Dill 



type of fish were observed to school above the rocky regions. The 

 schools appeared as large clouds of reflectors (on traverses over the 

 terrace areas) on records of an echo sounder operating at a frequency 

 of 12. 5 Kc/ sec. Too little is known to assess the problems of false 

 echos in the regions of the terraces and sea cliffs but the possibility 

 that they may exist must be investigated. 



Another aspect of the biological population in the vicinity of the 

 rocky terrace is that they constitute an abundant source of sessil 

 organisms which could foul instruments placed on the bottom in these 

 areas. These include sponges, corals, bryozoans, brachiopods, 

 giant anemones, and burrowing clams. 



What are the military implications of such a great change in sea 

 level? What were its effect on the sea floor, and how can a knowledge 

 of this occurrence benefit the Navy? Most of the new electronic 

 acoustic equipment in use by the Navy is in some way environmentally 

 limited. Especially if it must differentiate between a foreign object 

 in an environment that contains similar, naturally-occurring bodies, 

 or false echo-producing organisms. Size of the object being looked 

 for is important because it dictates the target strength and frequency 

 of search sonars. It is in this respect that the sea cliffs and their 

 associated sediments become important. 



It is almost impossible to find a bottomed mine, or a lost atomic 

 bomb, by acoustic means in a boulder bed containing individual 

 boulders that are the same size as the object being searched for 

 (Swanson, 1967). Even more important, how is one to find a sub- 

 marine nestled against or cruising, submerged, along a sea cliff 

 6 0-feet high. Could an enemy ASW group detect a submarine that is 

 running slowly along the 600-foot contour a short distance (100 yards) 

 away from a steep cliff? If our submarine is also equipped with a 

 side-looking sonar using rapidly attenuated, very high-frequency 

 sound, it could safely maneuver clear of the cliff and still be acous- 

 tically invisible to surface-search sonars. The other aspect of this 

 problem is, could we detect an enemy submarine doing the same 

 thing? I have been asked whether or not a submarine captain would 

 care to venture into these rock- cliff areas. My answer is that these 

 features were discovered by a small submarine, and that with the 

 proper equipment (well within the state of the art), it would be no 

 problem for a larger submarine to move with ease in the same areas. 

 Such navigation would be much easier than an under-the-ice Polar 

 traverse. 



CONCLUSION 



The great CHANGES of sea level that have taken place in the 

 relatively recent past have greatly affected the nature of the sea 

 floor. These changes are not visible on the charts provided the 

 fleet. Practically nothing has been done to exploit the occurrence 

 of terraces and sea cliffs as far as being areas of stabile rock for 



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