Ancient Fish Ear Bones Reveal Arctic Cod History Near the North Pole
Tiny ear bones found on the Arctic seafloor show that two kinds of cod lived near the North Pole tens of thousands of years ago.
Scientists have found tiny ear bones from fish in deep-sea sediment, and these bones tell a story about cold waters in the far north. The discovery was made during an expedition aboard the Swedish icebreaker Oden. The bones, called otoliths, were found in five sediment samples from different locations across the Arctic Ocean.
An otolith is a small structure made of calcium carbonate that sits in the inner ear of bony fish. The study was published in the journal Nature Communications.
The otoliths were dated at the Alfred Wegener Institute's radiocarbon-dating facility, known as MICADAS. This work showed that ice cod and polar cod lived in the central Arctic Ocean between 48,000 and 35,000 years ago. Both species were found at latitudes of 87 to 89 degrees north, which is close to the North Pole.
The Last Glacial Maximum was a cold period that lasted from around 27,000 to 19,000 years ago. During this time, both species disappeared from the North Pole area. However, ice cod survived the peak of this cold period around 20,000 years ago at latitudes of 84 to 85 degrees north.
The researchers suggest that ice cod may have survived in polynyas. A polynya is an area of open water surrounded by sea ice. Both species came back to the area around 12,000 years ago, when the climate warmed.
Ice cod and polar cod are thought to have split into separate species between 5 and 10 million years ago. Today, sea ice over the central Arctic Ocean is becoming thinner, younger and more dynamic. The study also notes that the northward spread of Atlantic cod and Alaska pollock will increase competition and predation in the Arctic Ocean.
The study's lead author is Pauline Snoeijs-Leijonmalm, and the first author is Julek Chawarski, both from Stockholm University.
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