■ TO-Se-l (MAY- JUN. I9SS) 



• TO-38-2 (NOV. 1938 ) 



• T0-S9-I (JAN.-FEa. I9S9) 

 A TO-59-8 (SeP. 1959) 



SURFACE CMlOIOPHYlL 



(MG./M3.) 



Figure 5.- -Surface chlorophyll a and in situ produc- 

 tivity measurements from all cruises in the Gulf of 

 Tehuantepec. 



Figures 4A and 4B are consistent with the 

 above-mejitioned ideas and observations about 

 surface current and surface temperature dis- 

 tribution, except that the feature called a 

 "dome" by Brandhorst (1958) would be better 

 called a "ridge" (Cromwell, 1958) running 

 more or less south-southwestward from the 

 head of the Gulf between meridians 94° and 

 96° W, The dynamic topography predicts a 

 weak northwesterly current to the east of this 

 ridge and a strong southwesterly current to 

 the west of it. GEK observations confirm the 

 latter, and further indicate some clockwise 

 flow around a "hollow" (Cromwell, 1958) to 

 the west of the ridge; they also suggest anti- 

 clockwise flow arounci the southern end of the 

 ridge, accompanied by divergence of current 

 in the vicinity of HOlO' N., 95O10' W, Surface 

 temperatures were generally lower above this 

 ridge than elsewhere, but lowest along its 



western edge (especially about 15° N.,950 W.) 

 rather than in its center. 



The higher surface salinities (>34. l°/oo) 

 occurred mainly but not entirely in the ridge 

 area (fig, 4C). Surface oxygen concentration 

 ranged from 3,5 ml. /I, at one station on the 

 ridge to 4.5 ml,/l, at several stations along 

 its western flank (fig, 4D), Phosphate values 

 were consistently higher over the ridge than 

 elsewhere (fig, 4E). 



The two highest measurements of zooplank- 

 ton standing crop (150-200 ml,/l,000 m.3) 

 were at ridge stations (fig. 4F), but it would 

 be most correct to say that zooplankton abun- 

 dance was highest on and west of the ridge, 

 at a level about average for the eastern 

 tropical Pacific (Holmes, 1958). No con- 

 clusion can be drawn about the distribution 

 of micronekton (only six observations); most 

 of the values were higher than average for 

 the eastern tropical Pacific (Blackburn and 

 Associates, 1962'). Chlorophyll a and pro- 

 ductivity values (figs. 5A and 5B) were mainly 

 lower than average for the eastern tropical 

 Pacific (Holmes, 1958), and nothing definite 

 can be said about their distribution within 

 the Gulf region. 



Surface temperatures east and west of the 

 ridge (fig. 4B) were much higher than average 

 for the time of year. This is a manifestation 

 of the anomalous temperature conditions that 

 prevailed in the eastern Pacific generally 

 in 1958 (Rodewald, 1959). 



Vertical distributions of properties 



Figure 6 shows profiles of (A) temperature, 

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

 oxygen, and (E) phosphate, to 200 m. along the 

 east-west section A-A (fig. 3). In this group 

 of sections, and similar groups elsewhere in 

 the paper, no attempt has been made to draw 

 isopleths of salinity, thermosteric anomaly, 

 etc. to agree with the extra detail available, 

 from BT data, for the isotherms; that is to 

 say, assumptions regarding the similarity 

 of temperature distributions to other distribu- 

 tions have been kept to a minimum. 



All these figures show; a very gradual 

 elevation of the top of the discontinuity layer 

 from about 92O40' to about 94O20' W., where 

 the top of the ridge occurs at about 20 m. 

 below the surface; further west, to about 



8 Refer to figure 12 of this paper. 



