casts at selected stations (fig. 9). In a few cases, 

 negative temperature and sound-velocity gradients 

 started at the surface, as at station 23. These were 

 generally along the Aleutian chain and in the south- 

 eastern section. Farther away from the chain, a mixed 

 layer of the order of 20 to 25 meters in depth oc- 

 curred at every station, the layer becoming slightly 

 less deep near the edge of the continental shelf. 

 Depending upon the slight variation of gradients in 

 temperature and salinity, this mixed layer at times 

 might be an isovelocity layer, as at station 20. At 

 other times, when well mixed, it would have a weak 

 positive sound-velocity gradient, as at station 26. In 

 these latter two cases, long sonar ranges on surface 

 ships and submarines above layer depth are pre- 

 dicted from the sound-velocity structure. However, 

 on this cruise this surface layer and the accompany- 

 ing long predicted ranges were coincident with fairly 

 high sea state of about 4 and 5, which in turn re- 

 duces the effective ranges. Because of the stratus 

 overcast these mixed layers would persist much longer 

 than average after the wind decreased. Thus, it can 

 be concluded that ranges would be limited by sea 

 state and that usually, in the absence of high sea 

 state, surface sound ranges in the deep Bering Sea 

 would be above average compared with summer 

 ranges in other parts of the north Pacific Ocean. 



deep sound channel 



The most striking feature of the sound-velocity 

 distribution is the deep sound or Sofar channel. This 

 channel is directly related to the temperature mini- 

 mum but does not necessarily coincide with it, be- 

 cause of the effect of pressure and salinity on sound 

 velocity. 



The axis of the sound channel — the depth of 

 minimum velocity — is at a depth of 75 to 200 meters 

 and the velocity at the axis increases from northwest 

 to southeast (fig. 10). This is a very shallow depth 

 compared with that occurring most generally in the 

 open oceans; for example, the sound-channel axis 

 over the major portion of the northeast Pacific Sofar 



Figure 9. Sound-velocity structure, computed 

 from data obtained by bottle cost, at se- 

 lected stations (see figure 3b for locations). 



