Scientists find coastal seas acidifying shockingly fast

Because atmospheric CO₂ and ocean pH (acidity) rise and fall together, any increase in CO₂ above the ocean is soon reflected in the water below. This steady absorption of carbon makes seawater progressively more acidic over time.

Upwelling Systems Intensify Ocean Acidification

In a study published on November 13th in Nature Communications, the research team used the California Current as a case study and found that upwelling regions significantly intensify ocean acidification rather than simply reflecting atmospheric trends.

Upwelling occurs when deeper ocean layers, which are already nutrient rich and naturally acidic, move upward toward the shore. Organic material from surface waters sinks and is broken down by microbes in the deep ocean, a process that releases CO₂ and increases acidity. When these deep waters rise again, they deliver this accumulated acidity back to the surface, where the water interacts with atmospheric CO₂ and becomes even more acidic.

Historic Corals Reveal Long-Term Changes

To examine how acidity has evolved over time, the researchers analyzed historic coral samples and measured boron isotope signatures preserved in their skeletons. These records helped reconstruct changes in coastal acidity over the 20th century. The team then used a regional ocean model to estimate how acidity is likely to shift during the 21st century.

Their findings show that upwelling zones experience acidification rates that exceed those "expected" from atmospheric CO₂ alone. The key factor is that upwelled water is already acidic, and rising CO₂ from human activities further intensifies this effect.

Implications for Fisheries and Climate Change

Upwelling systems rank among the most biologically productive regions on Earth and play an essential role in supporting global fisheries. Understanding how these systems respond to rising CO₂ is therefore vital for both ocean science and the long-term stability of fisheries that depend on them.

Co Author Dr. Hana Jurikova, Senior Research Fellow in 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."

Global Upwelling Regions Show Similar Risks

The California Current is only one example of a much broader pattern. Other major upwelling systems include the Humboldt Current off Peru and the Benguela and Canary Currents along the west coast of Africa. Each of these regions may experience similar intensification of acidification as CO₂ levels continue to rise.

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."