GEO PROFESSOR'S HYPOTHESIS CONFIRMED BY TWO STUDIES

A flood of fresh water released into the Atlantic Ocean by the melting of an ice dam played a major role in an abrupt climate change that depressed temperatures in Europe for a period of about three centuries some 8,200 years ago, two recent studies conclude. The papers, published in The Proceedings of the Academy of Natural Sciences and Quaternary Science Reviews, support a hypothesis advanced in a paper published in Nature by Assistant Professor of Geology Don Barber and several colleagues in 1999, when Barber was a doctoral student at the University of Colorado.

Evidence of the cool spell, thought to be the most abrupt and widespread in the last 10,000 years of Earth's history, has long been known to geologists. So has the evidence that two enormous freshwater lakes left in North America by retreating glaciers burst through an ice sheet that had been restraining them. Barber worked out the connection between these two events by precise radiocarbon dating of the lakes' sudden drainage. He went on to hypothesize that the influx of fresh water into the Atlantic changed salinity levels enough to interrupt thermohaline circulation, the process that normally causes water from the tropics to flow northward. Disruption of these currents effectively shut off the heat supply to Europe and the Arctic, he said.

The publication of Barber's paper created a major stir in the world of paleoclimatology that rippled into the popular press all over the world. "The idea that changes in salinity could affect thermohaline circulation had been suggested before," Barber says, "but only in theory. People thought perhaps this had happened during an ice age. But this showed a concrete case of it in a context that is much more relevant to current and possible future climate change."

Scientists are now looking carefully at the potential effects of changes in the ocean's salinity. For an overview of the current research, Barber suggests a story recently published in The Philadelphia Inquirer.

The two teams of researchers tested Barber's hypothesis with two different computer models; both indicate that the freshwater flood that resulted from the drainage of the two glacial lakes could have interrupted ocean circulation to produce temperature change consistent with the geological record. "I felt at the time that it was an important finding," Barber says, "and the fact that it has stood the test of time in the rapidly evolving field of paleoclimatology is gratifying."

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