DISCUSSION 



Section A5 



Standard Section A5 had three major water 

 masses in the upper 1500 meters during 1967 to 

 1969. Beginning at the coast and proceeding 

 seaward they were Coastal Water, Slope Water 

 and North Atlantic Central Water (NAC). At the 

 surface these water masses were characterized 

 by increasing temperature and increasing salin- 

 ity as one moved seaward. At a depth of about 

 1000 meters the water masses all converged to- 

 ward NAC water (figs. 2-19). 



Coastal Water was characterized by a very 

 steep salinity gradient in the vertical and hori- 

 zontal directions. The vertical salinity gradient 

 was as large as 0.04%c. to 0.087imi per meter. A 

 surface salinity gradient of 0. 1°/im. per mile was 

 not unusual neai- the boundary between Slope 

 Water and Coastal Water. Coastal Water ex- 

 tended to a depth of about 200 meters, the depth 

 of the shelf break, where the salinity reached 

 34.87m-35.47oo. Often at the lower boundary of 

 Coastal Water there was a salinity maximum if the 

 salinity reached at least 35%o. This appeared to 

 be a result of an intrusion of Slope Water beneath 

 the Coastal Water. Whether or not a salinity 

 maximum existed. Coastal Water was underlaid 

 by the more isohaline deeper portions of the Slope 

 Water. Coastal Water covered the continental 

 shelf and slope. It extended beyond the shelf 

 break by 50 to 100 nmi on A5. 



Above the seaward edge of the continental 

 slope and extending at times almost 300 miles 

 beyond the Coastal Water was a water mass 

 known as Slope Water. As pointed out by Iselin 

 (1936), Slope Water has properties intermediate 

 between the Coastal Water and the waters of the 

 Gulf Stream. At the location of standard section 

 A5, Slope Water had a lateral extent varying 

 from about 40 nmi to about 280 nmi. The wide 

 variation in the lateral extent of Slope Water was 

 more a function of the Gulf Stream position than 

 a function of Coastal Water position. 



In most cases, the isohalines and isotherms of 

 the A5 section were fairly level in the Slope 



Water region with the notable exception of sec- 

 tion A5-4 (figs. 8 and 9). On this particular sec- 

 tion taken in December 1967 there was an appar- 

 ent anticyclonic eddy centered on station nine. 

 This eddy had a salinity maximum of greater 

 than 36.6°/cici and a temperature greater than 

 19°C at 100 meters. The upper 50 to 75 meters 

 of the eddy had been eroded, probably due to the 

 storms and cooling present at this time of year. 

 This eddy must have disconnected from the Gulf 

 Stream only a short time before the section was 

 taken since the core of the eddy was only about 

 30 nmi from the axis of the Gulf Stream as de- 

 fined by the 15°C isotherm at 200 meters. This 

 eddy was very shallow and appeared only in the 

 upper 300 meters although it affected isopleths 

 of temperature and salinity down to 600—700 

 meters. 



The isopycnals of the Slope Water broke fairly 

 sharply at the edge of the Gulf Stream and 

 curved downward toward the east, but between 

 the Slope Water and the Coastal Water there was 

 no such break. The isopycnals generally sloped 

 upward to the west in the Slope Water — Coastal 

 Water region. Slope Water deeper than about 

 100—125 meters had characteristics very close to 

 that of NAC Water, only slightly less saline 

 (.020%(j to .0257oo) based on a least squares 

 analysis of the data. 



The high speed core of the Gulf Stream was 

 delineated by the 15°C isotherm at 200 meters. 

 This core also formed the shoreward boundary of 

 NAC Water. Normally at a temperature of 

 8°-9°C Slope Water merged into NAC Water. 



In one very interesting instance Slope Water 

 appeared to the east of the Gulf Stieain at 800 to 

 950 meters. This water was normally at 150 to 

 300 meters in the Slope Water region. This took 

 place on section A5-4 where the Gulf Stream 

 appeared to make a loop of about 180 nmi 

 diameter (figs. 8, 9, and 10). The water in the 

 center of the loop had the characteristics of NAC 

 down to about 500 meters (fig. 60). Below that it 

 began to have the lower salinity characteristic of 

 Slope Water. At 800 meters to 950 meters the 

 water in the loop coincided exactly with Slope 



