Less ice in the Arctic Ocean 6000-7000 years ago

Published on 27 October 2008

(Astigan.com) — Recent mapping of a number of raised beach ridges on

the north coast of Greenland suggests that the ice cover in the Arctic

Ocean was greatly reduced some 6000-7000 years ago. The Arctic Ocean

may have been periodically ice free.

"The climate in the northern regions has never been milder since the

last Ice Age than it was about 6000-7000 years ago. We still don't

know whether the Arctic Ocean was completely ice free, but there was

more open water in the area north of Greenland than there is today,"

says Astrid Lyså, a geologist and researcher at the Geological Survey

of Norway (NGU).

Shore features

Together with her NGU colleague, Eiliv Larsen, she has worked on the

north coast of Greenland with a group of scientists from the

University of Copenhagen, mapping sea-level changes and studying a

number of shore features. She has also collected samples of driftwood

that originated from Siberia or Alaska and had these dated, and has

collected shells and microfossils from shore sediments.

"The architecture of a sandy shore depends partly on whether wave

activity or pack ice has influenced its formation. Beach ridges, which

are generally distinct, very long, broad features running parallel to

the shoreline, form when there is wave activity and occasional storms.

This requires periodically open water," Astrid Lyså tells me.

Pack-ice ridges which form when drift ice is pressed onto the seashore

piling up shore sediments that lie in its path, have a completely

different character. They are generally shorter, narrower and more

irregular in shape.

Open sea

"The beach ridges which we have had dated to about 6000-7000 years ago

were shaped by wave activity," says Astrid Lyså. They are located at

the mouth of Independence Fjord in North Greenland, on an open, flat

plain facing directly onto the Arctic Ocean. Today, drift ice forms a

continuous cover from the land here. Astrid Lyså says that such old

beach formations require that the sea all the way to the North Pole

was periodically ice free for a long time.

"This stands in sharp contrast to the present-day situation where only

ridges piled up by pack ice are being formed," she says.

However, the scientists are very careful about drawing parallels with

the present-day trend in the Arctic Ocean where the cover of sea ice

seems to be decreasing.

"Changes that took place 6000-7000 years ago were controlled by other

climatic forces than those which seem to dominate today," Astrid Lyså

believes.

Inuit immigration

The mapping at 82 degrees North took place in summer 2007 as part of

the LongTerm project, a sub-project of the major International Polar

Year project, SciencePub. The scientists also studied ruined

settlements dating from the first Inuit immigration to these desolate

coasts.

The first people from Alaska and Canada, called the Independence I

Culture, travelled north-east as far as they could go on land as long

ago as 4000-4500 years ago. The scientists have found out that drift

ice had formed on the sea again in this period, which was essential

for the Inuit in connection with their hunting. No beach ridges have

been formed since then.

"Seals and driftwood were absolutely vital if they were to survive.

They needed seals for food and clothing, and driftwood for fuel when

the temperature crept towards minus 50 degrees. For us, it is

inconceivable and extremely impressive," says Eiliv Larsen, the NGU

scientist and geologist.

http://www.astigan.com/2008/10/27/less-ice-in-the-arctic-ocean-6000-7000-years-ago/