UK Waters Facing Accelerated Ocean Acidification, New PML-Led Study Reveals

Revealing critical insights into air-sea carbon dioxide exchanges, pH trends in the North Atlantic, and detailed observations in UK shelf seas, the study also details how ocean acidification impacts marine species through both direct physiological effects from changing pH and CO2 levels and indirect effects via food web disruption.

While some organisms like certain phytoplankton and seaweeds may show positive or neutral responses to elevated CO2, many marine invertebrates and fish species experience neutral or negative effects. Species that build calcium carbonate structures, including corals, shellfish, and important plankton groups, face particularly high risk. Even more developed organisms like fish, though less susceptible to direct impacts, could suffer from the loss of key prey species. The research highlights the need for better integrated approaches that scale from experiments to biogeochemical models. It also emphasizes the urgent need for enhanced observational capacity and improved model accuracy to better understand and address ocean acidification.

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Key highlights from the update:

• Atmospheric CO2 surpassed 420 ppm in 2024, continuing to rise by approximately 2.5 ppm annually over the past decade
• The global ocean absorbs roughly 25% of anthropogenic carbon dioxide emissions each year
• The North Atlantic Ocean, containing the highest levels of anthropogenic CO2 among ocean basins, is experiencing ongoing surface water acidification
• Bottom waters in some locations are acidifying faster than surface waters
• Certain marine species already show effects from ocean acidification during short-term fluctuations, potentially serving as indicators for long-term ecosystem impacts
• Models project that continental shelf seawater pH will continue to decline through 2050, with rates increasing in the second half of the century depending on emissions scenarios
• Coastal pH decline is projected to be faster in areas like the Bristol Channel compared to the Celtic Sea
• Under high-emission scenarios, bottom waters on the North-West European Shelf seas could become corrosive to aragonite as soon as 2030

Furthermore, by 2100, the projections suggest up to 90% of north-west European shelf seas will experience calcium carbonate undersaturation for at least one month yearly. This creates conditions where shellfish, corals, and important plankton species may struggle to form shells or experience shell dissolution, potentially causing significant harm to these organisms and broader marine ecosystems.

“This evidence update highlights the critical importance of continued monitoring and improved modelling of ocean acidification,” said Prof. Findlay. “The accelerating rates of acidification in UK waters demand urgent attention and action as they pose a growing threat to many of the marine species and ecosystems we depend on.”

MCCIP, established in 2005 and currently chaired by PML’s Professor Matt Frost, serves as the UK’s primary independent source of marine climate change evidence and adaptation advice, supporting policy development and industry response to climate risks.

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For more information on MCCIP visit: About MCCIP | Marine Climate Change Impacts Partnership