ridge and particularly near the head of the 

 Gulf, where maximal wind stress would be 

 expected; at an earlier very calm period 

 (part I of the cruise) there was no sign of any 

 such mixing anywhere along the same me- 

 ridian. 



On part 3 of the cruise the circulation 

 pattern resembled that of the Tehuantepecer 

 season (figs. 2B and 4A). The main difference 

 from the pattern of part 2 was the strong 

 south and southwest flow along 95°, which is 

 attributed to the strong northerly wind that 

 blew across the Isthmus after part 2. The 

 topography of the discontinuity layer was 

 altered by the circulation to make the crest 

 of the ridge higher and its flanks lower, 

 relative to the sea surface. The wind stirred 

 the upper part of the discontinuity layer 

 much more than it did before the norther, 

 in its southerly path along the western shoulder 

 of the ridge, bringing subsurface water up- 

 wards and greatly cooling and enriching the 

 sea surface. As on cruise TO-58-1, in May 

 and June, but not as on part 2 of TO-58-2, 

 the breakdown of the layer was greatest in 

 mid-Gulf waters (station 11), instead of in- 

 shore where wind stress should have been 

 greatest (see Discussion). Surface tempera- 

 ture and salinity were respectively lowest 

 and highest for the survey in the area of 

 minimum stratification. 



The difference in thermal structure be- 

 tween BT 1-18 on part 2 of the cruise and 

 station 11 at the same position on part 3, 

 as shown in figures 11 (A and B) and 12 

 (B and C), does not entirely agree with the 

 observations of previous workers who noted 

 the effects of real or simulated wind-stirring 

 upon thermoclines or pycnoclines (Francis 

 and Stommel, 1953; Cromwell and Reid, 1956; 

 Cromwell 1960). These authors considered 

 that the effect of an increase in wind on the 

 thermocline is (a) to deepen it relative to 

 the sea surface and (b) to steepen the tem- 

 perature gradient in its upper part. The 

 observations presented here, those for BT 

 1-18 being 4 days before a Tehuantepecer 

 and those for station 11 being 6 days after 

 it, show (a) but not (b); in fact they show the 

 reverse of (b), i.e., a weakened gradient in 

 the upper part of the thermocline; this is 

 presumed to represent an effect of internal 

 turbulence, possibly but not certainly con- 

 nected with wind-mixing during some stage of 

 the Tehuantepecer (cf. Cromwell, 1960, p. 77, 

 last paragraph). 



Surface and subsurface phosphate, chloro- 

 phyll a, productivity, and oxygen were greater 

 on part 3 of TO-58-2 than on cruise TO-58-1 

 in May and June. A large biomass of phyto- 

 plankton was observed in the region of mini- 

 mum stratification and westward, which was 

 also in the region of maximum surface oxygen; 

 productivity in the latter region was 161 

 mg.C/m.3/day. Zooplankton standing crops 

 were from two to four times as large as in 

 May and June on cruise TO-58-1 and were 

 concentrated in the same region, on the ridge 

 and westward. This is again consistent with 

 production in the eutrophic area and redis- 

 tribution by the current and eddy system to 

 the southwest and west, which doubtless played 

 a similar role as far as phytoplankton was 

 concerned. 



OBSERVATIONS ON CRUISE TO-59- 1 

 (JANUARY AND FEBRUARY 1959) 



There were two parts of this cruise in the 

 Gulf of Tehuantepec: part 1, January 27-31, 

 1959, was a station, BT, and GEK survey 

 (fig. 15A) which was abandoned about halfway 

 through when a Tehuantepecer caused the 

 ship to seek shelter in Salina Cruz; part 2, 

 February 3-7, was a BT and GEK survey 

 commenced at the end of the gale, and vir- 

 tually abandoned because of another gale 

 which caused the ship to restrict its activities 

 to the eastern periphery of the area (fig. 15B). 



A gale was reported on January 22 before 

 the ship's arrival in the Gulf. The weather on 

 part 1 consisted mostly of light variable winds 

 before station 23, and northerly winds in- 

 creasing up to force 6 after that station. Part 2 

 of the cruise was made in calm weather through 

 station 25, after which a northerly, up to 

 force 6, was encountered until the ship moved 

 east of 94° W. 



Horizontal distributions of properties 



Figure 16 shows the following distributions 

 for part 1 of the cruise: (A) dynamic height 

 anomaly, (B) surface temperature, (C) surface 

 salinity, (D) 30 m. phosphate, and (E) zoo- 

 plankton and micronekton. There is no surface 

 oxygen chart because oxygen concentrations 

 were not measured in surface samples. 



The dynamic topography in figure 16A is 

 recognizable as the western flank of a ridge 

 whose crest was not, in this incomplete survey, 

 observed over most of its area. The position in- 



15 



