Seasonal variation of the phytoplankton in the Southern Atlantic Ocean (18°20'-21°S - 41-37°W)

This study is part of the AMBES Environmental Characterization Project, led by PETROBRAS and with the aid of scientists of various specialities. Achieving a detailed analysis of the Espírito Santo basin, located at the Southern Atlantic Ocean (18°20’-21°S - 41-38°W), is its primary objective. Phytoplankton pigments and nutrients were analyzed in winter (2013) and summer (2014), from 40 sampling sites, collected at subsurface and at the deep chlorophyll maximum (DCM), encompassing shelf and oceanic waters. Temperature, salinity and depth of the euphotic zone were also available. Phytoplankton composition was calculated using the software CHEMTAX. Bayesian statistics of chlorophyll a concentrations (TChl a) revealed high probabilities of TChl a increase on the shelf in winter and at oceanic DCM in summer. The distinction between continental shelf water and oceanic water was clearer in winter. Higher TChl a was restricted in summer to areas with riverine input and anthropogenic influences, while in winter it spread over the shelf. Diatoms characterized the high biomass (maximum of 1.5 mg m^-3) stations; Prochlorococcus dominated the lower biomass ones. Cyanobacteria were located at the subsurface and pelagophytes at the DCM; haptophytes were present in both depths. Redundancy Analysis (RDA) associated the dominance of Prochlorococcus and haptophytes in summer to higher nitrogen and water temperature and lower phosphate. Diatoms, prasinophytes and picoplanktonic eukariotes were favoured in winter by higher phosphate and silicate. Cyanobacteria, cryptophytes and dinoflagellates were associated to high availability of nitrogen, low phosphate and moderate water temperatures.