<P> The NADW is a complex of several water masses formed by deep convection and also by overflow of dense water across the Greenland - Iceland - Scotland Ridge . </P> <P> The upper layers are formed by deep open ocean convection during winter . Labrador Sea Water (LSW), formed in the Labrador Sea can reach depths of 2000 m as dense water sinks downward . Classical Labrador Sea Water (CLSW) production is dependent on preconditioning of water in the Labrador Sea from the previous year, and the strength of the North Atlantic Oscillation . During a positive NAO phase, conditions exist for strong winter storms to develop . These storms freshen the surface water, and their winds increase cyclonic flow, which allows denser waters to sink . As a result, the temperature, salinity, and density vary yearly . In some years these conditions do not exist and CLSW is not formed . CLSW has characteristic potential temperature of 3 ° C, salinity of 34.88 psu, and density of 34.66 . Another component of LSW is the Upper Labrador Sea Water (ULSW). ULSW forms at a density lower than CLSW and has a CFC maximum between 1200 and 1500 m in the subtropical North Atlantic . Eddies of cold less saline ULSW have similar densities of warmer saltier water and flow along the DWBC, but maintain their high CFCs . The ULSW eddies erode rapidly as they mix laterally with this warmer saltier water . </P> <P> The lower waters mass of NADW form from overflow of the Greenland - Iceland - Scotland Ridge . They are Iceland - Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). The overflows are a combination of dense Arctic Ocean water (18%), modified Atlantic water (32%), and intermediate water from the Nordic seas (20%), that entrain and mix with other water masses (contributing 30%) as they flow over the Greenland - Iceland - Scotland Ridge . The formation of both of these waters involves the conversion of warm salty northward flowing surface waters to cold dense deep waters behind the Greenland - Iceland - Scotland Ridge . Water flow from the North Atlantic current enters the Arctic Ocean through the Norwegian Current which splits into the Fram Strait and Barents Sea Branch . Water from the Fram Strait recirculates, reaching a density of DSOW, sinks, and flows towards the Denmark Strait . Water flowing into the Barent Sea feeds ISOW . </P> <P> ISOW enters the eastern North Atlantic over the Iceland - Scotland Ridge through the Faeroe Bank Channel at a depth of 850 m, with some water flowing over the shallower Iceland - Faeroe Rise . ISOW has a low CFC concentrations and it has been estimated from these concentrations that ISOW resides behind the ridge for 45 years . As the water flows southward at the bottom of the channel, it entrains surrounding water of the eastern North Atlantic, and flows to the western North Atlantic through the Charlie - Gibbs Fracture Zone, entraining with LSW . This water is less dense than (DSOW) and lays above it as it flows cyclonically in the Irminger Basin . </P>

At what rate does the water in the north atlantic ocean sink