Researchers at the University of Edinburgh have warned that the Arctic Ocean may have passed an ecological tipping point caused by the long-term loss of sea ice.
A new study led by Edinburgh scientists found that melting Arctic sea ice is driving major chemical changes in the ocean, disrupting the marine food chain and potentially affecting commercial fishing and global climate systems.
The research identified a sharp decline in nitrate levels, a vital nutrient needed for plankton growth.
Plankton forms the foundation of the marine food chain, supporting fish, seabirds and marine mammals throughout the Arctic ecosystem.
Scientists say the decline is linked to benthic denitrification, a process where nitrate is removed from seawater and converted into nitrogen gas.
The process has accelerated in shallow Arctic regions newly exposed to sunlight following significant sea ice loss since 2009.
Researchers analysed more than 20 years of data collected from the Fram Strait, the main passage between the Arctic Ocean and the Atlantic Ocean.
The study identified a clear shift beginning around 2009, when nitrate levels in waters leaving the Arctic began falling alongside shrinking sea ice coverage.
They warned the changes could have long-term consequences for marine ecosystems, carbon storage and fisheries in the North Atlantic.
The study also suggests the Arctic may increasingly support only smaller plankton species, reducing food availability for larger marine animals higher up the food chain.
Scientists believe the changes are unlikely to reverse due to the continuing decline in sea ice.
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Marta Santos-García, PhD student at the University of Edinburgh’s School of GeoSciences and co-lead author of the study, said: "For years, sea-ice loss in the Arctic Ocean was expected to increase phytoplankton growth because more sunlight could reach surface waters.
"Our findings suggest that this relationship has changed: the Arctic Ocean appears to have shifted from a system mainly limited by light to one increasingly limited by nitrate availability, with far-reaching consequences for marine ecosystems, food chains and the role of the Arctic in the Earth’s climate."
Professor Raja Ganeshram, of the University of Edinburgh’s School of GeoSciences, said: "The changes we report suggest that the Arctic Ocean ecosystem passed a tipping point around 2009.
"How this change cascades through the food chain needs to be closely monitored as this has profound implications for us, including on commercial fishing in the North Atlantic Ocean."
