Ocean alkalinity enhancement (OAE) artificially increases seawater alkalinity, chemically enabling the ocean to permanently absorb more atmospheric carbon dioxide (CO₂) while reverse some of the chemical changes resulting from CO₂-induced acidification. However, its long-term effects on ocean carbonate chemistry remain poorly constrained by field observations. Here, we analyze a 26-year time series from the South China Sea as part of the Joint Global Ocean Flux Study. Surface seawater total alkalinity increased at a rate of 0.56 μmol kg⁻¹ yr⁻¹, although the mechanism driving this trend remains unclear and requires further investigation. Of note is that, this increase enhanced the ocean's CO₂ uptake by 28% and offset declines in seawater pH and calcium carbonate saturation state by 14% and 22%, respectively. These observations provide a regional, field-based example consistent with the theoretical expectations of OAE.

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