Digital Varves

Varve Project News

Work linking New England glacial sediments with Greenland ice core records published


Prof. Jack Ridge and a colleague from the Berkeley Geochronology Center, along with six former Tufts undergraduates have published a landmark paper now available in the American Journal of Science entitled "The new North American Varve Chronology: A precise record of southeastern Laurentide Ice Sheet deglaciation and climate, 18.2-12.5 kyr BP, and correlations with Greenland ice core records."

Key to this research was work supported by a grant from the National Science Foundation that located and sampled new sections of glacial varves in the Connecticut River valley. Varves are annual deposits of sediment distinguished by a winter layer and summer layer, and in this case they were deposited in a glacial lake that filled the valley during the end of the last Ice Age. By counting the annual layers and using carbon dating on the new sections of varves, much of which was work performed by Tufts undergraduates, Ridge and colleagues were able to piece together the "missing links" in the timeline of the retreat of the ice sheet from New England. In addition, more precision in the new varve records provided links to some key archives of climate change during the last ice age: Greenland ice cores. This result allowed Ridge and colleagues to infer that the processes of climate change that affected the Greenland ice sheet starting at about 15,000 years ago were synchronous with changes in the ice sheet in New England. They conclude that a widespread regional change in climate mechanisms, rather than local ice sheet conditions in either locale, were acting to cause ice retreat.

The paper can be located at the American Journal of Science or downloaded from the North American Glacial Varve Project website.

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