A high-resolution record of the flux of ice-rafted debris in deep-sea cores from the Northeast Pacific indicates that the major interstadials that punctuated the last glaciation are concurrent between the North Pacific and the North Atlantic. In the North Atlantic these major interstadials immediately followed episodes of massive iceberg discharge, thought to result from extensive collapse of the Laurentide icesheet. A mechanistic scenario is presented to explain how collapse of the Laurentide icesheet could cause concurrent interstadials between the two oceans. ¿ 1997 American Geophysical Union