WARM DEEP LAYER Si 



The presence of a warm deep layer in the Antarctic region south of the Atlantic 

 Ocean was probably first noted by Powell as long ago as 1821, 1 but it was not until 1922 

 that Merz and Wust proved that the layer has its origin in a highly saline current com- 

 posed of water which sinks from the surface in the subtropical region of the North 

 Atlantic Ocean. 2 They showed that the current has its axis at a depth of about 2000 m. 

 in io° N and that it flows almost horizontally southwards as far as 40 S, where it 

 rises in a great slope almost to the surface. They called the current the North Atlantic 

 deep current (1922, pp. 22-3). 



In the Indian Ocean the observations of Schott (1902) in the ' Valdivia' and Brennecke 

 (1909) in the 'Planet' demonstrate the existence of a warm deep layer, but they are too 

 few to give a clear idea of its properties. Those made by Drygalski (1926) on board the 

 ' Gauss ' show that the warm layer has a high salinity, but the salinity measurements are 

 not accurate enough to give a reliable indication of the water movements in the layer. 

 Farther east, south of Australia, and in the Pacific Ocean the data are very scanty. There 

 are a few temperature series made by Captain Scott in the Ross Sea, 3 a few others made 

 in the Bellingshausen Sea during the cruise of the ' Belgica ' (Arctowski and Mill, 1908) 

 and a small number of temperature and salinity measurements made in the same region 

 on board the 'Pourquoi Pas?' (Rouch, 1913). More recently observations have been 

 made, principally in the Bellingshausen Sea, by the ' Discovery II ' and ' William 

 Scoresby ' but in the greater part of the Indian and Pacific sectors of the Southern 

 Ocean the data have so far been too few to allow the properties of the deep water to be 

 described, or to allow its origin to be determined with any certainty. 



At the surface in the Antarctic Zone the principal movement of Antarctic water is 

 towards the north ; in one or two regions, chiefly in the western part of the Indian Ocean, 

 east of the large cyclonic circulation over the Atlantic Antarctic basin, it may have a 

 small tendency towards the south, but it is evident that such movements can only be 

 small compared with the northward movement found elsewhere. It will also be shown 

 in the following section of the report that there is also a general movement away from 

 the Antarctic continent towards the north in the bottom layer, and since both the 

 surface and bottom currents are found in all sectors of the Southern Ocean they can 

 only exist if there is a compensating movement towards the south in the intermediate 

 deep water. 



The properties of the deep water are found to be identical with those which would 



1 See Marr, 1935, pp. 290-1. 



2 In their review of the theories which have been put forward as to the nature of the circulation 

 in the Atlantic Ocean, Merz and Wust (1922) point out that the current might have been described 

 sooner on the grounds of the observations made by H.M.S. 'Challenger' in 1873-6, but it was not 

 recognized by Buchanan (Tizard and others, 1885) and Buchan (1895), and the importance of the data 

 was for a time overlooked. The modern representation of the circulation owed its ultimate discovery 

 largely to the comprehensive series of observations made by Brennecke (1 921) on the voyage of the 

 'Deutschland' to the Weddell Sea in 1911-12. 



3 List of oceanic depths, Hydrographic Department, Admiralty, 1904 ; and Scott's Last Expedition, Smith, 

 Elder, and Co. London, 1913. 



