THE BENGUELA CURRENT 



By T. John Hart and Ronald I. Currie 

 (Text-figs. 1-96) 



INTRODUCTION 



When the National Institute of Oceanography took over the ships of the 'Discovery Investiga- 

 tions' in 1949 one of the first objects was to round off some of the work done in the southern 

 hemisphere by the older organization. That research had included a survey of the Peru coastal 

 current, carried out by the R.R.S. 'William Scoresby' in 1931. The late E. R. Gunther, who was in 

 charge of the scientific work at sea, published a valuable report on the results of that survey, which 

 clearly demonstrated the need for further research in such areas. Other duties prevented further 

 work on the data collected from the Peru current prior to the war, and since then much work has 

 been done there by scientists from other countries. The smaller analogous region off South-west 

 Africa on the other hand has received less attention. The 'William Scoresby', however, was recom- 

 missioned in 1950 for a voyage to South Africa and the Indian Ocean, and accordingly our new 

 programme, planned in outline by Dr N. A. Mackintosh, allowed for a hydrological and plankton 

 survey of the Benguela current, at first in February-March, and (after subsequent alterations to the 

 ship's programme) again in September-October. There were thus two surveys, the first in the autumn 

 and the second in the spring. They were carried out on similar lines, but within the limits imposed by 

 other items in the programme, of which whale-marking was the most important. 



In this report, which aims at providing a general interpretation of the observations made during 

 these two surveys, we apply the name ' Benguela current ' to the region of cool upwelled coastal water 

 along the South-west coast of Africa. This water, characterized by a pronounced negative surface 

 temperature anomaly is found mainly between 15 S. and 34 S., and within 100 sea-miles of the 

 coast. Thus it forms only the eastern periphery of the anticyclonic gyral of the South Atlantic, and 

 the adjacent circulation of warmer subtropical water to the westward is excluded. The latter we prefer 

 to speak of as the South-east Trade Wind Drift. 1 This choice of nomenclature, avoiding the applica- 

 tion of the name Benguela current to the whole northward flowing limb of the gyral, has arisen from 

 evidence brought together both by Defant (1936) and in the present report, indicating that two 

 distinct current systems are involved, very much as Gunther (19360) found in the Peru current. 

 Moreover, the name ' Benguela current ' is very generally associated with the cold water, so that we 

 hope our restriction of the use of this name to the coastal element will not be misleading, and that it 

 may eventually become generally accepted. 



The Benguela current, then, is one of those regions off the western coasts of the continents, where, 

 through the action of the prevailing winds, the effect of the earth's rotation, etc., the cool, nutrient- 

 rich subsurface waters well up to the surface. An intense production of phytoplankton throughout 

 most of the year is promoted thereby, resulting in an abundance of marine life of all kinds. 



The rich life of the sea in this region is in striking contrast to the desert or semi-desert conditions 

 that prevail in the adjacent land areas. The cool water along the coast condenses the moisture from 

 the sea-breezes blowing towards the land, in much the same way as if a mountain range intervened, 

 and the coast lying to leeward, in the rain-shadow, as it were, becomes arid and desolate. 



1 Hydrographic Department, 1939. 



