66 DISCOVERY REPORTS 



the sinking of the cold Antarctic water in the south will tend to cause a compensating 

 movement towards the south at the surface. Such a movement is actually prevented at 

 the surface by the northward transport of water in the wind drift currents, but in the 

 sub-Antarctic Zone it can take place in the subsurface stratum. In addition to being 

 the result of thermohaline differences the current may compensate for the northward 

 movement of the surface drift currents. Owing to the gradual decrease in the strength 

 of the wind towards the north in the sub-Antarctic Zone the surface transport towards 

 the north is smaller in the northern part of the zone, and some of the water which is 

 carried more rapidly towards the north by the stronger winds farther south may return 

 towards the south in the subsurface current. The salinity distribution in the neighbour- 

 hood of the subtropical convergence and the properties of the water in the subsurface 

 stratum show that the current also contains the sub-antarctic water which is carried 

 northwards by the wind to sink at the subtropical convergence. 



THE ANTARCTIC INTERMEDIATE CURRENT 



The repeated crossing of the sub-Antarctic Zone has given much new information 

 about the part played by the Antarctic water in the formation of the intermediate cur- 

 rent. In the region extending 100-200 miles north of the Antarctic convergence there 

 is a large volume of mixed water which is formed by the mixing of the sinking Antarctic 

 water with the warmer and more saline waters carried southwards by the subsurface and 

 warm deep currents. The mixture is not quite homogeneous, and the warmer and 

 lighter part is carried northwards at the surface whilst the colder heavier part sinks to 

 form the intermediate current. 



The path taken by the intermediate current lies below the subsurface current and 

 above the warm deep current, and in longitudinal sections through each of the three 

 main oceans it appears as a poorly saline layer between these highly saline waters. The 

 upper and lower boundaries of the current have not yet been determined exactly, and 

 except for the measurements described in the author's previous report (1933, pp. 223-6) 

 no quantitative examination of the transport of the water in it has been possible. Some 

 idea of the relative strengths of the current in the different sectors of the Southern 

 Ocean can, however, be obtained from the distance to which the poorly saline water 

 penetrates towards the north. 



The positions of the 34-20-34-70 °/ 00 isohalines are shown on a circumpolar chart in 

 Fig. 16; the chart is only approximate, since the data are rather scattered and no 

 allowance has been made for seasonal or annual changes, but it will serve the purpose of 

 an investigation which is necessarily only introductory. 



In the western and central parts of the Atlantic Ocean the volume and strength of the 

 current seem to be particularly great. The chart in Fig. 16 and the vertical salinity 

 section along 30 W (Fig. 13) show that the poorly saline water is carried far north, and 

 the slow increase of salinity along its path suggests that the current has a large volume. 

 The current can be followed by its low salinity as far as 25 N, and as far as 5 S the water 



