Transports, frontal motions and eddies at the Brazil-Malvinas currents confluence

Abstract

Three inverted echo sounders were deployed to study the dynamics of the western South Atlantic Brazil-Malvinas Confluence region. From the original travel time data obtained with the sounders, the dynamic height of the surface relative to 800 m at the three locations was obtained and geostrophic velocities between sites calculated. The time-averaged geostrophic velocity of the Brazil Current (relative to 800 m) during the observed period is 35 cm s −1 (±2.2 cm s −1) and the mean transport relative to 800 m is 11 Sv. For the Malvinas Current return flow, the mean geostrophic velocity is 9 cm s −1 (±2.0 cm s −1) and the mean associated transport 3.5 Sv. Cold intrusions are observed in offshore records during the 17-month recorded period, some of them associated with cold cyclonic eddies with available potential energy of 6.3 × 10 15 J. Using a simple model the location of the thermal front is obtained from the time series of the depth of the thermocline. Results show that the main motion of the front is an east-west displacement for distances of about 100 km; the observed period occurs with a periodicity of 12 months and is related to a variability in the latitude of maximum northward penetration of the Malvinas Current. Motions of the front, with a period of 1–2 months, are probably related to a north-south variation of the latitude of return of the Brazil Current.