366 THE RENEWAL OF ANTARCTIC EXPLORATION. 



at 80 fatlionis. The surface layer ranges from 29° in tlie south to .'^8° in 

 the nortli, and the deeper bottom layers range from 32° to 35°. 



Mr. lUichanan found that the density of tlie cohl hiyer, and indeed 

 of all the deeper waters, was higher than that of the surface, and his 

 admirable researches on the effects produced by freezing sea water, 

 appear to give a satisfactory explanation of the effect of these phenomena 

 on the distribution of temperature in this ocean. Jt has been found 

 that sea water oti freezing is divided into two saliniferous parts, one 

 solid, which is richer in sulphates, and one licpiid, which contains pro- 

 portionally more chlorides than the parent sea ^ivater.* The liipiid 

 brine thus i)r()duced is denser, and sinks into the underlying water, thus 

 rendering the deeper water more saline and at the same time lowering 

 its temperature. In a basin isolated from general oceanic circulation, 

 like the Xorwegian basin of the Arctic regicuis, there is produced in this 

 way an uniform teiniierature of about 29° ¥. in all the dcejier waters, 

 but no tiace of this state of matters is found ni the Antarctic. On the 

 contrary, at the areater dej^ths a temperature is found somewhere 

 between 32° and 34° F. as far south as the Antarctic circle, and not 

 therefore \ery different from the temperature of the deepest bottom 

 Avater of the tropical regions of the ocean. 



The i)resence of this relatively warm water in the deeper parts of the 

 Antarctic Ocean may be explained by a considtiration of general oceanic 

 circulation. The warm tropical waters which are driven southwards 

 along the eastern coasts of South America, Africa, and Australia, into 

 the great all-encircling Southern Ocean, there become cooled as they 

 are driven to the east by the strong westerly winds. These waters on 

 account of their Iiigh salinity, can suffer nnu-li dilution with Antarctic 

 Avater, and still be denser than water from these higher latitudes at the 

 same temperature. Here again, the density obsei'vations indicate that 

 the cold water found at the greater depths of the ocean probably leaves 

 the surface and sinks toward the bottom in the Southern Ocean between 

 the latitudes of 4.")° and 5G° south. These deeper, but not necessarily 

 bottom, layers are then drawn slowly northward toward the tropics to 

 supply the deficiencies there produced ])y evaporation and southward- 

 flowing surface currents, and these deeper layers of relatively warm 

 water appear ]ikeA\ise to be slowly drawn southwards to the Antarctic 

 area to supply the place of the ice-cold currents of surface water drifted 

 to the north. This warm underlying water is evidently a potent factor 

 in the melting and destruction of the huge table-topped icebergs of the 

 southern hemisphere. While these views as to circulation appear to 

 be well established, still a fuller examiuatiou of these waters is most 



* Petterssea has shown that sea ice exj)an(ls irregnlarly witli heat, and that the 

 latent heat is abnormal, being less than that of pnre ice. He also found that the 

 chemical composition of the brines formed in Arctic seas by the freezing of ice out 

 of a limited quantity of water is different from that of sea water itself. There is, 

 however, uo certainty that this behavior of the ice and free sea water is due to the 

 formation of the hypothetical cryohydrates of Guthrie. 



