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Ice Age and Climate Change: Heat-Pond in Arctic Blew Up?

Aug 18, 2015 10:55 AM EDT

In the continuing story of what happened before humans walked the Earth, particularly involving warm and cold changes in climate, researchers say that when warm, stagnant water from the deep Arctic Ocean and Nordic Seas suddenly built up and released in the Arctic, this had a significant hand in finishing the last Ice Age.

That is, scientists from the University College London, Woods Hole Oceanographic Institution and elsewhere said in their recent report in the journal Science that ocean circulation north of Iceland, which is known as the Arctic Mediterranean, altered since the end of the last Ice Age--20,000 to 30,000 years ago.

It turns out that everything is different in the far north these days, and not just because of current climate changes. In today's conditions, the ocean's atmosphere cools during winter-dense water sinks, then flushes through the area. But in the past, the Arctic Mediterranean sat still and stagnant like a pond. Its deep waters were not flushed for as long as 10,000 years, according to a release.

After all that stillness, the Arctic Mediterranean likely had a thick, extensive layer of sea ice and fresh water during the Ice Age. Therefore, the atmosphere was not able to cool and make denser the ocean beneath, said the release.

Along with sitting undisturbed like a stagnant pond, the waters became warm and accumulated geothermal heat from the seafloor. Finally, that heat was released into the upper ocean. The scientists have evidence for a large meltwater release into the Nordic Seas. That sudden influx of meltwater was likely brought about by deep ocean heat being released, which melted icebergs, sea ice and ice sheets that finished up at the ocean, a release noted.

In the study, the researchers analyzed calcite shells called foraminifera, which are found in ocean floor sediment. In those, they were able to read records of deep-ocean chemistry at the time they were living. For instance, the scientists measured the shells' radiocarbon content and learned how quickly deep water formed in the Arctic Mediterranean. They also learned about past temperature changes from the ratio of magnesium and calcium, and the arrangement of carbon and oxygen isotopes within the shells. These would vary according to water temperature, the release said.

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