Comparisons between ihe SOOF transects. Gulf- 

 stream monthly summaries (National Weather Service 

 1975). Experimental Gult Stream Analysis (.\-69) charts 

 (National Environmental Satellite Service 1975), and 

 NAV'OCEANO Experimental Ocean Frontal Analysis 

 Charts (U.S. Naval Oceanographic Office 1975) provided 

 a good check on the many fluctuations in the Gulf 

 Stream position. 



The XBT transects and the satellite data complement 

 each other in that the XBT data provided the needed 

 ground truth to verify the satellite data, and the satellite 

 data provided the necessary surface synopticity for such 

 a large monitoring program. In addition, the XBT data 

 provided another dimension to the monitoring network 

 in the form of subsurface data. The subsurface data 

 provided the means for monitoring subsurface features 

 such as the "cold cell," the depth of anticyclonic eddies 

 that impinged upon the continental slope and shelf, and 

 the bottom temperatures on the continental shelf that af- 

 fect many of the commercial finfish and shellfish species. 



On 15 .June the Chase (App. Fig. 33) crossed the Gulf 

 Stream between stations 8 and 9 at about lat. 36°21'N, 

 long. 73°40'\V. As usual an increase in the sea surface 

 temperature was noted. An unusual subsurface feature 

 should be noted with this figure. A "bubble" or intrusion 

 of colder water (<8°C) appeared along the edge or north 

 wall of the Gulf Stream at about ItX)-m depth. This could 

 have been an example of the "calving" process men- 

 tioned by Whitcomb (1970) where parcels of the cold cell 

 on the continental shelf appear to break off and detach 

 from the main body of the cold cell and How seaward off 

 the continental shelf. 



In this area around Cape Hatteras three different 

 water masses, shelf, slope, and Gulf Stream water, meet 

 and mix (Fisher 1972). The shelf water mixes directly 

 with Gulf Stream water and in the process pinches out 

 the slope water. One possibility was that the Gulf Stream 

 had moved closer to shore and impinged upon the shelf 

 water mass where the cold cell had formed, and in turn, 

 torn loose a piece of the cold cell and had dragged this 

 cold parcel along the north wall of the Gulf Stream with 

 some colder water reaching the surface. The cold fila- 

 ment mentioned by Fisher (1972) suggests that this could 

 be the mechanism at work here. 



Shoreward movement in this area of < 30 n.mi. (55.6 

 km) by the north wall of the Gulf Stream would be 

 enough for the Stream influence to act upon the shelf 

 water and cold cell. Comparing this XBT transect (App. 

 Fig. 33) with the next (App. Fig. 34) obtained the very 

 next day indicates that translational movements of the 

 north wall of over 10 n.mi. /day (18.5 km/day) can occur. 

 What we might have detected was the north wall 

 retreating seaward dragging this parcel of cool water 

 behind it. Examination of the NAVOCEANO Ex- 

 perimental Ocean Frontal Analysis Charts for 9, 11. and 

 16 .June support the contention of a shoreward, then 

 seaward, movement in the north wall on the order of 

 about 10 n.mi. /day (18.5 km/day). 



The sharp decrease in sea surface temperature (App. 

 Fig. 33) at the shelf water-slope water front (station 7) in- 



dicates that the cool filament extended from >100-m 

 depth all the way to the surface. 



Another crossing of the Gulf Stream occurred along the 

 same transect only 28 h later (App. Fig. 34). The dif- 

 ference in positions of the north wall crossings was 12 

 n.mi. (22.2 km), indicating translational movement of 

 over 10 n.mi. /day (18.5 km/day) which is the same order 

 of magnitude for translational movements estimated in 

 the past for both the Gulf Stream and Loop Current dis- 

 cussed earlier. 



On 30 October the Santa Cruz (App. Fig. 41) made the 

 .second of two Gulf Stream crossings south of Cape Hat- 

 teras. The first was shown in Appendix Figure 31. As 

 before, the north wall was so close to the shelf and the 

 scale is so large on these vertical sections that it was dif- 

 ficult to pinpoint the exact position. The crossing of the 

 north wall probably occurred between stations 2 and 3 at 

 about lat. 32°10'N and long. 79°14'W. The transition be- 

 tween shelf water and Gulf Stream water was so abrupt 

 that the surface parameters only indicated a gradual rise 

 rather than a sharp step increase. 



The Mormac Argu (App. Fig. 42) crossed through an 

 eddy (discussed later) before transecting the Gulf 

 Stream between stations 10 and 11 on 31 October at 

 about lat. 36°22'N and long. 68°21'W. The anticipated 

 increase in surface salinity showed up on the surface 

 parameter plot and a decrease in sea surface temperature 

 was noted at the point of crossing. The decrease in sur- 

 face temperature could have been a cold filament similar 

 to those discu.ssed by Fisher (1972). 



The last Gulf Stream crossing in the Cape Hatteras 

 area in 1975 was obtained by Santa Cru! (App. Fig. 45) 

 on 7 December. Again an eddy was transected prior to 

 the crossing, which occurred between stations 12 and 13 

 at about lat. 35°4rN and long. 74°26'W. On this transect 

 the surface parameter plots of sea surface temperature 

 and surface salinity show an almost "textbook" example 

 of the transitions between shelf water, slope water, eddy 

 water, Gulf Stream water, and Sargasso Sea water. 



Cold cell. — The formation, structure, and modifica- 

 tion of the cold cell that exists on the Atlantic continen- 

 tal shelf between Cape Hatteras and Cape Cod have been 

 discussed for more than 40 yr since Bigelow (1933) to 

 Beardsley et al. (1976). Other descriptions of the cold cell 

 hav been given by Ketchum and Corwin (1964) and 

 Whitcomb (1970). Less detailed descriptions utilizing 

 only SOOP data have been given by Cook (1976) and 

 Cook and Hausknecht (1977). 



.So far the concensus appears to be that the cold cell is 

 formed from winter water on the shelf and that the cold 

 cell persists throughout the summer months decreasing 

 in size and extent and increasing in in situ temperature. 

 Some evidence suggests replenishment from the north- 

 ea.st (Beardsley et al. 1976) and that "calving" parcels of 

 the cold cell into deeper slope water may contribute to 

 the exchange of shelf and slope water (Wright 1976). 



In 1975 SOOP vessels transected the cold cell in the 

 Cape Hatteras area on seven occasions (see Table 5 and 

 App. Figs. 28, 32 through .34, 36, 39, and 42). 



