upwelling 191 



Centres of upwelling 

 The recurrence of upwelling in particular localities has been demonstrated by Schott (1931) and 

 Gunther (1936) in the Peru current. In the Benguela current this question has not received so much 

 attention, but Copenhagen (1953) has suggested that seven such localities exist off the South-west 

 African coast. He goes on to correlate these centres with the bottom topography. The position of the 

 centres of upwelling is deduced from a comparison of the coastal temperature with the temperature 

 of an arbitrary latitudinal standard, taken by Copenhagen as the temperature 200 miles from the coast. 



Although the 'William Scoresby's' observations are insufficient to apply this method, it is note- 

 worthy that the areas of low surface-temperature (Fig. ya, b) were found in more or less the same 

 regions as those outlined by Copenhagen, that is to say: (1) Saldanha Bay to Orange river mouth; 

 (2) north and south of Luderitz Bay and extending to Walvis Bay on survey II; (3) Cape Frio to 

 Cunene river mouth. 



A closer examination of the charts, however, shows that the colder water in the vicinity of Orange 

 river mouth lay in 28 S. in survey I, while in survey II it was centred on 29 S. some 60 miles farther 

 south. It is noteworthy also that the 200 m. contour representing the edge of the continental shelf is 

 50 miles offshore in 28 S., but 90 miles offshore in 29 S. This area of cold water appeared to show no 

 particular correlation with the topography of the sea-bed. 



Probably the most that can be said from the present results is that the conditions on survey II, 

 which represent a characteristically active period of upwelling, show that upwelling was most pro- 

 nounced in the regions: (1) from 29 to 30 or 31 S. ; (2) from 28 S. to Luderitz Bay and northwards 

 to Walvis Bay; (3) possibly an additional area from Cape Frio to Cunene river mouth. To the south 

 of 30 S. we have insufficient data to allow any conclusions to be drawn. 



Influence of the direction of the coastline 

 The absence of any pronounced upwelling from Cape Frio southwards to 22° S. while it is present 

 both to the north and south of this area appears to be rather significant when the shape or direction 

 of the coastline is considered. North of Cape Frio, the coastline runs approximately north-south. 

 From Cape Frio to Walvis Bay its direction changes to about 330 to 150 and south of Walvis Bay 

 to about 352 to 174 . With a S.S.W. (202^°) wind, assuming that the drift is 45 to the left of the 

 wind direction, the resultant water-movement in the region between Cape Frio and Walvis Bay would 

 be in the direction 160 to 340 about io° onshore towards the coast. Clearly, therefore, along this 

 stretch of coastline the effect of the sea-breeze which is S.S.W. in this area would be to pile water 

 against the coast, rather than remove it and create upwelling. 



North of Cunene river mouth (17 S.) the coastline bends away gradually in an easterly direction. 

 This marks the northern boundary of the upwelling and it is possible that Schott's suggestion that the 

 replacement flow for water carried offshore by the wind can occur on the surface, without necessi- 

 tating the vertical circulation of upwelling along this stretch of coast. 



The southern boundary of the current which lies at the Cape of Good Hope may also be considered 

 to be an effect of the direction of coastline relative to the wind direction. 



Seasonal variation of upwelling 

 The observations made by the ' William Scoresby ' cannot alone be regarded as illustrative of seasonal 

 variation of the current. The overall lower temperatures and greater wind and upwelling during 

 survey II, while probably characteristic enough of winter conditions, could no doubt be found at 

 least to some extent at almost any time of the year in suitable meteorological conditions. It is, therefore, 



