SUB-ANTARCTIC WATER: SURFACE CURRENT 51 



Additional evidence of the existence of a greater northward movement of sub- 

 Antarctic water during the summer months is furnished by the records of the occurrence 

 of drifting icebergs. In the ordinary track of vessels the greatest number has been 

 sighted in the months November-January, and the least in June and July. The relative 

 frequency during the two periods being about 13 to 1 (Admiralty Chart, No. 1241, 

 1910). 



The sub-Antarctic water is also made to flow north or south in certain localities where 

 the general current towards the east is deflected by the effect of land masses and sub- 

 marine ridges. 



Although the influence of each of the factors which act on the surface water cannot as 

 yet be judged with certainty they may reasonably be supposed to lead mainly to a 

 movement slightly north of east in agreement with the conclusion drawn from the 

 current charts, ice charts, and temperature and salinity data. 



In the Drake Passage there is a strong surface current, part of the West Wind Drift, 

 flowing from the Pacific Ocean to the Atlantic Ocean. The current observations and the 

 temperature and salinity data from this region suggest that the current flows through 

 the passage at an increased rate, owing to the main drift across the Pacific Ocean being 

 compressed into comparatively narrow limits ; sometimes it attains a rate of as much as 

 40 miles a day. The current appears to be particularly strong in the neighbourhood of 

 Cape Horn, where it is supplemented by a stream of poorly saline and slightly -.warmer 

 water from the coastal region west of Tierra-del-Fuego and Chile (see Figs. 6 and 7, 

 pp. 26, 27). 



At the eastern end of the Drake Passage the current bends sharply to the north and 

 branches into two streams. One flows northwards, passing east and west of the Falkland 

 Islands and along the Patagonian coast as far as the River Plate. This branch is known 

 generally as the Falkland current. The second and main branch flows first towards the 

 north-east and then almost due east across the Atlantic Ocean. Between this current and 

 the Falkland current there is a tongue of warmer and more saline water which marks 

 the southern extremity of the Brazil current (see Figs. 8, n, pp. 29, 45). Another 

 notable feature of the sub- Antarctic current east of the Falkland Islands is its tendency 

 to spread southwards for a short distance over the Antarctic water (see p. 33). 



In the Drake Passage the depth of the well-mixed surface stratum is generally about 

 100-150 m., being somewhat deeper in winter (Sts. 385-8, Station List, 1932), and 

 shallower in summer (Sts. WS 405-9, Station List, 1930). East of the Falkland Islands 

 the depth appears on the whole to be slightly less — about 60-80 m.— but at Sts. 

 WS 251-3 (ibid.), in winter, the water was almost uniform down to 150-200 m. In the 

 northern part of the zone, north-east of the Falkland Islands (Sts. 71 and 72, Station 

 List, 1929), there was a well-marked surface stratum with a depth of about 75 m. The 

 shallow water near the Falkland Islands and on the Patagonian shelf is in winter almost 

 completely mixed from surface to bottom, but in summer there is a warm and poorly 

 saline surface stratum which becomes more and more marked towards the north. 



East of the region between the Falkland Islands and South Georgia, as far as 0-10 E, 



7-2 



