GROSS FEATURES IN THE MERIDIONAL 

 DISSOLVED OXYGEN DISTRIBUTION 



Finally, the salinity sections can be used to make gross 

 estimates of the concentration of dissolved oxygen in the dif- 

 ferent water masses. To illustrate, figure 5 shows the salin- 

 ity and dissolved oxygen concentration in a vertical section 

 along long. 148" W. for September 1964. 



In the North Pacific Central and the North Paciiic Equa- 

 torial Waters the oxygen concentration is greater than 4 ml. /Ji- 

 lt declines in the transition to the intermediate water masses. 

 The decline in oxygen concentration is most rapid in the tran- 

 sition to the Pacific Equatorial Intermediate Water where it is 

 less than 0.5 ml./ a. 



In the southern portion of the sections the Pacific Equatorial 

 Intermediate Water with the low oxygen concentration may be 

 found within 100 m. of the surface. Again this condition is of in- 

 terest in longline fishing since hooks may fish deeper than 100 

 m. It is unlikely that active species of fish with a high oxygen 

 demand are found in water with an oxygen concentration as low 

 as that in the Pacific Equatorial Intermediate Water. 



Interesting features in the vertical distribution ot oxygen 

 are relatively thin layers of higher oxygen concentration in 

 the upper portion ot the thermocline. Two such layers are 

 apparent in figure 5. A thin layer with an oxygen concentra- 

 tion of more than 5 ml./t. occurs at 30 to 40 m. between lat. 

 10" and 13° N., and another layer occurs at 50 to 100 m. Ije- 

 tween lat. 16° and 23° N. These layers are common in the 

 region where the salinity increases with depth in the upper 

 portion of the thermocline. Although the continuity or season- 

 ality of these layers of higher oxygen concentration is not 

 known, they are probably of biological significance. 



