Researchers have found evidence that the Arctic Ocean was once a large freshwater puddle covered with an ice shelf half as thick as the US Grand Canyon.
The scientists were surprised by this discovery. For a better understanding, you can think of the relationship between ice sheets and oceans. As the ice sheets melt, they dump water into the ocean, raising sea levels. But as the ice sheets grow, like during Earth’s ice age, sea levels drop.
Now, new research shows that during these times of lower sea levels, the Arctic Ocean’s connection to the Pacific and Atlantic oceans was very limited, with Greenland, Iceland, Northern Europe and Siberia playing roles. acts like the rim of the bowl containing the North Pole. The ice itself may have restricted circulation further. The land and sea are both covered by an ice sheet 900 meters thick.
At that time, the land and sea were both covered by an ice sheet 900 meters thick.
Glaciers, estuaries and runoff from the continents have kept fresh water from entering the Arctic Ocean, while salt water from the Atlantic and Pacific Oceans cannot. The exact timing of the sweetening process is unclear, but the researchers have calculated that it could have occurred in about 8,000 years.
“These results mean a real change to our understanding of the Arctic Ocean in glacial climates. To our knowledge, this is the first time that a complete sweetening of the North has occurred. The Nordic ocean and sea ice considered occurred not once but twice,” said study author Walter Geibert, a geochemist at the Alfred Wegener Institute’s Helmholtz Center for Polar and Marine Research.
These two periods of a freshwater Arctic occurred between 150,000 and 130,000 years ago and 70,000 to 60,000 years ago. During particularly cold times in climate history, a giant European ice sheet extended more than 5,000 kilometers from Scotland in Scandinavia to the Kara Sea east, north of Siberia. Another pair of ice sheets that covered much of what is now Canada and Alaska, Greenland was also under an even larger ice sheet today.
Until now, it was unclear what the Arctic Ocean looked like at this point, as icebergs leave much less geological footprint than land-based ice sheets and glaciers.
Geibert and his colleagues turned to the study of sediment cores from the Arctic, the Fram Strait between Greenland and the Svalbard Islands, the Nordic seas. These deposits contain a stacked history of the different conditions under which each layer formed.
Two layers in these cores stand out. Each element lacks an isotope or version of an element, called thorium-230 . Thorium-230 forms when natural uranium breaks down in salt water. In marine sediments, no thorium-230 means no saltwater.
Microbiologist Jutta Wollenburg of the Alfred Wegener Institute said: “Here, the repeated and widespread absence of thorium-230 reveals to us what happened. To our knowledge , the only plausible explanation for this pattern is that the Arctic Ocean has been filled with fresh water twice in its history in frozen and liquid form”.
At that time, sea level was 130 m lower than today, and parts of the seafloor terrain, such as the shallow part of the Bering Strait, were above sea level. However, when the ice recedes, the reversal of the Arctic back into salt water would be rapid.
Jutta Wollenburg added: “Once the ice containment mechanism fails, heavier saltwater could spill into the Arctic Ocean again. We believe it could then rapidly shift lighter freshwater, leading to the sudden discharge of accumulated freshwater … into the North Atlantic Ocean”.
It’s unclear exactly how quickly the Arctic would re-salt, but a similar event may have occurred around 13,000 years ago during a frigid period known as the Younger Dryas . That event raised sea levels by 20 meters over 500 years and may have actually caused the cold by changing ocean circulation.
This may explain some of the biases in previous estimates of sea level. For example, some studies of reef ruins show higher sea levels than studies of Antarctic ice cores indicate. If fresh water were not only stored on land but in an Arctic reservoir under the ice it could account for some of the gap between the estimates.
Such a freshwater reservoir also has its own impacts on its surroundings, as might have happened with the Younger Dryas cold period later in history.