An international scientific team which has been drilling beneath
the bed of the Arctic Ocean says the region enjoyed a sub-tropical
climate 55 million years ago.
The Arctic Coring Expedition (Acex) has recovered sediment cores
from nearly 400m (1,300ft) below the sea floor.
It says fossilised algae in the cores show the sea temperature
was once about 20C, instead of the average now, -1.5C.
The expedition, which has relied on three icebreakers during its
work, is now heading back to Tromso in Norway.
Unlocking the Arctic's history
The scientists, from eight nations, recovered the cores from
below the sea floor in waters 1,300m (4,260ft) deep.
Acex has been taking cores from the Lomonosov Ridge between
Siberia and Greenland. The ridge, 1,500km (930 miles) long, rises to
800m (2,625ft) below sea level and is topped by 450m (1,475ft) of
The scientists said before they set sail from Tromso last month
their findings would help science to work out how long the Arctic
sea ice, now in retreat, had persisted.
The cores they have extracted show the Arctic Ocean was once a
subtropical, shallow sea. The evidence, Acex says, is in the form of
tiny algal fossils found in the cores, which were once marine plants