Vermillion rockfish and soft coral observed during an expedition in Channel Islands National Marine Sanctuary. Image courtesy of Marine Applied Research and Exploration, NOAA.
- When compared with historical samples, corals show that the Salish Sea and California Current System are acidifying faster than anticipated because of greenhouse gas emissions. Models indicate that at this rate, carbon dioxide levels in the oceans will continue rising faster than concentrations in the atmosphere.
- Increasingly acidic seas pose growing risks to sensitive marine life, from clams and oysters to any organism with a spine, as well as economically important fisheries and the communities that depend on them.
- British marine ecologist Stephen Widdicombe calls the threat existential. Our continued failure to cut emissions can only lead to “a world where uncontrolled climate change including ocean acidification leaves us with an ocean that is less productive, less diverse and less able to provide humans with the wealth of services that we currently all benefit from,” he said.
In 1888, researchers aboard the R/V Albatross began the world’s first concentrated marine research expeditions off California’s Pacific coast. The team collected untold plant and animal specimens, including orange cup corals, which they carefully preserved and stored in collections at the Smithsonian Institution.
These specimens have now become rare physical evidence of ongoing changes in the chemistry of the Pacific Ocean as seawater absorbs the carbon dioxide released into the atmosphere by burning fossil fuels.
Researchers recently analyzed these 130-year-old samples, which come from a time before the Industrial Revolution’s greenhouse gas impacts had really kicked in. Then they compared them with new specimens collected in the same locations by a team aboard another research vessel, the R/V Rachel Carson, in 2020.
They discovered that this region is acidifying, far faster than models have predicted, findings they recently published in the journal Nature Communications.
“Ocean acidification is not a distant or abstract phenomenon. It is already underway, it is amplified in some regions, and it has real consequences for ecosystems and coastal economies today,” study lead author Mary Margaret Stoll, from the University of Washington, told Mongabay.
This research focused on the Salish Sea and the cold California Current System, an interweave of four currents predominantly flowing south from the Canadian province of British Columbia to the Mexican state of Baja California. Prevailing winds push water away from the coast along these currents, drawing water up from the deep, bringing nutrient-rich sediments along with it. These support exceptional biodiversity and lucrative fisheries.
Bringing orange cup coral samples from the Salish Sea aboard the research ship R/V Rachel Carson. Image by Mary Margaret Stoll.
The waters off the North America Pacific form one of the most productive marine ecosystems on Earth. But now, industrial carbon emissions, deforestation and other human activities are changing ocean chemistry, lowering the pH and making waters more acidic in a process known as ocean acidification.
This threatens the long-term survival of economically and ecologically important marine creatures, including clams, sea urchins, oysters, and both shallow- and deep-water corals, as well as certain plankton, which form the base of the ocean food web.
If current trends continue, ocean surface waters could reach acidity levels about 150% higher than pre-industrial levels — higher than they’ve been for more than 20 million years — according to the U.S. National Oceanic and Atmospheric Administration.
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Ocean chemistry
CO₂ absorbed by the ocean reduces the availability of carbonate ions in seawater, making it harder for marine organisms to form calcium carbonate shells. That leaves species like crustaceans and corals with thinner, weaker shells and other organisms with more fragile skeletons.
This ocean chemistry imbalance continues to worsen with rising atmospheric CO₂. The discovery that acidity is increasing faster than greenhouse gas levels in the atmosphere is worrying, Stoll said.
“What concerns me most from our study is that acidification in the Salish Sea and the California Current System isn’t just keeping pace with atmospheric CO₂, it’s actually amplified,” she said.
CO₂ concentrations in the atmosphere rose by about 120 parts per million (ppm) since 1888, to more than 414 ppm by 2020. Meanwhile dissolved CO₂ in the Salish Sea rose even faster, by the equivalent of around 172 ppm, the study found.
…The bigger picture
Earth’s oceans have so far protected us from the more severe effects of climate change by absorbing about 31% of fossil fuel emissions since the 1800s, according to previous research published in the journal Science.
But there’s no such thing as a free lunch: This increase corresponds almost exactly to 30% higher ocean acidity than during the early years of the Industrial Revolution, when steel and textile manufacturing, petroleum refining and other carbon-intensive industries emerged and emissions rose. Prior to that, global greenhouse gas emissions were low.
While the California Current System supports exceptional biodiversity and lucrative fisheries, nutrient-rich seawater from these depths also carries a sting in its tail: It’s loaded with CO₂ absorbed decades ago.
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Mongabay, 22 December 2025. Full article.
