Ocean in coastal areas becoming more acidic than previously thought

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https://news.st-andrews.ac.uk/archive/ocean-in-coastal-areas-becoming-more-acidic-than-previously-thought/

Tuesday 18 November 2025

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 CO2 that 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 20th century, and then applied a regional ocean model to predict how acidity will change during the 21st century.   The study showed that in these upwelling regions of the ocean, ocean acidification outpaces the level “expected” from rising atmospheric CO2 alone. This is because the upwelled water masses are acidic to start with and anthropogenically rising CO2 exacerbates the acidity.  

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https://doi.org/10.1038/s41467-025-63207-6

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1. Great Dying - what caused Earth's biggest mass extinction?

https://news.st-andrews.ac.uk/archive/great-dying-what-caused-earths-biggest-mass-extinction/

Monday 19 October 2020

New research led by the University of St Andrews and renowned German research centres helps answer one of the most asked questions in geoscience: what exactly caused the Earth’s biggest mass extinction?

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The team of researchers, led by Dr Hana Jurikova, now based at the University of St Andrews, used a novel analytical approach of different isotopes of the elements boron and carbon, retrieving the pH of the ancient ocean from fossil brachiopod shells. Although numerous brachiopod species also became extinct during the Great Dying, the team found brachiopod shells within the critical time interval which offered a snapshot of the rapid onset of the extinction. Seawater pH is a critical indicator that not only records ocean acidity, which varies depending on the amount of absorbed carbon dioxide (CO2), but together with carbon isotope constraints it also allowed the team to determine changes in the amount and sources of atmospheric CO2 at the time of the extinction event.

The team were able to determine that the trigger of the Permian-Triassic crisis was a large pulse of CO2 to the atmosphere originating from a massive flood basalt province, the result of a giant volcanic eruption in today’s Siberia. Analyses showed that the volcanisms released more than 100,000 billion tonnes of carbon into the atmosphere, triggering the onset of the extinction. This is more than 40 times the amount of all carbon available in modern fossil fuel reserves including carbon already burned since the industrial revolution.

The research team used innovative modelling to reconstruct the effect of such large CO2 release on global biogeochemical cycles and the marine environment. The findings showed that, initially, the CO2 perturbation led to extreme warming and acidification of the ocean that was lethal to many organisms, especially those building calcium carbonate shells and skeletons. The greenhouse effect, however, led to further dramatic changes in chemical weathering rates on land and nutrient input and cycling in the ocean that resulted in vast deoxygenation and probably also sulphide poisoning of the oceans, killing the remaining organism groups.

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https://doi.org/10.1038/s41561-020-00646-4

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2. Greatest mass extinction driven by changes to oceans, study finds

https://news-archive.exeter.ac.uk/2015/april/title_445410_en.html

Changes to the Earth’s oceans, caused by extreme volcanic activity, triggered the greatest extinction of all time, a study suggests. The event, which took place 252 million years ago, wiped out more than 90 per cent of marine species and more than two-thirds of the animals living on land.

It happened when Earth’s oceans absorbed huge amounts of carbon dioxide from volcanic eruptions, researchers say.

This changed the chemical composition of the oceans – making them more acidic – with catastrophic consequences for life on Earth.

The study, which is published in the journal Science and included authors from the University of Exeter, is the first to show that highly acidic oceans were to blame.

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Date: 10 April 2015

https://doi.org/10.1038/s41467-025-59038-0