Antarctic Circumpolar Current
The Antarctic Circumpolar Current (ACC) is a major eastward flowing current that circles the globe in the Southern Ocean. It is principally driven by surface wind stress, although there is a significant thermohaline circulation component that is not well understood. In the way of vorticity dynamics a simple Sverdrup balance with dissipative mechanisms of form drag by bottom topography and lateral dissipation in western boundary layers has been found consistent with the data. The present best estimates of its transport through Drake Passage give a net mean transport of 125 Sv (with a standard deviation of 10 Sv) above 2500 metres.
Schematic diagram of the Antarctic Circumpolar Current. The transport of the ACC is concentrated in two current cores separated by a transition zone with surface water characteristics intermediate between those found to the south in the Antarctic Zone and to the north in the Subantarctic Zone, with the transition zone being known as the Polar Frontal Zone. The maximum geostrophic surface speeds in these cores have been calculated as 25-45 cm s−1 in Drake Passage.
There is also considerable mesoscale variability in the ACC region due to instabilities causing both cold and warm core rings to be shed. These eddies have been found to have spatial scales varying from 30 to 100 km, surface velocities typically 30 cm s−1 or greater, and are vertically coherent from surface to bottom. The regions of highest variability have been found to be correlated with prominent topographic features on the sea floor.
The ACC is a region of complicated and large meridional heat flux, with a mean ocean heat loss to the south estimated at about 0.45 petawatts due to ocean-atmosphere heat exchange and equatorward Ekman transport. This is thought to be balanced by the import of heat via eddy processes and deep boundary currents, although the proportions are known only vaguely as yet.
See Also
- Antarctica Collection of the Encyclopedia of Earth
- Amundsen Sea
- Bellingshausen Sea
- Ross Sea
- Scotia Sea
- Weddell Sea
References
- Peter Saundry. 2011. Seas of the world. Topic ed. C.Michael Hogan. Ed. C.Michael Hogan Encyclopedia of Earth
- Worth D. Nowlin, Jr. and John M. Klinck. The physics of the Antarctic Circumpolar Current. Rev. Geophys. Space Phys., 24:469–491, 1986.
