Chinese Ice Cores Provide Climate Records Of Four Ice Ages
COLUMBUS, Ohio -- An American-Chinese expedition to a glacier high on the Tibetan plateau has obtained the longest and highest ice cores ever retrieved -- cores which may contain climate records more than 200,000 years old.
While the cores still must be analyzed, preliminary examinations of dust, air bubbles and ice crystal size suggest the team obtained a stratigraphic record of snowfall which could possibly date back much further. If that is true, it will make this the oldest ice core climate record ever obtained.
Current climate models which assess the threat and impact of global warming suggest that the areas where the cores were taken may serve as a barometer of global change.
"This may be the best climate record we've obtained so far, based on the preliminary analysis," said Lonnie Thompson, a research scientist at the Byrd Polar Research Center and associate professor of geological sciences at Ohio State University. He has spent the last 20 years drilling into ice caps around the world in an attempt to piece together a long-range climate history.
The expedition was a joint effort between Ohio State, the Polar Ice Coring Office of the University of Alaska and the Chinese Lanzhou Institute of Glaciology and Geocryology. The 22 members of the expedition, including American, Chinese, Russian and Peruvian scientists, spent almost two months working on the Guliya ice cap, a 200-square-kilometer glacier 21,000 feet up the Western Kunlun Mountains of Tibet. They returned with three cores -- one 308.6 meters, one 93.2 meters, and one 34.5 meters long.
Thompson said the shortest core (114 feet) should yield climate records back to about 1900, while the 93.2-meter (306 feet) core should date back to 1450 A.D. If so, it may offer clues to the cause and demise of the Little Ice Age, a recent 500-year period when the climate in the northern hemisphere was colder.
The third and longest core -- 308.6 meters (1,013 feet) -- easily contains more than 200,000 years of snowfall, and perhaps twice that, Thompson said. "If that's the case, it is the oldest ice that has been recovered on earth." The annual accumulation layers were readily visible in the core as it was drilled.
"In the field, we were comfortable that what we saw was that last complete glacial cycle and possibly more. The previous interglacial, a warmer period between glacial stages, or "ice ages," appeared at 180 meters down the core. If that is so, then it would make the core 100,000 years old at the 180 meter level.
"And there is still more than 128 meters of core below that. Since time is being compressed the deeper you go, this could provide a tremendously long record."
Thompson admits to being conservative with his estimates for what the remaining part of the core represents. Depending on how well the bottom of the core is preserved, it may contain ice that began as the first snows fell on the plateau 1 million years ago. The Tibetan Plateau on which the ice cap sits is young in geological terms In the last 2 million years, this area has risen to a level where snow and ice fields can develop and these have a definite impact on the climate in the region.
The Guliya ice cap is also important because, although it sits at an altitude of 21,000 feet in the mountains, it is also at 35 degrees north latitude, about the same distance from the equator as Oklahoma. "That's within the range of latitudes where most of human beings live, which makes this a very significant climate record," Thompson says.
He sees ice caps like Guliya as meteorological stations set around the Tibetan plateau that monitor and preserve a record of the climate there.
"Our only limitation is our ability to interpret that record."
The cores were split in the field, kept frozen and taken to both the Lanzhou Institute and Ohio State for analysis. Researchers will analyze the core ice for particle content and size, oxygen isotope ratios, chemistry, precipitation rates, ice crystal size, radioactivity and possibly trapped gases--all methods to determine the composition of the atmosphere at the time the snow originally fell. That analysis is expected to take up to two years.
"These long-term archives will let us look at the natural variability of the climate over long periods of time and consequently determine if and how the 20th century is different," Thompson said. "There are so many aspects of the climate system recorded in this ice. We should be able to really look at the environment and start to see the linkages between mechanisms and forces which drive the climate system.
"These kinds of records are absolutely essential when you start discussing changing policies to reduce the impact of human activity on the future," he said.
The Guliya research program is supported by the National Science Foundation's Office of Climate Dynamics and the Division of Polar Programs, the National Geographic Society, Academia Sinica (the Chinese Academy of Science) and Ohio State University.#
Contact: Lonnie Thompson, (614) 292-6652 Written by Earle Holland, (614) 292-8384