Geostrophic velocity and transport variability in the Brazil-Malvinas Confluence

This paper presents the results from a study of the dynamics of the Brazil-Malvinas Confluence in the southwestern Atlantic based on data collected with an array of inverted echo sounders. Dynamic height series were obtained at 10 different sites for a period of 15 months. The data are analyzed in terms of dynamic height, geostrophic velocities and transports. The large variability previously inferred from satellite observations is observed in the dynamic height field of the surface, relative to 100 m, and is attributed to changes in the latitude of separation, the meandering of the Confluence front towards the east, and eddy generation. The eddy circulation observed is both cyclonic and anticyclonic. These eddies are observed both between the southward edge of the Brazil Current and the northward edge of the Malvinas Current and superimposed to the main flows. The diameter of the eddies is two to three times the Rossby Radius of deformation. The highest observed values of the geostrophic velocities (102 cm s −1 at 36.5°S and −61 to −62 cm s −1 at 37.6°S) are associated with the large shear in frontal situations. The northward penetration of the Malvinas Current occurs during 1988 and 1990 during the southern hemisphere winter. This is in agreement woth results from a previous deployment, satellite observations and model results. The Brazil Current transport is at 35.2 and 36.5°S, −24 Sv towards the south and −20 Sv between 37.7 and 38°S (reference 1000 m). The transport of the Brazil Current return at 35.2°S is of the same value as the southward flow: 24 Sv. For the Malvinas Current, the estimates indicate a northward transport of 5 Sv at 37.7°S (reference 1000 m). These values are considered as a lower limit. The array captured only about half the flow due to the location of the deployments, and only the baroclinic component. The transport should be at least doubled to compensate the value obtained for the Malvinas return flow at the same latitudes, −24 Sv.