OCEANOGRAPHIC INFORMATION FOR SUBMARINE CABLES 1001 



is reciuired, 1 : 1 profiles as illustrated in Fig. 2(b) are prepared by careful 

 interpretation of precision depth records and their correction for actual 

 sound velocity and slope. 



The physiographic diagram (in envelope inside rear cover) was 

 prepared by combining evaluated and corrected depth measurements 

 with all other ocean bottom and geological information. The construc- 

 tion of these diagrams is preceded by the preparation of 40 : 1 exaggerated 

 profiles along all available sounding tracks through the region under 

 consideration. After study and evaluation of the profiles, areas of dif- 

 ferent texture are defined, and the various physiographic provinces 

 are outlined. The relief shown on the profiles is then drawn in perspective 

 view along the appropriate track of the chart. After all available tracks 

 have been drawn, the remaining blank areas are sketched in, basing 

 the interpretation on geological information. 



Fig. 6 shows the physiographic provinces of the North Atlantic and 

 the existing submarine cables on a great circle chart. A plot such as 

 this is useful in preliminary studies of new routes. More detailed charts 

 to a scale of 1 : 1 million showing contours, actual sounding tracks, 

 existing cable routes and cable fault records can be prepared for specific 

 engineering of new cable routes. 



2.4 North Atlantic Topography 



The relief of the continents naturally divides itself into mountain 

 ranges, plateaus, and plains — physiographic provinces which can be 

 recognized by distinct differences in topography, form and texture. 

 Geologists recognize these differences as directly related to underlying 

 geological structures. The topography of the ocean floor can also be 

 divided into physiographic provinces similar to those familiar on land. 

 In general, the relief of the deep sea topography is greater than on land 

 due to the fact that the smoothing effects of erosion are less under the 

 deep sea. Fig. 7 shows the relief along a continuous line extending 

 from Peru across South America and thence across the South Atlantic. 



The three major divisions of the Atlantic Ocean — Continental 

 Margins, Ocean Basins, and Mid-Atlantic Ridge — each occupy about 

 one third of the ocean floor. Since detailed topographic information is 

 available for so little of the area covered by the oceans, the following 

 descriptions of the relief must of necessity be general. Where specific 

 details are available, they are pi-esented as examples. The area to be 

 described, the North Atlantic, is well outlined on the Physiographic 

 Diagram. Frecjuent reference to this illustration should help to make 

 the word descriptions more meaningful. 



