HYDROLOGY OF THE SOUTH ATLANTIC 227 



In any series of vertical observations made inside the Antarctic Zone it will be seen 

 that the temperature either remains constant or decreases with depth down to the level 

 of the cold stratum of the Antarctic surface layer. Below this level it increases to a 

 maximum in the warm deep water, and then it decreases again, down to the sea-bottom. 

 If there were no current southwards in the warm deep layer, the maximum temperature 

 of the warm deep water would soon disappear as a result of vertical mixing between the 

 water in the layer and the colder waters above and below it. 



There can be no doubt then that the water at the level of maximum temperature in 

 the Antarctic Zone has a component of movement southwards. The way in which the 

 warm deep layer feeds the surface layer has already been described in the first section 

 of this report, and it will be shown later that it also gives rise to Antarctic bottom water. 

 The origin of the warm deep water in the Antarctic Zone can best be decided from sec- 

 tions which show the vertical distribution of temperature and salinity . 



In both the sections shown on Plate VIII it appears that the water in the warm deep 

 layer south of 50° S has its origin in the North Atlantic deep current, which climbs rapidly 

 towards the surface at the Antarctic convergence. It must, however, be remembered 

 that the deep currents may have zonal as well as meridional movements : a deep current 

 from the Pacific Ocean, in which the water is very similar to that in the North Atlantic 

 deep current, will not be distinguished in the sections. None the less the sections show 

 that the warm deep layer in the Antarctic Zone is continuous with the warm deep layer 

 below the sub- Antarctic and Antarctic intermediate waters, even ahhough the warm 

 deep water in the continuous layer is not all of the same origin. 



Clowes (1933) has shown that the warm deep water south of 46° S in 30" W has its 

 origin in the Pacific Ocean. Further work shows that most of the Pacific deep water is 

 probably stopped at the Scotia Arc, and also that in 40° S between the observations in 

 30' W and those of the ' Deutschland' in 50° W, there is a strong movement of North 

 Atlantic deep water southwards. The conclusion that the water south of 46° S had its 

 origin in the Pacific Ocean was based partly on the differences of salinity and tempera- 

 ture at St. 666 and 671. These differences are alternatively explained by the slope of the 

 warm deep layer and the greater reduction of the layer at St. 666 by vertical mixing. 

 So great is the similarity between North Atlantic and Pacific deep water that there is 

 as yet no very reliable evidence to show the origin of the warm deep water just north of 

 the Scotia Arc. The temperature at its level of maximum salinity is greater than the 

 temperature of the water of maximum salinity in the Pacific Ocean, and at the same time 

 the maximum salinity itself is greater. The water north of the Scotia Arc must therefore 

 contain additions from the Atlantic Ocean. The warm deep water in the Scotia Sea 

 probably has a Pacific origin, but this in my opinion is as yet uncertam. 



Fig. 24 shows the temperature of the warm deep layer in the Falkland Sector. It 

 has been constructed by plotting the maximum temperature which has been found in 

 the layer, and not the temperature at any particular depth. The diagram does not 

 necessarily show direction of movement, but there is usually a component of movement 

 from warm to cold regions and not from cold to warm. Regions of low temperature 



