Coastal waters are acidifying much faster than scientists expected

Coastal waters in the Pacific Ocean are becoming more acidic faster than expected. New research shows that subsurface waters in the California Current are becoming acidic roughly 50% faster than atmospheric CO2 alone would suggest.

The California Current is a major ocean current that flows southward along the western coast of North America. These waters feed fisheries from British Columbia down to Baja California.

The rise of acidic coastal water

The work was led by Mary Margaret V. Stoll, a marine scientist at the University of Washington (UW). Her research focuses on using coral skeletons to reconstruct changes in ocean chemistry through time.

These coasts sit atop intense upwelling, the wind-driven rise of deep seawater along shores. That deep water carries extra carbon and is already more acidic when it reaches the surface.

As organic matter sinks, microbes release CO2 that adds to the carbon load. Earlier evidence showed corrosive water already reaching the shelf decades sooner than expected.

Once this carbon-rich water reaches the surface, it mixes with modern air and loses some of its buffering capacity – the property that helps seawater resist shifts in pH.

This weakened buffering allows added carbon to have a stronger effect, causing pH to drop even faster.

Anticipating future ocean changes

Beneath Puget Sound and the Salish Sea, cold water corals quietly record history. The team measured boron isotopes, natural variants of boron atoms used as pH tracers, in museum and modern samples.

The researchers paired those records with a coastal ocean model to compare past and present.

In the Salish Sea, the partial pressure of dissolved carbon dioxide (pCO2), climbed by 172 microatmospheres while pH fell by about 0.095.

Globally, surface ocean pH has dropped by about 0.1 as the ocean has absorbed roughly one-quarter to one-third of human carbon dioxide emissions. Those broad changes provide the backdrop for what coastal waters are now showing.

Dr. Hana Jurikova, senior research fellow at the University of St Andrews, explained that 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.” said Dr. Jurikova.

Marine life in acidic coastal waters

Model simulations indicate the amplification will continue through this century in mid-depth layers.

The subsurface increase outpaces the atmospheric trend by 20 to 60 percent, which puts added pressure on coastal ecosystems.

Long-term records tell a similar story in the south, where experts previously found a steady pH decline since the 1980s. 

The California Current supports valuable fisheries and coastal economies. Early life stages of iconic species depend on water chemistry that allows shells to form.

Larval Dungeness crabs are already showing shell pitting and sensory damage in today’s coastal waters, according to a 2020 study. These problems can cut survival rates, with consequences that can spread through the entire fishery.

This is not only a Pacific Northwest story. Upwelling coasts off Peru, Namibia, and northwest Africa face similar chemical pressures. Local communities depend on the productivity of those waters.

How food webs shift

Marine food webs along the Pacific coast depend on tiny drifting organisms that react quickly to chemical shifts.

These plankton form the first link in a chain that supports fish, birds, and even marine mammals, and many species struggle when pH drops in mid depth waters. 

Acidification also alters nutrient cycles in ways that can favor some organisms over others, which reshapes the balance of species that have lived in these waters for generations.

Shifts in food web structure often develop slowly at first, then gain speed as conditions cross biological thresholds.

Researchers tracking long-term coastal datasets have noted early signs of these changes, including altered plankton communities during low pH events. 

Those changes can ripple upward into fisheries when young fish lose access to stable food sources, which adds another layer of stress for coastal regions already facing economic pressure.

The risks of an acidic ocean

“The ocean becoming more acidic poses major risks to marine ecosystems and the communities and economies they support,” said study co-author Dr. James W. B. Rae.

“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.”

According to NOAA, the most direct way to slow ocean acidification is to cut carbon dioxide emissions.

Improved monitoring and local planning can help coastal communities and shellfish growers cope in the short term, but the chemistry ultimately follows the global emissions curve.

The study is published in the journal Nature Communications.

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