Deep Ocean Water Is Making Coastal Seas Acidify Much Faster, Scientists Say

New research reveals that coastal upwelling regions are acidifying much faster than expected as deep CO₂-rich waters rise to the surface. This accelerated change threatens marine ecosystems, major fisheries, and coastal communities worldwide.

Scientists have found that coastal seas are acidifying far faster than previously believed — particularly in regions where strong upwelling currents pull deep, CO₂-rich waters toward the surface. New research from the University of St Andrews shows that these coastal zones may become significantly more acidic than predicted from atmospheric CO₂ trends alone, raising urgent concerns for marine ecosystems, fisheries, and coastal livelihoods.

Upwelling Waters Intensify Coastal Acidification

Under normal conditions, seawater becomes gradually more acidic as it absorbs additional carbon dioxide from the atmosphere. But upwelling regions behave differently. Here, deep waters — naturally more acidic due to the microbial breakdown of organic material — rise to the surface and bring accumulated CO₂ with them. Once exposed to the air, they absorb even more CO₂, creating a powerful double effect that accelerates acidification at an alarming rate.

Coral Records Reveal How Fast Conditions Are Changing

To understand long-term trends, scientists examined boron isotope signatures in historic coral samples. These corals capture chemical changes in seawater, offering a window into past acidity levels. By pairing these natural archives with advanced regional ocean models, the research team was able to reconstruct historic shifts and project future acidity in upwelling regions such as the California Current.

The findings show that these coastal zones are acidifying at rates far beyond what atmospheric CO₂ alone would cause — a warning sign for marine life and coastal economies that depend heavily on healthy ocean ecosystems. The study is published in Nature Communications. 

Global Upwelling Zones Face Similar Threats

The California Current is only one example. Other major upwelling systems  including the Humboldt Current off Peru and the Benguela and Canary Currents along the west coast of Africa may face the same extreme intensification of acidification as global CO₂ levels rise.

Researchers stress that climate solutions like renewable energy adoption, electrification, and reducing carbon emissions will not only slow global warming but also help curb the rapid acidification of coastal seas. Without swift action, these highly productive regions — home to some of the world’s most vital fisheries — could undergo profound ecological and economic disruption.