ANTARCTIC BOTTOM WATER: MOVEMENTS 117 



preceding pages shows that it is no longer possible to assume that the bottom water is 

 formed by the sinking of shelf water all round the Antarctic continent, nor as Sverdrup 

 (193 1, p. 102) supposes, that it is deflected to the left on account of the earth's rotation 

 as it flows northwards, turning towards the west. It is on the contrary formed only in 

 one region, the Weddell Sea, and its principal movement is towards the east. The 

 northward currents at the bottom of the Atlantic, Indian and Pacific Oceans are, how- 

 ever, not derived only from the eastward current. Some of the warm water which flows 

 southwards in the deep layer becomes mixed with the bottom water and returns to 

 the north. The temperature and salinity distribution in the deep and bottom layers of 

 the Indian Ocean shows that some of the North Atlantic deep water, which enters the 

 ocean south of the Cape of Good Hope, spreads northwards in the bottom layer, and it 

 was also shown in the section on Pacific Ocean deep currents that the northward move- 

 ment in the bottom layer is largely composed of the highly saline water which enters 

 the Pacific from the Indian and Atlantic Oceans, south of Australia. 



The part played by cold shelf water in the formation of the northward currents 

 by cooling the warm deep water in the neighbourhood of the Antarctic Continent is not 

 fully understood. It is certain that the coldest bottom water in all three oceans comes 

 from the Weddell Sea, and that the increase of temperature and salinity towards the 

 east is due to the mixing of this current with warm and highly saline water flowing 

 southwards in the deep layer. The cold surface water apparently does not mix with the 

 deep water near the continental shelf and sink into the bottom layer. Drygalski's 

 work in the neighbourhood of Gaussberg (1926) showed that the surface water on the 

 Antarctic shelf never reached so high a salinity that by mixing with the deep water it 

 could produce water of the same temperature and salinity as that found in the bottom 

 layer. As far as is known at present, water with a sufficient salinity is only formed in the 

 Weddell Sea, where the formation of bottom water plainly takes place, and in the Ross 

 Sea, where bottom water is formed without being able to escape to the open ocean. 

 At other points round the Antarctic shelf the cold surface water may, however, exert 

 a less direct influence on the bottom water movements by mixing with the warm deep 

 water : a small volume of shelf water mixed with deep water may combine with the 

 eastward bottom current without having any appreciable effect on the gradual change 

 of its properties, and further work may show that the cooling and dilution of the deep 

 current by the shelf water is just as essential to the continued existence of the eastward 

 and northward currents as the bottom current from the Weddell Sea. 



