Model-inferred upper ocean circulation in the eastern tropics of the North Atlantic

Model experiments with two different wind forcings were carried out to estimate the transports across 12°N, an approximate gyre central latitude. The time-averaged transport for densities lower than σ1=32.3 and to the east of 35°W is around 4 Sv northward, about one-third of the basin-wide net value which measures the Meridional Overturning Circulation. The near-surface layer accounts for about 3 Sv, and the Central Water for more than 1 Sv, in keeping with the presence of South Atlantic Central Water in the tropical eastern basin. The eastern basin near-surface flow is lowest in summer, when the trade winds nearly vanish at this latitude. In this season the NECC, though having entered its phase of intensification, leaves the region of positive wind stress curl, and temporarily does not act as the tropical gyre southern limb. At the subsurface, most of the NEUC folds up westward at ∼10°N in winter, thus forming an inner circulation of the basin-wide gyre, previously reported from observations. The cyclonic flow associated with the Guinea Dome is another inner circulation, which the model found to be permanent below the surface down to 400-500 m, but masked in the Ekman layer, except in summer.