Ocean Acidification and Long‐Term Changes in the Carbonate System Properties of the South Atlantic Ocean

The wind‐driven part of the South Atlantic Ocean is primarily ventilated through central and intermediate water formation. Through the water mass formation processes, anthropogenic carbon (Cant) is introduced into the ocean's interior which in turn makes the South Atlantic region vulnerable to ocean acidification. Cant and the accompanying acidification effects have been estimated for individual sections in the region since the 1980s but a comprehensive synthesis for the entire basin is still lacking. Here, we quantified the Cant accumulation rates and examined the changes in the carbonate system properties for the South Atlantic using a modified extended multiple linear regression method applied to five hydrographic sections and data from the GLODAPv2.2021 product. From 1989 to 2019, a mean Cant column inventory change of 0.94 ± 0.39 mol C m−2 yr−1 was found. Cant accumulation rates of 0.89 ± 0.33 μmol kg−1 yr−1 and 0.30 ± 0.29 μmol kg−1 yr−1 were observed in central and intermediate waters, accompanied by acidification rates of −0.0020 ± 0.0007 pH units yr−1 and −0.0009 ± 0.0009 pH units yr−1, respectively. Furthermore, increased remineralization was observed in intermediate waters, amplifying the acidification of this water mass, especially at the African coast along 25°S. This increase in remineralization is likely related to circulation changes and increased biological activity nearshore. Assuming no changes in the observed trends, South Atlantic intermediate waters will become unsaturated with respect to aragonite in ∼30 years, while the central water of the eastern margins will become unsaturated in ∼10 years. Key Points The western margin and southern limit of the South Atlantic Ocean are more impacted by anthropogenic carbon (Cant) uptake A Cant column inventory change of 0.94 ± 0.39 mol C m−2 yr−1 was found in the region, higher than the global mean storage rate Aragonite unsaturation is expected in the next two decades along the eastern margin if the anthropogenic changes maintain the present trend