Sediment core record from remote Siberian lake shows unusually warm Arctic periods coincided with deglaciation of West Antarctica
By Bob Berwyn
SUMMIT COUNTY — Researchers studying sediment cores dating back nearly 3 million years found evidence that the Arctic has experienced several intensely warm climate intervals, and that there may be a link between those periods and episodes of dramatic changes in the West Antarctic ice sheet.
“We found eight warm intervals … the majority relatively early in the Quarternary, when temperatures were 4 to 5 degrees Celsius warmer — as well as wetter — than during normal interglacial periods. They occurred irregularly, not following orbital cycles,” said Professor Martin Melles, of the University of Cologne, one of the lead researchers.
Other lead scientists include Julie Brigham-Grette of the University of Massachusetts Amherst; and Pavel Minyuk of Russia’s North-East Interdisciplinary Scientific Research Institute in Magadan.
“That’s what we know. Then we wanted to know the reasons for that. It can’t be explained by greenhouse gas variations or orbital variations, so we compared the interglacial warm intervals with other records,” said Melles, explaining that the warm intervals seemed to match up well with an Antarctic sediment core showing that the West Antarctic ice sheet disintegrated approximately during these same periods.
“There was a remarkable coincidence between deglaciation in Antarctica and the warm intervals in the Arctic,” Melles said.
The new and continuous record of Arctic climate cycles came from drilling in remote, ice-covered Lake El’gygytgyn (pronounced El’gee-git-gin) in the northeastern Russian Arctic. When compared with data from Antarctica, the results suggest a previously unknown inter-hemispheric link, according to Paul Filmer, program director in NSF’s Division of Earth Sciences, which funded the “Lake E” project along with NSF’s Office of Polar Programs.
The lake is of interest to scientists because it has never been covered by glaciers. That has allowed the uninterrupted build-up of sediment at the bottom of the lake, recording previously undiscovered information on climate change.
Cores from Lake E go back almost 30 times farther than Greenland ice cores covering the past 110,000 years.The climate reconstructions are based on pollen found in the sediment cores. The lake was formed 3.6 million years ago when a huge meteorite hit Earth, leaving an 11-mile-wide crater. It’s been collecting layers of sediment ever since.
Climate model show that the high temperature and precipitation during the super interglacials can’t be explained by changes in the Earth’s orbi or variations in atmospheric greenhouse gases alone, which geologists usually see as driving the glacial/interglacial pattern during ice ages.
That suggests that additional climate feedbacks are at work — and the researcher think that changes in Antarctica might be driving the changes at the other end of the Earth.
“We think there are two possible explanations that we regard as possible,” Melles said. “One is a change in the thermohaline circulation in the world’s ocean … that’s driven by Antarctic bottom water,” he said, explaining that a massive pool of extremely cold water that forms around Antarctica gradually spreads northward, adjusting the global heat balance of the oceans.
Other recent studies have shown that the amount of Antarctic bottom water appears to be dwindling rapidly.
“Our speculation is that, without the West Antarctic ice sheet, there is no upwelling in the North Pacific, making the North Pacific much warmer,” he said. The warmer ocean surface could also explain the sediment record of much higher precipitation during the extraordinarily warm super-interglacials.
“Second, if you melt the West Antarctic ice sheet, sea level is five meters higher. Then you significantly increase the size of the gateway between the Pacific and the Arctic Ocean … through the Bering Strait. If you increase this warm water intrusion into the Arctic ocean … it affects the surrounding land masses,” he said.
The West Antarctic ice sheet is decreasing right now. It could drive these changes that we’re describing in this paper,” Melles concluded.
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