While global attention often focuses on warming oceans and melting ice sheets, a new scientific investigation has uncovered another accelerating crisis beneath the surface: rapidly intensifying ocean acidification in one of the world’s most productive marine ecosystems. A groundbreaking study published on 28 January 2025 in Nature Communications, titled “A century of change in the California Current: upwelling system amplifies acidification,” shows that the California Current System (CCS) has been acidifying significantly faster than previously understood.
Led by Mary Margaret V. Stoll, together with a multidisciplinary team of ocean chemists and climate scientists across the United States, the research reveals that the rate of acidification in many subsurface layers of the CCS has exceeded the pace of atmospheric CO₂ rise by a wide margin. The findings point to a powerful interaction between anthropogenic CO₂ and natural ocean processes that is accelerating chemical change in coastal waters.
The team reconstructed historical ocean chemistry dating back to the 1890s using boron isotope (δ¹¹B) measurements preserved in the skeletons of the deep-water coral Balanophyllia elegans. These coral archives allowed scientists to compare pre-industrial ocean acidity with modern conditions. Their analysis shows that waters in the Salish Sea—an important northern component of the CCS—experienced an average increase of 172 ± 41 µatm in pCO₂ over the past century. This rise is substantially larger than the increase in atmospheric CO₂ over the same timeframe.
Coastal Ocean is Changing Faster
According to the study, the amplified acidification is driven not only by atmospheric carbon absorption but also by internal ocean processes, particularly upwelling. This mechanism brings carbon-rich deep waters to the surface, intensifying acidification in the productive mid-water zones where many species reproduce and feed. Additional carbon release from the decomposition of organic matter further lowers pH levels, creating chemical conditions that are increasingly corrosive to marine life.
The research team integrated the coral geochemical data with a high-resolution biogeochemical-physical ocean model—the Regional Ocean Modeling System (ROMS)—to examine long-term trends across the California Current. The model reveals an alarming pattern: while surface waters track atmospheric trends, subsurface layers between 50 and 200 meters have acidified up to 50 percent faster than the atmosphere.
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At around 75 meters depth, simulations indicate that pH levels could fall to 7.5, a threshold considered dangerous for calcifying organisms such as shellfish, crustaceans, and certain species of plankton. The model also projects declines in aragonite saturation to levels where water becomes corrosive to shells and skeletons, particularly under high-emission scenarios for the remainder of this century.
“This research shows that the coastal ocean is changing faster than we thought,” said Stoll, the study’s lead author.
“Ocean acidification in the California Current is not just a reflection of atmospheric CO₂ increases—it is being heightened by the natural dynamics of the system. That means marine organisms are facing chemical changes at a rate that many cannot adapt to.” Stoll added that the most severe acidification is happening in subsurface layers that are critical for commercially important species. “When these mid-depth habitats become chemically unstable, the impacts cascade through the entire food web.”
Adaptive Capacity
Co-author Curtis A. Deutsch warned that the speed of chemical change could exceed the adaptive capacity of many organisms. “Marine life has dealt with temperature and pH shifts in the past, but never at the pace we are now observing,” he said.
Deutsch emphasized that fisheries dependent on crab, salmon, and shellfish could face long-term impacts if acidification continues unchecked. “What we’re seeing suggests a potential ecological tipping point.”
The study’s projections for the next century raise further concerns. If global carbon emissions remain high, the CCS could experience an additional 0.30 drop in pH in its subsurface zones by 2100. Waters may also become undersaturated with respect to aragonite, inhibiting shell formation and increasing mortality among vulnerable species. These chemical changes, the researchers argue, could disrupt marine ecosystems long before the end of the century.
Beyond the California coast, the findings carry global implications. The authors note that similar upwelling-driven systems exist off Peru, Chile, South Africa, and West Africa—regions that support major fisheries and coastal economies. The same amplification mechanisms observed in the CCS may be occurring in other regions but remain under-studied due to limited long-term chemical records.
“The California Current may be a warning signal for upwelling systems worldwide,” Stoll said. “If this trend is global, the scale of the ecological and economic risk is far greater than currently understood.”
The authors argue that conventional climate models and monitoring systems have underestimated the speed of ocean acidification in coastal and mid-depth environments. They call for expanded chemical monitoring and urgent global mitigation measures to slow CO₂ emissions.
The new research underscores that ocean acidification is no longer a slow-moving phenomenon. It is accelerating, intensifying, and unfolding in critical marine zones that support some of the world’s most productive fisheries. Without swift action, scientists warn, the consequences—both ecological and economic—could unfold within decades, not centuries. (Sulung Prasetyo)
