106 DISCOVERY REPORTS 



have a low oxygen content in the terminal region of the North Atlantic current. The 

 deep water at St. 1019 (section 1), north of the Scotia Arc and near the Falkland Islands, 

 had a salinity of 3475 °/ 00 ; it seems most likely to be North Atlantic water, and its 

 oxygen content at the level of maximum salinity was only 3-51 cc. per litre. The fact 

 that the oxygen content of the deep water increases both towards the south-west and 

 north-east from the eastern end of the passage is in accordance with the assumption 

 that the region is a terminal region between the Atlantic and Pacific deep currents. 



The deep water in the Scotia Sea appears to be a most comprehensive mixture of 

 waters, which can be traced back to the Atlantic, Indian and Pacific Oceans. It is 

 probably derived largely from the eastward movement in the Pacific Ocean and is there- 

 fore likely to contain Indian and Atlantic Ocean waters which have found their way more 

 than half round the Antarctic Continent towards the east, as well as the less saline water 

 which flows southwards in the Pacific Ocean. It also appears to contain Atlantic water 

 from a direct southward movement over the northern arm of the Scotia Arc, and in the 

 lower part of the layer, Weddell Sea deep water which has been formed from a westward 

 movement of Atlantic and Indian deep waters along the Antarctic slope. The com- 

 position of the less saline upper part of the layer is even less certain than that of the 

 deeper part, and the Atlantic and Pacific waters cannot as yet be distinguished. The 

 temperature sections indicate, however, that there must be a southward movement in 

 the layer to maintain the large temperature difference between the deep water and the 

 surface and bottom waters in the Antarctic Zone, and it seems likely that such a move- 

 ment will bring Atlantic water into the Scotia Sea. 



The observations made across the sub-Antarctic Zone in the Pacific Ocean suggest 

 that the volume of Antarctic intermediate water carried back towards the south in the 

 upper part of the warm deep current is exceptionally large; within a narrow zone 

 extending about 100 miles north of the convergence there is a well-defined temperature 

 inversion between the level of minimum salinity, where the sub-Antarctic water contains 

 the greatest percentage of Antarctic water, and the more saline deeper layer, where the 

 water which may be supposed to flow southwards. It is not, however, safe to assume 

 that all the water at the level of maximum temperature in the deep water north of the 

 convergence finds its way into the upper part of the warm deep layer in the Antarctic 

 Zone because it usually has too low a salinity (see p. 70) ; it appears to be part of a 

 southward eddy and is eventually returned to the north with the surface water which 

 sinks at the convergence. 



THE ANTARCTIC BOTTOM WATER 



According to the historical account given by Merz and Wiist (1922) the first observer 

 to prove the existence of the bottom current was A. von Humboldt in 18 14. He found 

 that the deep water below the equatorial region in the Atlantic Ocean was too cold to 

 have been formed at the surface during the winter, and concluded that there was a deep 

 current towards the equator from the polar regions. Since the time of Humboldt the 

 existence of such a current, having its origin in the Antarctic regions, has been de- 



