Ancient fish bones reveal how Arctic cod species survived the last ice age

The glacial Arctic Ocean was not a barren ice desert but a breeding ground for the evolution of cold adaptation in marine fish. This article has been reviewed according to Science X's editorial process and policies.

This is the main conclusion of a new scientific publication from Stockholm University that examines small fish bones found in deep-sea sediments during an expedition aboard the Swedish icebreaker Oden. The paper is published in the journal Nature Communications.

But when the first bottom samples arrived on deck, we immediately noticed a fish otolith," says lead author of the study, professor Pauline Snoeijs-Leijonmalm from the Department of Ecology, Environment and Plant Sciences at Stockholm University. The researchers found more otoliths in the first sediment sample, and four additional samples from different locations across the Arctic Ocean also contained otoliths.

The measurements revealed the distribution patterns of two cold-adapted Arctic-endemic fish species, ice cod and polar cod, over the past 50, 000 years," says Snoeijs-Leijonmalm. The otoliths show that ice cod and polar cod were present in the central Arctic Ocean between 48, 000 and 35, 000 years ago, during the last ice age when ecosystem productivity was very low.

Both species were found at latitudes of 87, 89°N, close to the North Pole. During the Last Glacial Maximum, the coldest period of the last ice age, which lasted from around 27, 000 to 19, 000 years ago, both species disappeared from the North Pole area.

However, ice cod survived the peak of this period around 20, 000 years ago farther south, at 84, 85°N.

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