128 THE OCEAN 



forties," and by and by necessarily become 

 colder, hence denser, and sink to greater 

 depths. Both salinity and temperature con- 

 tribute to this effect, and the sinking waters 

 carry with them the atmospheric gases to aerate 

 the deeper waters of the ocean. Towards 

 the south these waters on sinking are drawp 

 farther southward and become overlaid by the 

 cold and less saline waters diluted from the 

 melted snow and icebergs of the Antarctic 

 regions. They are also slowly drawn equator- 

 wards to supply the place of the warm surface 

 currents driven south by the winds. From 

 the enormous quantities of warm water they 

 impel before them into the Southern Ocean, 

 these strong north-westerly winds may be 

 regarded as playing the most conspicuous part 

 of all the prevailing winds in the circulation of 

 the waters of the ocean. A striking feature of 

 the waters of the Southern Ocean is the inter- 

 digitation of currents differing widely from each 

 other both in temperature and salinity, the 

 colder of these currents having their origin, 

 doubtless, in the Antarctic regions. Another 

 important part played by the vast currents of 

 warm and salt water is to mitigate most 

 materially the cold of the Antarctic region, 

 particularly at great depths, and thus to 

 restrict the ice-clad area to its present limits. 

 In the North Atlantic and in a less degree 



