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This is probably what the Arctic looked like during the last glacial maximum, when large parts of Scandinavia were covered with ice. (Photo: By Ittiz – Personal work, CC BY-SA 3.0)
The Arctic during the last ice age was essentially a desert. Earth and ocean were both hidden under a thick layer of ice. But scientists have long wondered if there are ice-free openings between earth ice and sea ice, called polynyas, in which life could flourish.
Researchers from the Geological Survey of Norway, and the UK, are now reporting evidence of these ice-free patches dating back 20,000 years ago, during what is known as the last glacial maximum.
The last glacial maximum was a time when much of Europe was covered with a thick layer of ice, with a thickness of over three kilometers in Norway. The ice extended from the North Pole, all over the Barents Sea and over a large part of the Norwegian Sea. This environment was not particularly welcoming to plants or animals.
But life seems to have persisted in long, narrow, ice-free corridors when land ice meets sea ice.
Several hundred kilometers
The researchers relied on sediment samples taken from a long stretch of ocean from the south-west Barents Sea, north of Svalbard and beyond, to the east. The researchers used dating techniques to determine the age of the sediments and then examined the contents of the samples. They were looking for signs of life, such as small sea creatures and seaweed.
The researchers found many biological remains as proof of life, showing that there must be ice-free openings or polynyas where the fast ice was encountering the land. This ice-free corridor must extend for hundreds of kilometers and exist for more than 5,000 years.
"By discovering chemical fossils of algae living on the high seas and in sea ice, we have shown that polynyas must have existed during the last ice age," said Simon Belt, professor of chemistry at the University of Ottawa. 39; University of Plymouth, UK, in a press release of the geological survey of Norway.
The results have now been published in Nature Communications.
The sun's rays as a source of life
Jochen Knies of the Geological Survey of Norway and the Center for Arctic Gas Hydrate, Environment and Climate of the Arctic University of Norway, led the Norwegian part of the study. He said these cleared passages were of great importance to allow life to survive in the Arctic during the last ice age.
"When the ocean is covered with ice, the sun can not penetrate through the ice cover, creating very difficult conditions for the survival of organisms, and the earth was covered with kilometers of ice in all directions. "It was like a desert," Knies said.
The ice-free areas were able to promote life on a microscopic scale, which would in turn form the basis of an ecosystem and other types of life, he says.
ILLUSTRATION: An arctic oasis in front of the ice cap of northwestern Eurasia during the last ice age, 20,000 years ago (according to Knies et al., 2018, Nature Communications / Irene Lundquist )
It was likely that seals, walruses, and polar bears hunted for food in these ice-free passages, which enabled them to survive the last glacial maximum.
Researchers do not know if polynyas also exist along the cut coast of Norway, since they have not examined the sediment cores of the region. But it's certainly possible, they say.
Wind and warmer water
Polynyas are formed by strong winds from land to sea, combined with ocean circulation that brings warm water to the ocean surface.
"The winds that form on large masses of ice inland can chase sea ice. At the same time, we know that a stream of warm water has been directed towards the north during the ice age, "said Knies.
Today, polynyas are fairly common around the North Pole and Greenland.
"We see these oases forming regularly and with them an explosion of life," he says.
But global warming has created an opposite situation in the Arctic, which researchers have also addressed in their article.
When the pack ice began to melt catastrophically at the end of the ice age, a sudden influx of fresh water interrupted the formation of polynyas, marine productivity dropped dramatically and sea ice covered all the seas Nordic. This dramatic decline in productivity has not recovered for about 2,000 years, they write.
In the press release, the research is described as demonstrating the vulnerability of marine ecosystems in the northern oceans to periods of rapid climate change, but also their adaptability to various extreme weather conditions.
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More information in the Norwegian version of this article on forskning.no
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