ZONES OF THE SEA- WHERE THEY LIVE H 



(1951) give the following percentages for the distribution of the depths of 

 the seas over the earth. 



15.6 per cent of the sea bottom is 0-5,900 feet deep 



19.3 " " " " " " " 5,900-11,800 " " 



58.4 " " " " " " " 11,800-17,750 " " 

 6.5 " " " " " " " 17,750-35,600 " " 



The Movements of Water 



This is a complex subject which concerns waves, tides, horizontal water 

 currents such as the Gulf Stream and vertical currents such as upwelling. It 

 is very difficult to clearly separate these factors. All of them cause a mixing of 

 ocean water in complex patterns and are thus vital to the life of the sea, 

 particularly in distributing animals and plants and in fertilizing surface waters 

 from below. 



Waves constitute the least massive of the various types of water movement. 

 They are surface phenomena, rarely having any effect on waters greater than 

 300 feet (or a maximum of 600 feet) deep. 



Winds provide the energv necessary to create a wave. The size of a wave 

 depends mainly on four factors of winds: (1) velocity— the stronger the wind 

 the higher the wave, (2) duration— the longer the wind blows, the higher 

 waves will become, (3) fetch— the longer the distance over water that the 

 wind can blow without obstruction, the larger the waves, and (4) direction— 

 the longer the wind blows in an unchanging direction, the bigger the waves 

 will be. These four factors interplay and vary greatly to produce waves of 

 a few inches high to a probable maximum of 40 feet in height. Barnett (1954) 

 states that it would take a 60-mile gale blowing steadily in one direction for 

 a distance of 900 miles to produce a 40-foot wave, and since such conditions 

 are not often met, such waves are rare. The very high velocity of gusty winds 

 does not produce high waves because it literally blows the waves' tops off. 



The water itself moves very little in the horizontal direction of the wave. 

 It merely rises and falls in a circular fashion as the wave form passes through 

 it. To prove this, all one has to do is to place a floating object on the water's 

 surface and notice that it bobs up and down in a circular pattern with the 

 waves, but does not move forward with them. When a wave reaches shallow 

 water, the circular pattern of the water movement becomes flattened because 

 of the proximity of the bottom. This causes the forward edge of the wave 

 to become steeper and steeper until it falls over on top of itself and breaks 

 Cfig. 2). The force of a breaking wave can be tremendous. It is enough to 

 carve holes in rocks or to lift large stones and even throw them through the 

 air. It has been calculated that some huge waves strike with a force of up to 

 3 tons per square foot, ample warning that swimming in large breakers near 

 shore can be very dangerous business. 



Tides are very different from waves, in that they are of cosmic origin. The 

 gravitational pulls of the sun and the moon provide the energy of the tides. 

 When the sun and moon are both lined up with the earth and with each other, 



