Oceanography

Water on the Move

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Science  02 Aug 2002:
Vol. 297, Issue 5582, pp. 739-741
DOI: 10.1126/science.297.5582.739e

Variations in the rate of thermohaline circulation are intimately connected with climate change. The ventilation age—the time that it takes for a given mass of water to be replaced by a new one—provides a measure of the rate of ocean circulation. The ventilation age of the North Atlantic Ocean has varied between approximately 500 and 700 years during the Holocene, the 10,000 years of relatively warm climate since the end of the last glacial period. Was it different during geologically recent periods of cold climate.

Keigwin and Schlegel have combined measurements of stable oxygen isotope ratios, radiocarbon ages, and mineralogical and foraminiferal compositions of sediments from the western subtropical North Atlantic in order to estimate ventilation ages during two important cold periods. Ventilation ages for the Younger Dryas, a cold interval that occurred in the Northern Hemisphere (at least) between 12,900 and 11,600 years ago, and the Last Glacial Maximum, 21,000 years ago, were 1000 years and 2000 years, respectively. These ages, much greater than some previous estimates, help to provide a more quantitative estimate of the weakening of circulation in the North Atlantic during recent cold periods. — HJS

Geochem. Geophys. Geosys.3, 10.1029/2001GC000283 (2002).

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