Is the Vertical Variability of the Ocean in Santos Bight, Brazil, Dominated by the Western Boundary Current Meanders?

The Brazil Current (CB) flows southwestward as vertically stratified and organized western boundary jet in the Brazilian shelf-break region ranging from 20–40° S, where the CB’s mass transport grows vertically. This geographical band show intense mesoescale activity due to passageway of eddies and meanders, superimposed over oceanic large-scale recirculation features which influence the oceanic circulation in the Santos Bight Pre-salt cluster area 300 km offshore. Based on 2-year observed data series of an oceanographic mooring array at Lula Field, and based on repeated hydrographic data (seawater temperature, salinity and N² profiles) we used statistical and dynamical orthogonal modes in order to approach the local vertical current profile variability. We verified that it is 85 % explained by EOF-1. This variability is essentially of 1^st baroclinic mode. Great part of it occupies the first 400–600 m water depth, with no predominant direction. We also found remarkable water column seasonal stratification. Albeit of relative weaker mean flows (0.1–0.2 m s⁻¹), the study area is eddy dominated which are geostrophically adjusted to the 1^st baroclinic mode. Furthermore, we observed that the significant directional variability over the São Paulo Plateau occurs far away from the mean current jets that flow parallel to the continental shelf-break geometry.