SIMULATION OF ABRUPT CLIMATE-CHANGE INDUCED BY FRESH-WATER INPUT TO THE NORTH-ATLANTIC OCEAN

TEMPERATURE records from Greenland ice cores(1,2) suggest that large a nd abrupt changes of North Atlantic climate occurred frequently during both glacial and postglacial periods; one example is the Younger Drya s cold event. Broecker(3) speculated that these changes result from ra pid changes in the thermohaline circulation of the Atlantic Ocean, whi ch were caused by the release of large amounts of melt water from cont inental ice sheets. Here we describe an attempt to explore this intrig uing phenomenon using a coupled ocean-atmosphere model. In response to a massive surface flux of fresh water to the northern North Atlantic of the model, the thermohaline circulation weakens abruptly, intensifi es and weakens again, followed by a gradual recovery, generating episo des that resemble the abrupt changes of the ocean-atmosphere system re corded in ice and deep-sea cores(4). The associated change of surface air temperature is particularly large in the northern North Atlantic O cean and its neighbourhood, but is relatively small in the rest of the world.