56 DISCOVERY REPORTS 



west north of 35-30 S, but the salinity distribution as shown by Schott suggests that 

 the westward movement begins farther south. 



In the southern part of the zone the current is not deflected southwards in order to 

 round Cape Horn until it reaches about 90 W. The isotherms suggest that the current 

 is forced farthest south in 70-80 W, and farther east it bends northwards into the Drake 

 Passage. 



The uniform surface stratum, in which the water movement is probably in more or 

 less the same direction as the surface current, has almost the same depth in the Indian 

 Ocean as in the Atlantic Ocean. South of Africa it appears from the observations at 

 Sts. 107 and 451 (Station Lists, 1929, 1932) to have a depth of 100-150 m. in winter, 

 and from those at Sts. 1162 and 1163 in section 7 (Plates X-XII) one of about 100 m. 

 in summer. South-west and south of Australia the water was generally found to be 

 uniform to a depth of 100 m. 



The observations made in the southern part of the zone in the Pacific Ocean show 

 that in winter the water is practically uniform down to a depth of 400 m., and probably 

 because of intense vertical mixing the surface water has almost the same properties as 

 the subsurface and intermediate waters. In summer, however, according to data col- 

 lected during the last cruise of the ' Discovery II ', the vertical differences are slightly 

 greater and there is a surface stratum 50-100 m. deep in which the salinity is 0-06- 

 0-14 °/ 00 less than that of the subsurface water. 



The observations made in winter along the line of section 14 south-east of New 

 Zealand show that there was very little difference of temperature and salinity between 

 the surface and subsurface waters even at the northernmost stations. In summer the 

 difference is slightly greater. At St. 1279 (Appendix I), 2 east of St. 946 (section 14), 

 the water in the first 60 m. is 3-4 C. warmer and 0-17 °/ 00 less saline than the subsurface 

 water at a depth of 150m. In the central part of the ocean (sections 15 and 16, Plates 

 XXXIV-XXXIX) there was a well-defined surface stratum north of 45 S even in 

 winter. At St. 967 the surface water was as much as 0-27 °/ 00 less saline than the sub- 

 surface water and 0-17 °/ 00 less than the lowest salinity of the intermediate water. This 

 poorly saline water is not, however, part of the general drift towards the east, but 

 apparently belongs to a current towards the west from the poorly saline coastal region west 

 of Chile. A preliminary examination of observations made in the northern part of the 

 zone in the eastern part of the Pacific, in the Humboldt current region, shows that there 

 also the surface stratum is much less saline than the subsurface stratum, again no doubt 

 because of the surface current from the poorly saline coastal region. 



THE SUBTROPICAL CONVERGENCE 



The observations made in the northern part of the sub-Antarctic zone and the 

 southern part of the subtropical zone show that the waters in these two regions have 

 very different properties and that there is generally a sharp transition from one to 

 the other. The existence of such a sharp boundary suggests that the two currents form 

 a convergence in which at least one of them sinks below the surface. The evidence that 



