Seasonal variability of the South Equatorial Current bifurcation in the Atlantic Ocean: A numerical study

In this study, a reduced-gravity, primitive equation OGCM is used to investigate the seasonal variability of the bifurcation of the South Equatorial Current (SEC) into the Brazil Current (BC) to the south and the North Brazil Undercurrent/Current (NBUC/NBC) system to the north. Annual mean meridional velocity averaged within a 2 degrees longitude band off the South American coast shows that the SEC bifurcation occurs at about 10 degrees-14 degrees S near the surface, shifting poleward with increasing depth, reaching 27 degrees S at 1000 m, in both observations and model. The bifurcation latitude reaches its southernmost position in July (similar to 17 degrees S in the top 200 m) and its northernmost position in November (similar to 13 degrees S in the top 200 m). The model results show that most of the seasonal variability of the bifurcation latitude in the upper thermocline is associated with changes in the local wind stress curl due to the annual north-south excursion of the marine ITCZ complex. As the SEC bifurcation latitude moves south (north) the NBUC transport increases (decreases) and the BC transport decreases (increases). The remote forcing (i.e., westward propagation of anomalies) appears to have a smaller impact on the seasonal variability of the bifurcation in the upper thermocline.