This is the sixth of a series of descriptive reports on mid-Pacific 

 oceanography by the Pacific Oceanic Fishery Investigations. The previous oceano- 

 graphic reports presented and discussed data collected in the equatorial waters of 

 the mid-Pacific. 1/ The present report covers the data collected during the first 

 three of a seriea of six general oceanographic cruises of the research vessel Hugh 

 M. 3ml th in the waters adjacent to the Hawaiian Islands. The periods covered by 

 the oceanographic phases of the cruises were: cruise 1, December 13-21, 1949; 

 cruise 10, July 19-31, 1951; and cruise 12, October 23 to November 2, 1951. 



The surveys of Hawaiian waters were initiated on the premise that the 

 abundance and movements of the skipjack, Katsuwonus pelamis (Linnaeus), which forms 

 the basis for the principal fishery of the islands, are controlled by events in the 

 sea (Sette et al. 1954). The skipjack catches of the local fleet were used as a 

 guide in planning the geographical and seasonal coverage of cruises 10 and 12. 

 Cruise 10 was made when the fishery was at the summer peak, and cruise 12 was made 

 during the middle of the fall decline. 



The observational programs of these cruises were designed to collect 

 chemical, physical, and biological data which could be used to map the circulation 

 pattern of the Island waters, i'roca the circulation pattern it was hoped to locate 

 areas where enough vertical motion might occur to enrich the surface layers and in- 

 crease biological activity, un each cruise observations of temperature and salinity 

 suitable for computation of currents in the upper 1,000 m. were made as well as 

 bathythermograph lowerings for details of the temperature structure in the upper 

 900 ft. (270 m. J . Other observations varied from cruise to cruise. Analyses for 

 dissolved oxygen, which together with determinations of temperature and salinity 

 help in tracing the circulation of different water masses and in their discussion, 

 were made on cruises 1 and 10. Observations of inorganic phosphate, which is use- 

 ful as an indicator of areas where turbulence and upwelling are sufficient to carry 

 nutrients from the deep water to the euphotic zone, were made on cruise 12. Col- 

 lections of zoGplankton, which serves to indicate areas of past enrichment, were 

 made on cruises 10 and 12. A geomagnetic electrokinetograph (GSK) was used to 

 make current measurements during cruise 12. 



Since the primary purpose of this report is to present the processed data 

 in a form that is usable to POFI biologists and others interested in the hydrography 

 of the area, the discussion of the results is purely descriptive. The major fea- 

 tures of the circulation pattern and the results of the various observations-' are 

 described separately for each cruise. In the final discussion the features re- 

 current from cruise to cruise are explained in terms of the effect the island chain 

 has on the general oceanic circulation in the area. These features are then exam- 

 ined further for areas in which enrichment of the euphotic zone might occur. 



PR0CSDUR3S 



The vessel equipment, sampling methods, and most of the procedures used 

 in processing the basic data have been described in the earlier reports by Cromwell 

 (1951 and 1954), Austin (1954), and Stroup (1954). Minor changes which were made 

 in the construction of cross sections, and procedures used in the construction of 

 lateral (on sigma-t surfaces) and horizontal plots and in preparing types of data 

 not used in the previous reports are described below. 



A slightly different procedure was used in the preparation of the salini- 

 ty, dissolved oxygen, and inorganic phosphate profiles. In the previous reports, 

 which were concerned primarily with meridional aspects, the principle of drawing 



1/ Mid-Pacific Oceanography, Transequatorial Waters, Part I, Cromwell (1952); 

 Part II, Cromwell (1954); Part III, Austin U954) ; Part IV, Stroup U954) ; Part V, 

 Austin (1954). 



2/ Except for zooplankton, which was the subject of a separate report by King 

 and Hida (1954). 



