THE SOUTHERN OCEAN 19 



there is, beneath the surface, a zone of warmer 

 water, which has been thought to be flowing 

 from north to south. The Southern Ocean 

 and the Southern Pacific, moreover, are known 

 to be the great refrigerators that cool the deep 

 waters of the tropical and northern seas. The 

 water of the deep sea all the world over, is 

 almost ice-cold, and may be even colder than 

 the freezing point of fresh water. This cold- 

 ness is attributed mainly to the melting of the 

 Antarctic ice, the waters formed thereby sinking, 

 and drifting northward ; for the deeper parts 

 of both the Northern Atlantic and the Northern 

 Pacific are warmer than the corresponding 

 positions in the southern parts of the same 

 oceans. 



The general idea as to the nature of the 

 Southern Ocean at the close of the work of the 

 Challenger Expedition is well expressed in 

 Wild's " Thalassa."* (fig. 2). The northern 

 boundary was taken as the parallel of 40 S., 

 which was represented as crossing alternately 

 meridional depressions, ranging from 2500103000 

 fathoms deep, and submarine plateaus approach- 

 ing to within 1 500 fathoms of the surface. The 

 Southern Pacific was thought to consist of one 

 long depression occupying the area between the 

 submerged plateau of Patagonia, the islands of 

 the South Pacific Chain, and the shallow water 

 beside the Antarctic lands. The Southern 

 Atlantic was represented as divided into two 



*London 1877, pi. 2, pp. 23-4. 



