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°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. Plain Language Summary: We use the results of a suite of ocean model experiments to investigate the variability of the shelf circulation off southern Brazil and Uruguay and the exchange between the shelf and the open ocean. Ocean internal variability (e.g., from eddies) represents more than 50% of the total shelf transport variability and reaches values up to 90% in the northern shelf region. Supported by maps of satellite chlorophyll‐a and using model passive tracers and Lagrangian floats, we also find that eddies along the shelfbreak play an important role in the advection of colder, fresher, and more nutrient‐rich shelf water to the open‐ocean. This is particularly significant where the shelfbreak changes its orientation (shelfbreak bights) where cyclonic small‐scale eddies are detected more than 15% of the time. Key Points: The variability of the shelf circulation and cross‐shelf exchanges off Southern Brazil and Uruguay is investigated using model experimentsMore than 50% of the total shelf transport variability is explained by internal ocean variabilityEddies along the shelfbreak play an important role in the advection of colder, fresher, and nutrient‐rich shelf water to the open‐ocean [ABSTRACT FROM AUTHOR]