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A fresher North Atlantic could lead to changes in ocean circulation and climate
A global system of currents, often called the ?ocean conveyor,? carries warm surface waters from the tropics northward. At high latitudes, the waters cool, releasing heat to the atmosphere and moderating wintertime climate in the North Atlantic region. The colder (and denser) waters sink and flow southward in the deep ocean to keep the conveyor moving.Cold, dense waters that propel the ocean conveyor form and accumulate in strategic locations in the North Atlantic?in the Greenland, Iceland, and Norwegian Seas and in the Labrador, Irminger, and Iceland Basins.
A new analysis of salinity measurements over the past 55 years shows that waters in critical North Atlantic locations have been getting fresher?fed by melting glaciers and increased precipitation associated with greenhouse warming (saltier waters are red, orange, and yellow; fresher waters are blue and green). Continued freshening of the North Atlantic could slow the ocean conveyor, diminishing the amount of heat transported northward and significantly cooling areas of the Northern Hemisphere.Of particular concern are changes in the Greenland, Iceland, and Norwegian Seas, where dense waters accumulate (darker blues represent denser waters). A density contrast between these waters and those in the North Atlantic drives water southward across the Greenland-Scotland Ridge in the Denmark Strait. As excess fresh water accumulates in the northern seas, the density contrast of waters north and south of the ridge will diminish. The southward flow of dense waters will decrease, the ocean conveyor will weaken, and the North Atlantic region will cool.

  
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Of particular concern are changes in the Greenland, Iceland, and Norwegian Seas, where dense waters accumulate (darker blues represent denser waters). A density contrast between these waters and those in the North Atlantic drives water southward across the Greenland-Scotland Ridge in the Denmark Strait. As excess fresh water accumulates in the northern seas, the density contrast of waters north and south of the ridge will diminish. The southward flow of dense waters will decrease, the ocean conveyor will weaken, and the North Atlantic region will cool.
WATER OVER THE DAM?Of particular concern are changes in the Greenland, Iceland, and Norwegian Seas, where dense waters accumulate (darker blues represent denser waters). A density contrast between these waters and those in the North Atlantic drives water southward across the Greenland-Scotland Ridge in the Denmark Strait. As excess fresh water accumulates in the northern seas, the density contrast of waters north and south of the ridge will diminish. The southward flow of dense waters will decrease, the ocean conveyor will weaken, and the North Atlantic region will cool. (Illustration by Jack Cook, WHOI)

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Posted: March 7, 2007

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