Figure 9.- -Surface current (GEK) and temperature 

 distributions on cruise TO-58-2, part 2. 



thermocline top reached the surface to the 

 west of the crest of the ridge, the coldest 

 surface isotherms being respectively 28° and 

 26° before and after the gale; in the first 

 case the lower part of the thermocline re- 

 mained well-developed in the region of upward 

 movement of cold water, but in the second 

 case it was greatly weakened. Figures IIC, 

 IID, and UF (salinity, thermosteric anomaly, 

 and phosphate) agree with figure IIB (tem- 

 perature on the same part of the cruise): 

 the secondary (upper) halocline on the right 

 of figure IIC probably indicates diluted water 

 off river mouths on the east side of the Gulf; 

 figure IIP shows water with over 0.5 Ag.-at./l. 

 of phosphate reaching the surface. Figure HE 

 (oxygen) is consistent with the others in re- 

 spect to the discontinuity layer although not in 

 respect to thedistributionofisopleths, towards 

 the surface; the latter could be associated 

 with the high algal crops at stations 1 1 and 1 5. 



Figure 12 shows the following profiles 

 along the north-south section B-B: (A), (B), 

 and (C), temperature on parts 1, 2, and 3 of 

 the cruise, respectively; (D-G), salinity, ther- 

 mosteric anomaly, oxygen, and phosphate, all 

 on part 3. 



Figure 12A provides no clear evidence of 

 stirring of the thermocline; figure 12B shows 

 slight stirring of the upper part of the ther- 

 mocline at the inshore end of the section; 

 and figure 12C, after the northerly gale, 

 shows a weakening of the whole thermocline 

 in mid-Gulf at station 11, more obviously 

 than the same feature was shown in figure UB. 

 Figures 12D-12G are in agreement with fig- 

 ure 12C. 



Figures 13A and 13B show temperature on 

 parts 2 and 3 of the cruise along section D-D 

 (96° W., see fig. 8). The thermoclines are 

 deeper than the corresponding ones on section 

 B-B a degree further east (figs. 12B and 12C), 

 and the one in figure 13B is much deeper 

 than the one in figure 13A. This agrees with 

 earlier observations, section D-D being close 

 to the hollow shown in figures lOA, HA, and 

 IIB. 



On the other hand figures 14A and 14B, 

 which present similar information along sec- 

 tion C-C at 940 W., at the crest of the thermal 

 ridge, show the thermocline generally closer 

 to the surface on part 3 of the cruise than on 

 part 2. 



Interpretation 



During part 2 of the cruise (the pre-Tehuan- 

 tepecer survey with light norther lies) the 

 circulation in the Gulf approximated a condi- 

 tion somewhat between the schematic dia- 

 grams for September and October-January 

 in figure 2B; there was only partial develop- 

 ment of the sinuous line of flow discussed 

 in connection with figure 2B, which can be 

 attributed to the absence or scarcity of strong 

 northers during previous weeks. Consistently, 

 the topography of the discontinuity layer was 

 smoother than at the end of the Tehuantepecer 

 season on cruise TO- 58-1 although it showed 

 the same major features — a north-south ridge 

 with the isopleths sloping more gradually 

 eastward than westward from a crest about 

 20 m. below the surface in longitude 94° W., 

 and a hollow west of 96° W. Waters of the 

 upper part of the layer were mixed upwards 

 to the surface along the western flank of the 



13 



