| Summary: | Historical hydrographic data from the Southern Ocean are projected into a baroclinic stream function space, generating a three-dimensional gravest empirical mode (GEM) that explains more than 97% of the total density and temperature variance in the Antarctic Circumpolar Current (ACC) region. An analysis of the ACC fronts and frontal water masses in this streamfunction space shows that both the Subantarctic Mode Water and the Antarctic Intermediate Water are formed by along-isopycnal subduction of polar surface water in the southeast Pacific. The method is then used to calculate the heat flux by the ACC mean flow, showing the primary heat sources for the ACC system are two western boundary currents, the Brazil Current and the Agulhas Current. The mean flow carries 0.14 PW poleward heat flux across 56°S and 0.08 PW across 60°S. The study suggests that traditional methods based on air sea flux integration may include large uncertainty. Combining this streamfunction method with empirical orthogonal function (EOF) analysis, we identify a large-scale low-frequency thermohaline variation in the ACC south of Australia, which we call the pulsation mode and hypothesize that it is related to the ACC barotropic transport and is a response to the large-scale wind stress variation.
|
|---|