Sea surface temperature variability along the path of the Antarctic circumpolar current

The spatial and temporal distribution of sea surface temperature (SST) anomalies in the Antarctic Circumpolar current (ACC) is investigated, using monthly data from the NCEP-NCAR Reanalysis for the period 1980-2004. Patterns of atmospheric forcing are identified in observations of sea level pressure and air-sea heat fluxes. It is found that a significant fraction of SST variability in the ACC can be understood as a linear response to surface forcing by the Southern Annular Mode (SAM) and remote forcing by ENSO. The physical mechanisms rely on the interplay between atmospheric variability and mean advection by the ACC. SAM and ENSO drive a low-level anomalous circulation pattern localized over the South Pacific, inducing surface heat fluxes (Fs) and Ekman heat advection anomalies (Fek). A simple model of SST propagating in the ACC, forced with heat fluxes estimated from the Reanalysis, suggests that Fs and Fek are equally important in explaining the observed SST variability. Further diagnostics indicate that SST anomalies, generated mainly upstream of Drake Passage, are subsequently advected by the ACC.