This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The glacial Arctic Ocean was not a barren ice desert but a breeding ground for the evolution of cold adaptation in marine fish. 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.
"These tiny bones, the otoliths, provide a direct record of when and where fish occupied Arctic waters during major climate transitions," says first author Julek Chawarski, who worked in the Department of Ecology, Environment and Plant Sciences at Stockholm University during the research project. The paper is published in the journal Nature Communications. Otoliths are small calcium carbonate structures in the inner ear of bony fish.
They function as part of the fish's balance and hearing organs, detecting movement, gravity and sound vibrations. The otoliths were found during a research expedition to the Arctic, coordinated by Stockholm University, aiming to map today's fish stocks using echo sounding and fish catches in the water column. "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 sediment otoliths provided direct evidence of past vertebrate life in the central Arctic Ocean, a region where such evidence is exceptionally scarce. "The presence of fish indicates that a complex food web similar to the one today existed here during the last ice age as well. Fish are key organisms in the food web.
Their presence indicates the presence of plankton, which serves as fish food, and fish themselves provide food for seabirds and marine mammals," Snoeijs-Leijonmalm continues. The researchers found more otoliths in the first sediment sample, and four additional samples from different locations across the Arctic Ocean also contained otoliths. After the expedition, the remains were identified and dated at the Alfred Wegener Institute's radiocarbon-dating facility (MICADAS).
"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. "Otoliths were rare in the samples; we needed to carefully sieve through large volumes of sediment to find them, but it was well worth it. Otoliths provide an excellent way to study past Arctic ecosystems," says co-author Flor Vermassen, a researcher in the Department of Geological Sciences at Stockholm University.
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