Wind stress forcing in a narrow tropical western boundary continental shelf: Northeastern Brazil

Abstract

Current and wind time series observed in the continental shelf of Northeastern Brazil (approximately 11oS), are analyzed, together with hydrographic profiles from 2 oceanographic campaigns. The objective is to identify the forcing mechanisms for the current variability in this narrow shelf (20–40 km wide). Although the strong North Brazil Undercurrent (NBUC) flows along the continental slope, over most of the time the currents present a high correlation with the local wind forcing. This wind-driven circulation points mainly towards the southwest. Only during periods of weak wind regime the currents are driven by some other mechanism, that could be either the influence of the NBUC or the river discharge. The tidal currents do not play a major role in the alongshore component, which is dominated by the seasonal signal but is of major importance for the cross-shore component of the velocity. The tide current ellipses are mainly oriented in the alongshore direction, even though they are not important in this same direction. Vertically, the currents are dominated by the barotropic mode, both in the alongshore and cross-shore components. The hydrographic data shows a very homogeneous continental shelf dominated by the presence of Tropical Water, with a possible influence of water exchange with the open ocean near the Japaratuba canyon.