Circulation and Cross‐Shelf Exchanges in the Northern Shelf of the Southwestern Atlantic: Dynamics

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.