Tidal forcing on sea-ice drift and deformation in the western Weddell Sea in early austral summer, 2004

Sea-ice drift and deformation in the western Weddell Sea in early austral summer of 2004 are characterised using in situ data from a meso-scale array of 24 drifting ice buoys. Horizontal GPS-derived position measurements are available from drifting buoys deployed as part of the Ice Station POLarstern [ISPOL] experiment for 26 days during late November and December 2004, at various temporal resolutions and spatial accuracies. These data form the basis for sea-ice velocity and deformation measurements across the meso-scale ISPOL array and at two remote sites. Analysis of the sea-ice velocities reveals coherence for sea-ice drift at separations of less than 70 km; and a correlation length scale of 60 km. Within the limits of the ISPOL array, at larger separations zonal ice drift remains correlated, while meridional ice drift becomes uncorrelated. This together with the east–west gradient in ice velocities indicates the influence of bathymetry, via tidal forcing, on local dynamic processes. Atmospheric forcing also contributes to the sea-ice drift: about 40% of variability in the sea-ice velocity is explained by changes in wind velocity, which is significantly less than other studies have found for the region during winter. Sea-ice deformation has been derived for the overall array and four sub-arrays. There appeared to be no spatial scale dependency of ice deformation, although considerable spatial variability was observed between sub-arrays. The net divergence of the ISPOL array was in excess of 30%, with the largest contributions to divergence being from the southern section and along the eastern side of the overall ISPOL array. Temporal variability for all deformation parameters is dominated by high-frequency (sub-daily) processes, namely tidal forcing and inertial response. Low-frequency (multiple days) processes, including atmospheric changes, played a secondary role in forcing sea-ice deformation during ISPOL.