Peruvian Glacial Retreat Uncovers Evidence Of Ancient Climate Shifts

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COLUMBUS , Ohio – For the third time in as many years, glaciologist Lonnie Thompson has returned from an Andean ice field in Peru with samples from beds of ancient plants exposed for the first time in perhaps as much as 6,500 years. In 2002, he first stumbled across some non-fossilized plants exposed by the steadily retreating Quelccaya ice cap. Carbon dating showed that plant material was at least 5,000 years old.

Then in 2004, Thompson found additional plant beds revealed by the continued retreat of the melting ice and when tested, these proved to be carbon-free, suggesting that they might date back more than 50,000 years. If true, that would suggest that the climate in that region may not have been as warm as it is today in more than 500 centuries.

In June, he went back to the ice field and found at least 20 new plant collection sites that had been newly exposed. An analysis of the plant material from these sites suggested that it ranged from 4,500 to 6,500 years old. Some of these sites contained thick, multiple layers of plant material and soil which might provide a chronology of when in the past this now high, cold, ice-covered locale harbored flourishing wetland bogs, an ecosystem requiring much warmer temperatures. Thompson, a professor of geological sciences and researcher with the Byrd Polar Research Center at Ohio State , calls that ice cap the "Rosetta Stone" for climate change.

"Quelccaya is the biggest tropical ice cap on earth and is probably the best-documented as far as its response to recent climate change," he said. "And the retreat of the Qori Kalis glacier that spills off Quelccaya is perhaps the best-studied retreat of any tropical glacier." He should know. He's led 22 expeditions to this forbidding region since 1974, drilling cores through the ice cap that have yielded a detailed climate history of the region. Frozen areas once surrounding Quelccaya now harbor massive meltwater lakes hundreds of feet deep.

This time, Thompson brought with him two botanists to help identify new deposits. Blanca Leon, a research fellow from the Herbarium, Plant Resources Center , and her colleague Kenneth Young, an associate professor of geography, both at the University of Texas at Austin , had identified the plant species in samples from Thompson's earlier expedition. The plants proved to be alpaca moss, Distichia muscoides, a hardy species that still inhabits the region. The researchers also identified at least two additional species of moss and grasses that were recently uncovered by the ice. The 20 plant samples were sent to both Lawrence Livermore National Laboratories and Woods Hole Oceanographic Institute for carbon dating.

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http://www.eurekalert.org/pub_releases/2005-09/osu-npf091405.php