Reduced sea ice appears to be causing a decrease in the nutrient nitrate, affecting tiny organisms that form the base of the ocean food chain and absorb carbon dioxide from the atmosphere, according to a new study.
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Sarah Hashemi |
July 8, 2026
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Scientists analyzed about 25 years’ worth of data from the Fram Strait, the passageway where the Arctic and Atlantic oceans meet.
Lawrence Hislop / Norwegian Polar Institute
The Arctic Ocean is losing sea ice at an unprecedented rate, largely due to anthropogenic climate change. The amount waxes and wanes with the seasons, but satellite images show that in recent decades more and more ice has melted in the summer and less ice has formed in the winter.
Scientists now say ice water loss has crossed a critical tipping point, a change that could have devastating effects on wildlife and the ocean’s ability to stabilize Earth’s climate.
Research published in journals Communication Earth and Environment On May 28, scientists discovered that melting ice has significantly reduced levels of nitrate, a key nutrient in the ocean. The researchers believe this change is irreversible, but it may mean that in the future the Arctic Ocean will only be able to support phytoplankton (plant-like microorganisms), which are smaller and less nutritious than the larger microorganisms that play a major role at the base of ocean food webs.
“For years, it has been expected that reduced sea ice in the Arctic Ocean would increase phytoplankton growth as more sunlight could reach surface waters,” study co-author Marta Santos García, a marine biogeochemist at the University of Edinburgh in Scotland, said in a statement.
But she and her colleagues noticed that relationship changing. To do so, the researchers examined ocean sampling data collected from 1998 to 2023 in the Fram Strait, the passage between Greenland and Svalbard in the Norwegian archipelago, where the Arctic and Atlantic oceans meet. Previous studies have shown that sea ice has become thinner in recent years. So scientists wanted to know how it affects the interactions between biology, chemistry, and geology.
Their analysis suggests that nitrate levels crossed a tipping point around 2009. Since then, nutrients in the Fram Strait have steadily declined, coinciding with a dramatic decline in sea ice.
Did you know? ice-free arctic
In 2024, researchers running computer simulations of the climate reported that the Arctic could experience its first ice-free summer day as early as 2027.
The shrinking sea ice likely accelerated a process called bottom denitrification, the researchers said. Large areas of the region are now exposed to sunlight, allowing photosynthetic phytoplankton to thrive. When microorganisms die, they sink to the ocean floor, where they are broken down by bacteria and archaea. Eventually all the nitrates will be used up. This means the water flowing into Fram Strait and other areas will have very few nutrients, and smaller, more nitrate-efficient phytoplankton (called microplankton) will take over.
“A shift towards smaller phytoplankton has already been observed in parts of the Arctic, but these changes have not previously been associated with nitrate loss,” Santos García told Sacha Paré. live science. Microplankton are generally not good at moving energy up the food web, which means less food for larger species of plankton, fish, seabirds and marine mammals, she added.
Earth’s climate can also be affected. This change could reduce the ocean’s carbon storage capacity because phytoplankton require nitrate for photosynthesis, which removes heat-trapping carbon dioxide from the atmosphere. That’s a big loss. According to a study published in 2019, the ocean absorbed about 30 percent of the carbon dioxide emitted by humans between 1994 and 2004.
The new study reveals that the Arctic Ocean has transitioned from a system primarily limited by sunlight to one limited primarily by nitrates, Jean-Eric Tremblay, a biologist at Canada’s Laval University who was not involved in the study, told Alec Loon. new scientist.
“What this shows is that the Arctic Ocean will not be the oasis of the future,” he added. “Increasing[phytoplankton]production increases denitrification, removes nitrates, and ultimately reduces productivity.”
Unfortunately, researchers believe that denitrification has passed the point of no return.
“Even if there is a temporary increase in sea ice, the Arctic trophic system responds over much longer time scales,” Santos-Garcia said. live science. “Increasing sea ice in the short term is unlikely to rapidly reverse the decline in nitrate stocks, and recovery may take longer.”
