Decadal Progress of Ocean Acidification over the Southern Ocean

The Southern Ocean (SO, south of 30°S) covers 30% of the global ocean surface area and is presumed to account for 40% of the whole ocean's anthropogenic CO ₂ (DIC _anth ) absorption ¹ . This may lead to intensive anthropogenic acidification in the SO. However, natural processes also influence the change of ocean pH. Distinguishing anthropogenic and natural components from the observed dissolved inorganic carbon (DIC) and pH is essential for clarifying the acidification in the SO. Here we separated the anthropogenic and natural components by combining new parameterization techniques with high-resolution grid data constructed based on ship-based observations. During the 1990s‒2010s, ocean acidification affected by the anthropogenic effect covered most of the surface and intermediate depths by 3500 m over the SO, and the maximum decreasing rate of anthropogenic pH was 0.004 pH year ^–1 as twice decreasing of the global average. This remarkable decline of pH in the SO must result from the increase in DIC _anth of 10.9 Pg-C. The increase of DIC _anth in the SO was comparable to 11% of the global emission amount of CO ₂ , implying the SO absorbing half of the global ocean's DIC _anth is the largest uptake region of atmospheric anthropogenic carbon into the ocean interior.