The circulation of norwegian sea overflow water in the eastern north-atlantic

Neutral surfaces are defined from historical hydrographie data on which the spreading of Iceland-Scotland overflow water (ISOW) may be examined in the eastern North Atlantic and the lrminger Basin. Each of these neutral surfaces occurs at less than 400 rn on the Iceland-Faroe rise, but they descend to depths in excess of 2 600 rn (shallowest) and 3 600 rn (deepest) in the area of study. Salinity distribution on these surfaces provides a first indication of circulation patterns. e-S water mass analysis, using successive mixing stages of ISOW is generally found to be satisfactory, but in the south-eastern part of the region a third water mass characteristic is required. Oxygen data from cruises between 1957 and 1962 are re-examined and, after the ·application of new corrections, are considered to be internally consistent and sui table for this purpose. The resultant charts of the spreading of ISOW on neutral surfaces show that more than 40% of the water flowing through the Charlie-Gibbs fracture zone (CGFZ) at about 2400 rn has the original overflow water characteristics. Geostrophic calculations with a reference level of no motion selected on the basis of the water mass analysis are used to derive quantitative circulation patterns of all deep water below the reference level and of the original overflow water. A total of 5.5 Sv of deep water including 1.8 Sv of original overflow water are found to enter the eastern basin between Iceland and Scotland; sorne appears to undergo cyclonic circulation in the Iceland Basin, before it all passes through the CGFZ into the western basin.