when this occurred the low salinity water appeared on 

 only the northern side of the eddy. Peaks in the surface 

 salinity (Appendix Figs. 4, 9, 11, 12) indicate the in- 

 stances where low salinity water was transected, exited, 

 and then transected again, which we interpreted as low 

 salinity surface waters being entrained by the leading 

 edges of eddies. The interaction of coastal water with ed- 

 dies probably is a significant mechanism for the mixing 

 of the less saline coastal waters with the more saline 

 oceanic waters in the Gulf of Mexico. 



Western Atlantic Transects 



(Figs. 2-10 and Appendix Figs. 17-35) 



Specific features that were monitored in the western 

 North Atlantic by the program were the position of the 

 Gulf Stream, variations in temperature and position of 

 the bottom water cold cell on the continental shelf, posi- 

 tion of the Shelf Water-Slope Water front, and eddies 

 formed from the Gulf Stream. Where data were available 

 and observations were close enough in time to permit 

 comparison, correlations were made with the National 

 Environmental Satellite Service (NESS) Experimental 

 Gulf Stream Analysis (N-69) charts and The Gulf 

 Stream Monthly Summary which show the positions of 

 the Gulf Stream and associated features. 



Characteristics of the bottom water cold cell. — In 



his discussion of temperature patterns in continental 

 shelf water, Bigelow (1933) described a core of cold bot- 

 tom water that extended from south of Long Island to the 

 mouth of the Chesapeake and was evident throughout 

 the summer months. According to Bigelow, this core was 

 surrounded entirely by warmer water and could receive 

 no replenishment during the summer; thus, he con- 

 cluded it was formed in wintertime and then persisted 

 throughout the year. Further descriptions of this cold cell 

 have been given by Ketchum and Corwin (1964) and 

 Whitcomb (1970). The data which are presented here 

 show the formation, structure, and modification of this 

 cell during 1974. 



Nine observations of the cold cell were made by SOOP 

 vessels in 1974 (summarized in Table 4). For purposes of 

 discussion, the observations have been grouped into 



three separate geographic areas, chosen because they 

 represent regularly scheduled merchant ship cruise 

 tracks. These tracks have been designated as the MOR- 

 MAC transect (Fig. 2), Santa Cruz transect (Fig. 3), and 

 HOTEL transect (Fig. 4). The MORMAC transect is the 

 cruise track used by Moore McCormack Line ships and 

 closely follows a line between New York and Bermuda. 

 The Santa Cruz transect extends from New York to Cape 

 Hatteras, approximately along long. 74°W. The HOTEL 

 transect is the cruise track used by Coast Guard cutters 

 operating between Norfolk and OWSH. In the following 

 discussion, the seasonal characteristics and variations in 

 the cold cell temperature and position along each tran- 

 sect are summarized. 



The temperature structure of water on the continental 

 shelf during February (Appendix Fig. 17) should be con- 

 sidered, because the cold cell was formed from these 

 waters and the minimum temperature that could be at- 

 tained in the cell was dependent upon conditions during 

 the winter months. At this time, cold water (7°-12°C) ex- 

 tended from surface to bottom on the shelf and the struc- 

 ture of the cell had not yet been established by stratifica- 

 tion. 



Along the MORMAC transect, the first evidence that 

 the cell had formed was obtained on 6 May (Appendix 

 Fig. 21). The characteristic shape of the cell was shown 

 by the outline of the 11°C isotherm in shelf waters. 

 Within this "cell-like" structure, temperatures ranged 

 from less than 9° to 11°C and the cell extended from a 

 minimum bottom depth of 20 m to a maximum of 38 m. 

 The horizontal extent was 65 nautical miles (120 km) and 

 the cell was approximately 20 m thick at the center. 

 When next observed on 14 August (Appendix Fig. 25), 

 temperatures in the cell ranged from less than 9° to 13°C 

 and the bottom depth range of 40-55 m indicated that the 

 cell was migrating into deeper water. The last obser- 

 vation was made on 3 October (Appendix Fig. 30). By 

 this time, temperatures had warmed to 14°C in the outer 

 edges of the cell and it had moved over the shelf break. 

 The depth range extended from 34 to 99 m. These 

 changes in temperature and depth are summarized in 

 Figure 2. 



Along the Santa Cruz transect the earliest obser- 

 vation of the cold cell was made on 6 May (Appendix Fig. 



Table 4.— Characteristics of the bottom water cold cell detected by SOOP vessels in 1974. 











Minimum 



Maximum 



Depth 



Approximate 



Tempera- 











Appen- 



bottom 



bottom 



at 



thickness 



ture 



Horizontal 



Tran- 







dix 



depth 



depth 



center 



at center 



range 



extent 



sect 



Ship 



Date 



figure 



(m) 



(m) 



(m) 



(m) 



(°C) 



nm (km) 



A 



Santa Cruz 



6 May 



20 



28 



41 



35 



18 



<8-9 



68 (126) 



B 



Mormac Argo 



5-6 May 



21 



20 



38 



29 



20 



< 9-11 



65 (120) 



C 



Santa Cruz 



11-12 June 



23 



32 



49 



45 



23 



<9-13 



100(185) 



D 



Mormac Rigel 



14 Aug. 



25 



40 



55 



50 



23 



<9-13 



53 ( 98) 



E 



Santa Cruz 



3-4 Sept. 



27 



45 



70 



50 



19 



<9-14 



90 (167) 



F 



USCGC Taney 



29-30 Sept. 



28 



40 



55 



50 



15 



< 12-15 



15 ( 28) 



G 



Export Defender 



1 Oct. 



29 



40 



63 



60 



22 



< 12-16 



29 ( 54) 



H 



Mormac Rigel 



3 Oct. 



30 



34 



99 



72 



30 



< 11-14 



110 (203) 



I 



Santa Cruz 



9-10 Oct. 



31 



45 



70 



50 



20 



< 12-14 



75 (139) 



