Atlantic South Current

The South Atlantic reaches toward the circumpolar ocean and exchanges water with it around southern South America. The Drake Passage is a crucial opening in this geography. About fifty million years ago, changes in the relative motion of the South American and Antarctic plates began to open the passage; a shallow gateway appeared first, and a deeper seaway developed between thirty-four and thirty million years ago. The growing connection accompanied climatic cooling and the expansion of the Antarctic ice sheet.

In the later ocean, Antarctic Intermediate Water originates in the upper circumpolar region near the Drake Passage and the Falkland Islands. South Atlantic Central Water comes from the southern subtropical gyre, and both receive some contribution from the Indian Ocean. North Atlantic Deep Water flows southward beneath the subtropical thermocline. These water masses make the southern Atlantic a meeting place for tropical, subpolar and deep origins rather than an isolated basin.

The physical route around the south also passed through bodies of water shaped by earlier continental separation. West Gondwana broke apart in the Early Cretaceous, opening the South Atlantic between South America and Africa. The Mid-Atlantic Ridge continues to mark that spreading boundary, while the Walvis Ridge and Rio Grande Rise obstruct currents. The Drake Passage completes a wider system in which seabed structure, winds and layered circulation determine how the Atlantic connects with the rest of the world ocean.