SECT. 3] EASTERN BOUNDARY CURRENTS 271 



squares along the Peruvian coast from 4°S to 17°S (Wooster, 1960) showed a 

 marked seasonal change in surface temperature, with highest values in summer 

 and lowest in winter. There are too few oceanographic observations to permit 

 a study of the seasonal variations of upwelling, and the various reported up- 

 welling centers along the coast (Schott, 1931 ; Gunther, 1936) are too small to 

 be revealed by the five-degree scale of our analysis. Negative values of the 

 index south of 45°S are consistent with the distribution of surface isotherms 

 which at all seasons are either zonal or dip to the south near the coast (Meteoro- 

 logical Office, 1956). 



(Hi ) Benguela Current 



The seasonal variation of upwelling is described by Marchand (1953) who 

 says : 



"The influence of the Benguela Current on coastal upwelling increases in 

 summer while in winter it is decreased. This decrease occurs because in the 

 winter north to southwesterly winds [through west] tend to blow, and 

 northwesterly winds in particular have the effect of piling water up on the 

 west coast ; no upwelling takes place from this cause, and the inshore 

 countercurrent is increased but this does not induce upwelling . . . thus, 

 maximum salinity occurs in August [winter, Southern Hemisphere]. This 

 is to be expected as upwelling, which produces lower salinity in the upper 

 layers, is at a minimum in winter. Conversely, minimum salinity occurs in 

 the months of January and February. These are summer months with 

 high frequencies of southeasterly winds, and hence with considerable up- 

 welling of water of lower salinity." 



This picture of seasonal variation is generally consistent with that suggested 

 by the index. However, Hart and Currie (1960) report an interesting diversity 

 of opinion as to the seasons of maximum and minimum upwelling, quoting the 

 following authorities : 



Reference Max. upwelling Min. upwelling 



Schott (1902) August November 



Franz (1920) August February 



Bobzin (1922) October-December June 



Defant (1936) May-June December-January 



Another indication of time and space variation in the intensity of coastal 

 upwelling comes from Bohnecke's (1936) surface temperature anomaly charts 

 (with respect to five-degree zones of the Atlantic) for the months of January, 

 April, July and October (Fig. 14). These suggest that upwelling occurs through- 

 out the year, is most intense in summer and fall, and migrates northward from 

 summer to winter. 



