The Arctic Ocean was once a pool of fresh water with an ice shelf half as thick as the Grand Canyon is deep.
Do not despair if it is difficult to imagine. Scientists were surprised by the discovery, which was published in the journal on Wednesday (February 3). Nature, too. The trick to proposing this strange arrangement is to think about the relationship between ice sheets and the ocean. When ice sheets melt, it dumps water into the ocean and raises sea levels. But when ice sheets grow, as during Earthice ages lower sea levels.
New research shows that the Arctic Ocean during these periods with a lower sea level was very limited to the Pacific Ocean and the Atlantic Ocean. Greenland, Iceland and Northern Europe and Siberia acting as the rim of a bowl containing the North Pole. (Ice itself could further restrict circulation.) Land and sea could be overlapped with an ice sheet 900 meters thick.
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Glaciers, river discharges and runoff from the continents hold fresh water in this closed Arctic Ocean, while salt water from the Atlantic and Pacific Oceans could not enter. The exact time of the refreshment process is not clear, but the researchers calculated that it could have happened in about 8,000 years.
“These results represent a real change in our understanding of the Arctic Ocean in glacial climates,” said first study author Walter Geibert, a geochemist at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research. statement said. To our knowledge, this is the first time that a complete refreshment of the Northern Ocean and the North Sea is being considered – not just once, but also twice. ‘
The missing element
These two periods of a freshwater Arctic took place from 150,000 to 130,000 years ago and again 70,000 to 60,000 years ago. During these extremely cold times in climatic history, an enormous European ice sheet stretched more than 5,000 kilometers from Scotland across Scandinavia to the eastern Karase Sea, north of Siberia. A few more ice sheets covered much of present-day Canada and Alaska, and Greenland was also under an even larger ice sheet than today.
Until now, it was not clear what the Arctic Ocean looked like, because floating ice sheets leave far fewer geological traces than ice sheets and glaciers on land. Geibert and his colleagues turn to sediment cores from the North Pole, the Fram Sea Strait between Greenland and the Svalbard archipelago and the Nordic seas. These long cylinders of the sediment contain a stack history of the conditions under which each layer was formed.
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Two layers in these cores stood out. Each one is missing an isotope or a version of an element thorium-230. Thorium-230 forms when it occurs naturally uranium decay into salt water. In marine sediment, the absence of thorium-230 means the absence of salt water.
‘Here, [thorium-230’s] repeated and widespread absence is the giving away that reveals to us what happened, “said the micropaleontologist of Alfred Wegener Institute, Jutta Wollenburg, in the statement.” To our knowledge, the only reasonable explanation for this pattern is that the Arctic Ocean has been filled twice with fresh water in its recent history – in frozen and liquid form. ‘
An Arctic freshwater
At that time the sea level was 130 m 426 feet lower than today, and parts of the seabed topography, such as the shallow parts of the Bering Street, were above sea level.
But when the ice retreated, the North Pole return to salt water would have been rapid, Geibert said.
“Once the mechanism of ice barriers has failed, heavier salt water could fill the North Ocean again,” he said. “We believe that it could then quickly displace the lighter fresh water, which could lead to the sudden discharge of the accumulated fresh water … into the North Atlantic Ocean.”
It is not clear exactly how quickly the North Pole would have salted again, but a similar pulse occurred about 13,000 years ago during a cold moment called the Younger Dryas. That event raised the sea level for 20 years 20 meters and possibly caused the cold by changing the circulation of the ocean.
This may explain some differences in previous sea level estimates, Geibert said. For example, some studies of coral reefs indicate that sea levels were higher than studies of Antarctica ice cores indicate. If fresh water is not only stored on land, but in an under-ice reservoir in the Arctic, it could be part of the gap between the estimates.
Such a freshwater reservoir would also have had its own effect on the surrounding environment, as may have happened with the cold period of the youngest Dryas later in history.
“Now we need to examine in more detail how these processes are interconnected,” Geibert said.
Originally published on Live Science.