Geology 



Thus, in spite of the fact that the surface temperatures 

 are on the whole higher on the sea than on the land, the 

 great oceans are filled to more than three-fourths of 

 their capacity by water whose temperature is very near 

 the freezing-point, i.e. considerably lower than the normal 

 temperature of the rocks which form the ocean floor. 



Under these circumstances we should expect that 

 the waters of the deep basins would be slowly warmed 

 up, and this would undoubtedly be the case were it not 

 for the fact that cold water is heavier than warm water, 

 and that as a consequence a circulation similar to that 

 in hot-water heating apparatus is set up. 



The great oceans are all open to the southward, and 

 therefore in communication with the Antarctic Ocean, 

 where even at the surface the temperature of the water 

 is near the freezing-point. They are also, though to a 

 considerably less extent, in communication with the 

 Arctic Ocean. 



From these two oceans, but principally from the 

 Antarctic, the cold water flows slowly along the bottom 

 towards the equator, displacing and floating upwards 

 the warmer waters of the tropics, which in their turn 

 flow outwards from the equator towards the poles, thus 

 completing a circulation not unlike that which we have 

 already traced in the atmosphere. 



The surface currents of the ocean are, however, also 

 greatly influenced by the winds, and, indeed, so powerful 

 are some of these wind-produced currents that they 

 obliterate the convection circulation described in the 

 last paragraph. 



It is the cold bottom currents mentioned above 

 which keep up the supply of cold water to the great 



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