Figure 19.--Vertical distributions of properties on cruise TO-59-1, parts 1 and 2, along section D-D (see fig. 15); 

 depth scale in m. 



concentrations were still found in the ridge 

 area and westward (fig, 21E). Standing crops 

 of chlorophyll a_ were also lower than on 

 any other cruise (fig. 5A); productivity values 

 tended to be higher than on TO- 58-1 (May 

 and June), although much lower than on TO-58-2 

 (November) and TO-59-1 (January and Feb- 

 ruary), as shown in figure 5B. 



Vertical distributions of properties 



Figure 22 presents profiles along the east- 

 west section A-A of; (A) temperature, (B) 

 salinity, (C) thermosteric anomaly, and (D) 

 oxygen. There is no figure for phosphate 

 because of a shortage of observations in the 

 upper part of the column at station 78. 



All these profiles show a discontinuity layer 

 topography like that of all previous surveys 

 but smoother than that found on most of them, 

 most comparable with the situation on part 2 

 of TO-58-2 in November (fig. UA). The top 

 of the layer reaches to about 25 m. below the 

 sea surface on the crest of the ridge; on 

 meridian 97° the corresponding depth is about 

 40 m. The longitude of the crest of the ridge 

 is further west than usual (95° instead of 94°), 

 and there is upward extension of a few iso- 

 pleths in this region and westward. 



Figure 23 gives the corresponding profiles 

 along the north-south section B-B. They show 

 a comparatively small amount of vertical 

 mixing of the upper part of the discontinuity 

 layer and that confined, as in May and June 

 on cruise TO-58-1 and in November on cruise 

 TO-58-2 (part 3), to the mid-Gulf region at 

 about latitude 15° N. There is a pronounced 

 downward slope of isopleths to the coast, 

 where the top of the discontinuity layer is 

 perhaps too deep for wind-stirring to have 

 occurred. 



Int e rp r et at ion 



The circulation during this September sur- 

 vey resembled that of the right-hand schematic 

 diagram in figure 2B (for May and September). 

 There was no indication of either a western 

 or an eastern eddy, and in general both the 

 surface and the geostrophic current were 

 weaker than on previous cruises. The topog- 

 raphy of the discontinuity layer was consistent 

 with the circulation, i.e., comparatively 

 smooth. The locations of the main features 

 of this topography, with respect to the coast 

 and the direction of the predominant wind, 

 were, nevertheless, much as on previous 

 cruises. So was the location of the area of 

 maximum destratification, although this 



23 



