Both species were present near the North Pole 48,000–35,000 years ago, when ecosystem productivity was low. During the coldest period of the ice age, they disappeared from the North Pole region. Ice cod appears to have survived north of Greenland, possibly in polynyas. Both species returned as the climate warmed around 12,000 years ago.

The findings provide rare evidence of vertebrate life in the central Arctic Ocean. The presence of fish suggests that a food web including plankton, fish, seabirds and marine mammals existed there during the ice age. Today, their adaptations to cold may make them vulnerable as the ocean warms and species such as Atlantic cod and Alaska pollock spread northwards.

The Synoptic Arctic Survey 2021 expedition was carried out by the Swedish Polar Research Secretariat. Pauline Snoeijs-Leijonmalm, Professor of Marine Ecology at the Department of Ecology, Environment and Plant Sciences at Stockholm University, was the expedition’s Chief Scientist. The expedition was also part of an international initiative in which Oden was one of around ten research vessels surveying the Arctic Ocean in 2020, 2021 and 2022.