214 WATER MASSES AND CURRENTS OF THE OCEANS 



which are of lower saUnity. In a vertical section the deep water of 

 the South Atlantic Ocean is therefore characterized b}^ a salinity maxi- 

 mum, but, owing to mixing with the overlying and the underlying 

 water, the absolute value of the maximum salinity decreases toward the 

 south. 



The bottom water of antarctic origin is colder than the deep water, and 

 south of about latitude 20°S the Antarctic Intermediate Water is also 

 colder. In a vertical section the deep water therefore shows a tempera- 

 ture maximum and also a decreasing temperature to the south, owing to 

 admixture from above and from below. 



In the South Atlantic Ocean a large amount of water of antarctic 

 origin, bottom water or intermediate water, returns to the Antarctic after 

 having been mixed with the south-moving deep water. According to 

 the computations that were discussed on pp. 116, 186 the transport across 

 the Equator of North Atlantic Deep Water amounts to about 9 milHon 

 m^/sec, whereas between 20° and 30°S the corresponding transport 

 toward the south of deep water is about 18 million m^/sec. If these 

 figures are approximately correct, they indicate that 9 million m^ of 

 water of antarctic origin return toward the Antarctic every second. An 

 examination of the salinity in the South Atlantic Ocean at depths below 

 1600 m confirms this conclusion. At the Equator the average salinity 

 of the North Atlantic Deep Water between 2000 and 3500 m is approxi- 

 mately 34.93°/oo. If this water is mixed with an equal amount of 

 intermediate and bottom water of salinity approximately 34.7°/oo, the 

 salinity will decrease to 34.81°/oo, which approximates the salinity of 

 the deep water in latitude 40°S. Thus, the deep-water circulation of the 

 Atlantic appears to represent a superposition of two types of circulation : 

 (1) an exchange of water between the North Atlantic and the South 

 Atlantic Ocean that is of such a nature that North Atlantic Deep Water 

 flows south across the Equator, whereas Antarctic Bottom and Inter- 

 mediate Waters flow north, and (2) a circulation within the South 

 Atlantic Ocean, where large quantities of Antarctic Bottom and Inter- 

 mediate Water mix with the south-flowing deep water and return to the 

 Antarctic. The final result of these processes is that the deep water that 

 reaches the Antarctic Ocean from the north is diluted as compared to 

 the deep water of the North Atlantic and is of a lower temperature. It 

 is this water which contributes to the formation of the large body of 

 Antarctic Circumpolar Water flowing around the Antarctic Continent. 

 The circulation that has been described is present in the western part of 

 the South Atlantic Ocean, but in the eastern part it is impeded by the 

 Walfish ridge. 



In the Indian Ocean there is no large southward transport of deep 

 water across the Equator. The data in table 22 show that to the north 

 of the Equator the deep water contains an admixture of Red Sea Water, 



