204 DISCOVERY REPORTS 



these areas of cold water and the submerged valleys or other regions in which the depth 

 increases rapidly with increasing distance from the coast. For example, the cold areas 

 north of Point Dune are close to two submerged valleys as shown by the one hundred 

 and the five hundred meter contours." 



To ascertain the effect of the bottom topography off Peru and Chile, the sections 

 illustrated in Figs. 18-41 may be arranged according to the mean gradient of the 

 continental shelf which is assumed to end at the point where the slope suddenly be- 

 comes steeper. As will be seen from Table XVIII, little correlation can be made out 

 between this gradient and depression of surface temperature. 



The Chilean and Peruvian coasts are not directly comparable and have been listed 

 separately. Off Peru water is not only more homogeneous, but the shelf is much broader 

 than off Chile, and the area of shelf whose depth is less than two and a half times 

 Ekman's " Upper depth of frictional influence " (2-5 Z)') is more extensive off Peru than 

 off Chile. Off Peru, D' would work out at about 1 50 m. for homogeneous water, whereas 

 off Chile, owing to weaker wind and higher latitude, the depth would work out at about 

 70 m. 



On these grounds one might have expected the restraining influence of the coast 

 upon divergence of surface current to be less and upwelling to be greater off Chile than 

 off Peru : the fact that it does not appear to be so suggests that other factors are also of 

 importance. 



Conditions within a mile or two of the beach were not explored very thoroughly. 

 Although irregularities of the bottom contour might influence upwelling more here than 

 out to sea, the zone is probably too narrow to have far-reaching effects upon the current 

 as a whole. Moreover, upwelling in this zone was frequently interrupted by counter- 

 currents. The data collected on this survey afford no support to the suggestions of 

 Murphy (1925, p. 162) or McEwen (1912, p. 272). 



Table XVIII. Depression of inshore surface temperature at different localities arranged 

 according to the gradient of the sea bottom in the upwelling region 



* The depression of surface temperature off Capo Blanco has reference to a record of 16-84° C. at 31-35 

 miles offshore, the coolest temperature beyond the water of the Equatorial Counter-current. 



