The seasonal circulation of the Eastern Brazilian Shelf between 10S and 16S: a modeling approach

A regional model based on ROMS-AGRIF, configured with a refined grid (1/36°) and realistic forcings (6-hourly winds and surface fluxes, daily large scale lateral boundary conditions and tides) was implemented to describe the seasonal circulation within the Eastern Brazilian Shelf (EBS) between 10°S-16°S, and its interaction with the meso-scale dynamics associated with the Western Boundary Currents (WBC), as well as the contribution of the forcing mechanisms on the generation of the shelf/slope currents. The WBC flows over the slope and includes the Brazil Current (BC), the North Brazil Current (NBC), and the North Brazil Undercurrent (NBUC). The model results show that for the northern limit (10°S) the northward NBC/NBUC system is the dominant pattern and the southward flow appears as a thin flow confined to the top 50 m of the water column during the spring and summer. The surface circulation at the inner- and mid-shelves of this region are more influenced by the wind, while at the shelf-break the currents are mainly driven by the slope currents during all seasons. In the middle (14°S) and southern (16°S) regions, there is an alternate dominance of the BC and NBC currents in the top 150m of the water column. The BC (NBC) current dominates between September-February (April-July) at 14°S. However, the annual net transport in these regions is southward. Contrarily, at the sub-surface (~150-400 m), the annual net transport is northward and the dominance of the NBUC flow is clear. At 14°S, the inner-shelf circulation is mainly driven by the wind; the mid-shelf circulation is forced by both the wind and the flow over the slope; the currents at the shelf-break are more influenced by the currents at the slope. Finally, the inner- and mid-shelf currents at 16°S are mainly driven by the winds, but the shelf-break currents present a poor correlation with the winds and are strongly influenced by the WBC dynamics.

Affiliations:

Fabiola N. Amorim, Universidade de Aveiro, Portugal
Mauro Cirano, Universidade Federal da Bahia, Brazil
Martinho Marta-Almeida, Universidade de Aveiro, Portugal
John F. Middleton, South Australia Research and Development Institute, Australia
Edmo J. D. Campos, Instituto Oceanográfico da Universidade de São Paulo, Brazil