The pathways associated with the transformation of warm subtropical waters into colder subpolar and polar waters in the northern North Atlantic. Along the subpolar gyre pathway the red to yellow transition indicates the cooling to Labrador Sea Water, which flows back to the subtropical gyre in the west as an intermediate depth current (yellow). In the Norwegian and Greenland Seas the red to blue/purple transitions indicate the transformation to a variety of colder waters that spill southwards across the shallow ridge system connecting northern Europe, Iceland, Green-land, and northern North America. These overflows form up into a deep current also flowing back to the subtropics (purple), but beneath the Labrador Sea Water. The green pathway also indicates cold waters--but so influenced by continental runnoff as to remain light and near the sea surface on the continental shelf.
Temperature (°C) of the deep mixed layer near the end of winter in the areas where that depth exceeds 200 meters. It is based on hydrographic survey data recorded from 1957 to 1967
Examples of the variation of temperature with depth from the stations used for the figure above.
The history of temperature (circles and black line) of the Labrador Sea Water convecting in the central Labrador Basin to depths sometimes exceeding 2,000 meters. This is compared to the interdecadal march of an index of the North Atlantic Oscillation, with the reds indicating the high index periods of strong westerlies, and the blues the low index periods of weak westerlies. See the North Atlantic Oscillation inset box in the Deser article for an explanation of the high and low states of the "NAO". The NAO index plotted here is formed from the sea-level pressure difference between the subtropical Azores high pressure center and the subarctic low pressure center near Iceland. The authors thank James Hurrell (National Center for Atmospheric Research) for the latest updates of NAO index data.
A time series of maps derived from winter SST measurements from 1949 to 1996. Pronounced warm SST anomalies are indicated by red and pronounced cold SST anomalies by blue.
Maps of temperature and salinity changes for successive time periods at a depth near 400 meters in the northern North Atlantic. Reds and yellows indicate that the later of the two periods is warmer or saltier, while blues and greens indicate the later period is cooler or fresher. Gray areas indicate small salinity and temperature change. White areas indicate a lack of data.