This work describes the circulation over the continental slope and the São Paulo Plateau in the Santos Basin during the SANSED winter 2019 survey. The cruise consisted of four legs in the period between June, 11 and August, 03 2019. The observed circulation is dominated by the Atlantic southwestern boundary current regime and remotely-generated anticyclones and cyclones. The former is composed by the Brazil Current, the Intermediate Western Boundary Current and their mesoscale meanders; the latter are 300km vortical rings with origin in the eastern side of the South Atlantic Basin. A Lagrangian scheme applied over satellite altimeter maps indicate that the origin of these rings is primarily the Cape Basin off South Africa. The interaction between the boundary currents, their cyclonic meanders, and the anticyclonic rings is complex, and varies widely. During the SANSED winter 2019 survey period, three anticyclones interacted with the Brazil Current, instabilizing it, forming dipoles with the current cyclonic meanders, leading to their downstream propagation. Ancienter cyclonic eddies within Santos Basin may interfere with the propagation of the large anticyclones further south. In addition, the continuous arrival of remotely-originated anticyclones, the larger portion over the São Paulo Plateau presented a tendency of counter-clockwise circulation during the whole cruise period.
The South Brazil Bight is a section of the Brazilian margin mainly
dominated by the poleward Brazil Current flow, their meanderings and
eddies. We evaluated the mean mesoscale for the region, and an
anticyclonic feature was highlighted over the São Paulo Plateau. Around
that feature, cyclonic eddies were also accentuated. The combination of
these structures dominate the region, forming an eddy corridor. Using
eddy detection dataset, we reveal that the signal on the plateau was
directly related to the presence of anticyclones. The cyclones in the
region present both local and remote origins, however, most of the
anticyclones are from remote sources. More than 95% of these
anticyclones were Agulhas Rings, which could or could not have been
subjected to splitting or merging processes. On the plateau we observe
an average of 5.3 anticyclones per year. However, these rate is related
not only to the number of anticyclones but also to the time they remain
there. We observe that Agulhas Rings reside in the region for 50.8 days,
consequently, they occupy the plateau for almost 75% of the year.
During half of the residence time, there is a multi-pattern interaction
with cyclones. This relationship between eddies of opposite polarity
creates a shielding process. The anticyclones become shielded and
trapped by the cyclones, have their progress delayed, and their course
deflected toward the Brazil Current. This was the first observation of
this process involving the Agulhas Rings and the first study of the
subsequent eddy-current interaction in the region.
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