Chapter 16 — FUNDAMENTALS OF OCEANOGRAPHY 



is defined by a portion of a T-S curve. It 

 usually consists of a mixture of two or more 

 water types. 



WATER TYPE. — Sea water of a single 

 temperature value and a single salinity value, 

 and hence defined by a single point on a 

 temperature- salinity (T-S) diagram. Water types 

 form at the sea surface in areas of constant 

 climatic conditions . 



SUBMARINE TOPOGRAPHY 



In prior chapters of this manual it has been 

 mentioned that the physical shape of land 

 masses (mountains, valleys, etc.) above sea 

 level has an important effect on the character- 

 istics of the surrounding atmosphere. This is 

 also true o* the topography of the ocean floor. 

 The irregular terrain of the ocean floor affects 

 the characteristics of the sea in varying 

 degrees, such as the movement of ocean water, 

 the reflection of sound from the ocean floor, 

 variations in temperature gradients due to the 

 channeling and entrapment of water masses, etc. 



As shown in figure 16-1, the ocean floor 

 consists of mountains and valley features in 

 the same manner that terrain above sea level 

 does. 



There are many divisions and subdivisions 

 of classifications of ocean relief features. 

 However, three of the more commonly used 

 classifications are the continental shelf, the 

 continental slope, and the ocean basins. They 

 are described as follows: 



CONTINENTAL SHELF 



The continental shelf extends outward from 

 the coast to a depth of 100 fathoms. The width 

 of the shelf varies from zero in areas where 

 the coast drops rapidly, to a maximum of about 

 800 miles along the glaciated coast of Siberia, 

 with an average width of about 30 miles. (See 

 fig. 16-1.) The continental shelf comprises 

 about 7.5 percent of the total ocean bottom „ 

 The shelf region is a transition zone between 

 fresh water runnoff from land and the more 

 saline waters of the sea; consequently it is 

 an area of great mixing of water with 

 generally unstable water conditions. In the 

 continental shelf region it is common for the 

 currents to run parallel to the shore line. 



CONTINENTAL SLOPE 



The continental slope extends outward from 

 the seaward end of the continental shelf to a 

 depth of 1,500 fathoms. Ths continental slopes 

 of the world comprise about 12 percent of the 

 oceanic area. A slope resembles a terrestrial 

 cliff that has been eroded by heavy rains, with 

 the most striking features being the prevalence 

 of submarine canyons, some equal in size to 

 the Grand Canyon. A portion of the continental 

 slope is indicated west of the Kuril Trench 

 near Japan in figure 16-1. 



OCEAN BASINS 



The ocean basins range in depth from 1,500 

 fathoms at the end of the continental slopes 

 to 3,000 fathoms at the deepest part of the 

 ocean. The area of the basin is clearly 

 delineated In figure 16-1. The Eastern portion 

 of the figure, between the continental slope off 

 the West Coast of U. S. to the Hawaiian Ridge, 

 marks the boundaries of the Eastern Basin. 

 The Western Basin lies between the Hawaiian 

 Ridge and the continental slope off Japan. 



About 80 percent of the ocean floor is a 

 basin, having very rugged relief features ranging 

 from ridges to trenches and deeps. Less than 

 1 percent of the oceanic area may be called a 

 "deep" as defined earlier in this chapter. 



PHYSICAL PROPERTIES 

 OF SEA WATER 



A convenient method of visualizing the sea 

 is to divide it into layers in much the same 

 way that we do the atmosphere. The term 

 applied to this concept is the "three-layered 

 ocean." The divisions of the ocean in accord- 

 ance with this concept are illustrated in 

 figure 16-2. 



A general description of the three principal 

 layers is as follows: 



1. The mixed layer — a region of fairly 

 constant warm (15° C) temperatures which in 

 middle latitudes exist from the surface to a 

 maximum depth of about 1,500 feet. In this 

 layer the mixing of water is caused by action 

 of thermohaline circulation, surface storms, wind 

 friction, and wave action. Below the mixed 

 layer, no matter how violent the storm, very 

 little mixing will occur.. 



373 



