Climate Science

A Splash of Cold Water

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Science  26 Jan 2007:
Vol. 315, Issue 5811, pp. 439
DOI: 10.1126/science.315.5811.439b

During the last degalciation, a large and rapid injection of glacial meltwater from the Laurentide Ice Sheet to the North Atlantic (called meltwater pulse 1a, or mwp-1a) raised sea level by ∼20 m in only about two centuries. This enormous freshwater addition has variously been posited as the trigger of the Bølling warming period 14,600 years ago or as the cause of the Older Dryas cold event that terminated the Bølling 14,000 years ago; uncertainty about the age of mwp-1a has prevented resolution of these conflicting claims. Stanford et al. present a record of North Atlantic Deep Water (NADW) flow intensity from Eirik Drift that, combined with previously published improved dating for mwp-1a, establishes a relatively minor 200-year weakening of NADW flow 14,600 years ago, coincident with mwp-1a. The data also show that no discernible sea-level rise accompanied the clear NADW slowdown during the Younger Dryas. These results demonstrate that NADW formation and climate are not controlled exclusively by the magnitude or rate of meltwater addition, because the largest meltwater pulse resulted in the relatively minor Older Dryas whereas the climatologically much more dramatic Younger Dryas was not associated with discernable rises in sea level. Thus, the location of meltwater additions may be important. — HJS

Paleoceanography 21, PA4103 (2006).

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