Atlantic cod and squid, which have large eyes, have invaded as sunlight penetrates previously darkened waters.
They are also providing a food source for mammals. Seals and walruses can dive more than 500 metres.
Co author Dr Hauke Flores, a biologist at the Alfred Wegener Institute, Bremerhaven, said: “The availability of small and even some larger fish in the Atlantic water layer could explain why seals, walrus and polar bear can be found even at the North Pole.”
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