Ocean in coastal areas becoming more acidic than previously thought

New research from the university of St Andrews has found that some coastal areas will become much more acidic than previously anticipated.

Because atmospheric CO₂ and ocean pH (acidity) are tightly coupled, the more CO₂that is released into the atmosphere, the more is absorbed by seawater, making the ocean progressively more acidic.   However,  in a paper published in Nature Communications,  researchers, using the California Current as an example, show that oceanic upwelling systems actually amplify ocean acidification.   

Upwelling is where nutrient- rich and already acidic  waters from deep in the oceans rise along the coast. When organic matter from the surface ocean sinks to the deep ocean, microbes gradually break it down in a chemical reaction that releases CO₂ and increases seawater acidity. When this deep water upwells, it brings the acidity to the surface, where it further reacts with the atmospheric CO₂, which makes these water masses even more acidic.  

The researchers used historic coral samples and boron isotope signatures recorded in their skeletons to reconstruct how acidity changed over the 20^th century, and then applied a regional ocean model to predict how acidity will change during the 21^st century.   The study showed that in these upwelling regions of the ocean, ocean acidification outpaces the level “expected” from rising atmospheric CO₂alone. This is because the upwelled water masses are acidic to start with and anthropogenically rising CO₂ exacerbates the acidity.   

Upwelling systems are among the most productive systems on our planet and support much of the world’s fisheries. Understanding how they respond to rising CO₂₂ is therefore not only critical for ocean science, but also carries major implications for fisheries and their potential vulnerabilities.  

Co Author Dr Hana Jurikova, Senior Research Fellow in from the School of Earth and Environmental Science, said: “Predicting how upwelling systems will respond to climate change is highly complex, as anthropogenic influences interact with natural sources of ocean acidification. Our research shows that such interactions can amplify environmental change in the California Current System, highlighting the need for similar studies in other regions to better anticipate future change.”  

The California Current can be used as an example of other upwelling systems. Other important areas of coastal upwelling around the world include the Humbold Current off the coast of Peru or the Benguela and Canary Currents off the coast of west Africa.   

Co Author Dr James Rae, Reader in the School of Earth and Environmental Science, said: “the ocean becoming more acidic poses major risks to marine ecosystems and the communities and economies they support. The solutions we now have for climate change, like heat pumps and electric vehicles, also fix ocean acidification, so it’s critical that we support them”.