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

A frequency domain singular value decomposition is performed on 20 years (1979-1998) of monthly sea ice concentration, sea ice drift and sea level pressure data in the Weddell Sea, Antarctica. Interannual oscillations with periods of around 3-4 years are found to dominate the variability in this region. Anomalous atmospheric patterns periodically reach the 'Weddell Sea from the west and perturb the sea ice circulation and distribution in the Weddell Gyre through changes in the intensity and direction of the climatological winds. Sea ice accumulates in the southeastern Weddell Sea every 3-4 years owing to two atmospherically driven processes: (1) weak ice export to the north due to a weak northward branch of the gyre (driven by weak southerly winds) and (2) large ice import from the east due to a strong East Wind Drift (driven by strong easterly winds along the coast). The opposite situation gives rise to a depletion of sea ice in the same region half a cycle later. Sea ice anomalies are then advected north-northeastward before turning eastward in the gyre circulation. The eastward propagation of ice anomalies along the ice margin accounts for the passage of the Antarctic Circumpolar Wave through the Atlantic sector of the Southern Ocean. A low frequency signal is also detected in the Weddell Sea variations, albeit rather speculatively in this 20-year-long record. Sea ice variability on this timescale appears to be associated with a change in the shape and characteristics of the Weddell Gyre circulation around 1990. This mode of variability implicates feedbacks between the gyre and Weddell Deep Water temperature variations, whose impact is observed near the Maud Rise topographic feature.