HYDROLOGY OF THE SOUTH ATLANTIC 229 



are regions where there is greater mixing of the warm deep layer with Antarctic surface 

 and bottom waters. 



Although the isotherms do not show the direction of movement of the warm deep 

 water, they show the relative strength of the deep and bottom movements. When the 

 strength of the bottom current towards the north or north-west increases, or when the 

 strength of the warm deep current towards the south-east decreases, the isotherms 

 recede towards the north. When there is a stronger flow of warm deep water, or a lesser 

 flow of cold bottom water they advance towards the south. 



In an investigation of the origin of the deep water in the Falkland Sector the problem 

 is complicated by the presence of a cold deep current flowing out of the Weddell Sea. 

 It has been shown by Wiist in 5° E, by Brennecke in 30° W, and by ourselves in 

 I5°E, 15° W and 20° W, that south of about 66° S the temperature in the warm deep layer 

 increases towards the south, and it is now almost certain that north of this warmer deep 

 water there is a continuous belt of colder water stretching from the Weddell Sea to I5°E. 

 East of is" E, however, warm deep water gets far south without interruption, and the 

 warm deep current in the Atlantic south of 66° S has its origin east of 15° E. It flows 

 westwards as a result of the prevailing easterly winds south of 66° S, and Wiist has 

 pointed out that this is proved by its decrease in temperature towards the west. As it 

 flows round the Weddell Sea in a cyclonic movement similar to that which takes place 

 at the surface the deep current is cooled by vertical mixing. 



There is, however, always a warm deep layer in the Weddell Sea (except perhaps very 

 close inshore in the west of the sea) : the temperature always increases below the 

 Antarctic surface layer to a maximum in this deep water before it decreases to a 

 minimum value at the bottom. By the time it flows out of the northern side of the 

 sea the deep water has only a maximum temperature of about 0-40° C. or less, and 

 as soon as it meets warm deep waters of Pacific and Atlantic origin it both sinks 

 below them and mixes with them. It is then perhaps best described as a cold deep 

 current. 



The cold deep current from the Weddell Sea follows the bottom current. Part of it 

 flows eastwards across the Atlantic Ocean; part of it flows north across the Scotia Sea, 

 or round the outside of the Scotia Arc, and sinks below the warm deep water north of 

 South Georgia. The cold deep current is partly responsible for the sudden climb of 

 the warm deep layer north of South Georgia, and also for the sudden difl'erences in 

 temperature and salinity in deep levels south of 40° S, north of South Georgia. Its 

 effect on the deep temperature distribution in the east of the Scotia Sea and north-east 

 of South Georgia is shown in Fig. 24. 



As mentioned above, Brennecke and Wiist have shown that the warm deep water of 

 Atlantic origin is formed in the sub-tropical region of the North Atlantic. It sinks 

 below the surface in the convergence region between the Canary current, the North 

 Equatorial current, and the Gulf Stream. It is also mixed with the last traces of Antarctic 

 intermediate water from the same region, and in the east with water from the Mediter- 

 ranean Sea (Wust, 1928, p. 522). As it flows southwards it mixes with Antarctic inter- 



