Water. Apparently what had happened was that 

 the loop formed rapidly and pushed to the north 

 and west causing a convergence of Slope and 

 Gulf Stream Waters which then were forced 

 below the Gulf Stream into a position normally 

 occupied by NAC Water. 



At a point just below the seaward edge of Coas- 

 tal Water and extending at times into the Slope 

 Water was a narrow band of water with a salinity 

 much below that of either NAC or Slope Water for 

 a given temperature. This water type appeared as 

 a bulge on T-S diagrams of A5-3 and A5-4 (figs. 

 59 and 60) at about 5°-7°C and 34.77oo-34.97oo 

 and a depth of 250— 500 meters. Subarctic inter- 

 mediate water was the most likely source for this 

 water type. 



There was a salinity maximum at the eastern 

 end of some of the A5 sections which appeared at 

 a depth of 1000-1300 meters on A5-2 and A5-3 

 (figs. 2 and 5). The salinity was about 35.01%o to 

 35.04%o and had a sigma-t of 27.6-27.7. The 

 temperature was about 0.5°C higher than im- 

 mediately to the west. This most likely was the 

 western extent of Mediterranean influence. 



Section A6 



Section A6 was dominated by North Atlantic 

 Central Water (NAC) (figs. 20-46). There was a 

 band on the shoreward end of Section A6 which 

 was occupied by the Gulf Stream, although the 

 Gulf Stream was rarely crossed completely during 

 sampling. The Gulf Stream was located about at 

 the shelf break. No pronounced eddies appeared 

 in any of the sections. What might have been a 

 weak decayed eddy was centered on station eight 

 of A6-8 (figs. 35-37). No effect was seen in the 

 upper 200 meters of water. 



The main feature of NAC Water on A6 was the 

 broad band of water centered on the 18°C 

 isotherm that was characterized by low gradients 

 of both salinity and temperature. This layer 

 existed on all sections in both summer and winter. 

 The pycnocline, about 26.4 sigma-t, which ap- 

 proximated the position of the 18°C isotherm, 

 never completely broke down in this area. The 



water in this layer which divided the upper and 

 lower pycnocline must have been formed 

 elsewhere. The gradient of temperature in this 

 layer of low gradient was .004 or .005°C/m year 

 round. The thermocline below the low gradient 

 layer had a constant gradient of approximately 

 .020 to .025°C/m. The surface thermocline on the 

 other hand had a highly variable temperature 

 gradient that varied from .02°C/m in January 

 1967 to .17°C/m in October 1968. In January 

 1967, the mixed layer depth was approximately 

 130 meters. In February and March the mixed 

 layer deepened, but it was never deeper than 200 

 meters since the gradient from 200-500 meters 

 was constant as stated above. 



The 18°C isotherm formed an inflection point 

 between the positive curvature of the deep ther- 

 mocline and the negative curvature of the tem- 

 perature in the shallow thermocline. If mixing 

 does not take place down to 500 meters what 

 accounts for the layer 300 meters thick which is 

 relatively uniform? This water mass matched very 

 closely the 18°C water of Worthington (1959) 

 which was characterized by an inflection point at 

 17.9±0.3°C and 36.50±0.107oo. The combina- 

 tion of the mean sea surface temperature by one 

 degree squares (Gulf Stream Reports, 1969) for 

 January, February and March with the mean sur- 

 face salinity (USNOO, 1967) for the first quarter 

 of the year gave a possible area for the formation 

 of 18°C water. This gave an area in January (fig. 

 61) roughly between 36°N to 40°N and 55°W to 

 60°W. By February this potential formation area 

 covered 33°N to 40°N and 55°W to 70°W (fig. 

 62). In March the area stayed much as in Feb- 

 ruary and was 32°N to 39°N and 55°W to 71°W 

 (fig. 63). Not surprisingly the 18°C surface water 

 had a salinity in this area that closely matched the 

 36.507cH) salinity for 18°C water formation. Tem- 

 peratures to the south were too high and salinities 

 to the north were too low to form the required 27.4 

 sigma-t. The mean sea surface temperature by 1° 

 squares was not computed east of 55°W. A6 lies 

 directly to the south of this potential formation 

 area. This is an explanation why the 18°C water 

 layer exists at A6 while mixing there did not reach 



