WARM DEEP WATER g 9 



The silicate content of the warm deep water in the eastern part of the South Atlantic 

 Ocean between 69 20-8' S and 3 46-2' N is shown in Plate VI. At the far south the 

 warm deep water is flowing to the west, and the silicate content of this current both at 

 the depths of maximum temperature and salinity was lower in March 1933 than that of 

 the eastward-flowing water which had made the circuit of the Weddell Sea and which 

 was encountered farther north in the same section. The westward-flowing deep water 

 had a content of about 3700-3900 mg. in its upper layers and of about 4000 mg. at the 

 depth of maximum salinity, whilst, as may be seen at St. 1 158, the content at these same 

 two positions in the eastward current from the Weddell Sea was 4950 mg. and 5000 mg. 

 respectively. North of the cold Weddell Sea deep water the current is of North Atlantic 

 origin and had a content of 4550 mg. at the depth of maximum salinity. North of this 

 the content decreased until at 12-i S the value was 2250 mg. 



In the course of some observations in April 1932 along section 5 between Cape Town 

 and the ice-edge north of Enderby Land, which are shown in Plate IX, the existence of 

 a large cyclonic circulation in the deep layers was shown. The section in Plate IX cuts 

 across this circulation near its eastern end. Near South Africa where the deep water is 

 flowing towards the east the silicate content at the depth of maximum salinity of the 

 layer was 2550 mg. As the section progressed southwards the content at this position 

 in the current increased until at Sts. 850 and 85 1 in 50 43 -8' and 56° 22- 1 ' S respectively, 

 where there are indications that the eastward-flowing warm deep water turns to the 

 south and west, the content was about 4750-4950 mg. at the depth of maximum salinity ; 

 the higher value was recorded at St. 850, where the existence of a particularly active 

 current eddy has been noted by Deacon (1937, p. 92) and active upwelling was in 

 progress. In general the silicate content of the warm deep water increased southwards, 

 and in 65 15' S, 48 44' E the content was 4650 mg. in the upper part of the current 

 and 5850 mg. at the depth of maximum salinity. 



A somewhat similar section (4) was made between the ice-edge in 42^° E and Cape 

 Town in March 1935; the silicate distribution in this section is shown in Plate VIII. 

 The section appears to lie east of the cold deep current which flows across the South 

 Atlantic from the Weddell Sea. Towards the south the water is flowing westwards, 

 whilst near Cape Town the movement is towards the east. The content in the upper layers 

 of the current fell from an ice-edge value of 4450 mg. to 3250 mg. just south of the 

 Antarctic convergence. Immediately to the north the content in the upper part of the 

 current was 1 200-1 700 mg. At the greater depth of the salinity maximum the content 

 fell northwards from an ice-edge value of 4850 mg. to one of 2850 mg. at the station 

 nearest the coast of Africa. 



A combination of observations made north of Enderby Land over the ridge between 

 Marion Island and the Crozets in May 1934 with stations made between Marion Island 

 and Guardafui in April-May 1935, gave a section (6) in the western part of the South 

 Indian Ocean from 64^° S to n|°N. The silicate distribution in these combined 

 observations is shown in Plate XL At the most southerly station where the warm deep 

 water was colder and less saline and shows evidence of mixing, the silicate content was 



