The ocean absorbs about a quarter of our annual carbon dioxide emission, making it the largest natural sink of carbon dioxide. CO2 makes the ocean’s surface acidic. The uptake of carbon due to rapid industrialization has acidification sinking into marine regions as deep as 1500 meters, posing new threats to organisms like sea butterflies, sea snails, and cold-water corals.
Research by scientists from the Federal Institute of Technology Zurich, Switzerland found that acidification has reached down to 1000 metres in most of the ocean. Some areas, such as the North Atlantic – where the powerful Atlantic meridional overturning current (AMOC) carries carbon from the surface to deeper waters – saw acidification down to 1500 meters. Some pockets of deeper water that are naturally more acidic saw even more acidification than the surface.
Their original acidity reduces their capacity to absorb any added CO2,” says Jens Daniel Müller, a researcher from the institute.
Scientists and climate activists have expressed concerns about the reality of the effects of climate change, as about half of all the acidification since 1800 occurred after 1994, and our CO2 emissions have risen exponentially.
Speaking on the data, Hongjie Wang at the University of Rhode Island says, “This is more or less what researchers expected would happen as the ocean takes up more CO2.” He further added that it was a different thing seeing the data coming in to affirm their expectations.
The magnitude of the acidification is enough to threaten the survival of organisms in large areas of the ocean. Pteropods like sea snails and sea butterflies are at particular risk because they build their shells out of calcium, which dissolves if the water gets too acidic.
The rise in acidification has also doubled the areas where cold-water corals will have trouble surviving. Studies have shown that the aragonite saturation horizon (ASH)—the depth below which aragonite (a form of calcium carbonate) dissolves—has risen in many areas due to acidification. Research on cold-water corals off the coast of Norway indicates a measurable decline in skeletal growth as the waters become less saturated with aragonite. These changes threaten not just the corals but also the diverse marine species that rely on them for habitat.
“Even if we were able to stop CO2 emissions immediately, we would still – for a couple of hundred years or so – see a process of ocean acidification in the interior,” says Müller.
