitions for East Antarctic sea ice dynamics during spring 2003

During austral spring 2003, mesoscale sea ice drift and deformation off East Antarctica were investigated using in situ data from a nine‐buoy array. Upon deployment, the array comprised an area of about 4000 km 2 with a mean ice concentration of 96%. Half‐hourly sea ice velocities were coherent across all buoys at zonal (meridional) separations of less than 160 km (70 km). Regional cross‐spectral correlation was high at synoptic scales and also at semidiurnal periods off the continental shelf. Atmospheric synoptic‐scale forcing explained in excess of 85% of the ice drift variability. This is significantly more than found in the Weddell Sea, where significant ice drift variability is derived from oceanic forcing. Peak frequencies of semidiurnal contributions covaried with latitude and are largely associated with the inertial response. Over the continental shelf, coincident diurnal and semidiurnal variances in ice motion arose from tidal forcing. Net divergence over 37 days resulted in an expansion to 270% of the initial area, although regional ice concentration reduced only slightly. High‐frequency processes, namely inertial response and to a lesser degree tidal forcing, dominated the variability of all deformation parameters. In contrast to ice motion, low‐frequency processes played a secondary role in sea ice deformation. This high‐frequency dominance is similar to what has been found in the Weddell Sea, although many observations there were limited to the continental shelf, where tidal processes dominate. Sea ice motion and deformation were not affected by a seasonal transition, nor did the regional ice characteristics show any signal of seasonal change. Instead, local ice dynamics were strongly influenced by bathymetrically dependent processes.