Acid test: are the world’s oceans becoming too ‘acidic’ to support life?

A hogfish in the coral reefs of Cuba. Image by abrice Dudenhofer / Ocean Image Bank.

Hours after being born, oysters are already working to form their protective, chalk-layered shells. Drawing calcium and carbonate from seawater, they combine the two to form hardened shells.

But as humans have pumped voluminous sums of carbon dioxide into the atmosphere, this ancient process has come under threat. It’s estimated that the global ocean absorbs around 30% of human carbon emissions. While this carbon sequestration creates a powerful buffer against climate change by reducing the amount of CO2 flowing into the atmosphere, it changes the chemistry of seawater, decreasing the pH and causing seawater to become more acidic.

Besides affecting oysters, ocean acidification can dissolve the aragonite (a form of calcium carbonate) shells of pteropods, tiny marine snails that swim through the water column, and which whales, seabirds and fish rely on as a food source. Acidification slows corals’ ability to grow their skeletons. Marine animals like sea urchins find it more difficult to reproduce. New research has also shown that ocean acidification can exacerbate other issues, including marine heat waves, compounding stress on an already stressed-out ocean.

Ocean acidification is considered to have such wide-ranging global impacts that scientists have designated it as one of nine planetary boundaries responsible for regulating and maintaining Earth’s functionality. Each of these nine boundaries refers to a biophysical subsystem or process that has a clear limit to which it can withstand anthropogenic changes. The theory, which was first introduced in a 2009 paper and updated in a 2015 paper, suggests that Earth can function properly if humanity remains within the “safe operating limits” of these boundaries. But once a certain threshold is crossed for one or more of these boundaries, the concept suggests that Earth will move into a new and dangerous state — one that is far less supportive of biological life.

Elizabeth Claire Alberts, Mongabay, 12 September 2022. Full article.

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