ZOOGEOGRAPHY 207 



Text-figs. (15-22 1 ) of temperature and salinity sections on the Greenwich Meridian have been 

 prepared from data in the Discovery Station Lists. They indicate the seasonal and depth fluctuations 

 in hydrological conditions and the movements of the principal water masses. I have drawn freely 

 from the work of Deacon (1933, 1937) on the hydrology of the Antarctic Sector of the South Atlantic 

 and along the meridian of 30 W., and from Mackintosh (1946) on the varying positions of the 

 Antarctic Convergence. 



I 



OM 



IOOOM 



2000 M 



3000 M 



4000M 



ANTARCTIC BOTTOM 

 WATER 



Text- fig. 14. Diagram indicating the circulation of water approximately along the meridian of 30° W. The arrows indicate 

 the general movement of the water masses. A. C. = Antarctic Convergence, S.T.C. = Sub-Tropical Convergence, T.C. = 

 Tropical Convergence. 



(i) SURFACE WATER MASSES 



(a) Antarctic Surface Water is found around Antarctica as a cold poorly saline layer lying in the 

 surface 100-250 m. above warmer water of higher salinity. In the South Atlantic Ocean, three main 

 sources of water contribute to its composition: (1) Water from the Bellingshausen Sea which flows 

 in along the southern side of the Drake Strait, (2) water flowing out of the Weddell Sea in a north- 

 easterly direction, and (3) water from the East Wind Drift which flows in a westerly direction from 

 the southern Indian Ocean into the Weddell Sea. Of these three components the Weddell Sea 

 Water (Weddell Drift) probably exerts the greatest influence because in winter it carries the main 

 body of pack-ice across the South Atlantic. 



1 The vertical scale in these sections has been much exaggerated, and to avoid confusion all the readings have not been 

 included on the figures but they have all been taken into account in drawing the isotherms and isohalines. It is not con- 

 sidered that temperature and salinity are more, or less, important than other hydrological features but they are more easily 

 interpreted and for this reason have been more widely used. 



