172 A TEXTBOOK OF OCEANOGRAPHY 



From Table Bay northwards to the Congo estuary this cold 

 current runs with an average velocity of 12 miles per day, the 

 rare maxima being 30. 



Near the land the current is feeble and irregular, although 

 it is strong enough off the mouth of the Congo to drive the 

 river water north-west into the open ocean. Drift-wood from 

 the Congo is often found in the neighbourhood of St. Thomas 

 Island. 



As a result of the prevailing winds the cold Benguela 

 Current flows up along the West African coast to the Congo 

 estuary. 



There is thus also in the South Atlantic a circular system 

 of ocean currents running counter-clockwise. In the centre of 

 this system, between 20 and 35 S. Lat., is a zone of feeble 

 winds and currents with high barometric pressure, in this 

 respect resembling the Sargasso Sea. 



Deep- Water Currents of the Atlantic. Very little is known 

 of the currents in the deeper layers of the great oceans. 

 Vertical circulation of the ocean waters depends on three main 

 causes : 



(1) The pull of the winds on the surface waters resulting in 

 upwelling. 



(2) Differences in salinity between different layers of water. 



(3) Differences in temperature causing differences in 

 density. 



Schott in the Valdivia report gives a temperature profile 

 for the Atlantic Ocean (see Fig. 33) to a depth of 2,500 metres 

 (1,367 fathoms). It is seen that there is a marked influx at 

 depths of from 1,500 to 2,500 metres (820 to 1,370 fathoms) of 

 cold water of 3 C. and less from high southerly latitudes, and 

 this reaches as far as the Equator, and may even be traced to 

 20 N. Lat. 



Apparently there is a current from the north, which is 

 ascertainable in from 55 to 25 N. Lat. moving south. It is 

 well known that there is a mixture of Arctic and Atlantic water 

 at depths of 500 to 550 metres (273 to 300 fathoms) on the ridge 



