SEA SURFACE 



12 MILES -— -l 12 MILES- 



i SURFACE] 



! LAYER i 



I, , STRONGEST (MAIN) 



:> :<x — w-..-,, THERMOCLINE 



,, 1, , 



V <rJ6°C 



~^~ "-—"' .vT"-; z ' .-'• 



~y'. 



y**** 



.~M2°C 



-•■-v.-'^'-'V 



«. 



^ 





" — ~tC^ 



•■/ 



T 



~100 FT f 



J_ 3 MILES 



Figure 6. A common thermal structure (Position 1, fig. 5). 



800 feet. Throughout the depth was an upper mixed layer with no 

 whole-degree isotherms from the surface down to about 200 feet. 

 Close vertical spacing of isotherms directly under the mixed layer 

 revealed a sharp thermocline. Below this was a gradual widening 

 of isotherm spacing. This, the most common type of vertical 

 temperature structure in the upper layers of all oceans, is present 

 in 85 percent of the Pacific. 14 



Horizontally, the most obvious feature is large undulations 

 of the main thermocline. These were about 12 miles long, 50-100 

 feet high, and probably associated with the tidal cycle. The height 

 of the long wave decreased with depth (fig. 6). The deepest iso- 

 therm (10°C), occurring in a weak vertical gradient, fluctuated 

 widely and showed no definite long -wave length cycles, as do the 

 16°C isotherm and others in the sharper part of the thermocline. 



Small vertical oscillations appeared generally at a rate of 

 2 to 4 per mile, but 5 or 6 per mile were noted. Such oscillations, 

 with amplitudes from several to around 20 feet, are present in all 

 the isotherms in the thermocline, and are largely in phase with 

 one another throughout the strongest part. Amplitudes of the small 

 vertical oscillations increased inversely with the strength of the 



10 



