Research on global climate change has increasingly focused on rapid (century-scale and decadal) changes. One such climate shift, the Younger Dryas cooling event(1), took place during the last deglaciation, from 13,000 to 11,700 years BP. Climate records from Greenland ice cores and North Atlantic sediment cores show high-frequency fluctuations implying significant (>5 degrees C) shifts in temperature at this time, taking place within 50-100 years (ref. 2), The origin of the Younger Dryas has recently been attributed to a reduction or cessation of deep-water production in the North Atlantic and a concurrent lessening of the heat flux from Low latitudes(3,4), The role of intermediate waters (1,000-2,000 m depth) is less certain, however, because climate proxies for this ocean reservoir are rare and ambiguous. Here we report on the use of a new climate archive, deep-sea corals from Orphan knoll (1,600 m depth) in the northwestern Atlantic Ocean. The oxygen isotope ratios in the coral skeletons (accurately dated by the Th-230/U-234 chronometric method) change markedly coincident with the initiation of the Younger Dryas, suggesting that there were profound changes in intermediate-water circulation at this time.