The Escape Latitude

 

To establish the influence of the Brazil/Malvinas Confluence on the detrainment of the waters from the Rio de la Plata we compare the time series of the latitude at which the LPR waters leave the shelf, which we call the “escape latitude”, with the time series of the location of the BMC. We define LPR waters as waters with a shelfbreak SSS < 34.0, and the escape latitude as the middle point of the shelfbreak region with an outflow of waters with a SSS < 34.0.

The escape latitude and the latitude of the Brazil/Malvinas Confluence defined according to the SSS criterion (panels a and c) and the passive tracer criterion (panels b and d)

The escape latitude is highly variable (Movie 1). In general, the outflow from the Rio de la Plata moves to the south during the summer and to the north during the winter. The high correlation, r = 0.76, between the time series of the escape latitude and the BMC indicates that the outflow of the waters of the Rio de la Plata from the shelf is largely controlled by the western boundary currents.

The escape latitude estimated with a passive tracer has a smaller correlation with the Brazil/Malvinas Confluence than the escape latitude estimated with the SSS criterion. The largest discrepancies are observed during the winter months (Figure). The difference between the time series of the tracer and the SSS indicates that during the winter months the waters waters from the river leave the shelf north of the the Brazil/Malvinas Confluence. Downwelling favorable winds during the winter months trap the plume of the Rio de la Plata against the coast, where it is advected alongshore instead of offshore (Figure). After reaching Cape Santa Marta (~28˚S) the plume is returned south by an inshore intrusion of the BC flowing along the shelfbreak. Intense mixing along this pathway increases the salinity of the plume’s waters so by the time that they reach the Brazil/Malvinas Confluence they have a SSS > 34.0.