FlGliRE 19. In winter and fall, the Hawaiian I^land^ are 

 usually bathed by the highly saline waters of the North 

 Pacific (Central type, in summer their shores are washed 

 hv less saline waters from the California (Current Extension. 



Hawaiian Islands in the fall and winter and shifts northward 

 to bathe the archipelago in the spring and summer. It 

 separates the highly saline water of the North Pacific 

 Central water type on the northwest from the less saline 

 water of the North Pacific Equatorial water type on the 

 southeast (fig. 19). To interpret seasonal changes in the 

 positions of these three bodies of water, Seckel formulated 

 a simplified heat budget for the region. This budget indi- 

 cated that warm water was flowing into the region during 

 the early spring, and cold water at times in other seasons. 

 Thus sea surface temperatures responded not only to the 

 amount of solar radiation in the region itself, but reflected 

 processes that had their origin far out in the Pacific. The 

 sea surface temperatures, however, described massive water 

 movements far less clearly than did salinity values. Because 

 the Hawaiian region is neither one of extreme evaporation 

 nor precipitation, surface salinity is less affected by seasonal 

 changes than is surface temperature, which is primarily 

 responsive to the seasonal march of the sun. For this rea- 

 son, the movement of isohalines, lines of equal salinity value, 

 within the region can be interpreted to depict the movement 

 of the boundaries of the water types in the area. He found 

 that these movements could be predicted to some degree 

 from temperature and salinity data gathered twice weekly 

 at Koko Head, Oahu, Hawaii. 



The movements of the upper layers of the water are 

 largely determined by the winds, and the dominant wind 

 system of the lower latitudes of the North Pacific is that of 

 the trade winds. On the basis of the studies briefly sum- 

 marized above, Seckel proposed that the Bureau's Laboratory 

 in Honolulu begin a long-term investigation of the oceano- 

 graphy of the Trade Wind Zone, an area larger than the 



continental United States and reaching from long. 135° W. 

 to 180% and from lat. 10" N. to 30" N. (fig. 20). The proposal 

 called for a three-phase study: design and planning, field 

 work, and evaluation of the results. 



When the Toioisend Cromwell sailed on the June 1965 

 cruise, she was concluding the initial part of the first phase, 

 which has been called the Trade Wind Zone Oceanography 

 Pilot Study. Although about twice the size of Texas, the 

 area covered by the Townsend Cromwell in the Pilot Study 

 is small in comparison with the entire Trade Wind Zone 

 (fig. 21). It is only as large as one ship, even as swift and 

 well-equipped for scientific work as the Townsend Cromwell, 

 can cover in a single month. The pattern for the scientific 

 observations (fig. 22) was established early in the series 

 of cruises and did not vary significantly throughout. This 

 unchanging routine, in fact, was the heart of the study, 

 whose object was to document month-to-month changes in 

 the oceanographic and meteorological properties in the area, 

 with the ultimate aim of understanding the relation of winds 

 and weather to the oceanographic properties at the surface 

 and to a depth of more than a quarter of a mile, particularly 

 as they affect the commercial fisheries. 



The plan for the investigations included 43 oceanographic 

 stations 90 miles apart. Samples were obtained at 20 levels 

 to about 4,500 feet. After July 1964, casts to about 12,000 

 feet were made on three stations each cruise. Bathythermo- 

 graphs, which record temperature in the upper layers of the 

 ocean, were taken at 30-mile intervals along the cruise tracks, 

 except at three locations on each cruise, where they were 

 made at 10-mile intervals. In addition, meteorological obser- 

 vations were made and the radiation from sun and sky was 

 recorded. 



Seven persons are now engaged full time in processing 

 the data gathered on the cruises. The data are being trans- 

 ferred to cards for analysis by computers at the University 

 of Hawaii. The data are scheduled to be published in 1966. 



29 



