| To better understand the South Atlantic wind-driven circulation, mean absolute transport potential for the upper 1000 dbar is estimated for the regions of the Brazil Current (BC) between 25°S and 40°S and the South Atlantic Current (SAC) between 40°S and 45°S. These transports are obtained by combining Gravest Empirical Mode (GEM) fields, calculated from historical hydrography, with data from isobaric RAFOS floats deployed in the area. The results show: a BC transport of 5 Sv (1 Sv = 106 m3 s-1) at 25°S and 25 Sv at 35°S; a pair of recirculation cells in the southwest corner of the subtropical gyre north of 40°S, one west of 30°W recirculating 25 Sv and the other centered at 39°W and 37°S recirculating 15 Sv; a swift SAC transporting 45 Sv at 30°W; at the eastern side of the basin, the SAC weakens and splits into a branch north of 39°S (transporting 15 Sv) and one south of 41°S (transporting 10 Sv). Also in this study, a reduced-gravity, primitive-equation, ocean model is used to investigate subsurface pathways from the South Atlantic to the tropical Atlantic, with emphasis on the seasonal variability of the bifurcation of the South Equatorial Current (SEC). Observations and model results show that the SEC bifurcation occurs at about 14°S at 100 m, shifting poleward with increasing depth, to reach 27°S at 1000 m. The bifurcation latitude reaches its southernmost position in July and northernmost position in November. The model results also show that most of the seasonal variability of the bifurcation latitude is associated with changes in the amplitude of local wind stress curl due to the annual north-south excursion of the marine Intertropical Convergence Zone (ITCZ) complex, with remote forcing being less important. Nevertheless, the seasonal variability of the SEC, BC, and North Brazil Undercurrent (NBUC) transports are related to the wind stress curl over the entire basin, and not to the local forcing alone. |
