418 SCIENTIFIC ADVANTAGES OF AN ANTARCTIC EXPEDITION. 



materials characteristic of that deep-sea deposit. Since these views, 

 however, as to the distribution of deep sea deposits throughout these 

 high southern latitudes are founded upon relatively few samples, it 

 can not be doubted that further samples from different depths in the 

 unexplored regions would yield most interesting information. 



TEMPERATURE OF THE ANTARCTIC OCEAN. 



The mean daily temperature of the surface waters of the Antarctic, 

 as recorded by Ross, to the south of latitude 63° S. in the summer 

 months, varies from 27.3° to 33.6°, and the mean of all his observations 

 is 29.85°. As already stated, his mean for the air during the same 

 period is somewhat lower, being 28.74°. In fact, all observations seem 

 to show that the surface water is warmer than the air during the 

 summer months. 



The Challenger observations of temperature beneath the surface indi- 

 cate the presence of a stratum of colder water wedged between warmer 

 water at the surface, and warm water at the bottom. This wedge- 

 shaped stratum of cold water extends through about 12° of latitude, 

 the thin end terminating about latitude 53° S., its temperature varying 

 from 28° at the southern thick end to 32.5° at the northern thin end, 

 while the temperature of the overlying water ranges from 29° in the 

 south to 38° in the north, and that of the underlying water from 32° to 

 35°. This must be regarded as the distribution of temperature only 

 during the summer, for it is improbable that during the winter months 

 there is a warmer surface layer. 



In the greater depths of the Antarctic, as far south as the Antarctic 

 circle, the temperature of the water varies between 32° and 35° F., and 

 is not, therefore, very different from the temperature of the deepest 

 bottom water 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 consideration of general oceanic circulation. 

 The warm tropical waters which are driven southward along the east- 

 ern 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 high salinity, can suffer much dilution with Antarctic water, and 

 still be denser than water from these higher latitudes at the same tem- 

 perature. Here the density observations and the sea- water gases indi- 

 cate that a large part of 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 45° and 56° S. These 

 deeper, but not necessarily bottom, layers are then drawn slowly north- 

 ward toward the tropics, to supply the deficiencies there produced by 

 evaporation and southward-flowing surface currents, and these deeper 

 layers of relatively warm water appear likewise to be slowly drawn 

 southward to the Antarctic area to supply the place of the ice-cold 



