depth intervals in tlie upper 300 m., and at 100-ni. intervals 

 from 300 m. to 600 m. 



In the North Pacific trade wind zone the salinity distribution 

 can be used to identify water masses (Seckel, 1968). Those of 

 concern in this circular are the North Pacific Central, the 

 North Pacific Equatorial, the North Pacific Intermediate, and 

 the Pacific Equatorial Intermediate Waters. In the salinity 

 sections each water mass is shaded differently. The transi- 

 tion waters between water masses have been left unshaded. 



The North Pacific Central Water occurs at the surface in 

 the northern portion of the sections and protrudes southward 

 in a tongue below the surface layer. It has a salinity ol more 

 than 34.8°/oo and in the charts of this circular is warmer than 

 16.5° C. 



The North Pacific Equatorial Water occurs as a shallow 

 surface layer in the southern portion of the sections. It is 

 generally found in the eastern Pacific centered about lat. 

 10° N., but may extend into the region shown here, as in sum- 

 mer and fall of 1964, when it has a salinity oi less than 34.2Voo 

 and a temperature of more than 15° C. 



The North Pacific Intermediate Water, with a salinity ot 

 less than 34.4°/oo and a temperature of less than 15° C., occurs 

 below the North Pacific Central Water in the northern jjortion 

 of the sections. It markedly decreases in thickness southward 

 of lat. 18° N. 



The Pacific Equatorial Intermediate Water, with salinity of 

 more than 34.6°/oo and temperature of less than 16° C.. occurs 

 below the North Pacific Equatorial Water in the southern por- 

 tion of the sections. It is found at intermediate depths in a 

 band across the equatorial Pacific. 



