HYDROLOGY OF THE SOUTH ATLANTIC 



177 



in winter is composed of almost homogeneous, cold, poorly saline water. There is prac- 

 tically no change in it with depth above the discontinuity level. The changes from 

 south to north are also very small, except in the neighbourhood of the convergence 

 with sub-Antarctic water. 



In summer the conditions are quite different. Figs. 3 and 4 show the distribution 

 of temperature and salinity in a vertical section through the southern half of the 

 Antarctic surface layer in summer. The section was made along a line north-west of 

 Adelaide Island and its position is shown as section II in Fig. 11 (p. 191). Although 

 section II was made in shallower water than section I the positions are not very far 



Om 



-1"C 



o°c 



l"C 



E°C 



250. 



500m 



750m 



I 000 m 



Fig. 5. The change in temperature with depth in the Antarctic Zone. 



apart, and a comparison of Figs. 3 and 4 with Figs, i and 2 shows how the layer changes 

 from winter to summer. Fig. 3 shows that in summer the surface of the layer is warmed, 

 and the temperature no longer remains constant with depth down to 100 m. Instead, 

 the temperature decreases with depth until a level is reached in which it is not much 

 different from the value it would have in winter. In summer there are two strata in the 

 layer, a surface stratum which has been warmed by the greater absorption of heat from 

 radiation, and by conduction, and a cold stratum where the water has been warmed 

 hardly at all. The minimum temperature in the cold stratum at each station is shown in 

 the section. In winter the salinity of the surface layer will be greater in section II than 

 it is in section I, because section II is closer inshore and affected to a greater extent by 



