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Shipboard acoustic Doppler current profiler velocity measurements and profiles of temperature, salinity, and dissolved oxygen measurements are used to map the flow field above the cr 0 = 26.8 isopycnal (approximately the upper 300 m of the water column) in the North Brazil Current (NBC) retroflection region (0 ø to 14øN, 60 ø to 40øW) during August of 1989. The water column is divided into a near-surface, upper thermocline layer (above cr 0 = 24.5) and a main to subthermocline layer (or 0 = 24.5 to cr 0 = 26.8). In the upper layer the eastward flowing North Equatorial Countercurrent

[1] High-resolution shipboard surveys of four North Brazil Current rings are presented, which are the first such dedicated surveys to be made of these features. Of the four rings surveyed, three fundamentally different types of ring structures are found: (1) a shallow, surface-trapped structure with velocities confined to the top 200 m (two rings), (2) a deep-reaching structure with significant swirl velocities ($0.2 m/s) extending to 2000 m (one ring), and (3) a thermocline-intensified structure with almost no detectable surface signature (one ring). The results of this study indicate that North Brazil Current rings can have highly variable vertical structures, and that assessing their overall role in cross gyre exchange in the tropical Atlantic will require a careful combination of remote sensing and in-situ observations.

Absolute velocity and temperature profiles are used to estimate the volume transport through the Straits of Florida and, in combination with historical midbasin data, to estimate the total meridional heat flux through a section at 27 degrees N. The mean annual volume transport of the Florida Current from April 1982 through August 1983 is 30.5 (+/- 1)x 10(6) cubic meters per second. The net northward heat flux through the 27 degrees N section is 1.2 (+/- 0.1)x 10(15) watts. The volume transport is characterized by high values in the late spring and early summer and low values in the late fall and early winter. There is a similar cycle in total heat flux.