Antarctic Ice Core Hints Abrupt Warming Some 12,500 Years Ago May Have Been Global

October 01, 1998

An analysis of an ancient Antarctic ice core indicates an abrupt climate warming occurred there about 12,500 years ago, an event previously thought to have primarily influenced climate in the Northern Hemisphere.

James White, a paleo-climatologist at the University of Colorado at Boulder, said changes in stable isotope ratios -- an indicator of past temperatures in the Taylor Dome ice core from Antarctica -- are almost identical to changes seen in cores from Greenland's GISP 2 core from the same period.

"The ice cores from opposite ends of the earth can be accurately cross-dated using the large, rapid climate changes in the methane concentrations from the atmosphere that accompanied the warming," White said.

The evidence from the greenhouse gas bubbles indicates temperatures from the end of the Younger Dryas Period to the beginning of the Holocene some 12,500 years ago rose about 20 degrees Fahrenheit in a 50-year period in Antarctica, much of it in several major leaps lasting less than a decade.

"We used to think this climate change signal from the Younger Dryas to the Holocene was a big event in the Arctic, but not much more than a blip on the screen in the Antarctic," said White, also a CU associate professor of geology and former interim director of the National Ice Core Laboratory in Lakewood, Colo. "But these findings throw a monkey wrench into paleo-climate research and rearrange our thinking about climate change at that time."

A paper principally authored by research associate Eric Steig and co-authored by White and Scott Lehman, all of CU's Institute of Arctic and Alpine Research, was published in the Oct. 2 issue of Science. The paper also included co-authors from Washington State University, the University of Rhode Island, Princeton University, the University of Texas at Austin, the University of Washington and the U. S. Geological Survey.

Deep-sea sediment cores from temperate regions, combined with arctic ice core evidence, confirm the climate warmed rapidly at the end of the Younger Dryas in the Northern Hemisphere, said White. But the amount of methane -- a greenhouse gas primarily produced in tropical regions -- that was found recently in the Taylor Dome Antarctic ice core argues for a more global climate-warming episode 12,500 years ago.

"What the Taylor Dome ice core seems to be telling us is there was a synchronization of warming at the end of the Younger Dryas at both poles," said White. "This strengthens the argument that the warming phenomenon was global since the cores from both poles seem to be dancing to the same tune at the same time."

Other Antarctic ice cores from the same time period like the Byrd and Vostok cores drilled in Antarctica's interior contain climate records that do not correlate well with the Taylor Dome ice core, which was drilled on the southern edge of the continent near the Ross Sea, said White.

"There is no Rosetta stone ice core," said White. "It is becoming clear that ice cores in different parts of the major ice sheets record the different climates in those areas. The Taylor Dome ice core may correlate more with Greenland ice cores in part because it was taken near the Ross Sea, an area of active ocean-atmosphere heat exchange today."

Chemical changes seen in ice cores are helping scientists understand how humans are "presently re-arranging Earth's energy budget and the global carbon cycle by increasing greenhouse gases in the atmosphere," he said. The research team used both changes in atmospheric methane and the differing isotopic ratios of molecular hydrogen found in ice cores at both poles to reach their conclusions.

University of Colorado at Boulder

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