of bedrock (fig. 32B) normally means the presence of 

 coarse sediments and bottom currents, with ripple marks 

 often resulting. The great areal extent of manganese 

 nodules (fig. 32C) in both the Indian and Pacific Oceans 

 requires that this type of microrelief be studied for its 

 possible influence on underwater sound transmission. (A 

 chart showing the distribution of manganese nodules at the 

 sediment-water interface is now in preparation. Source 

 information includes photographs, samples, dredge hauls, 

 and foreign and domestic scientific reports. ) 



When studied together these figures should permit 

 microrelief interrelationships to be established. The value 

 of such a series of figures will grow with the accumulation 

 of microrelief data. It is believed that the correlation of 

 type of microrelief with depth on specially constructed 

 bathymetric charts will permit a more accurate numerical 

 zoning of roughness and point up the effect of roughness on 

 the bottom reflection of sound. 



Zones of Isoroughness 



The general zones of isoroughness delineated in 

 figure 32A should be accepted with caution until much more 

 photographic sampling of the oceans has been performed. 

 At present there are many gaps in the data. 



The Gulf of Alaska and the area southward to just 

 north of the Mendocino Escarpment is largely an abyssal 

 plain with many isolated seamounts. No camera stations 

 have been occupied in this great area but, on the basis of 

 studies in other abyssal plain areas, a roughness rating of 

 2 has been assigned to it. The East Pacific Fracture Zone 

 and Baja Seamount Province constitute a fairly large area 

 of generally irregular topography. Roughness rating here 

 will vary from 2 to 3, and reach 4 in some coastal areas 

 where there is a high percentage of bedrock outcroppings. 

 The sediments in the southwestern Pacific Basin are largely 

 of pelagic origin. Red clays predominate but grade into 

 coarser calcareous oozes on the flanks. Microroughness 

 rating varies between 2 and 3 because of the presence of 

 manganese nodules in the deeper areas. Most of the semi- 

 closed deep-sea basins in the Pacific Ocean are largely 



63 



