224 DISCOVERY REPORTS 



part of the ocean, is here subordinated to the overwhelming effect of local cooling. 

 It is to be noted that this trend of the isotherms parallel to the coast holds over the 

 entire region surveyed by the 'William Scoresby'. This means that the controlling 

 influence of the upwelled water covers an area extending into the ocean at least as far as 

 50-130 miles oflt Chile and 150-250 miles off Peru (Figs. 16 and 17). The length of any 

 line was terminated when the isotherms beneath the surface showed an almost horizontal 

 tendency. This was necessary on grounds of economy, but it cannot be regarded as 

 the limit of influence of the upwelling water, because our figure shows that surface 

 isotherms still run parallel to the coast. Moreover, the presence of a series of anti- 

 cyclonic eddies offshore, shows that coastal disturbances extend much farther. The 

 limit of influence is evidently outside the area investigated by the 'William Scoresby'. 



Schott and Schu's diagrams illustrating the mean annual disposition of surface iso- 

 therms in the Pacific lends support to this conception (Fig. 68). The isotherms run east 

 and west over the majority of the ocean, but on approach to the South American continent 

 they curve northwards until they run in a direction similar to those in Figs. 16 and 17. 

 The isotherms show the effect of the coastal influence at very much greater distances off 

 Peru than off Chile. Thus off southern Chile the isotherm of 13° C. shows distinct 

 northerly displacement in 40° S at a distance of about 300 miles off land (say in 80° W) ; 

 whereas off Peru the isotherm of 26° C. becomes displaced in 15° S at a distance of 

 3600-4000 miles off the coast, that is in mid-Pacific. Thus there is a gigantic wedge- 

 shaped area of ocean with its apex in the south and its base almost over the Equator, and 

 the temperatures over the whole of this area have the appearance of being depressed by 

 upwelled water off the coast, Fig. 68. In this cooling below the mean temperature of 

 waters in the eastern South Pacific it must not be overlooked, as pointed out by 

 Sverdrup (193 1), that water is being carried northwards from cooler latitudes (see 

 pp. 195-6). 



Although the influence of upwelled water may be carried westwards for great dis- 

 tances, and in the path of the South Equatorial Current indefinitely, the area which with 

 advantage can be looked upon as the Peru Coastal Current proper must be very much 

 smaller. 



Owing to the variability of the Peru Coastal Current, no exact boundary can be placed 

 between it and the Peru Oceanic Current. Not only are the zones occupied by 

 marked northerly current, upwelling, rich nutrient salts, guano birds, coloured water, 

 rich phytoplankton, rich zooplankton, cool water, etc., all of different breadths, but they 

 are ever variable. Thus the temperature charts published by the Deutsche Seewarte 

 show considerable variations in the position of isotherms from one season to another. 

 Moreover, as a result of its deflection the water drifts across the westward boundary 

 from the Coastal Current to the Oceanic Current. 



The agreed actual position of the western boundary will therefore be arbitrary. If 

 temperature is accepted as the criterion, one might be guided by the trend of the mean 

 annual isotherms. It is where they change direction and run north-east and south- 

 west that the western boundary of the Coastal Current might be placed. Using the chart 



