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

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 degrees S and 25 degrees S comes from ocean internal variability which represents similar to 50%-70% of the total variability. Between 25 degrees S and 21 degrees 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.

Automated summary

The interaction between the Brazil Current and the adjacent shelf can be observed in satellite-derived products. However, these assessments are limited to the surface layer. This study uses numerical experiments to analyze the regional circulation and dynamics, identifying high variability regions and the contribution of eddies to cross-shelf mass exchanges.