Figure 17. --Surface current (GEK) and temperature 

 distributions on cruise TO-59-1, part 2. 



such conditions the western flank of the 

 ridge can be expected to lose any sinuosity 

 it may previously have had, because the 

 geostrophic current should follow the simple 

 south or southwesterly path taken by the 

 strong northerly. The double thermocline at 

 about 150, 96° W., is believed to indicate 

 that such a change was taking place. 



The upward extension of isopleths to the 

 surface along the western edge of the ridge 

 is indicated in about the same longitude in 

 the charts and sections for both parts of the 

 cruise; it occurred in mid-Gulf waters, but 

 there are no observations to show whether 

 or not it also occurred inshore. There was 

 no great weakening of the discontinuity layer 

 comparable with that at station 11 on the 

 November cruise TO-58-2; apparently the 

 mixing was confined to the upper part of the 

 layer, at all places where observations were 

 made. 



The various measures of biomass and bio- 

 logical activity were of about the same order 

 as those in November on part 3 of TO-58-2, 

 although the highest values for chlorophyll a 

 and productivity on TO-58-2 were not again 

 observed and the area of most abundant 

 zooplankton was more restricted. 



The results of this cruise in general con- 

 firm those of the previous one in showing how 

 winter wind-connected ocean conditions stim- 

 ulate production of biota by reducing upper- 

 ocean stratification. 



the vertical and horizontal distributions ob- 

 served on part 2 agreed better than those on 

 part 1 with post-Tehuantepecer distributions 

 observed on part 2 of cruise TO-58-2 in 

 November. Actually the only important dif- 

 ference was in the sinuous western margin 

 of the ridge on part 1 as shown by isopleths 

 in figures 16 and 18. The surface current 

 on part 2 of this cruise was consistent with 

 post-Tehuantepecer conditions in the northern 

 part of the area of observation, i.e., fairly 

 strong towards the south and southwest; but 

 not so in the southern part where there were 

 indications of weaker currents in other direc- 

 tions. One cannot confidently interpret all 

 these features. 



The topography of the discontinuity layer 

 on part 2 was similar to that observed in 

 November on part 3 of cruise TO-58-2, 

 under similar post- northerly conditions. Under 



OBSERVATIONS ONCRUISE TO-59-2 

 (SEPTEMBER 1959) 



The sixth and last survey of the Gulf of 

 Tehuantepec was made on this cruise, in the 

 period September 6-13, 1959. It involved 

 station, BT, and GEK observations, as shown 

 in figure 20. It was not continued east of 

 940 W. because it was considered that the 

 general situation in the Gulf was already 

 evident from the results obtained in the area 

 between 97 o and 94° W, 



Winds were mainly light and variable (pre- 

 dominantly easterly) before station 77, near 

 the head of the Gulf, was reached. From 

 station 77 to station 80, they were northerly 

 and northeasterly at force 5, becoming weaker 

 and more variable during the remainder of 

 the survey. These are the conditions of a 

 moderate but not a strong Tehuantepecer and 



21 



