430 



Dr. J. Murray. 



Antarctic Ocean may be explained by a consideration 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 high salinity, can suffer much dilu- 

 tion with Antarctic water, and still be denser than water from these 

 higher latitudes at the same temperature. Here the density observa- 

 tions and the sea-water gases indicate that the cold water found at 

 the greater depths of the ocean probably leaves the surface and 

 sinks towards the bottom in the Southern Ocean, between the lati- 

 tudes of 45° and 56° S. These deeper, but not necessarily bottom, 

 layers are then drawn slowly northwards towards the tropics, to 

 supply the deficiencies there produced by evaporation and south- 

 ward-flowing surface currents, and these deeper layers of relatively 

 warm water appear likewise 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 nnderlying 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 examination 

 of these waters is most desirable at different seasons of the year, 

 with improved thermometers and sounding machines. Indeed, all 

 deep-sea apparatus has been so much improved as a result of the 

 " Challenger" explorations, that the labour of taking specific gravity 

 and all other oceanographical observations has been very much 

 lessened. 



Pelagic Life of the Antarctic Ocean. 



In the surface waters of the Antarctic there is a great abundance 

 of diatoms and other marine alga?. These floating banks or meadows 

 form primarily not only the food of pelagic animals, but also the 

 food of the abundant deep-sea life which covers the floor of the 

 ocean in these south polar regions. Pelagic animals, such as cope- 

 pods, amphipods, molluscs, and other marine organisms, are also very 

 abundant, although species are fewer than in tropical waters. Some 

 of these animals seem to be nearly, if not quite, identical with those 

 found in high northern latitudes, and they have not been met with 

 in the intervening tropical zones. The numerous species of shelled 

 Pteropods, Foraminifera, Coccoliths and Rhabdoliths, which exist in 

 the tropical surface waters, gradually disappear as we approach the 

 Antarctic circle, where the shelled Pteropods are represented by a 

 small Limacina, and the Eoraminifera by only two species of Globi- 

 gerina, which are apparently identical with those in the -Arctic Ocean. 

 A peculiarity of the tow-net gatherings made by the " Challenger" 



