Atlantic South Current

The southern South Atlantic is both part of the basin’s subtropical circulation and a route for water returning from the North Atlantic. Warm surface movement and cold deep movement occupy different depths across much of the same ocean. This layered structure matters because a current visible at the surface cannot reveal the full path of water below it.

The South Atlantic Gyre is anti-cyclonic and turns counter-clockwise. South Atlantic Central Water originates in this gyre, while Antarctic Intermediate Water forms in the upper circumpolar region near the Drake Passage and the Falkland Islands. Both currents receive some contribution from the Indian Ocean. North Atlantic Deep Water then flows southward beneath the subtropical thermocline, giving the southern Atlantic a key role in the meridional overturning circulation. The water moving south at depth carries the signature of distant northern origin regions.

That circulation crosses a seabed formed by the breakup of West Gondwana in the Early Cretaceous. The Mid-Atlantic Ridge divides the basin lengthwise; transverse ridges divide it into smaller deep basins; and the Walvis Ridge and Rio Grande Rise obstruct currents. Major transform faults allow bottom water to pass through the ridge at particular places. Surface winds, subsurface exchange and the submarine barriers therefore operate together. The southern waters are not merely the warm outer edge of the basin but a junction where upper and deep branches of the Atlantic system overlap.