Large-scale climate changes in the northern Atlantic region were often associated with changes in ocean currents. That is also the case for the last cold phase of the Würm Ice Age, known as the Younger Dryas. At this time, a new cold period occurred and the northern Atlantic region relapsed from a moderate climate back to glacial conditions in the course of just a few decades. Climate indicators provide nevertheless contradictory information concerning the origins of this cold phase. EAWAG is on the trail of additional clues in an ice core from Greenland.