Subthermocline Countercurrents in the Western Equatorial Atlantic Ocean

Abstract In each hemisphere of the Atlantic, a permanent countercurrent (eastward flow) having a core about 4.5° from the Equator is present in the subthermocline layer from 80 to 200 cl t−1 (centiliters per metric ton). Although currents along the Brazilian coast supply water to the countercurrents, much of the flow in each seems to be internal to the anticyclonic region on its equatorward side. West of 25°W, the region considered here, the south countercurrent is covered largely by westward flow, has a mean width of 209 km, and a mean geostrophic transport of 15 × 106 m3 s−1. The north countercurrent often lies below eastward flow, but its core is marked by a subthermocline velocity maximum and a path differing from that of the navifacial core. Between about 50 and 40°W, available data indicate a mean transport of 9 × 106 m3 s−1 in February–April and 26 × 106 m3 s−1 in July–September, a significant annual variation. From 40 to 28°W, roughly, evidence for a permanent subthermocline countercurrent is stro...