HYDROLOGY OF THE SOUTH ATLANTIC 215 



together with some which flows northwards to the east of the Falkland Islands forms 

 the Falkland current. The remainder turns eastwards and flows across the Atlantic Ocean. 

 The high surface temperatures north-east of the Falkland Islands are the efltect of sub- 

 tropical water, originating in the Brazil current, which has crossed the sub-tropical 

 convergence at the surface and mixed with sub-Antarctic water. 



Fig. 13 (p. 197) shows the saHnity of the surface 100 m. of water in the Falkland 

 Sector. It shows how great is the effect of the coastal water which flows southwards 

 down the west coast of South America and round Cape Horn, on the salinity of the sub- 

 Antarctic water as far east as the Falkland Islands. When this survey was made the sur- 

 face salinity south of Cape Horn increased from about 33-30 7oo or less close inshore, to 

 34-207^0 about 150 miles offshore. Between the Patagonian coast and the Falkland 

 Islands it increased from 33-28 to 337 '/q,.,, and then to 34-20 about 150 miles east of the 

 Falkland Islands. The temperature of the sub-Antarctic water affected by the coastal 

 water is about 0-5 to 1° C. higher than that outside its influence. 



OXYGEN CONTENT OF THE SUB-ANTARCTIC WATER 

 Fig. 18 (p. 204) shows that at the end of winter in the south of the sub-Antarctic Zone 

 in 80^ W the surface water is about 90 per cent saturated with oxygen ; at the level of 

 minimum salinity it is 80 per cent saturated. In 30" W the observations were made at 

 the end of April. The water was about 95 per cent saturated with oxygen at the surface, 

 90 per cent at a depth of 100 m. and still about 80 per cent in the region of minimum 

 salinity. There are not enough observations to tell how the oxygen content at one 

 particular place varies from season to season; but an examination of the Antarctic 

 intermediate layer, which has its origin in the region of intense mixing north of the 

 Antarctic convergence, shows that the water in this region has its maximum oxygen 

 content at about the same time as its minimum salinity. This indicates that the oxygen 

 content of the layer is renewed by oxygen carried down by the Antarctic surface water. 

 The distribution of oxygen in the sub-Antarctic surface layer is shown in Plate X, 

 which gives the distribution along 30° W expressed in cc. of oxygen per litre of sea 

 water. In the northern half of the zone just south of 40° S the oxygen content decreases 

 below the surface stratum to a secondary minimum between 80 and 100 m. Below this 

 stratum there is a small increase in oxygen content because the oxygen is renewed by 

 water from the region of intense mixing. The oxygen content then decreases with 

 depth ; but owing to the sinking of the Antarctic surface water, and the water from the 

 region of intense mixing, the water of the sub-Antarctic layer has a high oxygen content 

 compared with the rest of the water in the South Atlantic Ocean at the same level. 



PHOSPHATE AND NITRATE CONTENT OF THE SUB-ANTARCTIC WATER 



Measurements made along 30° W show that the phosphate content of sub-Antarctic 



water is about 80 mg. PgOg/m.* just north of the Antarctic convergence and about 



60 mg. PgOj/m.s just south of the sub-tropical convergence. Plate IX shows the vertical 



distribution of phosphate content along 30° W expressed as mg. PgOg/m.* It will be 



