Wednesday, November 30, 2022

Million-year-old Arctic sedimentary record sheds light on climate mystery

New research, led by the University of Massachusetts Amherst and recently published in the journal Climate of the past, is the first to give a continuous look at a shift in climate called the Mid-Pleistocene Transition, which has astonished scientists. Kurt Lindberg, the newspaper’s first author and currently a graduate student at the University of Buffalo, was only an undergraduate student when he completed his research as part of a team of climate scientists at UMass Amherst.

Somewhere about 1.2 million years ago, a dramatic shift in the Earth’s climate, known as the Mid-Pleistocene Transition, or MPT, took place. Previously, ice ages, with relative regularity, occurred every 40,000 years or so. But then, in a relatively short window of geological time, the time between ice ages more than doubled, to every 100,000 years. “It’s a real puzzle,” says Isla Castañeda, professor of earth sciences at UMass Amherst and one of the paper’s co-authors. “No one really knows why this shift took place.”

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One of the major obstacles to understanding the MPT is that very little data exists. The oldest Arctic ice cores date back only about 125,000 years. And older sedimentary cores are almost non-existent, because as ice ages came and went, the advancing and retreating ice sheets acted like enormous bulldozers, scraping much of the exposed land to the rock.

However, there is one place in the world, in the far northeast of Russia, which is both above the Arctic Circle and which has never been covered by glaciers: Lake El’gygytgyn. This is where polar scientist Julie Brigham-Grette, professor of geosciences at UMass Amherst and one of the paper’s co-authors, comes in.

In 2009, Brigham-Grette led an international team of scientists to Lake El’gygytgyn, where they drilled a 685.5-meter sediment core, representing approximately the last 3.6 million years of Earth’s history. Lindberg and his co-authors used the portion of this sedimentary core that stretches across the MPT and searched for specific biomarkers that could help them determine temperature and vegetation. With this information, they were able to reconstruct climatic conditions in the Arctic for the first time during the MPT.

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While the team did not solve the mystery of the MPT, they made some surprising discoveries. For example, an interglacial period, or era when ice was in retreat, known as MIS 31 is widely recognized as abnormally hot – and yet records at Lake El’gygytgyn show only moderate heat. Instead, three other interglacial periods, MIS 21, 27, and 29, were just as hot or hotter. Finally, the team’s research shows a long-term drought trend throughout the MPT.

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Material provided by University of Massachusetts Amherst. Note: Content can be edited for style and length.

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