23 



having a density of 1.0244 grams per cubic centimeter and 

 lying in an area between Hawaii and the Equator. This density 

 layer lies within the thermocline (the layer below the sea 

 surface that exhibits the most pronounced vertical tempera- 

 ture gradient) in the latitudes shown in the figure, and inter- 

 cepts the sea surface in winter somewhat farther north. As a 

 result of increased contact with the atmosphere, a seasonal 

 increase in the dissolved oxygen content of this water layer 

 occurs each winter, aneffect which can be seen by comparing 

 the northernmost parts of the two charts showing dissolved 

 oxygen concentration. Other seasonal changes can be detected 

 in the salinity and temperature charts. Changes in the current 

 systems can be deduced from changes in the depth of the water 

 layer under consideration. 



The distributions of temperature, salinity and dissolved 

 oxygen can also be shown in vertical sections which demon- 

 strate how these factors vary with depth and geographic loca- 

 tion. Figures 26, 27, and 28 show average annual temperature, 

 salinity, and oxygen conditions between 10° and 20° N., imme- 

 diately to the south of the Hawaiian Islands. These figures 



[mESAOBJMINITI •/.. 150 'W.-1«0'W. 



-J [ 1 1 L_ 



sou IH LATITUDE NORTH 



Figure 27. --Average vertical distribution of 

 salinity between 10° S. and 20° N. 



-LATITUDE NORTH 



Figure 26. — Average vertical distribution of tem- 

 perature between 10° S. and 20° N. 



Figure 28. — Average vertical distribution of 

 dissolved oxygen 10° S. and 20° N. 



