64 DISCOVERY REPORTS 



0-13 °/oo- The current can be traced to within about 100 miles of the Antarctic con- 

 vergence (St. WS 437). 



In the region south of the Cape of Good Hope there are very few series of observa- 

 tions in the sub-Antarctic Zone, but they are sufficient to show that the subsurface 

 current exists there. At St. 1 163, in section 7 (Plates X-XII), the salinity of the water 

 at a depth of 200-400 m. was o-io and 0-03 °/ 00 greater than the salinities of the 

 surface and intermediate waters. At St. 1162 the presence of the current was indicated 

 by a sharp increase of salinity with depth between 100 and 150 m., but, as at some 

 stations in the western part of the Atlantic Ocean (see above), its salinity was not as great 

 as that of the colder water which sinks towards the north in the intermediate current 

 below it. The subsurface current can also be detected at Sts. 414 and 431 (ibid.), but 

 not at St. 449, which appears to be in a strong current eddy, or at St. 450 where it 

 cannot be distinguished from the surface current. The scanty data indicate that the 

 current is not so well defined in this region as it is farther west ; it is also deeper, starting 

 at 300-400 m. and climbing to 100-150 m. 



The observations at Sts. 848 and 849 in section 8 (Plates XIII-XV), south-east of 

 the Cape of Good Hope, also point to the existence of a weak subsurface current at 

 a depth of about 300 m. The current appears to be stronger at St. 849 than at St. 848 

 although the station is farther south, and the temperature and salinity distribution in 

 this region indicates that the current does not flow simply towards the south-east, but 

 that it takes part in a large cyclonic eddy movement. The same cyclonic movement is 

 found in the surface and deep layers (see p. 52), and it is probably caused by the 

 irregularities of the bottom topography. 



In the central part of the Indian Ocean the subsurface current lies at a much greater 

 depth. The observations made by the ' Gauss ' at St. 88 (Drygalski, 1926, p. 481) point 

 to its existence at a depth of 400-600 m. 



In the eastern part of the Indian Ocean and in the region south of Australia there are 

 also evident indications of a southward movement at a very deep level. The observations 

 in sections 9-12 (Plates XVI-XXVII) show that north of 45-48 S the stratum has a 

 much higher salinity than it has in the Atlantic or western part of the Indian Ocean, and 

 it also has a remarkably great depth — as much as 600-800 m. In 45-48 S, however, 

 the movement suddenly shrinks and farther south it is confined to a much shallower 

 stratum — between 100 and 300 m. — and it also has a much lower salinity. The reason 

 for the sudden diminution in the current is not yet certain ; it may be the result of the 

 restriction of the space above the warm deep current as it climbs towards the surface 

 above the bottom water, or simply an extensive subsurface convergence between the 

 Antarctic intermediate water and the subsurface water as they are forced together in 

 the region south of Australia on their way towards the east. 



The salinity and temperature distribution in the Indian Ocean suggests that much of 

 the highly saline water found in the northern part of the subsurface current may be 

 formed in the western part of the ocean from the Agulhas and Agulhas return currents 

 (see p. 75). 



