Variability of the Shelf Circulation Around South Georgia, Southern Ocean

Abstract

A high-resolution ocean model is used to characterize the variability of the shelf circulation and cross-shelf transport around the South Georgia island (SG). The time-mean shelf circulation consists of a counterclockwise flow with a net onshelf mass flow in the south and a net offshelf mass flow in the north. In the south, the cross-shelf exchanges show a two-layer structure with an offshelf flow below 350 m and onshelf flow above. In the north, the cross-shelf exchanges show a three-layer structure with the onshelf flow found only between 350 and 50 m. Correlation analysis shows that winds and the Southern Antarctic Circumpolar Current Front (SACCF) current modulate the variability of the shelf circulation and cross-shelf transport. Local wind stress is significantly correlated with the coastal currents, mid-shelf jet, and cross-shelf transports in the upper layer, while the SACCF modulates the shelf and cross-shelf transports in the southwestern shelf. Likewise, an Empirical Orthogonal Function analysis indicates that the first mode of shelf circulation variability is highly correlated with the SACCF, while the second mode is explained by the local wind stress and significantly correlated with the Antarctic Oscillation. The El Niño Southern Oscillation does not significantly contribute to the shelf circulation but is significantly correlated with the surface temperature variability. The atmospheric teleconnection drives changes in local heat flux, such that warm El Niño conditions over the equatorial Pacific are associated with a cooling of the SG waters. This superposes local signals onto temperature anomalies advected from upstream in the ACC found in previous studies.