ANTARCTIC SURFACE WATER: WEST WIND DRIFT 25 



separation of the two waters suggests that their usual northward and southward 

 movements are almost entirely restricted. 



The strait is the only outlet towards the east for water which occupies a much wider 

 zone in the Pacific Ocean. Antarctic water is deflected northwards west of Graham 

 Land into the southern side of the strait, and sub-Antarctic water is deflected south- 

 wards west of Tierra-del-Fuego into the northern side. Such a large volume of water 

 being forced through the strait will of itself cause a predominance of the lengthwise 

 movement. 



The distribution of temperature and salinity in the surface layer (Figs. 6 and 7) 

 shows that on the southern side of the passage there is a current from the Bellingshausen 

 Sea ; at the end of winter it is made apparent by a stream of pack-ice which moves north- 

 east, generally making the South Shetland Islands unapproachable until October or 

 November. As it enters the Scotia Sea the current is joined by water which flows 

 northwards out of the Weddell Sea, and vertical sections made across the two currents 

 suggest that between them there is a convergence region in which the colder Weddell 

 Sea water sinks below the lighter Bellingshausen Sea water. 



Compared with the Antarctic convergence, that between the Weddell Sea and 

 Bellingshausen Sea currents is only of secondary importance, and it does not give rise 

 to such a well-marked boundary at the surface. In section 3 (Plate IV), the convergence 

 is indicated by a rise in surface temperature of 1-5° C. between Sts. 103 1 and 1030. 

 Farther north, particularly at St. 1029, the cold stratum of the surface layer may contain 

 a large proportion of Weddell Sea water, whilst the warm surface stratum belongs 

 to the Bellingshausen Sea current. The low temperature and high oxygen content of 

 the deep water at St. 1031 are evident indications of the existence of a convergence 

 region in which the surface water sinks and mixes with the deep water, and the salinity 

 distribution points to the same conclusion. 



The temperature and salinity distribution in section 4 (Plate VI) show that there 

 is a similar convergence region between the Weddell Sea and Bellingshausen Sea currents 

 north-west of Zavodovski Island, the northernmost of the South Sandwich group. The 

 convergence lies between Sts. 1051 and 1052; it is marked by an increase of i° C. in 

 the mean temperature of the first 100 m. of water, and by a small sinking of the iso- 

 therms and isohalines. The temperature distribution again suggests that Weddell Sea 

 water sinks into the lower stratum, below a surface stratum of Bellingshausen Sea 



water. 



East of the Scotia Sea, as far as the longitude of Bouvet Island, there are still signs of 

 a convergence between the two currents. Section 5 in 22 W shows that there is a 

 marked increase of temperature in 55 S between Sts. 804 and 801 (Plate VII) which 

 probably indicates the position of the convergence. On a voyage from Cape Town to 

 Bouvet Island in October 1930 the ' Discovery II ' crossed the Antarctic convergence in 

 48 35' S ; from this point as far as 51 20' S the surface temperature decreased gradually 

 from 2-5 to 1-5° C, but during the next 60 miles it fell more rapidly to - i°C. The 

 first ice (a growler) was sighted in 51 20' S, and during the remainder of the voyage 



