THE DEEP WESTERN BOUNDARY CURRENT IN THE TROPICAL NORTH-ATLANTIC OCEAN

Tracer and CTD data collected on four cruises to the western tropical North Atlantic during 1987-1989 are used to describe the water mass properties and geostrophic transport of the Deep Western Boundary Current (DWBC). The study area extends along the boundary and east to the mid-Atlantic Ridge from 14.5-degrees-N to the equator. Two cores of recently ventilated (with respect to the chlorofluorocarbon F11) northern hemisphere water are advected through the area. A shallow core is centered at about 1500 m and a deeper core at about 3500 m. The upper core of high F11 (bounded by the 3.2 and 4.7-degrees-C potential temperature isotherms) is typically located inshore of the deeper core (bounded by the 1.8 and 2.4-degrees-C isotherms). Geostrophic currents and transports were computed relative to a zero reference velocity on the 4.7-degrees-C potential temperature surface. Total transport below the 4.7-degrees-C surface for the most intense portion of the DWBC is 26 Sv (1 Sv = 10(6) m3 s-1). Of this total, 17 Sv are contained in the two recently ventilated high F11 cores. The Ceara Rise blocks equatorward flow in the DWBC below the 1.8-degrees-C potential temperature surface, causing at least the coldest waters to recirculate back to the north.