Arctic was once a sub-tropical sea

The North Pole once basked in sub-tropical conditions, researchers said yesterday.

The sea temperature of the Arctic Ocean, which lies mostly north of the Arctic Circle, was 20°C (68°F) about 55million years ago, they said. Today, it is just -1.5°C (35°F).

Evidence was gleaned from sediment recovered from nearly 400m below the sea floor.

In the samples, scientists from the Arctic Coring Expedition found tiny algal fossils that were once marine plants and animals.

They date back to a period known as the Palaeocene-Eocene thermal maximum, which occurred about 55million years ago.

It was characterised by an extremely warm climate which created a natural greenhouse effect.

Carbon levels in the atmosphere were then ten times higher than they are today and led to thousands of species being wiped out.

The sea was as warm as the waters off New York in summer in today.

Palaeontologist Dr Michael Kaminski said: 'We're seeing a mass extinction of sea-bottom-living organisms caused by these conditions. Only a few hardy survivors endure the thermal maximum.'

The expedition, from eight nations, used three icebreakers and is now heading back to Norway.