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The direct and secondary effects of rapidly changing climate caused large rivers draining the Atlantic passive margin to incise quickly into bedrock beginning about 35,000 years ago. Measured in samples from bedrock fluvial terraces, 10-beryllium shows that both the Susquehanna and Potomac Rivers incised 10- to 20-meter-deep gorges along steep, convex lower reaches during the last glacial cycle. This short-lived pulse of unusually rapid downcutting ended by 13,000 to 14,000 years ago. The timing and rate of downcutting are similar on the glaciated Susquehanna and unglaciated Potomac Rivers, indicating that regional changes, not simply glacial meltwater, initiated incision. [ABSTRACT FROM AUTHOR]

The article discusses research by paleoclimate modeler Ayako Abe-Ouchi of the University of Tokyo and colleagues in a 2013 issue of "Nature" magazine that linked a type of global climate model used to forecast global warming with a complex model of the northern ice sheets to study how slight changes in Earth's orbit could have driven the great ice ages. The team's discovery of two processes that they believe are key to a realistic glacial cycle are discussed.