Hydrographic structure of the continental shelf in Santos Basin and its causes: The SANAGU and SANSED campaigns (2019)

Abstract

This study describes the hydrography and water masses of the Santos Basin Continental Shelf (SBCS) during two hydrographic campaigns (SANAGU, SANSED) in 2019. Coastal Water (CW) is the dominant water mass in the southern portion of the SBCS, with relatively low salinity values (S<35.5 g kg^–1), and satellite data show that local precipitation and river discharge could not account for the low salinity observed during the cruises in the southern region of the domain. The low salinity observed is explained by the transport from the south influenced by Subtropical Shelf Water (STSW), which was influenced by the La Plata River discharge. In the northern region of the SBCS, the South Atlantic Central Water (SACW) dominates the bottom layers of the water column, with the wind playing a major role in the uplift of this water mass, as evidenced by a wind impulse analysis. In this part of the shelf, Tropical Water (TW) was the second water mass in volume and occupied the surface layers and offshore the shelf. CW is restricted to a thin surface layer, which reaches distances of a few kilometers from the coast. Our analysis show the differences in the hydrographic structure of the SBCS and suggests that the SBCS can be divided in two regions with distinct characteristics: 1) the area southwest of São Sebastião, where the hydrographic parameters were modulated by the presence of the Subtropical Shelf Water (STSW); 2) the area northeast of São Sebastião, where the uplifting of SACW was the dominant process.

Keywords:
Water Mass; Tropical Water; South Atlantic Central Water; Wind Impulse; Salinity; Continental Runoff