As Arctic sea ice vanishes, a vital nutrient is disappearing with it and putting the food chain at risk

A new Arctic study is drawing attention for a troubling reason. As sea ice disappears, so does a nutrient that helps keep the ocean food web intact, according to a University of Edinburgh news release.

Researchers said that loss could ripple from microscopic plankton all the way up to fish, seabirds, marine mammals, and even people who depend on healthy northern fisheries.

The study focused on Fram Strait, a major pathway for Arctic waters flowing into the Atlantic.

After analyzing more than 20 years of ocean sampling data, scientists found that nitrate in outflowing Arctic waters has been steadily declining since about 2009.

The decline coincides with a dramatic period of sea ice loss.

As more shallow Arctic waters are exposed to sunlight, benthic denitrification speeds up, converting nitrate into nitrogen gas and removing that nutrient from seawater.

"For years, sea-ice loss in the Arctic Ocean was expected to increase phytoplankton growth because more sunlight could reach surface waters," researcher Marta Santos-García said.

But the team has said the Arctic appears to be shifting "from a system mainly limited by light to one increasingly limited by nitrate availability."

Nitrate is essential for plankton growth, and those organisms form the base of the Arctic food chain.

If nitrate levels continue to fall, the region may eventually support only smaller plankton species. 

That would mean less energy and nutrition moving up the food web to fish, seabirds, and marine mammals.

Communities tied to commercial fishing in the North Atlantic could eventually feel the effects if food webs continue to shift.

The change could also affect carbon storage, because plankton help draw carbon from the atmosphere through photosynthesis.

If the Arctic produces less plankton, the ocean may also become less effective at storing carbon.

The researchers said this shift is unlikely to reverse as sea ice loss continues.

Santos-García called the implications "far-reaching" for marine life, food webs, and the Arctic's place in the climate system.

Professor Raja Ganeshram said the Arctic ecosystem appears to have crossed a "tipping point" around 2009.

He added that scientists now need to closely monitor how the shift moves through the food chain, warning that it could have "profound implications for us," including for North Atlantic commercial fishing.

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