The sea-air CO2 net fluxes in the South Atlantic Ocean and the role played by Agulhas eddies

Abstract The South Atlantic Ocean is vitally important to the global overturning circulation, which is influenced by heat, salt and other properties carried by Agulhas eddies. However, this influence is not yet fully understood, mainly in the context of the biogeochemistry changes on the CO 2 system. This study uses in situ data obtained during the Following Ocean Rings in the South Atlantic cruise, which occurred between Cape Town, South Africa and Arraial do Cabo, Brazil in July 2015 when six eddies and the surrounding waters were sampled. The seawater and atmospheric CO 2 molar fraction, surface temperature and salinity were continuously measured to calculate the oceanic and atmospheric CO 2 partial pressures ( p CO 2 sw and p CO 2 atm , respectively). This study investigated the role played by the Agulhas eddies in the sea-air CO 2 net flux (FCO 2 ) and modeled the seawater CO 2 as a function of environmental parameters. The mean p CO 2 sw and p CO 2 atm for the entire region were 351.5 and 390.6 μatm, respectively. The mean difference (Δ p CO 2 ) was −39.1 μatm. The CO 2 uptake was dominated by temperature ( r  = 0.88) during the period analyzed. The mean FCO 2 was −3.76 and −3.62 mmol m −2  d −1 using two different K T -models. We show that an Agulhas eddy can contribute to an ocean uptake of −3.16 kg CO 2  d −1 , leading to the capture of approximately 2.52 t CO 2  lifetime −1 . Thus, providing evidence that the Agulhas eddies propagation can likely play a key role on the rapid seawater acidification of the South Atlantic Central Water. A multiple linear regression model was developed that could reliably reconstruct the cruise survey with better results than previously published.