ANTARCTIC SURFACE WATER: WEST WIND DRIFT 33 



A comparison of the temperature and salinity distribution in the vertical sections in 

 the western half of the South Atlantic (sections 2, 3, and 4, Plates III-VI) with that 

 across the eastern end of the Drake Passage (section 1, Plate II) suggests that there is 

 a greater flow of Antarctic water to the north. The observations made just north of the 

 convergence show that there is a sharp temperature gradient within the first 400 m., 

 indicating that the cold Antarctic water sinks towards the north below the warmer 

 sub-Antarctic water. Longitudinal sections which extend throughout the whole length 

 of the Atlantic Ocean show that such a sinking of Antarctic water gives rise to the 

 poorly saline Antarctic intermediate current, which in the western half of the ocean can 

 be traced as far as 25°N. 



The longitudinal sections in 30 W. (Figs. 12, 13, p. 47), show that in this meridian 

 the boundary between the Antarctic and sub-Antarctic waters at the surface is found 

 just where the Antarctic water sinks abruptly to a deeper level, but the observations 

 made just north of the convergence in sections 2 and 3 show that in the region east of 

 the Falkland Islands a shallow stratum of sub-Antarctic water spreads some distance 

 farther south above the Antarctic current. 



At St. 1027 in section 3 the mean temperature in the first 50 m. was 3-53° C, but in 

 the stratum between 100 and 200 m. it was only o-68° C. Such a large difference be- 

 tween the two strata suggests that they belong to different currents, the surface water 

 flowing southwards, and the deeper water, part of the main Antarctic current which 

 sinks towards the north and gives rise to the Antarctic intermediate current, flowing 

 northwards. The isotherms and isohalines in the section show that the Antarctic current 

 starts to sink between Sts. 1027 and 1026, although the principal direction of movement 

 is probably not in the plane of the section. 



In 30 W, and during the summer in most other regions except between the Falkland 

 Islands and South Georgia, the surface water appears to flow northwards as well as the 

 deeper water; both currents sink together in the region where the warm deep water 

 makes its steep ascent, and there is a sharp convergence between the Antarctic and 

 sub-Antarctic waters at the surface. Between the Falkland Islands and South Georgia, 

 however, the southward movement at the surface causes the sub-Antarctic water to 

 flow southwards over the main body of the Antarctic water, and prevents the formation 

 of such a sharp convergence. 



In section 3 the mean temperature of the first 50 m. of water at Sts. 1026-9 was 4-62, 

 3"53> 2 '34> ar >d 1 "28° C. ; the surface water at St. 1029 is almost certain to be Antarctic 

 water flowing northwards, and at St. 1026 sub-Antarctic water flowing southwards: the 

 boundary between the two currents probably lies between Sts. 1027 and 1028, but it is 

 not well defined. The temperature and salinity distribution shows that part of the 

 Antarctic current sinks below the warmer sub-Antarctic water, but this convergence 

 at the surface seems to be a very small affair compared with that which is formed at a 

 deeper level where the main body of the Antarctic water sinks. It has, however, been 

 called the Antarctic convergence, since it is the boundary between the Antarctic and 

 sub-Antarctic waters at the surface. In section 3 it is not a well-defined boundary, but 



