LONDON - Sediment drilled from the floor beneath the Arctic Ocean holds prehistoric climate records that show Arctic temperatures reached subtropical levels about 55 million years ago, according to research reported on Wednesday.
The cylindrical sediment core provides new data showing that long ago the surface water was a warm 18 degrees Celsius (64 Fahrenheit) and then Arctic temperatures reached 23C (73.40F). The mean annual Arctic temperature today is around minus 20C.
"Today's models under-predict how warm the poles were back then, which tells you something disturbing -- that the models, if anything, aren't sensitive enough to greenhouse gases," said Matthew Huber of Purdue University in the United States.
The co-author of two of three reports in the journal Nature that analysed the 400-metre (yard) long sediment core said it provides climate modellers with a once in a lifetime experience.
In addition to the soaring temperatures which scientists think were triggered by a massive release of carbon from volcanoes or underwater stores of methane, the sediment revealed evidence that the Arctic Ocean was covered in fresh water ferns in the summer months around 50 million years ago.
"Imagine that the Arctic Ocean was a giant lake, with this vegetation growing on it," said Henk Brinkhuis, a researcher from Utrecht University in the Netherlands.
"What these findings say is that the Arctic Ocean must have been isolated, or nearly cut off, from the Atlantic Ocean by land masses that later shifted into the present continents," he added.
Pea-sized pebbles trapped inside the core also show that glaciers formed in the Arctic Ocean about 14 million years earlier than scientists had thought.
The scientists working on the Integrated Ocean Drilling Project obtained the sediment core from 1,000 metres (yards) below the ocean surface by using three ice breakers including one with a drill rig.
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