144 A TEXTBOOK OF OCEANOGRAPHY 



ooze dredged from the océan floor in the tropics is so cold that 

 it cannot be handled without discomfort. The lowest deep- 

 sea températures are foiind in the océans of the Southern 

 Hémisphère, and, broadly speaking, higher températures are 

 recorded as one recèdes from Antarctic régions. 



One theory of the cause of such low deep-sea températures 

 is that they are due to submerged Polar currents, and that 

 there is, in fact, a vertical circulation of the following kind : 



The cold surface waters of the Polar régions sink to the 

 bottom on account of their greater density. This water layer 

 moves towards the Equator, increasing in température from 2 

 to 3° C. on the way. In tropical régions the heated surface 

 waters move towards the Pôles. The facts which support the 

 theory of a bottom current from the Polar to tropical régions 

 may be grouped under six headings : 



1. Ail oceanic depths greater than 2,000 mètres are filled 

 with water of the same density (with small variations) and a 

 température between 0° and 3° C. This points to a vertical 

 circulation. In this enormous volume of deep-sea water there 

 are only minute variations of température, and thèse would be 

 still smaller but for the fact that near the freezing-point there 

 are but slight variations in the density of sea-water for each 

 degree of change in the température. 



2. The lowest bottom températures are found where the 

 great océans hâve both wide and deep connection with Polar 

 areas, and the bottom températures increase the farther one 

 recèdes from the Pôles and the nearer one approaches the 

 Equator. The depths of the North Polar seas are shut off from 

 neighbouring depths by slight ridges, so that the bulk of the 

 abyssal waters of the great océans comes from the Antarctic, 

 and it follows that the southern océans hâve the lowest bottom 

 températures. On the western side of the South Atlantic there 

 is a tongue of water of only 03° C, which reaches to 30° S. 

 Lat. (the Argentine Deep). This water is separated by a 

 comparatively narrow mixed layer from water of 28° C, 

 which is the average température of Atlantic water of that 



