The sea-air CO_2 net fluxes in the South Atlantic Ocean and the role played by Agulhas eddies

摘要

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 CO2system. This study usesin situdata obtained during theFollowing Ocean Rings in the South Atlanticcruise, 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 CO2molar fraction, surface temperature and salinity were continuously measured to calculate the oceanic and atmospheric CO2partial pressures (pCO2swandpCO2atm, respectively). This study investigated the role played by the Agulhas eddies in the sea-air CO2net flux (FCO2) and modeled the seawater CO2as a function of environmental parameters. The meanpCO2swandpCO2atmfor the entire region were 351.5 and 390.6 μatm, respectively. The mean difference (ΔpCO2) was −39.1 μatm. The CO2uptake was dominated by temperature (r = 0.88) during the period analyzed. The mean FCO2was −3.76 and −3.62 mmol m−2d−1using two different KT-models. We show that an Agulhas eddy can contribute to an ocean uptake of −3.16 kgCO2d−1, leading to the capture of approximately 2.52 tCO2lifetime−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.