Impressive new evidence suggests that the Arctic Ocean has been covered by a thick layer of ice and filled with fresh water on at least two occasions during the past 150,000 years. The observation could finally explain the strange and dramatic climatic anomalies associated with these glacial periods.
With all the man-induced melting that’s going on today, it’s hard to imagine our world covered in ice. But that was the case during the recent glacial periods, when significant portions of North America, northern Europe, Greenland and parts of the Bering Sea were dominated by huge sheets of ice. With much of the Earth’s water trapped in this ice, and with sea levels dramatically lower than they are today, something very strange has happened, for which we have no modern analogues.
New evidences presented today in Nature, it proposes an incredible explanation for the surprising lack of thorium-230 – an isotope that accumulates on the seabed of salty oceans – in marine deposits taken from the sedimentary layers of our northernmost oceans. This is a potential sign that the Arctic Ocean, isolated from the rest of the planet’s oceans, had a basin full of fresh water and covered by a 900-meter layer of ice.
Evidence suggestionsthis happened on at least two occasions, once between 150,000 and 130,000 years ago and again between 70,000 and 50,000 years ago. These unsalted seas were covered by a gigantic layer of ice and it lasted thousands of years, according to the article, co-authored by Walter Geibert, marine geochemist at the Helmholtz Center for Polar and Marine Research at the Alfred Wegener Institute.
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The thorium-230 gaps were detected in sediment cores taken from the Arctic Ocean, the Fram Strait (the passage between Greenland and Svalbard) and the Sand the. This isotope is a by-product of the dissolution of uranium, which occurs naturally in seawater. The thorium clings to solid particles, goes to the bottom of the sea, is buried in sediment and waits to be discovered by scientists.
Analysis of core samples dating back to around 200,000 years revealed at least two periods of time when thorium-230 was largely non-existent. For Geibert and his colleagues, this indicated the presence of salt-free bodies of water.
“We found that a natural trace of radioactive material, which is always left behind by seawater, was absent in a very large region for certain periods of time,” explained Geibert in an email.
To explain this, the authors presented a scenario in which huge ice platforms extended to the Nordic seas, extending from the Bering Strait to the high Greenland-Scotland crest (GSR). These ice shelves acted like a giant dam, separating the Arctic from the salty Atlantic and Pacific oceans. Low sea levels, whose waters were about 130 meters lower than they are today, contributed to this process. The Arctic basin, now isolated, has begun to fill with melted fresh water, forming a gigantic underground freshwater sea, the authors speculate.
“The fresh water accumulated in the Arctic Ocean that we are talking about would have occupied a greater volume than that of the Mediterranean Sea, but it was covered by extremely thick layers of ice,” said Geibert.
As the authors continue to explain, ice dams sometimes fail, resulting in the sudden influx of heavier salt water into the Arctic Occ.ean. When this happened, salt water quickly displaced the lighter fresh water, forcing it over the shallow limit to the North Atlantic. This sudden wave of freshwater freezing in the world’s oceans could explain strange climatic anomalies previously detected by scientists, including sudden spikes in temperature in Greenland.
“The effects – a very sudden warming of the Arctic seas and possibly a temporary cooling of the North Atlantic – it has been described for some time, ”explained Geibert. “What we have added now is a possible explanation for some of these substantial changes in temperature distribution that have not had a satisfactory explanation until now.”
To which he added: “We are sure that this concept will arouse much debate and research – now we need models of this very complex physical situation and link them to others.quality records, ”he said. “Ironically, some of the clear indicators of very cold periods that we find should help us now to identify periods of a warmer Arctic in the past with more confidence.”
However, paleoceanographer Sharon Hoffmann, writing in a News and Views article, he poured a little cold water over the new discoveries.
“Arctic sediments are notoriously difficult to date because of the lack of microfossils and because sedimentation rates vary. Therefore, it is uncertain whether the [thorium-deficient] the intervals in the cores were produced at exactly the same times in all locations in the ocean basins, ”wrote Hoffmann, who is not affiliated with the new research. In addition, “no freshwater fauna [animals] have been identified in the sediments in question, so direct evidence of freshwater intrusion into deep Arctic basins has yet to be found, ”she added.
That said, Hoffman said the new research presents “exciting avenues for future research” and that “geochemical and fossil analyzes may help support or challenge the claim that the Arctic Ocean could have been cool”.