North Atlantic Deep Water

North Atlantic Deep Water

North Atlantic Deep Water (NADW) is a water mass that forms in the North Atlantic Ocean. It is largely formed in the Labrador Sea and in the Greenland Sea by the sinking of highly saline, dense overflow water from the Greenland Sea. The watermass can be traced around the southern end of Greenland and then, at a depth of 2000–4000 meters, down the coast of Canada and the United States where it turns a bit east. It continues southeast, past the eastern tip of South America and across the South Atlantic. Its path can ultimately be traced into the Southern Ocean and around the tip of Africa as it mixes with Circumpolar Deep Water.

In the "conveyor belt" model of the thermohaline circulation of the world ocean, the sinking of NADW pulls the waters of the North Atlantic drift northward; however, this is almost certainly an oversimplification of the actual relationship between NADW formation and the strength of the Gulf Stream/North Atlantic drift. NADW's distinctive composition (particularly high-salinity) compared to other watermasses allows its path to be traced as it mixes with Circumpolar Deep Water, which in turn fills the deep Indian Ocean and part of the South Pacific.

It is believed that North Atlantic Deep Water formation has been dramatically reduced at times during the past (such as during the Younger Dryas or during Heinrich events), and that this might correlate with a decrease in the strength of the Gulf Stream and the North Atlantic drift, in turn cooling the climate of northwestern Europe. There is concern that global warming might cause this to happen again. It is also hypothesized that during the Last Glacial Maximum (LGM), NADW was replaced with an analogous watermass that occupied a shallower depth known as Glacial North Atlantic Intermediate Water (GNAIW).