POLAR ORIGIN OF ABYSSAL WATERS 145 



depth. The uniform bottom température of the Pacific Océan, 

 which averages r6° C, also supports the idea of a bottom 

 Polar current. 



3. The colder bottom water of Polar origin is not found in 

 sea and océan areas shut off from Polar régions by submarine 

 ridges. In such cases the bottom température is practically 

 the same as that found at the apex of the ridge. 



4. In the North Atlantic there are strong surface currents, 

 which are sharply marked off from deeper water by a sudden 

 increase of température of from 4° to 5° C. This shows that 

 the bottom layers of water are uninfluenced by strong surface 



600 



I 



20 fi3ilhC3l Mis. 



fig. 28. — isotherms indicating bottom currext over the 

 Wyville-Thomsox Ridge. 



currents, that there is little or no mixture of currents, and that 

 the surface currents pursue their way unaffected by, and 

 unaffecting, the movements of the deeper oceanic waters. 



5. As a matter of fact, cold Polar water sinks, and this 

 has been practically demonstrated by the celebrated explorer 

 Amundsen in the neighbourhood of Spitsbergen. The depth 

 of the Norwegian Sea is fiUed with Atlantic water of high 

 salinity (the so-called Gulf Stream drift) ; this water, from its 

 nitrogen contents, must hâve been previously on the surface, 

 and has sunk owing to its having been cooled. 



