134 DISCOVERY REPORTS 



TEMPERATURE 



Figs. 1 6 and 17 show that surface isotherms are generally parallel to the coast, thereby 

 emphasizing the contrast between inshore and offshore temperatures : the temperature 

 off southern Chile is less than off northern Peru, and isotherms consequently slant 

 gradually towards the coast. If we sail out to sea across the current we find that the 

 temperature of the water rises as the distance from land increases, and at 50-100 miles 

 or more it is higher by 1-5°. During the present survey this rise varied at every point 

 along the coast as shown by the irregularity of the curves in Figs. 29 and 30, and the 

 positions of isotherms vary greatly at different times and in different localities. 



Off the Peruvian coast lay a wedge of warmer water, whose temperature was higher 

 than that of adjoining waters east and west. It shows as a dome-shaped hump in the 

 graphs of surface temperature (Fig. 30) for the Lobos Islands, the Guanape Islands, 

 Callao, San Juan, and possibly also for Arica (Fig. 29) ; off San Juan, off Callao in 

 July, and off Callao in August, this warmer water had a breadth of about 50 miles at 

 distances offshore of respectively 100-150, 25-75, and 10-60 miles (p. 148 et sqq.). On 

 these lines the observations extend beyond the warm water to cool temperatures, but 

 the Guanape Islands line terminated before the warm water was crossed. The warm- 

 water wedge lies therefore on the edge of the area examined, and the observations may 

 be too few fully to determine its character. In Fig. 16 the available data are con- 

 toured as straightforwardly as possible. An alternative if not more attractive theory 

 is discussed on p. 192. 



The difference between the temperature of the warm- water wedge and that of adjoining 

 oceanic water to the west was small but never indistinguishable between the parallels of 

 17 and 6° S, from June 22 to August 20. Off San Juan this warmer water seemed dif- 

 ferent from the cooler surrounding water, and its fauna contained species such as 

 flying fish which were never found in the cooler waters. Here also the wedge appeared 

 to differ in its movement (see p. 129). In the northern part of the region the wedge was 

 relatively less warm than surrounding water but could still be recognized. Its distance 

 from the shore may be placed at 50 miles off the Guafiape Islands, 140 miles from the 

 Lobos Islands, and 180 miles off Punta Aguja. Its western margin in these latitudes was 

 ragged, irregular and ill-defined, and its nature as a distinct body of water less well 

 established. Off Punta Aguja its western margin (the isotherm of 20° C.) left the area 

 of our investigations. 



The northern boundary of the Peru Current off Capo Blanco is clearly discernible, 

 the surface temperature showing a reversal of the conditions found farther south. Off 

 Capo Blanco the hottest water lay near the coast, but in the space of 22 miles the surface 

 temperature dropped to the level formerly found inshore off Punta Aguja. The Peru 

 Current, hitherto coastal, seems to have swoing out to sea, and cutting across the line of 

 stations off Capo Blanco seems to have been pursuing a west-north-westerly course 

 towards the Galapagos Islands; inshore a tongue of hot water projected southwards 

 from the Gulf of Guayaquil. 



