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Cenozoic World

Sub-Tropical North Pole

by Alex Kirby, 7 September 2004

An international scientific team which was drilling beneath the bed of the Arctic Ocean announced that the region had enjoyed a sub-tropical climate around fifty-five million years ago.

The Arctic Coring Expedition (Acex) recovered sediment cores from nearly four hundred metres below the sea floor. Fossilised algae in the cores showed that the sea temperature was once about 20C, instead of the average now, -1.5C.

The expedition, which relied on three icebreakers during its work, headed back to Tromso in Norway in September 2004, its work now done.

Unlocking the Arctic's history

The scientists, from eight nations, recovered the cores from below the sea floor in waters 1,300 metres deep. Acex was taking cores from the Lomonosov Ridge between Siberia and Greenland. The ridge, 1,500 kilometres long, rises to 800 metres below sea level and is topped by 450 metres of layered sediments.

The scientists who took part in the expedition said, before they set sail from Tromso in August 2004, that their findings would help science to work out how long the Arctic sea ice, now in retreat, had persisted.

The cores they extracted showed that the Arctic Ocean was once a subtropical, shallow sea. The evidence, Acex said, was in the form of tiny algal fossils found in the cores, which were once marine plants and animals. They dated back to a period known as the Palaeocene-Eocene thermal maximum, a brief period which occurred around fifty-five million years ago.

Huge die-off

The period was characterised by an extremely warm climate which created a natural greenhouse effect, which caused massive amounts of carbon to be deposited in both sea and air. Atmospheric carbon levels at the time are thought to have been about 2-3,000 parts per million (ppm), compared with almost 380ppm today.

The algae found in the Lomonosov cores, which lived only in subtropical conditions, prove how warm the Arctic once was, according to Acex. The findings also showed that the ocean's temperature was once similar to the waters off New York in August.

Dr Michael Kaminski, a palaeontologist from University College London, UK, said that a mass extinction of sea-bottom-living organisms was being caused by these conditions. This eventually resulted in many species disappearing. Only a few hardy survivors endured the thermal maximum.

There was also evidence that part of the Arctic Ocean was once a freshwater lake, probably when the Lomonosov Ridge was part of what is now Siberia. The last 250,000 years of Arctic history were known already in some detail thanks to cores taken from the Greenland ice cap.

Coping with nature

Professor Jan Backman of Stockholm University, one of the two chief scientists of Acex, provided the final note to the report by saying that sediment records now existed which went back to a period around fifty-six million years ago, with their source resting on eighty million year-old bedrock.

The early history of the Arctic Basin would be re-evaluated based on the scientific results which were collected on this expedition.



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