380 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



a. 



80- 



SEPT 



/ 



MARCH 



20*-25*N 



28 



26 



24 Ir 



75 



80 



75 

 180° 



MARCH 



10*-15*M 



28 



26 



24 



170° 160° 



WEST LONGITUDE 



150° 



Figure 6. — Zonal profile of the surface temperature in 

 March and September, 10°-15° N., 15°-20° N., 20°- 

 25° N., 25°-30° N. and 150° W. to 180°. 



and 161° W. at 12°, 17°, 20°, 22° and 26° N. It 

 illustrates features which were demonstrated in 

 previous figures. The seasonal temperature range 

 increases only slightly northward from 3° F. 

 (1.7° C.) at 12° N. to 5° F. (2.8° C.) at 22° N., 

 and then almost doubles to 9.5° F. (5.3° C.) 

 at .26° N. This is also reflected in the break of 

 the meridional temperature gradient at 22° N. 

 from November to May. 



1 I 1 1 \ r 



n — I — I — r 



J I I L 



J I I I I 



J \ \ L 



JAN MAR MAY JUL SEP NOV JAN MAR 



Figure 7. — Seasonal variation of the surface temperature 

 at 12°, 17°, 20°, 22° and 26° N. between 153° and 

 161° W. 



3. SURFACE SALINITY 



The climatic indicator equivalent in importance 

 to the temperature is the salinity. Unfortunately, 

 in comparison with the temperature information, 

 sahnity data are scarce and it is therefore not 

 possible to construct meaningful monthly charts. 

 Despite this shortcoming, salinities obtained from 

 oceanographic expeditions and from surface 

 samples collected by Bureau of Commercial 

 Fisheries vessels are sufficient to indicate features 

 of climatic significance. 



An attempt was made initially to locate the 

 35°/oo (sahnity) isopleth throughout the year in 

 the vicinity of the Hawaiian archipelago. This 

 revealed that the isopleth started a generally 

 northward movement in April, reaching an 

 extrenie position in July, as indicated in figure 8. 

 It then begins a southward movement, reaching 

 its extreme winter position (17° to 19° N.), 

 during the November to February period. In 

 the Hawaiian Islands the maximum sahnity is 

 therefore to be expected during November to 

 February and the minimum during July. 



There were also enough samples to show (fig. 9) 

 the mean seasonal variation of salinity in the 

 meridional strip between 155° and 160° W., at 



