72 DISCOVERY REPORTS 



shallow soundings east of New Zealand. Some idea of the salinity distribution in the 

 intermediate current is given by the chart in Fig. 16 as well as by the vertical sections. 

 In the Atlantic and Indian Oceans the isotherms follow the isohalines approximately, 

 and where the low salinity suggests that there is a strong current towards the north, 

 the temperature is also low. This is also true of the Pacific Ocean, but the salinity- 

 temperature relation seems to differ considerably from that of the other oceans, probably 

 because there is no source of highly saline deep water in the northern part of the ocean. 

 The salinity and temperature of the intermediate layer are greatest in the regions south 

 of Australia and south of the Cape of Good Hope, and least in the western half of the 

 Atlantic Ocean and the eastern half of the Pacific Ocean. 



SUBTROPICAL WATER 



In the subtropical zone the surface water is much warmer and more saline than sub- 

 Antarctic water, and it can generally be traced to some southward current instead of 

 to a movement towards the north-east. The subtropical convergence, the boundary 

 between the sub-Antarctic and subtropical waters (see pp. 56-63), is the line along 

 which the northward and southward currents reach a balance. The water just north of 

 the convergence has a temperature of at least 1 1 -5° C. in winter and i4 - 5° C. in summer, 

 but where there is a strong southward movement the temperature may be as much as 

 5 C. higher, and there is an exceptionally large change of properties from north to 

 south across the convergence ; the salinity of the surface water is at least 34-9 °/ 00 , and 

 it may be as much as 35-5 °/ 00 . 



In the Southern Ocean the subtropical water has a well-mixed surface stratum, 

 generally with a depth of 60-100 m., but in some localities — near the Cape of Good Hope 

 and off the west coast of Australia — it is found to be almost uniform to as great a depth as 

 150-200 m. Below the surface stratum, especially in the southern part of the zone, there 

 is frequently a more saline subsurface stratum, in which the southward movement is 

 probably stronger than it is at the surface. The lower salinity of the surface water cannot 

 be due merely to the fact that the surface water retains all the precipitation which falls 

 on the sea, since in this region the dilution from such a cause will probably be more than 

 balanced by the evaporation. 



The subsurface stratum is, however, not always more saline than the surface water, 

 and south of Africa and New Zealand it has more frequently the same or a lesser salinity. 

 Theoretical considerations suggest that the southward movement will be stronger in the 

 subsurface stratum when the wind blows from the west so that the southward movement 

 at the surface is retarded. An examination of the data so far available gives some sup- 

 port to this suggestion, but the data are not conclusive. 



Below the subtropical water the temperature and salinity both decrease rapidly with 

 depth into the northward Antarctic intermediate current. The depth of the boundary 

 between the northward and southward currents cannot be decided accurately until more 

 information has been obtained about their rates of transport and the eddy viscosity 

 between them ; but a preliminary examination of the temperature and salinity sections 



