Antarctic Circumpolar Current - Structure

Structure

The ACC connects the Atlantic, Pacific and Indian Ocean basins, and serves as a principal pathway of exchange between these basins. The current is strongly constrained by landform and bathymetric features. To trace it starting arbitrarily at South America, it flows through the Drake Passage between South America and the Antarctic Peninsula and then is split by the Scotia Arc to the east, with a shallow warm branch flowing to the north in the Falkland Current and a deeper branch passing through the Arc more to the east before also turning to the north. Passing through the Indian Ocean, the current is split by the Kerguelen Plateau in the Indian Ocean, and then moving northward again. Deflection is also seen as it passes over the mid-ocean ridge in the Southeast Pacific.

The current is accompanied by a number of fronts. The northern boundary of the ACC is defined by the northern edge of the Subantarctic Front, this being the most northerly water to pass through Drake Passage and therefore be circumpolar. Much of the ACC transport is carried in this front, which is defined as the latitude at which a subsurface salinity minimum or a thick layer of unstratified Subantarctic Mode Water first appears, allowed by temperature dominating density stratification. Still further south lies the Polar front, which is marked by a transition to very cold, relatively fresh, Antarctic Surface Water at the surface. Here a temperature minimum is allowed by salinity dominating density stratification, due to the lower temperatures. Further south still is the Southern Antarctic Circumpolar Current Front (SACCF), which is determined as the southernmost extent of Circumpolar Deep Water (temperature of about 2°C at 400m). This water mass flows along the shelfbreak of the western Antarctic Peninsula and thus marks the most southerly water flowing through Drake Passage and therefore circumpolar. The bulk of the transport is carried in the middle two fronts. The total transport of the ACC at Drake Passage is estimated to be around 135 Sverdrups (135,000,000 m³/s), or about 135 times the transport of all the world's rivers combined. There is a relatively small addition of flow in the Indian Ocean, with the transport south of Tasmania reaching around 147 Sv, at which point the current is probably the largest on the planet.