Effects of the seasonality of mesoscale eddies on the planktonic dynamics off eastern Brazil

Abstract

The South Equatorial Current’s southern branch (SSEC) reaches the Brazilian continental margin through several bands between 30°S and 10°S. As the SSEC 14°S band reaches the Brazilian continental margin, it bifurcates into the poleward-flowing Brazil Current (BC), and the surface portion of the equatorward-flowing North Brazil Undercurrent (NBUC). Some semi-permanent eddies are formed in association with the bifurcation, and their variability is controlled by the seasonality of the SSEC bands. This work aims to investigate the role of the seasonality of these mesoscale eddies on the regional phytoplanktonic dynamics. We analyze chlorophyll-a satellite observations and perform two experiments using a Nutrients–Phytoplankton–Zooplankton (NPZ) model coupled to a 112-layer quasi-geostrophic model. The results show that the phytoplankton annual cycle off eastern Brazil is mainly controlled by the seasonally varying advection of material offshore caused by the mesoscale eddies. Such a mechanism may represent an important source of material to the tropical oligotrophic ocean.