SUB-ANTARCTIC WATER: TEMPERATURE AND SALINITY 71 



and 6-o° C. in summer. The temperature limits are not quite the same all round the 

 Southern Ocean : where the convergence is far south, as it is in the Pacific Ocean, the 

 sub-Antarctic water is as cold as 2-5° C. in winter and 5-0° C. in summer. 



The salinity of the surface water in the Falkland sector was found to vary between 

 34-10 °/ 00 at the end of winter and 33-95 % at the end of summer. Elsewhere the data 

 are only sufficient for a very approximate summary. The surface water just north of the 

 convergence in the eastern half of the Atlantic Ocean is usually slightly less saline than 

 that farther west; it varies between about 34-0 and 33-8 °/ 00 . In the Indian Ocean the 

 salinity is still lower — roughly 33-9-33-8 °/ 00 — and it is most likely that the low salinity 

 in this ocean, as well as in the eastern part of the Atlantic Ocean, is due to the large 

 volume of thaw-water which is added to the circumpolar drift by the Weddell Sea 

 current. South of the Pacific Ocean the salinity of the drift increases and it varies be- 

 tween 34-1 and 34-2 °/ 00 in winter and 34-0 and 34-1 °j 00 in summer. The data suggest 

 that there is less movement of thaw-water towards the north in the Pacific Ocean, but 

 a reliable comparison of the conditions in the ocean with those of the opposite sectors 

 cannot be made until the examination of the large number of observations made during 

 the last cruise of the 'Discovery II' (Mackintosh, 1935) has been completed. 



Both the temperature and salinity of the sub-Antarctic water increase towards the 

 north, but the properties of the water in the northern part of the zone are not the same 

 in all sectors. Where the movements of the sub-Antarctic and subtropical waters are 

 strongly opposed to each other, as they are south of the Brazil current and south of 

 Africa, the sub-Antarctic water just south of the convergence has a temperature and 

 salinity of only 7-8 C. and 34-3-34-4 °/ 00 . On the other hand, where the convergence 

 is not sharp and the sub-Antarctic current is both farther from its source and mixed to a 

 greater extent with highly saline water, such as is carried southwards by the subsurface 

 current, the temperature of surface water rises to 11-5° C. in winter and 14-5° C. in 

 summer and the salinity rises to 34-9 °/ 00 . These temperature and salinity limits are 

 always an approximate indication of the position of the northern boundary of the 

 sub-Antarctic water ; where there is a sharp convergence they coincide with it, and where 

 the sub-Antarctic and subtropical waters have no sharp boundary, they coincide 

 roughly with the position where the temperature and salinity sections suggest that the 

 northward and southward movements are balanced. Where the sub-Antarctic water 

 has been mixed with a southward movement of subtropical water, as frequently happens 

 south of the Brazil and Agulhas currents, the limits seem to give a good indication of 

 the point at which the two waters are mixed in equal proportions. 



The temperature and salinity distributions in the subsurface and intermediate cur- 

 rents cannot be given briefly and will most easily be ascertained by reference to the 

 vertical sections. Near the subtropical convergence the properties of the subsurface 

 waters are intermediate between those of the surface water and the subtropical water. 

 Farther south both the temperature and salinity depend on the strength of the south- 

 ward movement; they are greatest in the region south of Australia, and least in the 

 eastern part of the Atlantic Ocean, the western part of the Indian Ocean, and in the 



