temperature or nearby XB TobserNations. Consequently, 

 a vertical section plot may have one or two missing obser- 

 vations, resulting from the deletion of inaccurate subsur- 

 face data. 



During 1975 the data collection program was expanded 

 by the addition of the MV Hluenuse, an "auto/truck" fer- 

 ry operated by the Canadian National Railway between 

 Bar Harbor, Maine, and Yarmouth, Nova Scotia. Per- 

 sonnel from the NMF.S Atlantic Environmental Group or 

 Northeast Fisheries Center made the observations from 

 the M\' bluenose on a monthly basis. 



For purposes of consistency with this and past reports, 

 all vertical temperature figures have been organized 

 geographically and chronologically (Gulf of Mexico — 

 January through December, Cape Hatteras — January 

 through December, etc.) and included at the end of the 

 report as appendix figures. Consequently, any particular 

 feature being discussed first may not show up as the first 

 figure within the appendix figures. However, at the 

 beginning of each section that discusses a particular 

 feature, we have listed all figures in the order in which 

 they appear. 



For this report all figures have been annotated to show: 

 shelf water-slope water front — SSF; north wall of the 

 Gulf Stream — G.S.; anticyclonic warm core eddy — 

 clockwise circles; cold cell — cc; current flow direction: 

 into the page — circled X, out of the page — circled dot. 



RESULTS 



Gulf of Mexico Transects 



Loop Current. — The 20°C isotherm at 125 m depth 

 has been used in the past as an indicator of the position 

 of the left edge looking downstream of the Loop Current 

 (Cook 1976) and was applied again in this report for con- 

 sistency. Migrations of the Loop Current edge, along 

 SOOP transects that passed through the Yucatan 

 Straits, ranged from lat. 22°40'N to almost lat. 25°N. 



In 1975 the Loop Current was crossed on 11 occasions 

 (see Table 1 and App. Figs. 3, 4, 6, 11, 15, 17, and 21 

 through 25) by SOOP vessels. 



In March the Loop Current was crossed twice by the 

 Delta Sud. The two crossings of the Loop Current within 

 1 mo along the same transect provided the means of 



calculating the translational speed of the southward 

 movement of the edge. The Delta Sud (App. Fig. 4) cros- 

 sed the Loop Current at lat. 24°05'N and long. 86°22'W 

 on 16 March at 0500 h. The Delta Sud (App. Fig. 6) again 

 cros.sed the Loop ("urrent at lat. 22"40'N and long. 

 HB"15'\V on 23 March at 2400 h. The excursion of the 

 northern edge of the Loop Current was 80 n.mi. in 187 h, 

 or 10.;i n.mi. /day (19.1 km/day). 



Low salinity surface water. — River runoff along the 

 Gulf Coast forms a plume detectable by low surface 

 salinities. L'tilizing 34.57„ as the cutoff between coastal 

 and oceanic waters, it was possible to monitor the off- 

 shore extent of these low salinity plumes which 

 sometimes extended to well beyond the shelf break. Six 

 crossings of low salinity water were detected by SOOP 

 vessels in the Gulf of Mexico in 1975 (see Table 2 and 

 App. Figs. .3, 5, 12, 14, 20, and 23). Note that the surface 

 salinities for the Delta Morte 75-09 (App. Fig. 18) should 

 be considered suspect (they are all <34.5/.~ while the 

 transect is obviously in an oceanic region). They are in- 

 cluded in this report because there is no other evidence to 

 suggest that the values are false. 



Tabic 



-Low salinity ( <:U..5 /...) t-uastal water entuunttTtHl b> 

 SOOP vescls in Ihe Gulf of .Mexico in !»".■>. 



Eddies. — Analysis of the vertical sections contained in 

 this part shows 11 crossings of eddies or meanderlike 

 structures in the Gulf of Mexico by SOOP vessels in 1975 

 (see Table 3 and App. Figs. 3, 4, 7, 10-12, 14, 15, 20, and 



Table 3. — Kddies transected in the (iulf of Mexico b\ SOOP \csscls 

 in 1975. 



