Surprising new evidence suggests that the Arctic Ocean was covered by a thick layer of ice and filled with fresh water on at least two occasions over the past 150,000 years. The observation could finally explain strange and dramatic climatic anomalies associated with these glacial periods.
With all the human-induced thaw that is happening these days, it’s hard to imagine our world being frozen. But this was the case during the last glacial periods, when significant parts of North America, northern Europe, Greenland and some parts of the Bering Sea were dominated by massive ice sheets. With much of the Earth’s water tied to this ice and with sea levels dramatically lower than today, something very strange happened for which we have no modern analogues.
New tests presented today at Nature proposes an incredible explanation for the striking 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, featured a basin full of fresh water and covered with a 900-meter layer of ice.
Evidence suggestionsThis happened at least twice, once between 150,000 and 130,000 years ago and again between 70,000 i 50,000 years ago. These salt-free seas were covered by a gigantic layer of ice and it lasted thousands of years, according to the document, 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 lagoons were detected in sediment nuclei extracted from the Arctic Ocean, the Strait of Fram (the passage between Greenland and Svalbard) and northern SEAS. This isotope is a by-product of the dissolution of uranium, which occurs naturally in salt seawater. Thorium clings to solid particles, drifts to the seabed, is buried in sediment and waits to be discovered by scientists.
Analysis of basic samples dating back to about 200,000 years ago revealed at least two time periods in which thorium-230 was basically non-existent. For Geibert and his colleagues, this pointed to the presence of unsalted bodies of water.
“We found that a natural trace of radioactive material, which is always left behind by superimposed seawater, was absent in a very large region for certain periods of time,” Geibert explained in an email.
To explain this, the authors presented a scenario in which massive ice shelves stretched into the Nordic seas, from the Bering Strait to the high Greenland-Scotland (GSR) ridge. These ice shelves acted like a giant dam, separating the Arctic from the salty oceans of the Atlantic and Pacific. Low sea levels, in which the waters were about 130 meters (430 feet) lower than the current ones, contributed to this process. The Arctic basin, now isolated, began to fill with molten fresh water, forming a gigantic underground sea of fresh water, 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.
According to the authors, ice dams would sometimes fail, leading to the sudden influx of heavier saltwater into the Arctic.ean. When this happened, the salt water quickly displaced the lighter fresh water, forcing it over the surface boundary into the North Atlantic. This sudden blow of freezing fresh, cold water into the world’s oceans could explain strange climatic anomalies previously detected by scientists, including sudden temperature rises in Greenland.
“The effects: a sudden warming of the Arctic seas and possibly a temporary cooling of the North Atlantic, have been described for some time, “Geibert explained.” What we add now is a possible explanation for some of these substantial changes in temperature distribution that have so far they did not have a satisfactory explanation “.
To which he added: “We are confident that this concept will provoke much debate and research; we now need models of this physically very complex situation and relate them to others.quality records, “he said.” Ironically, some of the clear indicators of very cold periods we have found should now help us identify the periods of a warmer Arctic of the past with more confidence. “
However, paleoceanographer Sharon Hoffmann, writing in an accompanying News & Views article, he poured some cold water on the new finds.
“Arctic sediments are remarkably difficult to date due to the lack of microfossils and because sedimentation rates varied. Therefore, it is not known whether the [thorium-deficient] the intervals in the nuclei occurred at exactly the same time at all sites in the ocean basins, “wrote Hoffmann, who is not affiliated with the new research. In addition,” there is no freshwater fauna. [animals] the affected sediments have been identified, leaving direct evidence of freshwater intrusion in the deep Arctic basins, ”he added.
That said, Hoffman said the new research presents “exciting 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.”