Atlantic South Equatorial Current

The western edge of the southern equatorial Atlantic lies over the floor of an ocean that expanded northward after West Gondwana broke apart in the Early Cretaceous. The coastlines of South America and Africa once fitted closely together, although later reconstructions require deformation zones and intracontinental rifts to explain the breakup. In the equatorial segment, magnetic anomalies cannot be used for dating as reliably as elsewhere, so the opening of the Equatorial Atlantic Gateway is estimated at roughly 120 to 96 million years ago.

That final phase of separation also coincided with, or contributed to, the end of continental extension in Africa. Below the warm surface in that period, the Mid-Atlantic Ridge marks the boundary where the South American and African plates diverge, producing volcanic rock and new ocean floor.

Most of this long submarine range lies below water, and its rift valley exposes the structure of the spreading system. At the equator, fracture zones interrupt the ridge and create passages that influence the exchange of deep water. The tropical ocean above therefore combines a relatively young human geography of transatlantic travel with a far older record of continental rupture, volcanism, and the gradual establishment of a deep oceanic corridor.