Amazing new evidence suggests that the Arctic Ocean has been covered by a thick layer of ice and filled with fresh water at least twice in the last 150,000 years. The observation could eventually explain the strange and dramatic climatic anomalies associated with these glacial periods.
Despite all the man-made melting that is happening these days, it’s hard to imagine our world trapped in ice. But this has been the case in recent glacial periods, when significant portions of North America, northern Europe, Greenland and parts of the Bering Sea have been dominated by massive ice sheets. With much of the Earth’s water bound in this ice and a dramatically lower sea level than it is today, something very strange has happened, for which we have no modern analogues.
New evidence presented today in Nature offers an incredible explanation for the surprising lack of thorium-230 – an isotope that accumulates on the seabed of the salty oceans – in marine deposits extracted from the sedimentary layers of our northernmost oceans. This is a potential sign that the Arctic Ocean, cut off from the rest of the planet’s oceans, had a pool full of fresh water and covered with a 900-meter layer of ice.
Evidence suggestsThis has happened on at least two occasions, once between 150,000 and 130,000 years ago and then again between 70,000 and 50,000 years ago. These salt-free seas were covered with a gigantic sheet of ice and it lasted thousands of years, according to the newspaper, co-authored by Walter Geibert, a marine geochemist at the Helmholtz Center for Polar and Marine Research at the Alfred Wegener Institute.
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Thorium-230 gaps have been detected in sediment cores drawn from the Arctic Ocean, the Strait of Fram (crossing between Greenland and Svalbard) and northern SEAS. This isotope is a by-product of the dissolution of uranium, which occurs naturally in sea salt water. Thorium clings to solid particles, heads to the bottom of the sea, is buried in sediment and waits to be discovered by scientists.
Analysis of baseline samples dating back approximately 200,000 years revealed at least two periods of time in which thorium-230 was virtually non-existent. For Geibert and his colleagues, this indicated the presence of salt-free water bodies.
“We found that a natural trace of radioactive material, which is always left behind by the sea water above, was absent in a very large region for certain periods of time,” Geibert explained in an e-mail.
To explain this, the authors presented a scenario in which massive ice shelves extended to the North Sea, stretching from the Bering Strait to the high altitude of Greenland-Scotland (GSR). These ice shelves acted like a giant dam, separating the Arctic from the salty oceans of the Atlantic and Pacific. The low sea level, in which the waters were about 130 meters lower than they are today, contributed to this process. The Arctic Basin, now isolated, has begun to fill with freshly melted water, forming a gigantic underground freshwater sea, the authors speculate.
“The fresh water accumulated in the Arctic Ocean we are talking about would have occupied a larger volume than the Mediterranean Sea, but it was covered by extremely thick layers of ice,” Geibert said.
As the authors explain, ice dams would sometimes fail, leading to a sudden influx of heavier salt water into the Arctic Oc.ean. When this happened, the salt water quickly moved the freshwater lighter, forcing it over the surface boundary in the North Atlantic. This sudden rush of freezing cold fresh water in the world’s oceans could explain the strange climatic anomalies previously detected by scientists, including sudden temperature rises in Greenland.
“The effects – a very sudden warming of the Arctic Sea and possibly a temporary cooling of the North Atlantic – they have been described for a while, ”Geibert explained. “What we are adding now is a possible explanation for some of these substantial changes in temperature distribution, which have so far lacked a satisfactory explanation.”
To which he added: “We are sure that this concept will trigger a lot of debate and research – now we need models of this very complex physical situation and we will link them to otherquality recordings, ”he said. “Ironically, some of the clear indicators from the very cold times we’ve found should now help us identify the periods of a warmer Arctic in the past with more confidence.”
However, paleoceanographer Sharon Hoffmann, written in an article accompanying News & Views he poured some slightly cold water on the new discoveries.
“Arctic sediments are notoriously difficult to date due to the lack of microfossils and because sedimentation rates have varied. Therefore, it is not certain whether [thorium-deficient] the intervals in the nuclei were produced at exactly the same times, at all sites in the ocean basins, ”wrote Hoffmann, who is not affiliated with the new research. Also, “there is no freshwater fauna [animals] have been identified in the sediments in question, so direct evidence of freshwater entry into the deep Arctic basins remains to be found, ”she added.
That being said, Hoffman said the new research presents “interesting avenues for future research” and that future “geochemical and fossil analyzes could help support or challenge the claim that the Arctic Ocean could have been fresh.”