The international scientific team, taking part in the Integrated Ocean Drilling Program's Arctic Coring Expedition (ACEX), has just discovered that the Arctic Ocean once was ice-free because of prehistoric global warming.

The scientific team from eight nations has recovered sediment cores from nearly 400 metres below the seafloor, in waters 1300 metres deep.

"The early history of the Arctic Basin will be re-evaluated based on the scientific results collected on this expedition," said Professor Jan Backman, Stockholm University, one of the co-chief scientists.

The cores show evidence of subtropical, shallow seas in the form of tiny fossils-extinct marine plant and animals.

These date back to a period known as the "Palaeocene-Eocene thermal maximum", a brief period that occurred around 55 million years ago characterized by an extremely warm climate that created a natural greenhouse effect, which caused massive carbon input to sea and air.

Scientists identified the interval through specific algae, which lived only in subtropical conditions.

The algae fossils reveal that the Arctic ocean once were much warmer-around 20�C (68F), similar to the waters around New York in August (NOOA) compared with today's freezing temperatures that average -1.5�C.

"We're seeing a mass extinction of sea-bottom-living organisms caused by these conditions" said palaeontologist Dr. Michael Kaminski, University College London, UK, on board the icebreaker Oden "Moving forward in time, we see many species disappear. Only a few hardy survivors endure the thermal maximum."

Prof Backman added that "we were also surprised to find fresh water conditions and periods of extreme warmth. This indicates environmental conditions were more variable than anticipated. We have now sediment records going back to 56 million years, which are resting on 80 million years old bedrock."

The expedition returns to Tromso, Norway on September 14th. The scientists will meet again in November at the University of Bremen, Germany, to examine the data collected.

Further study will help explain the changes in the Arctic's climate, from greenhouse conditions to today's icy environment.

The $12.5M Arctic Coring Expedition (ACEX) is conducted under the auspices of the Integrated Ocean Drilling Program (IODP) by the European Consortium for Ocean Research Drilling.

A consortium of European scientific institutions, ECORD Science Operator, are responsible for fleet management, ice and weather monitoring, and science operations.

Related Links
Integrated Ocean Drilling Program
ACEX
European Consortium for Ocean Research Drilling
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