Atlantic South Current

Surface warmth and cold water from the far south overlap in the South Atlantic. The subtropical gyre is anti-cyclonic and turns counter-clockwise, carrying South Atlantic Central Water across the broad basin between South America and Africa. Antarctic Intermediate Water forms in the upper circumpolar region near the Drake Passage and the Falkland Islands and adds a cooler intermediate layer. Both systems receive some contribution from the Indian Ocean, and North Atlantic Deep Water travels south below the subtropical thermocline.

These water masses interact with a seabed divided by major ridges. The Mid-Atlantic Ridge follows the spreading boundary between the South American and African plates and separates eastern and western basins. Its long course is interrupted by transform faults, including the Romanche and Gibbs fracture zones, through which bottom water can move. Secondary transverse ridges divide the floor further, while the Walvis Ridge and Rio Grande Rise form substantial barriers to currents.

Geologically, the South Atlantic opened when West Gondwana broke apart in the Early Cretaceous. The separation of South America and Africa left matching continental margins and created the basin then crossed by layered water masses. Surface winds drive the gyre, the Ekman layer partly masks its deeper motion, and cold intermediate water enters near the southern gateway. Together these layers make the South Atlantic a meeting place of tropical circulation, polar origin water and deep Atlantic return flow.