New Study Solves Long-Standing Mystery of What May Have Triggered Ice Age

nickwinlund77 shares a report from Phys.Org: A new study led by University of Arizona researchers may have solved two mysteries that have long puzzled paleo-climate experts: Where did the ice sheets that rang in the last ice age more than 100,000 years ago come from, and how could they grow so quickly? Understanding what drives Earth's glacial -- interglacial cycles -- the periodic advance and retreat of ice sheets in the Northern Hemisphere -- is no easy feat, and researchers have devoted substantial effort to explaining the expansion and shrinking of large ice masses over thousands of years. The new study, published in the journal Nature Geoscience, proposes an explanation for the rapid expansion of the ice sheets that covered much of the Northern Hemisphere during the most recent ice age, and the findings could also apply to other glacial periods throughout Earth's history. About 100,000 years ago, when mammoths roamed the Earth, the Northern Hemisphere climate plummeted into a deep freeze that allowed massive ice sheets to form. Over a period of about 10,000 years, local mountain glaciers grew and formed large ice sheets covering much of today's Canada, Siberia and northern Europe. While it has been widely accepted that periodic "wobbling" in the Earth's orbit around the sun triggered cooling in the Northern Hemisphere summer that caused the onset of widespread glaciation, scientists have struggled to explain the extensive ice sheets covering much of Scandinavia and northern Europe, where temperatures are much more mild. [...] "Using both climate model simulations and marine sediment analysis, we show that ice forming in northern Canada can obstruct ocean gateways and divert water transport from the Arctic into the North Atlantic," [said Lofverstrom, an assistant professor of geosciences and head of the UArizona Earth System Dynamics Lab], "and that in turn leads to a weakened ocean circulation and cold conditions off the coast of Scandinavia, which is sufficient to start growing ice in that region." "These findings are supported by marine sediment records from the North Atlantic, which show evidence of glaciers in northern Canada several thousand years before the European side," said Diane Thompson, assistant professor in the UArizona Department of Geosciences. "The sediment records also show compelling evidence of a weakened deep ocean circulation before the glaciers form in Scandinavia, similar to our modeling results." Together, the experiments suggest that the formation of marine ice in northern Canada may be a necessary precursor to glaciation in Scandinavia, the authors write. [...] "It is possible that the mechanisms we identified here apply to every glacial period, not just the most recent one," [Lofverstrom] said. "It may even help explain more short-lived cold periods such as the Younger Dryas cold reversal (12,900 to 11,700 years ago) that punctuated the general warming at the end of the last ice age."

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