The High Arctic: from hot to cold

A 400-metre-long ice core recovered near the North Pole provides additional proof that the High Arctic region was subtropical about 55 million years ago.

And it’s provided even more evidence about climate swings when carbon dioxide levels in the atmosphere change.

In 2004, the Arctic Coring Expedition used two icebreakers equipped with drilling rigs on the Lomonosov ridge on the Arctic seabed, about 250 kilometres north of Ellesmere Island.

In three studies in last Thursday’s issue of the journal Nature, researchers tell how the region went from greenhouse to snowhouse conditions.

First, the Arctic Ocean went through a period with temperatures of 23°C, like those of a warm bath.

The remains of this warmer period can still be found in Nunavut’s High Arctic. Axel Heiberg’s so-called fossil forest contains mummified stumps and other vegetation from when tropical vegetation flourished in the high latitudes.

“It probably was (a tropical paradise) but the mosquitoes were probably the size of your head,” geology professor Mark Pagani of Yale University, a study co-author, told Reuters.

Then, about 49 million years ago, freshwater was released into the Arctic, cooling it to about 10°C.

The amount of salt in the water was still low enough for freshwater ferns called Azolla to cover much of the surface of the water in the summer.

These ferns likely absorbed carbon dioxide quickly, helping to cool the Arctic over a period of about 800,000 years, said Henk Brinkhuis of Utrecht University, a co-author of one of the papers.