Cold climate lingered after ice age.

For generations of geology students, the term Younger Dryas has meant the end of the last ice age. During this period, from 10,800 to 10,300 years ago, the globe shivered through one final cold spell before entering the warm Holocene epoch, according to standard wisdom. Now, a lake in upstate New York is revising scientists' ideas about the ice age's demise.

Evidence from the bottom of Seneca Lake reveals that this part of North America remained cold long after the Younger Dryas. William T. Anderson of the Swiss Federal Institute of Technology in Zurich and his colleagues made the discovery by drilling into the soft layers of clay that have gradually accumulated on the bottom of the lake. Oxygen isotope ratios within the clay serve as a sort of atomic thermometer, allowing the researchers to gauge the region's temperature thousands of years ago.

The oxygen record and other signs within the sediments suggest that Seneca Lake went through a prolonged chill from roughly 10,000 years ago to 8,000 years ago, the scientists report in the February Geology. This previously unknown cold period lasted longer and was more intense than the well-documented Younger Dryas. The scientists trace the frosty conditions to the shrinking ice cap in Canada, which was melting rapidly at this time and filling the Great Lakes with cold water.

The frigid weather apparently stretched around much of the Northern Hemisphere. Anderson and his colleagues have found hints of a cold spell occurring at a similar time in Europe, Alaska, Greenland, and the Atlantic Ocean.