Biogeographical regions of the tropical and subtropical Atlantic Ocean off South America: classification based on pigment (CZCS) and chlorophyll-a (SeaWiFS) variability

Tropical and subtropical Atlantic Ocean waters off the coasts of Brazil, Uruguay and Argentina are influenced by a variety of hydrographic processes that lead to a great diversity in the biological system. In situ observations are scarce and sparsely distributed over this zone. Phytoplankton pigment concentrations were estimated utilizing the Coastal Zone Colour Scanner for the area located between 5°N and 45°S, and from the coast of South America eastward to 25°W. Advanced Very High Resolution Radiometer (sea surface temperature) and data from literature were used to differentiate regions, considering space and time variations of the phytoplankton biomass. Monthly pigment concentration time series were used for the period of January 1982–May 1986 as input for a Principal Component Analysis (PCA). The PCA analysis grouped 152 locations into 14 regions, most of them associated to clear surface circulation patterns and hydrographic features. These results were confirmed using monthly composites of chlorophyll-a concentration from Sea-viewing Wide Field-of-view Sensor for the period September 1997–April 2002. A connection between the 1982/83 and 1997/98 ENSO events and pigment distribution over southern and southeastern Brazil, as well as the Argentinean continental shelf, was clearly evidenced in temporal pigment distributions. Results presented in this work contribute to the idea that ocean colour images are an appropriate tool to identify and follow the seasonal displacement of biogeographical region boundaries.