Summary Points
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Tiny ear stones rewrote Arctic history: Researchers found evidence that ice and polar cod lived near the North Pole nearly 48,000 years ago.
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Food shaped survival: Cod vanished from the northern record during the ice age’s harshest stretch, likely because thick ice and reduced ocean circulation limited food.
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Ice cod found a refuge: It survived north of Greenland, possibly around open-water patches called polynyas,polar cod seems to have moved farther south.
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Warming brings new threats: Today’s resident cod may face competition and predators moving north, with ice cod especially at risk due to its reliance on icy waters and low genetic diversity.
Ear stones reveal life under the ice
Tiny fish ear stones can outlast the fish that carried them. By studying their shapes and ages, researchers traced Arctic cod through nearly 48,000 years of history.
The team found both ice cod and polar cod near the North Pole during milder periods. Thinner ice may have let more sunlight reach the water, helping algae grow. Ocean currents could also have brought nutrients and plankton. Together, those clues suggest that a food web once thrived beneath Arctic ice.
Cold brought a different kind of pressure
The record near the pole goes quiet from about 35,000 to 12,000 years ago. During the coldest stretch, thick summer ice and weaker ocean flows may have limited food. Farther north, however, ice cod left ear stones from around 20,000 years ago. Small open-water patches may have helped them survive, though the stones cannot confirm that explanation.
The two species also followed different paths. Ice cod may have endured the deep freeze in a small refuge and lost genetic variety. Polar cod likely moved south and retained more. After the ice age, both returned to the northern record.
Warming changes the challenge
Today, thinner Arctic ice may seem like good news for fish. Yet warmer water also lets Atlantic cod and Alaska pollock move north. These newcomers could compete for food and prey on resident fish. Ice cod may face the greatest risk because it relies on cold conditions and has less genetic variety.
There is no simple fix for a warming ocean. Still, researchers can use ear stones in more seafloor samples to track change across the Arctic. That practical approach will not protect fish on its own, but it can help guide monitoring and decisions. Their story also offers a wider lesson: life adapts, but each new climate brings costs as well as opportunities.
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