Sea-air carbon dioxide fluxes along 35°S in the South Atlantic Ocean

• Three distinct regions of the South Atlantic Ocean were evaluated for fCO2sw and FCO2.
• The hydrodynamics of each sub-region demonstrated a specific and relevant impact over fCO2sw distribution.
• Multiple linear regression models using temperature-normalized fCO2sw showed, in general, much better results than fCO2sw models.

The oceans play an important role in absorbing a significant fraction of the atmospheric CO2 surplus, but there are still uncertainties concerning several open ocean regions, such as the under-sampled South Atlantic Ocean. This study assessed the net sea-air CO2 fluxes and distribution of sea-surface CO2 fugacity (fCO2sw) along the 35°S latitude in the South Atlantic, during 2011 spring and early summer periods. Underway CO2 molar fraction, temperature, salinity and dissolved oxygen measurements were taken continuously from South American to South African continental shelves. Values of both satellite and discrete in situ   chlorophyll-a concentration along the ship's track were used as ancillary data. Both fCO2sw and difference in sea-air fugacity (ΔfCO2) showed high variability along the cruise track, with higher values found on the continental shelf and slope regions. All ΔfCO2 values were negative, implying that a sinking process was occurring during the cruise period, with an average net CO2 flux of −3.1±2.2 mmol CO2 m−2 day−1 (using Wanninkhof, 1992). Physical variables were the main drivers of fCO2sw variability in South American continental shelf and open ocean regions, while the biological factor dominated the South African continental shelf. Algorithms for estimating fCO2fCO2 and temperature-normalized fCO2fCO2 were developed and applied separately to the three defined sub-regions: the South American shelf, the open ocean and the South African continental shelf, with the regional temperature-normalized fCO2fCO2 models showing better results.