Large‐scale relative dynamic topography of the Southern Ocean

Abstract

The large‐scale or climatic distribution of relative dynamic topography south of 30°S using a selective set of hydrographic stations indicates significant deviations from a purely latitudinal dependence of the isopleths. The geostrophic flow relative to 1000‐dbar level shows the Antarctic Circumpolar Current to vary greatly in its intensity and latitude during its course around Antarctica. High‐intensity flow occurs over the northern slope of the midocean ridge from 105°E eastward to the fracture zones near 145°W, significant perturbations being introduced in the vicinity of the Macquarie Ridge and Campbell Plateau. A strong expression of the Antarctic Circumpolar Current is found in the Drake Passage downstream of weak baroclinicity in the southeast Pacific. East of the Drake Passage strong meridional trends of the dynamic height isopleths occur with significant latitudinal offset (about 1100 km) of the main axis of geostrophic flow. In the southwest Indian Ocean, maximum baroclinicity is associated with the Agulhas Return Current near 40°S rather than the more continuous branch of Circumpolar flow to the south near 50°S. The two axes may combine east of Kerguelen Island. The dynamic height anomaly to the south of the main circumpolar current indicates the presence of weak baroclinic gyres in the western Weddell Basin and to the north and northeast of the Ross Sea and much meridional trend of the isopleths over the south eastern flank of the Kerguelen Plateau. North of the main circumpolar flow dynamic height anomaly also indicates weak baroclinicity, though a relatively strong axis of northward geostrophic flow occurs over the eastern flank of Campbell Plateau.