REVIEW OF THE MAIN FEATURES OF THE BENGUELA CURRENT 277 



the vicinity of Walvis Bay, and may only affect the northernmost guano islands. Other adverse 

 phenomena such as abnormal meteorological conditions may have a more general effect over the 

 whole region of the Benguela current. 



REVIEW OF THE MAIN FEATURES OF THE BENGUELA CURRENT 



The detailed description of the ' William Scoresby's ' observations has presented a large number of 

 facts and clearly, before advancing further, we must endeavour to bring these together to create a 

 picture of the current as a whole. 



Probably the most obvious feature of this, as of any other upwelling region, is the presence of water 

 at the sea-surface many degrees cooler and incomparably richer in life than that normally found in the 

 open ocean in the same latitude. On account of the temperature anomaly we find, as has been clearly 

 demonstrated by the two 'William Scoresby' surveys, that the surface isotherms are disposed more 

 or less meridionally in contrast to their latitudinal disposition over the greater width of the ocean. 

 This is paralleled in the salinity distribution, and combines with the distribution of many of the other 

 properties investigated in defining the entity of the Benguela current. 



Within this general scheme a more detailed picture emerges, and one of the first things to notice 

 is that nearly all of the physical, chemical and biological properties of the current exhibit discontinuity 

 or irregularity both in time and in space. The Benguela current consists of a series of anticyclonic 

 eddies, of interlocking tongues of cool and warmer water, of areas of rich and relatively poor phyto- 

 plankton, all of which merge into a complex pattern which is in a constant state of change or flux. 

 This quality of irregularity and instability is in fact one of the features which emphasize the discrete 

 character of this upwelling region. 



In the 'William Scoresby's' two surveys there was a great contrast in conditions, and we have 

 presented evidence to show that while in survey II, in spring (September-October), a state of active 

 upwelling was encountered, on survey I, in autumn (March), the current was, at least in part, in a 

 quiescent phase. One cannot be dogmatic about the criterion of normal conditions in such a region, 

 but as the Benguela current is usually looked upon as a region of upwelling, we feel that there is a 

 precedent for accepting conditions of active upwelling as being normal within the current and periods 

 of quiescence as abnormal. It is in this light that we shall proceed to summarize the facts already 

 presented and go on to consider the significance of upwelling in relation to the economy of the ocean 

 as a whole. 



Normal conditions 



We have remarked on the greater activity of upwelling on the September-October (second) survey 

 of the R.R.S. 'William Scoresby' and perhaps the first and most striking feature can be seen in the 

 chart of surface isotherms (Fig. yb). Here the low surface-temperatures inshore compared with those 

 in the oceanic water to the west, and the configuration of the isotherms, gives one the impression of 

 the cold water masses inshore driving actively out from the coast and thrusting out into the warmer 

 oceanic waters. 



This cool, low salinity water (Fig. 8 b) moving offshore, clearly does not originate uniformly along 

 the coast, but is produced in localized regions. In some cases these may be related to specific features 

 on the sea-bed (Fig. 4), but in general it seems more probable that the dominating effect is that of the 

 local winds in the particular areas. Our results have led us to deduce that while the trade wind far 

 out at sea maintains a tension on the coastal water masses, the local diurnal winds are probably mainly 

 responsible for producing an effective northwards along-shore or offshore drag on the sea-surface 

 and supplying the energy necessary to create these localized centres of upwelling. 



