DEEP CURRENTS: PACIFIC OCEAN 105 



The deep-water transport between the Pacific and Atlantic Oceans is also likely to be 

 restricted by the narrowness of the passage between the continental shelves of South 

 America and Antarctica: in section 1, between Elephant Island and the Burdwood 

 Bank, the deep channel is not more than 360 miles wide. The further progress of the 

 eastward current is also likely to be hindered by the Scotia Arc, the well-defined sub- 

 marine connection between the Andes of South America and the mountains of Graham 

 Land through South Georgia, the South Sandwich Islands and the South Orkney 

 Islands (Herdman, 1932, pp. 214-19, andWilckens, 1933, pp. 320-35). The deep water of 

 the Scotia Sea is probably, as Wiist (1926) suggests, largely of Pacific origin; but owing 

 to the great similarity between the deep waters found in the eastern part of the Pacific 

 Ocean and the terminal region of the North Atlantic deep current, the composition 

 of the deep water in the boundary region between the two oceans cannot as yet be 

 determined with any certainty. 



The salinity measurements made up to the present (see Fig. 19) show that the deep 

 water in the middle part of the western end of the Drake Passage generally has a low 

 salinity, less than 3472 °/ 00 , and although the salinity is greater along the northern and 

 southern sides of the passage it seems likely that no large volume of water with a salinity 

 of as much as 34-74 °/ o0 flows eastwards from the Pacific Ocean to the Atlantic. There 

 is, however, a large area at the eastern end of the passage, from 50 to 54 S in 50-60 W 

 and extending 4-5 farther south in 57-59 W, in which the deep water has a salinity 

 of 3474-3475 7 00 > an d tne existence of such an area suggests that the deep layer at the 

 eastern end of the strait contains some North Atlantic deep water. Such a possibility 

 is strengthened by the fact that the water has a potential temperature 0-25-0-5° C. 

 higher than that of the highly saline water at the western end of the strait. The con- 

 clusion that Atlantic deep water approaches as far as the eastern end of the passage is, 

 however, put forward with some hesitation, since it is based on small temperature and 

 salinity differences. The conclusion is also based largely on data which have been col- 

 lected over a large number of years with no allowance for seasonal and annual changes, 

 but it is nevertheless justified on the grounds of the data illustrated in sections 17, 18, 19, 

 and 1 , which were obtained for the most part within the space of a few weeks. The 

 maximum salinity of the deep layer in section 18 across the western end of the passage 

 varied between 34-72 and 34-74 °/ 00 , with a potential temperature of 0-8-1-5° C., whilst 

 that in section 1 across the eastern end varied between 34-74 and 34-75 °/ 00 with a 

 potential temperature of 1-2-1-9° C. 



The observations made at the eastern end of the Drake Passage show that the deep 

 water has a smaller oxygen content than it has at the western end (see Fig. 21) ; the most 

 saline water in section 1 had an oxygen content of 3-5-4-1 cc. per litre, whilst that in 

 section 18 had as much as 3-8-4-3 cc. per litre. Since the deep water in the Atlantic 

 Ocean has been found to have a much higher oxygen content where its salinity was high 

 enough to show that it must be of North Atlantic origin (cf. St. 1055, section 4, 2000m.), 

 the low oxygen content at the eastern end of the Drake Passage seems to point to the 

 absence of Atlantic water. It may, however, be supposed that the Atlantic water will 



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