9 o DISCOVERY REPORTS 



surprisingly low for the latitude ; the values at the maximum temperature and salinity of 

 the layer were 4250 mg. and 5200 mg. respectively. North of this station the content in the 

 upper part of the current reached a value of 5050 mg. and then decreased to 3250 mg. south 

 of the Antarctic convergence ; at the deeper position of the salinity maximum it increased to 

 6100 mg. and then decreased to about 4000 mg. At the south of the sub-Antarctic zone the 

 upper layers contained slightly less silicate but the content fell rapidly across the zone from 

 2900 mg. in the south to 1100 mg. just south of the subtropical convergence; the value 

 at the depth of maximum salinity decreased northwards across the zone from 4100 mg. to 

 3500 mg. In the subtropical zone, where the warm deep water is mainly composed of 

 North Atlantic Ocean deep water, the content at the depth of greatest salinity of the 

 layer was about 3150-3300 mg. In the tropical zone where south of 20 S, the warm 

 deep water is composed of North Atlantic deep water with a smaller proportion of North 

 Indian Ocean deep water, the content was about 3000-3400 mg. at the salinity maximum. 

 North of 20 S the warm deep current is composed of water of North Indian Ocean origin 

 and is considerably closer to the surface. The maximum salinity of the layer rises 

 from a depth of 1250 m. at i8i° S to 400 m. at 7 N, and the silicate content in this 

 stratum of the current decreased from a value of 3200 mg. at i8|° S to 1550 mg. at 7 N. 

 If this section be compared with section 3 in the eastern part of the South Atlantic Ocean 

 (Plate VI) it will be seen that the North Indian Ocean deep water has a much greater 

 silicate content than that of the North Atlantic deep water at corresponding latitudes ; 

 it was also found to have a higher phosphate content. 



South of Australia between Cape Leeuwin and the ice-edge in 63 41' S, 130 07' E 

 the warm deep water flows principally towards the east and south. Deacon (1937, p. 99) 

 suggests that the eastward movement is strongest in the deep channel close to Cape 

 Leeuwin, and along section 8 in May 1932 (Sts. 877-887, Plate XIII), the silicate content 

 of the warm deep water was greater in this position than anywhere else in the section. 

 In the subtropical region of the eastern part of the South Indian Ocean the deep water 

 has a complex structure consisting of a mixture of North Indian deep water, Antarctic 

 intermediate and bottom waters and North Atlantic deep water. The admixture of 

 North Indian deep water and Antarctic bottom water would account for the high content 

 of the deep water in the position noted above. From the deep channel near Cape Leeuwin 

 the silicate content of the warm deep water at first dropped towards the south from a 

 value of 5300 mg. at the depth of maximum salinity to one of 4450 mg. at the next 

 station farther south. At the most southerly station in the sub-Antarctic zone the 

 corresponding value was 4150 mg. ; south of this, in the Antarctic zone, the content 

 increased as the warm deep water became closer to the surface, so that at the ice-edge 

 where the maximum salinity was found at 900 m. the corresponding silicate value was 

 5055 mg. The upper layers of the current in the Antarctic zone south of Australia 

 had a content of about 3150 mg. in the north of the zone and 4300 mg. at the ice-edge. 



In September 1932 section 12 was made from Wellington, New Zealand, to the ice- 

 edge north of the Ross Sea in 62 12-8' S, 158 11' W; the section began in an area of 

 irregular depth, and except for St. 944 in 47 41-6' S the depths were less than about 



