Search for: All records

Abstract This modeling study analyzes the circulation over the Agulhas Bank (AB). It is suggested that the time mean circulation over the bank is primarily driven by the inflow of shelf waters from the northeastern region, and not by local forcing as previously postulated. Seasonal variations of the circulation and temperature and salinity fields are highly correlated with the atmospheric forcing. Currents shift inshore during the winter, returning to its original position during summer. The equatorward flow in the western AB, which includes a deep, previously unreported, countercurrent, strengthens during spring and summer and wanes during fall and winter. Tracer diagnostics and Eulerian mass balances reveal very energetics mass exchanges between the eastern AB and the Agulhas Current (AC). The AB Bight is the preferential site for these exchanges. Lagrangian diagnostic show 0.45 Sv of deep open‐ocean waters entrained into the bottom layer of the shelf. Cross‐shelf exchanges produce significant water mass transformations. Tides play an unexpectedly significant role on the AB circulation. Preliminary considerations suggest that shelf/open‐ocean interactions could have a significant impact on water mass conversions within the AC. 

Abstract The strong interaction between the Brazil Current and the adjacent shelf is clearly visible in satellite‐derived products (sea surface temperature, salinity, and chlorophyll‐a concentration). Assessments of circulation features and cross‐shelf exchanges from these products are, however, limited to the surface layer. Here we analyze the regional circulation and dynamics using the results of a suite of process‐oriented, high‐resolution numerical experiments. Passive tracers and Lagrangian floats characterize the exchanges between the shelf and the open ocean, identifying regions of high variability, and assessing the contribution of small‐scale eddies to the cross‐shelf mass exchanges. We estimate that 0.2–0.4 Sv of the shelf transport variability between 34°S and 25°S comes from ocean internal variability which represents ∼50%–70% of the total variability. Between 25°S and 21°S, internal ocean variability represents more than 90% of the shelf transport variability. We find that generation of cyclonic eddies is more frequent (>15% of the time) at the shelfbreak bights. The core of these eddies contains fresher, colder, and more nutrient‐rich shelf waters. Maps of satellite chlorophyll‐a concentration suggest that the horizontal and vertical exchanges of mass associated with these eddies are a critical element of the primary production cycle.