Seabed sediments tell the story of Greenland’s ancient summers – UB Now: News and insights for UB faculty and staff

For hundreds of thousands of years, sediments from southern Greenland have seeped into the ocean, where they are carried by underwater currents to a place in the Labrador Sea called the Eirik Drift.

Here they settle on the ocean floor, where they form a record of history, accumulating in layers that document the environmental past of the lands from which they came.

A new UB study is using these deposits to learn about the ancient climate of southern Greenland, focusing on summer temperature during periods of relative heat on Earth, called interglacials, over the past 600,000 years.

Scientists looked specifically at the chemicals in leaf waxes. These compounds are among the many materials found in the mud on the ocean floor, and for southern Greenland, the makeup of the chemicals changes very slightly, depending on how hot or how cool the area is, the former says. author Allison Cluett, doctoral student in the department. of Geology, College of Arts and Sciences.

One conclusion of the research: Periods of prolonged heat – where summers remain hot for several thousand years – can be particularly disastrous for the Greenland ice sheet. The findings are a warning for today, says Elizabeth Thomas, assistant professor of geology, who conducted the study with Cluett.

“What we’re seeing is that sustained summer heat is associated with a dramatic loss of ice cap mass,” says Thomas. “Today, we are releasing greenhouse gases, causing the Earth’s temperature to rise rapidly to levels last seen during those ancient warm periods. Climate models show that if we continue to emit greenhouse gases at the current rate, there could be long-term effects that will keep the Earth’s temperature warm for thousands of years. We must act now to dramatically reduce our emissions to minimize these potential very long-term impacts. “

The study was published on May 10 in the Proceedings of the National Academy of Sciences.

Research reveals that summer temperatures in southern Greenland have been high for around 20,000 years during a warm period that occurred around 400,000 years ago – a time when scientists believe the ice cap of Greenland has declined considerably.

This contrasts with a period of heat that took place about 125,000 years ago and lasted about 5,000 years. During this shorter interglacial, summer temperatures in southern Greenland were generally even warmer than during the warm period that occurred 400,000 years ago, the study concludes. And yet, it is believed that the Greenland ice sheet experienced a much greater decline during the warm period that took place 400,000 years ago.

“Strong ice cap retreat and forest cover in southern Greenland occurred during a period of sustained heat about 400,000 years ago,” says Cluett. “Today, with global temperatures rising again, we could follow a similar path if we don’t reduce greenhouse gas emissions. Our research really underscores the importance of heat duration for the ice sheet.

While potential scenarios on a scale of thousands of years may seem long, actions taken over a brief period can have intense effects that ripple far into the future, affecting from generation to generation, as Cluett and Thomas point out.

The study was supported by the National Science Foundation (NSF), including through an NSF Graduate Research Fellowship and Schlanger Ocean Drilling Fellowship in Cluett, and an NSF Earth Sciences Grant. Instrumentation and Facilities at Thomas. The leaf wax chemicals the scientists studied came from marine sediments collected in 1985 by the Ocean Drilling Program at a location on the Eirik Drift about 280 kilometers south of Greenland.

In addition to the hot spells of 125,000 and 400,000 years ago, Cluett and Thomas also used the sediment samples to reconstruct summer temperature trends for southern Greenland over four other interglacials.

“These are really tough times to study in the Arctic,” says Cluett. “Indeed, as the ice caps grow and shrink, land records like lake sediments that could provide insight into environmental changes are often eroded, so there is very little information on the climate of these. past times, which may be our best analogues. for future warming. “

The findings add to a wealth of information scientists are accumulating on Greenland’s climate history. For example, previous studies have provided insight into topics such as ancient year-round temperatures at the top of the ice cap; the potential size of the Greenland ice sheet at various points in history; and the presence of spruce forests in southern Greenland during the unusually long warm period about 400,000 years ago (indicated by pollen found in ocean mud). The new research adds to this image.

Taken together, this historical information could help scientists understand how the Greenland Ice Sheet may respond to modern climate change.

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