Ice Age Sent Shivers through the Tropics
Monastersky, Richard, Science News
Among climate scientists, the tropics have the reputation of unwavering stability. When the rest of the globe turned frosty during the last ice age, some 115,000 to 10,000 years ago, Earth's midsection seemed to weather the glacial epoch with little or no cooling.
But gathering evidence is shaking this appraisal by showing that parts of the tropics chilled substantially during the ice age. If duplicated at other sites, the new findings will remove one of the major problems plaguing people trying to forecast Earth's climate.
Martin Stute of Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y., and his colleagues took the temperature of the tropics during the ice age by analyzing groundwater from aquifers in northeastern Brazil at a latitude of 7oS. The researchers measured the concentrations of four noble gases--neon, argon, krypton, and xenon--in water samples pulled from enclosed aquifers hundreds of meters below the surface.
Because gas is more soluble in cooler water, the scientists could gauge the temperature of the water at the time it percolated down into the aquifers.
Using the carbon-14 dating technique, Stute and his colleagues determined an age for each water sample. Samples less than 10,000 years old had an average temperature of 29.6oC, while older samples, from the glacial epoch, averaged 24.2oC, the scientists report in the July 21 Science.
Evidence of a marked drop in temperature so close to the equator conflicts with data collected by oceanographers in the 1970s, which indicate that the low-latitude oceans cooled by less than 2oC.
Another recent study from South America also challenges the idea of unvarying tropical warmth during the ice age. In the July 7 Science, Lonnie G. Thompson of Ohio State University in Columbus and his coworkers describe new climate data collected during an expedition to the Peruvian Andes. …