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Thirty nine oceanographic stations were conducted off Rio de Janeiro and northern São Paulo states, encompassing Cabo Frio, Guanabara Bay, Sepetiba Bay and Ubatuba in the winter of 2010. Dissolved inorganic nutrients (ammonium, nitrite, nitrate, phosphate and silicate) and chlorophyll-a data were used to investigate biogeochemical and physical processes occurring on the continental shelf. The study area corresponded to a transition zone between two distinct biogeographic regions described in the literature, "Cabo Frio upwelling region (23ºS)" and "Continental shelf/ Santos Bight (23ºS to 29º40'S)", with some unique aspects highlighted in this study, as the coastal zone influenced by local estuarine plumes from Guanabara and Sepetiba bays; and areas where the SACW was present on the base of the mixed layer: i. off São Sebastião Island, due to the vertical and horizontal shear of currents with an inshore northwards flow; and ii. off Sepetiba Bay, in the midshelf, due to regeneration processes from the bottom up to the deep chlorophyll maximum.