UPWELLING 20S 



The line off Cape Carranza was situated south of the Juan Fernandez Rise, the others 

 to the north. Comparison of the upper 300 m., within which the upwelHng zone Hes, 

 shows no essential difference between the conditions off Cape Carranza and those off 

 other localities. The suggestion (Murphy, 1923, p. 67) that the commencement of the 

 Coastal Current may be determined by the Juan Fernandez Rise cannot therefore be 

 entertained. 



In view of the interest attaching to the possible influence of any island group upon 

 up welling, a special investigation of the Lobos Islands was made (see pp. 131, 153 and 

 Fig. 12). A line of stations was run both to the leeward and the windward of the Lobos 

 de Afuera and the isotherms at all depths from both lines were compared. Isotherms 

 north-west of the islands (i.e. off their sheltered side) showed traces of upwelling in the 

 upper 150 m., the isotherms of 15°, 16° and 17° showing a distinct hump in the vicinity 

 of the rocks, whereas on the south side, the exposed side of the islands, the isotherms 

 showed no disturbance. Signs of upwelling were, however, scarcely detected at the 

 surface (see Figs. 30 and 12) ; in the latter, the isotherm of 18^ C. is seen to run between 

 the two archipelagoes, and since this direction is more or less parallel to the coast-line, 

 nothing unusual is shown. According to the data given by Murphy (1923), in January 

 1920 the isotherms of 19 and 20° C. close together took an almost identical direction. 



Evidence of upwelling is, however, given by phosphate in the upper 60 m. In Table 

 XIX the data are averaged in the upper and lower layers in each of four regions. 

 Sts. WS 690 and 691 on the one hand, and Sts. WS 696 and 695 on the other, are at 

 roughly similar distances from the coast, but the first are off the exposed (south and 

 south-east) and the second off the sheltered (north and north-west) shore of the islands. 

 At the former, phosphate values were intermediate between those at shoreward and 

 seaward stations — a normal condition. At the latter, phosphate was as high as closer 

 inshore where upwelling occurs. Thus phosphate was richer off the sheltered than off 

 the exposed shores of the islands. 



EFFECT OF WIND 



The facts collected during the present survey suggest that upwelling may be caused 

 both by local and by remote winds. Conclusions on the effect of local wind are drawn 

 in regions where a change in the wind was followed by changes in hydrological condi- 

 tions. Winds at a distance are also supposed to be a cause, since upwelling was found at 

 every locality examined and in meteorological and hydrological conditions which locally 

 looked the reverse of favourable to it. 



Schott (1931) has described the distribution of barometric pressure in its relation, on 

 the one hand, to a northerly current with upwelling, and, on the other, to a reversal of 

 the current with an invasion of the coast by hot equatorial water known as El Nino. 

 Under normal conditions the south-east trades blow northwards towards a region of 

 low pressure at the meteorological equator. In their passage along the Peruvian coast 

 they impart a dry climate and they give rise to the currents conducive to upwelling and 

 so are the cause of cool inshore temperatures. It frequently happens, however, that 



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