Modelling teleconnections between the North Atlantic and North Pacific during the Younger Dryas

Evidence for a cooling event synchronous with the Younger Dryas (12,000 calendar years before present) has been found in the North Pacific Ocean north of 30 degrees N in records of surface(1-5) and subsurface water properties(6,7). These changes may be related to a temporary shut-down of North Atlantic Deep Water formation and associated surface cooling over the North Atlantic. It has remained unclear, however, whether this North Atlantic cooling was communicated to the North Pacific Ocean through the atmosphere or the ocean. Here we report results of a sensitivity experiment with a coupled ocean-atmosphere general circulation model that support a primarily atmospheric forcing of North Pacific climate variations. Changes in wind strongly affect coastal upwelling at the North American west coast, and surface cooling by the atmosphere causes better ventilation of the thermocline waters of the northeast Pacific. This effect is amplified by oceanic progagation to the Pacific of the signal arising from collapse of North Atlantic Deep Water formation. These teleconnections may also explain earlier North Pacific and western North American millenial-scale cooling events of a similar nature(8-12).