
Fresher Ocean, Cooler Climate
A less-salty North Atlantic Ocean could cool northern winters
Large and climatically sensitive regions of the North Atlantic Ocean have become less salty since the late 1960s, a trend that could alter global ocean circulation and spur climate changes by the 21st century.
Reporting in the June 17 edition of the journal Science, Ruth Curry of Woods Hole Oceanographic Institution and Cecilie Mauritzen of the Norwegian Meteorological Institute analyzed salinity data collected over the past half-century throughout the Greenland, Norwegian, Iceland, Labrador, and Irminger Seas in the North Atlantic.
Cold, salty—and therefore relatively dense—waters form in the North Atlantic and drive a global ocean circulation system, often called the ocean conveyor, which plays a big role in regulating Earth’s climate [see slide show].
“If you put too much fresh water in the right places in this part of the world, it can actually alter a portion of the ocean circulation that transports heat from the tropics up toward the North Pole,” Curry said.
The increased inflow of fresh water comes from increased precipitation and melting glaciers, associated with greenhouse warming.
“Given the projected 21st-century rise in greenhouse gases, we cannot rule out a significant slowing of the conveyor in the next 100 years,” Curry said. “We want to know exactly how fast that whole system is changing. It seems to be tipping out of balance as a consequence of global warming.”
The study was funded by the National Science Foundation, a WHOI Independent Study Award, and the Norwegian Research Council.
Slideshow

Slideshow
- THE OCEAN CONVEYOR?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. (Illustration by Jack Cook, WHOI)
- SENSITIVE SEAS?Cold, dense waters that propel the ocean conveyor form and accumulate primarily in certain locations in the North Atlantic?in the Greenland, Iceland, and Norwegian Seas and in the Labrador, Irminger, and Iceland Basins. (Illustration by Jack Cook, WHOI)
- RAPID OCEAN FRESHENING?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. (Data compiled by Ruth Curry, WHOI)
- 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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See Also
- How Much Excess Fresh Water Was Added to the North Atlantic in Recent Decades? News release on Ruth Curry research in Science
- Abrupt Climate Change Resources from the WHOI Ocean and Climate Change Institute