INGHAM ET AL: OXYCLINE AND SKIPJACK TUNA DISTRIBUTION 



5° 



0°- 



5°S 



10°- 



I5« 



20 c 



IO°E 



15' 



FIGURE 4. — Location of transects of dissolved oxygen concentra- 

 tion by Undaunted and Rockaway 15 October-21 November 

 1968. Derived from Cook et al. 1974. 



relatively incomplete sampling grid in the 

 February- April period, little can be learned from 

 any attempts to compare the results of the two 

 periods. 



Pycnocline 



The density field of the upper waters off south- 

 western Africa is determined mostly by tempera- 

 ture, except in the area influenced by the effluent 

 of the Congo River (Bubnov 1972). Results of the 

 JISETA cruises support this contention, showing 

 a well-developed thermocline throughout the 

 area. 



During the October-November period thermo- 

 cline gradients increased from south to north with 

 the most intense gradients found off the Congo 

 River. The sea-surface temperature ranged from 

 <17° C in the south (lat. 18° S) to >26° C near the 

 Equator. In the February-April period the ther- 

 mocline appeared to be more intense than during 

 the October-November period but generally con- 



ui 

 o 



FIGURE 5. — One of the transects of dissolved oxygen concentra- 

 tion (milliliter per liter) produced from Undaunted data (22-23 

 October 1968). From Cook et al. 1974. 



ROCKAWAY 



19-21 NOV 1968 



V «5 a> o w 



UNDAUNTED 



21-29 OCT 1968 

 ]_ 



ROCKAWAY 



19-28 OCT 1966 



FIGURE 6.— Synthetic transect of 

 oxygen concentration from Un- 

 daunted and Rockaway data col- 

 lected during 19 October-21 

 November 1968. 



861 



