Sea ice, atmosphere and upper ocean variability in the Weddell Sea, Antarctica

A frequency domain singular value decomposition is performed on 20 years (1 979-1998) of monthly sea ice concentration, sea ice drift and sea level pre ssure data in the Weddell Sea, Antarctica. Interannual oscillations with pe riods of around 3-4 years are found to dominate the variability in this reg ion. Anomalous atmospheric patterns periodically reach the 'Weddell Sea fro m the west and perturb the sea ice circulation and distribution in the Wedd ell Gyre through changes in the intensity and direction of the climatologic al winds. Sea ice accumulates in the southeastern Weddell Sea every 3-4 yea rs owing to two atmospherically driven processes: (1) weak ice export to th e north due to a weak northward branch of the gyre (driven by weak southerl y winds) and (2) large ice import from the east due to a strong East Wind D rift (driven by strong easterly winds along the coast). The opposite situat ion gives rise to a depletion of sea ice in the same region half a cycle la ter. Sea ice anomalies are then advected north-northeastward before turning eastward in the gyre circulation. The eastward propagation of ice anomalie s along the ice margin accounts for the passage of the Antarctic Circumpola r Wave through the Atlantic sector of the Southern Ocean. A low frequency s ignal is also detected in the Weddell Sea variations, albeit rather specula tively in this 20-year-long record. Sea ice variability on this timescale a ppears to be associated with a change in the shape and characteristics of t he Weddell Gyre circulation around 1990. This mode of variability implicate s feedbacks between the gyre and Weddell Deep Water temperature variations, whose impact is observed near the Maud Rise topographic feature.