Southern Ocean acidity might double by the end of the century

Almost 30 per cent of CO₂ released to the atmosphere is taken up by the oceans. As a consequence, the oceans become more acidic – in a process called ocean acidification.

Cold waters, such as those of the Southern Ocean, absorb even more CO2 than warm and temperate ones, making them especially susceptible to acidification. Changes in pH in the Southern Ocean have recently been studied by researchers from the University of Colorado Boulder. They observed existing and proposed marine protected areas in coastal waters of this region.

Using computer models to project end-of-the-century pH changes, the researchers found that the pH could be reduced by 0.36 in the upper 200-metre layer of the water column, translating into a doubling of the acidification.

So far, the average pH of the oceans’ surface has already dropped from 8.29 in the pre-industrial area to its present value of 8.1 (around a 30 per cent change in acidity).
Marine life is adapted to slightly alkaline conditions. More acidic waters have direct impacts on a number of marine organisms. For instance, phytoplankton grow more slowly. Because these organisms form the base of marine food chains, negative effects can be expected to cascade throughout these food chains. Another example comes from shellfish (e.g., sea urchins and sea snails). The shells of these organisms consist of calcium carbonate, and they start to dissolve under acidified conditions. Altogether, acidification effects can be expected to reach the very top of the food chains (e.g., whales and penguins) due to negative effects lower down in these food chains.
For the studied areas in the Southern Ocean, the researchers predict that the acidification would not be restricted to the ocean surface, but affect the entire water column, from the surface to the seabed.

Sources:
Polar Journal 17 January 2024, https://polarjournal.ch/en/2024/01/17/southern-ocean-acidification-could...
Nature Communications, 4 January 2024, https://www.nature.com/articles/s41467-023-44438-x