The latest expeditions to ice caps in the high, tropical Peruvian Andes Mountains by Ohio State University scientists may shed light on a mysterious global climate change they believe occurred more than 5,000 years ago. The researchers hope that ice cores retrieved from tropical ice caps there, as well as ancient plants retrieved from beneath the retreating glaciers, may contain clues that could link ancient events that changed daily life in South America, Europe and Asia.
     Something happened 5,200 years ago that was abrupt and very large-scale, explained Lonnie Thompson, professor of geological sciences at Ohio State and researcher with the Byrd Polar Research Center. In September, Thompson and his team returned from drilling ice cores from glaciers atop peaks in Peru. In 2002 at the Quelccaya ice cap the researchers made a surprising find: a wetland plant that had been remarkably preserved under the ice. Later testing yielded viable DNA from the plant and dated it back 5,200 years ago. "This is a soft-bodied plant. It had to be captured by a very large snowfall at the time, a snowfall and climate change that began very abruptly fast enough to capture a plant but not kill it. That is astounding. We know the first plant could not have been exposed at any time during in that 5,200-year history or it would have decayed."  said Thompson.
     This year, the researchers found a second plant near the southern tip of the ice field, some 6 kilometers south of their original plant find. Subsequent carbon dating of the second plant showed that it had been buried for the last 2,200 years, a time when other records showed another abrupt climate change.
     "We know the climate was different then. Before that, the proportion of warm water flowing off the coast of Peru was much greater. And we know that the Ice Man, a preserved Neolithic hunter exposed by a retreating glacier in the European Alps, was trapped by the ice around 5,200 years ago, and that had to occur very abruptly. " said Thomson. Earlier work by the Ohio State team on ice cores taken from Tanzanias Mount Kilimanjaro ice fields showed that a catastrophic drought had devastated the tropics around 5,200 years ago, a period of time when anthropologists believe that many people abandoned a nomadic lifestyle to form cities and social structures.

Source: Ohio State University Research News (6 November 2003)