Formation Details
The NADW comprises three different water masses, each of which is distinguished by a specific formation region (LSW, see below) or entry point (DSOW, see below) and has unique production and transformation history (I Yashayaev).
The upper one is the Labrador Sea Water (LSW), formed due to deep winter convection in the Labrador Sea. This water partwise recirculates in the Labrador Sea while sinking. (Other parts of Labrador Sea Water spreads over the whole northern atlantic.) After recirculation it enters the Deep Western Boundary Current (DWBC) between 1600 and 2500 m depth. The Formation of LSW is seasonal and does not occur every year. There seems to be a correlation to the state of the North Atlantic Oscillation.
The lower water mass is the Denmark Strait Overflow Water (DSOW). This water overflows the Denmark Strait, entraining water from its surrounding. Leaving the Greenland Sea with 2.5 Sv its flow increases to 10 Sv south of Greenland. It is cold and relatively fresh, flowing below 3500 m in the DWBC and spreading inward the deep Atlantic basins.
The third water mass originates from the Greenland Sea, too, but it leaves the basin between Iceland and Scotland. While flowing southward it entrains warm and saline Atlantic waters (which are much saltier than the overflow itself, this is where this water acquires its salty signature) and the Labrador Sea Water. It passes the Charlie-Gibbs Fracture Zone to the Irminger Sea, and arranges in the DWBC between 2500 and 3500 m. Because of its complex formation/transformation history this water has many names: Iceland-Scotland Overflow Water, Northeast Atlantic Deep Water and Gibbs Fracture Zone Water
Read more about this topic: North Atlantic Deep Water
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