136 EIGHTH PACIFIC SCIENCE CONGRESS 



tor. These are drawn proportional to the weighted mean resultant 

 travel of the wind. The arrows are longest and travel most nearly from 

 the southeast between 100° and 150°W. longitude. Farther west they 

 lose much of their strength and most of their northward component. 



Note also that the winds themselves are divergent in the eastern 

 part of the Pacific and become convergent in the western half. The 

 effect of this equatorial wind divergence on the water has not been 

 studied by oceanographers as far as I am aware. In the absence of a 

 deflecting force at the equator and assuming there is no pressure gra- 

 dient, the transport of the water should be in the direction of the wind 

 and the wind divergence itself should produce water divergence at the 

 sea surface along the equator east of 180° (and convergence west of 

 180°). It is not known how strong this effect may be, but any diver- 

 gence induced directly in this manner should reinforce and strengthen 

 the divergence caused by the forces considered in Cromwell's model. 



The east-west trend of plankton abundance is consistent with the 

 results expected from the pattern of the equatorial winds. As shown 

 in Fig. 8B the better catches were made east of 150°W. longitude and 

 there is a decided decline from there toward the west. However, to 

 gain enough material to plot plankton by latitude we have had to com- 

 bine all seasons of the year over an arbitrary span of latitude and we 

 cannot rely on these data to faithfully show the finer details of plank- 

 ton distribution. 



Similarly the material on yellowfin tuna is not sufficient to consi- 

 der August alone as was done with the wind data. In Fig. 8C, however, 

 the combined results of a group of fishing cruises during the months of 

 July to November are charted with shading proportional to the catch- 

 ing rate. As expected from the meridional aspect of equatorial circu- 

 lation the center of abundance is displaced northward from the equator 

 and as expected from the fact that the divergence-convergence structure 

 is contained within the westward flowing South Equatorial Current, 

 it is also displaced to the west of maximum divergence as judged from 

 wind pattern and plankton concentration. The relatively small dis- 

 placement northward is consistent with the relatively weak meridional 

 circulation and the large displacement westward is consistent with the 

 very much stronger zonal circulation. 



In assembling the above materials bearing on equatorial produc- 

 tivity and on the mechanisms involved, I have been highly selective. 

 In part this selectivity has been purposeful and intended to emphasize 

 the major elements of the productivity system. In part the selectivity 

 has been imposed by incompleteness of available information. It should 

 be noted particularly that the meridional aspect was portrayed by a 



