POLAR ORIGIN OK ABYSSAL \VATI-RS 145 



depth. The uniform bottom temperature of the Pacific Ocean, 

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

 Polar current. 



3. The colder bottom \vatrrof Polar origin is not found in 

 sea and ocean areas shut off from Polar regions by submarine 

 ridges. In such cases the bottom temperature 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 temperature of from 4 to 5 C. This shows that 

 the bottom layers of water are uninfluenced by strong surface 



20 



200 



400 



600 



BOO 



820 



630 



m 



885 675 613 375 558 375 600 



/O' 



200 

 400 



A/. 



600 

 800 



10 is 20 Nautical NIs. 



FIG. 28. ISOTHERMS INDICATING BOTTOM CURRENT OVER THE 

 WYVILLE-THOMSON 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 filled with Atlantic water of high 

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

 nitrogen contents, must have been previously on the surface, 

 and has sunk owing to its having been cooled. 



10 



