Spatial distribution of nutrients associated with water masses in the Tubarão Bight (20°S–22°S), Brazil

Abstract

The bathymetry in the region of the Tubarão Bight is complex. When associated with the morphological variations in the continental shelf and the presence of the Vitória-Trindade Chain, peculiar physical characteristics capable of modifying the hydrodynamic flow and the distribution of water masses on the continental shelf appear. Moreover, the presence of cyclonic eddies and the upwelling process reinforce the importance of this region from a physical and biological perspective, especially related to the input of nutrients to the euphotic zone. This study aimed to analyze the spatial distribution of nutrients and its relationship with water masses (Coastal Water (CW), Tropical Water (TW), South Atlantic Central Water (SACW), Antarctic Intermediate Water (AAIW), and Upper Circumpolar Deep Water (UCDW)). The spatial distribution of nutrients was calculated via extended optimum multiparameter analysis using conservative (temperature and salinity) and nonconservative (dissolved oxygen (O2), nitrate (NO3−), silicate (SiO2), and phosphate (PO43−)) parameters. In this region, the presence and distribution of water masses are conditioned by the dynamics and variability associated with continental discharge, the Brazil Current, and local hydrodynamics. The spatial-temporal distribution of nutrient concentrations was strongly related to the distribution of water masses and the processes related to regeneration, coastal upwelling, erosion of the upper thermocline, and cyclonic eddy presence. As a result, on the continental shelf, the highest concentrations of SiO2 and dissolved O2 occurred in the water column portion occupied by CW and TW, whereas NO3− was associated with SACW. Offshore, the highest nutrient concentrations (SiO2, NO3−, and PO43−) were related to intermediate water masses (AAIW and UCDW). Furthermore, the highest concentrations of dissolved O2 were associated with TW and AAIW as a result of ocean-atmosphere interactions and formation processes.