UPWELLING AND DISTANT WIND 211 



Thus the presence of a coast should have a restraining effect on the influence of the 

 earth's rotation. Our results off Antofagasta and the Guafiape Islands suggested that 

 the surface layers diverged from the coast under the influence of a wind parallel to it, 

 both over deep and shallow water: the restraining influence of the coast on the influence 

 of the earth's rotation must then have been partly overcome. The actual conditions in the 

 Peru Current differ from those employed in Ekman's type problems, and to this may 

 be due the apparent lack of agreement. If a current induced by aspiration is at all com- 

 parable with a current induced by wind, the inshore coastal current at Arica may be 

 expected to diverge, and on this account upwelling may be accentuated. 



Summarizing these conclusions, the current at the Guafiape Islands and especially 

 the strong coastal current in the absence of local wind at Arica are regarded as having 

 been produced through aspiration of the surface layers, by wind and wind drift outside 

 these regions. That such coastal current may induce upwelling is suggested by the 

 analogous behaviour of wind-induced current off Antofagasta and the Guanape Islands. 



The universality of upwelling off both Chile and Peru is evidence that westerly set of 

 the surface layers in the ocean at large is widespread. That such westerly set inshore 

 must be induced by aspiration as a result of winds and oceanic drift remote from the 

 coastal region is inferred by reference to the conditions at Pichidanque Bay and Callao, 

 and from the fact that winds are stronger and more easterly in the open ocean. At these 

 localities upwelling could be due to no other cause since no surface current was 

 observable. 



That the degree of upwelling showed a considerable uniformity over the whole coast 

 suggests that this indirect effect of distant wind may outweigh in importance the local 

 winds having a direct action. This may indeed be a principle operating along the length of 

 the west coast, and so to speak guarantees a minimal quantity of cool water close inshore 

 even under the most diverse local conditions. Upwelling would be greatly augmented 

 by local southerly wind and northerly current, but perhaps never altogether suppressed 

 by local contrary wind and counter-current. Thus the effect of swirls and eddies would 

 merely be to retard organic production in one place and to accelerate it in another. 



EFFECT OF LATITUDE 



Wind and current are stronger and more regular on the coasts of Peru than on the 

 coasts of Chile. There is, moreover, a greater difference between the densities of the 

 water at the surface and the water at the upwelling depth off Chile than there is off 

 Peru;^ so that off Chile more force is presumably required to cause upwelling. Yet up- 

 welling is not so very much more vigorous off Peru, and it certainly does not seem 

 commensurate with the stronger wind, the current and more uniform density ; and there 

 are probably other factors whose influence have yet to be considered. One of these may 

 be the greater area of shallow water and greater area of the current included in the 

 upper depth of frictional influence in Peruvian than in Chilean waters (see p. 204). 

 Another factor may be the effect produced on a current by the earth's rotation in 



1 Density, together with other physical and chemical data, will be published in due course in the Discovery 

 Reports. 



Dxiii 14 



