Summary of Cruise 



Cruise 21 of the Hugh M. Smith took place during summer 

 conditions, with typical trade wind weather prevailing. The systems 

 identified by the salinity minimum, the salinity maximum, and the sur- 

 face waters were again investigated separately. It was shown that the 

 surface current pattern southwest of the island chain was primarily 

 influenced by the system associated with the salinity maximunn (fig, 32, 

 which in its computation includes the surface distribution of mass). 

 Northeast of the island chain the dynamic connputation showed that the 

 lower intermediate system and the upper intermediate system together 

 with the surface system were of approximately equal importance. 



There was little or no net transport of water through the survey 

 region on the leeward side in either of the intermediate systems. On 

 the windward side water was renewed from the north or northeast and 

 then deflected both to the northwest and southeast. The northwest de- 

 flection was primarily due to the flow associated with the salinity 

 minimum. 



GEK observations showed general agreement with currents 

 obtained from dynamic computations. This might be expected when 

 one considers that the system during the summer becomes less complex 

 and that therefore the instantaneous GEK observations are in closer 

 agreement with average current conditions. 



Inorganic phosphate observations showed that the surface concen- 

 tration on the leeward side of the island chain was greater than on the 

 windward side, although the difference was small. This suggests, as 

 was shown by dynamic computations, that on the windward side there 

 exists a continuous influx of new, low-phosphate water. On the leeward 

 side, the stationary surface waters may be enriched by vertical mixing 

 or island drainage. 



DISCUSSION 



The purpose of this report has been the presentation of data 

 which were collected on cruises 17, 20, and 21 of the Hugh M. Smith . 

 Two of these occurred during the summer months of August and Septem- 

 ber and one during the winter months of February and March. 



The data for each cruise were examined separately, first the 

 surface and then the subsurface layers. Important and interesting 



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