Coastal Seas Are Acidifying Shockingly Fast

New research from the University of St Andrews reveals that coastal seas — especially in upwelling zones — are becoming acidic far more rapidly than previously understood. In these regions, deep, CO₂-rich waters rise to the surface, adding acidity well beyond what global atmospheric CO₂ increases alone would cause.

Why Upwelling Zones Are Especially Vulnerable

Upwelling is a natural ocean process: deep ocean waters — rich in nutrients but also naturally more acidic — are pushed upward toward the coast. Normally, when atmospheric CO₂ dissolves in surface water, gradual acidification follows. But in upwelling zones, these deep, acidic waters mix with surface waters already absorbing CO₂, amplifying the acidification effect.

To assess how acidity has changed over time, researchers examined historical coral records and measured boron-isotope signatures preserved in coral skeletons. Using these data along with a regional ocean model, they reconstructed acidity trends over the 20th century and projected future shifts. Their results show that acidification in these zones is occurring at rates far exceeding those expected from rising atmospheric CO₂ alone.

What It Means for Marine Life, Fisheries, and Communities

Upwelling systems are among the most biologically productive zones in the world’s oceans and are vital for global fisheries. Accelerated acidification threatens marine ecosystems — including coral reefs, shellfish, and plankton — which many coastal communities depend on for food and livelihoods.

The researchers warn that these changes not only endanger marine biodiversity but also risk the economic stability of millions who rely on coastal fisheries. According to co-author James W. B. Rae, “the ocean becoming more acidic poses major risks to marine ecosystems and the communities and economies they support.”

A Global Pattern, Not Just Local Concern

While the study focused on the California Current, similar upwelling systems worldwide — such as the Humboldt Current off Peru and the Benguela Current and Canary Current along Africa’s west coast — could undergo comparable intensification of acidification as CO₂ levels continue to rise.

The findings highlight a broader, global environmental challenge: many coastal communities around the world could face ecological and economic consequences unless climate change mitigation efforts curb CO₂ emissions.

Why This Study Matters

This research underscores how human-driven CO₂ emissions — combined with natural ocean processes like upwelling — can interact to accelerate environmental change in ways scientists are only beginning to understand. It calls attention to the need for region-specific monitoring of ocean chemistry, not just global averages.