the North Atlantic Current. He traced the position 

 of the current by examining the 10°C isothermal 

 surface (fig. 16). The steep gradients east of 50°W 

 define the North Atlantic Current. 



Dietrich (1964) continued this analysis and 

 called the geographic location of the 10°C isotherm 

 at 200 m the North Atlantic Current boundary 

 (Polar Front). This boundary separates cold, low- 

 saline, subpolar water and warm, high-saline, 

 subtropical water. The variations in the position 

 of the front are shown in figure 17 (Dietrich, 

 1964). Fluctuations of the North Atlantic Current 

 as determined by maximum cross current temper- 

 ature gradients are shown in figure 18 (Fuglister 

 and Worthington, 1951). 



Information provided by Boisvert (1967) indi- 

 cates that the North Atlantic Current is a rather 

 sluggish and slow moving regime ( < 1 .0 kt) subject 

 to the effects of shallow, wind driven surface 

 movement known as North Atlantic Drift (Stom- 

 mel, 1966). 



Due to wide seasonal variations and the limited 

 amount of available data for the North Atlantic 

 Current, exact limits of temperature and salinity 

 distribution cannot be clearly described. However, 

 Corton (1967) indicates that a high salinity core 

 (35.6%o-36.2%o) exists at approximately 100 m. 

 Temperatures at this depth vary between 16° and 

 17°C (Pub. No. 700, 1967). 



Contributing Water Masses 



The North Atlantic Current provides a dynamic 

 boundary between two distinct water masses 

 which are displaced and positioned along this 

 boundary as a function of the current velocity 

 and shape of developing meanders. The predomi- 

 nant water mass to the south has been designated 

 North Atlantic Central Water (NACW) (4°-17°C, 



35.10%o-36.29%o) (Sverdrup, et al. 1942, Defant, 

 1961). Corton (1967) has estimated this water 

 to extend from the surface to approximately 600 

 m in the vicinity of OS DELTA. Subarctic Water 

 (3°-5°C, 34.7%o-34.9%o) to the north of this 

 boundary is the dominant water mass from the 

 surface to 1,750 m (Corton, 1967). However the 

 observed characteristics at OS DELTA (8°-23°C, 

 35.10%o-36.70%o) indicate a regime whose physi- 

 cal properties are, at times, influenced by the 

 North Atlantic Current. This influence was espe- 

 cially noticeable during the summer months when 

 the wind mixed layer was at a minimum 

 thickness. 



The intermediate water at OS DELTA (600-1,- 

 750 m) was formed by the mixing of Subarctic 

 Water with the more saline water transported 

 by a northwestern fan of the Mediterranean 

 effluent. The lower limit of this intermediate 

 water mass can be identified by a salinity of 

 34.92%o and has been estimated to be at a depth 

 of 1,750 m in the vicinity of OS DELTA (Corton, 

 1967). 



Table 2 summarizes and compares the various 

 water masses found in the vicinity of OS DELTA. 

 T-S diagrams of the data collected at OS DELTA 

 emphasize these water masses and point out the 

 effects of seasonal variation (figs. 19-23). 



Seasonal Variations 



The observations made at OS DELTA indicated 

 the existence of a seasonal upper layer separated 

 from the non-seasonal layer at about 300 m as 

 can be seen from the vertical distribution of 

 temperature (figs. 26-38). A permanent thermo- 

 cline (approximately 1.5°C/100 m) existed from 

 a depth of 300 m to 800 m. The temperature 

 then decreased from 6°C at 800 m through the 



Table 2. — Description of water masses in the vicinity of Ocean Station DELTA. 



* According to Defant (1961, Table 83) 

 **From observed data 



