158 DISCOVERY REPORTS 



the counter-current is accessory to the cause of humid winds, tropical showers and its 

 own low salinity, while in the second, drying winds are the cause both of the coastal 

 deserts and the high saHnity of the Peru Current (see p. 229). 



Along the line of contact where the two currents converge, water movement gives rise 

 to extensive mixture. The triangular area of the Guayaquil-Galapagos-Panama region 

 is one of irregular currents and complex eddies. Water movements on a much vaster 

 scale result from variation in one or other of the controlling forces that lie outside this 

 province: thus failure of the trade wind or preponderance of the northerly will 

 cause a phenomenon like El Nifio. The boundary between hot and cold water possibly 

 affords a delicate indication of the balance between factors remote from the area itself. 



At the time of our visit the convergence of the cool Peru water and the warm water 

 from Ecuador, occurred off Capo Blanco : it followed an irregular S-shaped line within 

 50 miles of the coast, and here the isotherms lay close together. The convergence line 

 then pursued a north-west direction and was less defined (Figs. 16, 70 and 71). 



The sections across this region illustrate clearly the relation to one another of the 

 waters of different temperature (Figs. 36 and 39-41): that off Punta Aguja is typical of 

 sections south of this line in which cooler water is brought to the surface by upwelling. 

 The next section cuts across a tongue of hot water off Capo Blanco. The hot water was 

 scarcely 20 m. deep, lay over the cooler Peru Current and extended about 25 miles 

 from the coast; its temperature ranged from 19 to 22° C. The Peru Current beneath 

 sustained a local rise in temperature, but in other respects the section resembles 

 those already examined. Thus the 17° C. isotherm occurred at the surface although as 

 far out as 35 miles offshore beyond the hot-water tongue. A small patch of water of 

 19° C. at 55-65 miles from shore, like the hot-water tongue, was a sign that the northern 

 boundary of the Peru Current was near. 



Off Santa Elena, transformation of conditions was more complete. Hot water of 

 24-43° C. occupied the surface close inshore, and proceeding out to sea the temperature 

 fell instead of rising as it is wont to do off Chile and Peru (Figs. 29 and 30). At 50 miles 

 offshore the temperature was 23° C, a drop of 1-4° C, but the hot water probably 

 extends westwards a considerable distance before it comes into direct contact with the 

 cool Peru Current. Although this section is the converse of those we have been 

 describing, upwelling seemed not altogether absent ; it seemed to be held in check by a 

 thermocline at 20-56 m. In this layer the temperature dropped from 24 to 16° C, and 

 it is possible that such a layer of hot water might lie on the surface like a blanket and 

 effectually check vertical mixing even in conditions otherwise conducive to upwelling 

 (cf. conditions at Capo Blanco and conditions in the Gulf of Panama, p. 206). 



The surface temperature of the area just considered is illustrated in Fig. 34 in which the mean 

 changes in zones at varying distances from the shore can be traced from south to north. We have seen 

 in the preceding pages that wherever the warm-water wedge encroaches upon these zones the mean 

 temperature undergoes a sharp rise. This rise is shown in Fig. 34 by thickened Hues. The curves also 

 show the sudden increase in surface temperature as they leave the Peru Current and enter upon equa- 

 torial water in the Gulf of Guayaquil. They show too that the contrast is greatest close inshore when 

 they leave the upwelling region of Peru and enter the high temperatures off the Ecuador coast, 



