Observation of Decadal Natural Ocean Alkalinity Enhancement in the South China Sea

Abstract Ocean alkalinity enhancement (OAE) is a process of artificially increasing the alkalinity of seawater, chemically allowing the ocean to permanently absorb more carbon dioxide (CO 2 ) from the atmosphere and reverse some of the chemical changes resulting from CO 2 ‐induced acidification. However, the long‐term real impacts of OAE on ocean carbonate chemistry remain unexplored. This study examined a 26‐year time‐series study in the South China Sea as part of the Joint Global Ocean Flux Study, showing that the total alkalinity of the surface seawater increased annually by 0.56 μmol kg −1 . Consequently, seawater increased its CO 2 absorption by 28% and reversed the declines in seawater pH by 14% and calcium carbonate saturation state by 22%. The South China Sea provides a regional example of the consistency between the theory and field observations of OAE.