ZOOGEOGRAPHY 213 



(c) South Atlantic Central Water 1 is much warmer and more saline than Sub- Antarctic Surface 

 Water. Its surface temperature increases from approximately 11-5° C. in winter and 14-5° C. in 

 summer just north of the Sub-Tropical Convergence to 23 C. at the Tropical Convergence, under 

 which it sinks along a line of discontinuity marked by the 23 ° C. isotherm. Its surface salinity 

 maximum is 36%,,. The maximum depth of South Atlantic Central Water is rarely more than 500 m. 

 and is marked by a line of discontinuity with the Antarctic Intermediate layer, where the temperature 

 is about 10-5° C. and the salinity varies between 34-85 to 35 % . 



Table 13. Stations adjacent to the Sub-Tropical Convergence 



Station Temperature Salinity 



The general movement of South Atlantic Central Water is southwards under the influence of the 

 prevailing northerly winds. This is particularly marked in the western part of the South Atlantic 

 where the water flows in the Brazil current. The water is deflected eastwards when the region of the 

 West Winds is reached, and here its direction of flow is similar to that of the Sub-Antarctic Surface 

 Water, but owing to their very different properties the two types of water remain distinct to a large 

 extent. There is some evidence that part of the South Atlantic Central Water ' is possibly deflected 

 southwards near the Cape of Good Hope to mix with water which turns back from the Agulhas 

 current in an easterly direction across the Indian Ocean' (Deacon, 1937, p. 74). 



The 23 C. surface isotherm on the line between the Cape Verde Islands and the Falkland Islands 

 is situated between Sts. 710 and 711, and on the 30 W. Line between Sts. 677 and 678. Between 

 Cape Town and the Cape Verde Islands hydrological readings were not made at all stations, and in 

 Text-fig. 1 and all the distribution charts of species in this report, the position of the 23 ° C. isotherm 

 from the 'Meteor' results (Bohnecke, 1936) has been used to indicate the location of the Tropical 

 Convergence in the eastern Atlantic. 



(d) Tropical Surface Water rarely exceeds 145 m. in depth. It has a temperature range of 23 ° to 

 29 C. from south to north, and a salinity maximum of 37 % . As noted above, it forms a marked 



1 The term 'South Atlantic Central Water', is taken from Sverdrup, Johnson and Fleming (1946); it is synonymous with 

 Deacon's (1933) Sub-Tropical Surface Water and Sub-Tropical Under Water. 



