The break-in-slope between the continental slope and the 

 shelf is at a depth of 89 fathoms,* but the slope does not level 

 off until its depth is about 78 fathoms (fig. 3B). This break- 

 in-slope depth of the shelf margin is not much deeper than 

 the world average of approximately 72 fathoms for the depth 

 of the greatest change in slope. The reason for the break- 

 in-slope being at such a depth is controversial and not well 

 understood; however, this depth appears to be related to a 

 depth at which there is (or was at some time in the past) an 

 equilibrium between erosive processes, such as wave cutting, 

 and sedimentary processes. Eustatic changes in sea level, 

 especially in the lower sea levels of the Ice Age, have probably 

 played an important part in establishing the depth of the break- 

 in-slope. However, it is evident that this area has not been 

 glaciated, for the break-in-slope off glaciated shelves in both 



the arctic and the antarctic is characteristically much deeper. 



__-_ __ ___ - 



As the sound projector of the USS NEREUS was located 

 22 feet below the surface, 3.7 fathoms should be added to all 

 the depth records of figures 3, 4, 6, and 7. 





















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Figure 4. Fathogram of the central and northern portions of the Bering Sea, Bering Strait, and the Chukchi Sea (see fig. 1 for geo- 

 graphic location of the strips). The bottom profiles have a vertical exaggeration of about 26 times. The sea floor is remarkably smooth. 

 Add 3.7 fathoms to indicated depths. 



15 



