Hydrographic climatology of South Brazil Bight shelf waters between Sao Sebastiao (24°S) and Cabo Sao Tome (22°S)

Abstract

A hydrographic climatology was created with the goal of establishing the mean hydrographic conditions and oceanic waters intrusion mechanisms in the central and northern parts of the South Brazil Bight on a seasonal timescale. The climatology was constructed by applying objective analysis to a historical temperature and salinity database, by season and depth, considering the anisotropy and coastal and oceanic boundary conditions. The dominance of South Atlantic Central Water (SACW) in the bottom layer, the presence of Tropical Water in the surface layer, the seasonal onshore–offshore displacement of those water masses, and the along-shore remote southward advection of SACW from Cabo Frio (23°S) are well-defined features in the analyzed and derived fields. The inshore displacement increases the volume of SACW in the shelf by approximately 780km3 from winter to spring; the offshore displacement decreases the volume of SACW by approximately 840km3 from summer to autumn. The remote advection is linked to southwestward, along-shelf transport of SACW with temperatures lower than 15°C from Cabo Frio during summer, winter, and spring. In association with the remote advection, a primary intrusion pathway of SACW is identified off Cabo Frio during those same three seasons. In spring, a secondary SACW intrusion pathway is also detected off Ubatuba (23.5°S). The existence of those two SACW intrusion pathways is promoted by the combined effect of three factors: outer shelf deepening, upwelling-favorable winds, and Brazil Current mesoscale variability. Minimum volumes of SACW and maximum volumes of Tropical Water occur in autumn, when wind activity is minimal and the minimum bottom temperature on the shelf is approximately 1°C warmer than in the other seasons (colder than 16°C).