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REGIONAL DIFFERENCES OF THE AIR-SEA CO₂ FLUX BETWEEN 3ºS AND 14ºS IN THE SOUTHWESTERN TROPICAL ATLANTIC

Lucas Guimarães , Manuel Montes, Nathalie Lefèvre

Abstract

Context: The fugacity surface seawater CO₂ (fCO_2sw) and of the sea-air CO₂ fluxes in the Southwestern Tropical Atlantic (SWTA) have been studied to increase the knowledge about the carbon cycle in this region. Aims: To describe the distribution of fCO_2sw in SWTA. Methods: The fCO_2sw has been measured underway by a volunteer merchant ship from 2008 to 2020. Key results: Higher values north of 8ºS compared to the region south of 8ºS. The North is a strong source of CO₂ for the atmosphere with an annual mean value of 3.14 ± 0.52 mmol m^-2d^-1. The South is a weaker source of CO₂ with an annual average of 0.93 ± 0.90 mmol m^-2d^-1. In the months of July and August a weak sink of CO₂ is observed with a mean of -0.55 mmol m^-2d^-1. Conclusions: The differences between these two regions are explained by the origin of the surface water masses encountered along the ship track. The central branch of the South Equatorial Current (SEC) transports surface water, with higher CO₂ content and lower salinity, north of 8ºS, whereas the surface waters between 8ºS and 14ºS come from the southern branch of the SEC. The Intertropical Convergence Zone is another physical process influencing north of 8°S.

MF22276  Accepted 14 April 2024

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