The bifurcation of the western boundary current system of the South Atlantic Ocean

Abstract

The results of two high-resolution ocean global circulation models-OGCMs (Hybrid Coordinate Ocean Model-HYCOM and Ocean Circulation and Climate Advanced Modeling Project-OCCAM) are analyzed with a focus on the Western Boundary Current (WBC) system of the South Atlantic Ocean. The volume transports are calculated for different isopycnal ranges, which represent the most important water masses present in this region. The latitude of bifurcation of the zonal flows reaching the coast, which leads to the formation of southward or northward WBC flow at different depths (or isopycnal levels) is evaluated. For the Tropical Water, bifurcation of the South Equatorial Current occurs at 13◦-15◦S, giving rise to the Brazil Current, for the South Atlantic Central Water this process occurs at 22◦S. For the Antarctic Intermediate Water, bifurcation occurs near 28◦-30◦S, giving rise to a baroclinic unstable WBC at lower latitudes with a very strong vertical shear at mid-depths. Both models give similar results that are also consistent with previous observational studies. Observations of the South Atlantic WBC system have previously been sparse, consequently these two independent simulations which are based on realistic high-resolution OGCMs, add confidence to the values presented in the literature regarding flow bifurcations at the Brazilian coast.