Scientists led by the University of Arizona have proposed an explanation for the rapid expansion of the ice sheets that covered much of the northern hemisphere in the most recent ice age. Understanding what drives Earth’s glacial and interglacial cycles (the periodic advance and retreat of ice sheets in the northern hemisphere) is no easy task, and researchers have devoted considerable effort to explaining the expansion and the shrinking of large masses of ice over thousands of years. .
About 100,000 years ago, when mammoths roamed the Earth, the Northern Hemisphere’s climate plummeted to a deep freeze that allowed huge ice caps to form. Over a period of about 10,000 years, local mountain glaciers grew and formed large ice caps covering much of what is now Canada, Siberia and Northern Europe.
Although it has been widely believed that the periodic “wobble” of the Earth’s orbit around the sun triggers a cooling in the northern hemisphere summer triggering the start of a widespread glaciation, scientists have struggled to explain the vast ice sheets that cover much of Scandinavia and northern Europe. where the temperatures are much milder.
Unlike the cold Canadian Arctic Archipelago, where ice forms easily, Scandinavia should have remained virtually ice-free due to the North Atlantic Current, which brings warm water to the coasts of northwestern Europe. Although the two regions are located at similar latitudes, Scandinavian summer temperatures are well above freezing, while temperatures in much of the Canadian Arctic remain below freezing during the summer. , according to the researchers.
Because of this discrepancy, climate models struggled to account for the vast glaciers that advanced across northern Europe and ushered in the last ice age, said study lead author Marcus Lofverstrom. “The problem is that we don’t know where these ice caps came from. (in Scandinavia) and what caused them to grow in such a short time,” said Lofverstrom, assistant professor of geosciences and director of the Earth System Dynamics Laboratory at the University of Arizona, in a statement.
To find answers, Lofverstrom helped develop an extremely complex Earth system model, known as the Community Earth System Model, which allowed his team to realistically recreate the conditions that existed at the start of the most recent ice age.
In particular, he extended the domain of the Greenland Ice Sheet model to encompass most of the northern hemisphere with high spatial accuracy. Using this updated model setup, researchers identified ocean gateways in the Canadian Arctic Archipelago as a keystone determining the climate of the North Atlantic and, ultimately, determines whether or not ice caps could develop in Scandinavia.
The simulations revealed that even if the ocean gates in the Canadian Arctic Archipelago remained open, Earth’s orbital configuration has cooled the Northern Hemisphere enough to allow ice caps to form in northern Canada and Siberia, but not in Scandinavia.
In a second experiment, researchers simulated a previously unexplored scenario where ice caps blocked the waterways of the Canadian Arctic Archipelago. In this experiment, relatively cold water from the Arctic and North Pacific, typically channeled through the Canadian Arctic Archipelago, was diverted to eastern Greenland, where deep water masses typically form.
This drift led to a cooling and weakening of the deep North Atlantic circulation, expanding sea ice and cooler conditions in Scandinavia. “Using climate model simulations and marine sediment analyses, we show that ice formation in northern Canada can clog ocean gates and divert water transport from the Arctic to the North Atlantic” , Lofverstrom said, “and that, in turn, weakens the ocean circulation.” and cold conditions off the coast of Scandinavia, which is sufficient to trigger ice growth in this region.”
Supported by marine sediment records
“These findings are supported by marine sediment records from the North Atlantic, which show evidence of glaciers in northern Canada several thousand years earlier than on the European side,” said Diane Thompson, assistant professor in the department. of Geosciences from UArizona. “The sediment records also show compelling evidence for deep ocean circulation weakened before the formation of glaciers in Scandinavia, similar to the results of our model.”
Together, the experiments suggest that sea ice formation in northern Canada may be a necessary precursor to glaciation in Scandinavia, the authors write. Pushing climate models beyond their traditional application of predicting future climates offers the opportunity to identify previously unknown interactions in the Earth system, such as the complex and sometimes counter intuitive between ice caps and climate, Lofverstrom said.
“It is possible that the mechanisms we have identified here apply to all ice ages, not just the most recent,” he said. “Same may help explain shorter cold spellssuch as the Younger Dryas cold inversion (12,900 to 11,700 years ago) that marked the general warming at the end of the last ice age.”
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