Sea surface CO₂ fugacity in the southwestern South Atlantic Ocean: An evaluation based on satellite-derived images

The South Atlantic Ocean is historically less sampled than the North Atlantic Ocean. Recent efforts have improved our understanding of the carbonate system variable distribution, mainly on sea surface CO2 fugacity (fCO2). However, these studies have been regionally and temporally restricted. Hence, in this research we developed seasonal algorithms of sea surface fCO2 to investigate the CO2 dynamics along the southwestern South Atlantic Ocean during spring-summer and fall-winter periods. The studied region includes the continental shelf areas of the Abrolhos-Campos Region (an area under the influence of central water upwelling), the South Brazil Bight (a large embayment affected by the mesoscale variability in a westward boundary current), the Southern Brazilian Shelf (a coastal zone influenced by freshwater discharge from continent and water mass entrainment), and offshore waters in the open ocean domain of the southwestern South Atlantic Ocean. Monthly satellite images of sea surface temperature, salinity, and chlorophyll-a, which were concomitantly available from August 2011 to June 2015, were used to reconstruct and evaluate the sea surface fCO2 seasonal field. The predicted fields of sea surface fCO2 enabled an investigation of the main drivers that change this variable over the distinct biogeochemical provinces in the region. As expected, the sea surface temperature was the main driver of seasonal changes in sea surface fCO2, but total dissolved inorganic carbon (DIC) and total alkalinity changes were also relevant, mainly in the biogeochemical provinces under the influence of continental freshwater input or central water upwelling. The latter can play an unpredictable role in CO2 dynamics due to nutrient- and DIC-rich water transport close to the surface. Finally, the use of satellite-derived images is a powerful tool to increase biogeochemical knowledge of relatively undersampled ocean regions, while the development of seasonal sea surface fCO2 algorithms allows a better spatiotemporal comprehension of the CO2 distribution, dynamics, and drivers in the southwestern South Atlantic Ocean – a key region for improving the understanding of the global carbon cycle.