SALINITY 163 



CALDERA 



The sub-Antarctic water and the highly saUne return current are easily recognized in 

 Fig. 22. The observations off Caldera were only just south of the subtropical con- 

 vergence, and the latter's influence is reflected in the surface salinity offshore which now 

 has a value of almost 34-50 °l^^. It is therefore higher offshore than inshore; a con- 

 dition characteristic of the greater part of the Peru Coastal Current. As a result of up- 

 welling the saline return current is drawn to within 40 m. of the surface ; but if upwelling 

 had been more active, the return current might have been drawn to the surface and the 

 inshore waters would then have had the higher salinity. 



ANTOFAGASTA 



The rise of the highly saline return current to the surface suggests that Fig. 24 

 illustrates upwelling of unusual strength, yet the salinity offshore (St. WS 629) con- 

 tinues to be the higher; this is because the subtropical convergence was crossed in 

 approximately lat. 24-26° S, and the outermost of the stations on this line lay on its 

 northern edge. The sub-Antarctic water, formerly at the surface, is now below the 

 subtropical water but apparently still flowing towards the north; below it the return 

 current flows south. Figs. 23, 26 and 27 show that the temperature of the return current 

 off Antofagasta and Caldera is distinctly higher than water of the open ocean. 



If the inferences drawn on p. 142-5 are correct, the two sections illustrating salinity 

 off Antofagasta indicate first such upwelling that the highly saline return current has 

 been drawn to the surface inshore, and second that it has subsided beneath. In reaching 

 the surface, the return current has mixed with the sub-Antarctic water, with the resuh 

 that their salinities are modified; nevertheless the layers are clearly distinguishable. 

 Within the return current, salinity is in its highest concentration close to the coast, and 

 this distribution accords closely with the distribution of the layer off Cape Carranza 

 where upwelling had also been vigorous, and supports the suggestion that the layer is 

 restricted to the coastal region (cf. conditions off San Juan, p. 164). This is discussed 



further on p. 200. 



ARICA 



At Arica the return current did not reach the surface, but the arrangement of 

 water layers is seen (Fig. 43) to resemble that of other sections. The sub- Antarctic 

 water now having values of > 34-50 7oo is at the surface inshore, while subtropical 

 surface water now reaches values of > 3 5-00 %„. 



SAN JUAN 

 The concentration of surface salinity at San Juan is such that the sub-Antarctic water 

 is becoming obliterated but is recognizable at 60-120 m. (Fig. 45). For 60 miles 

 the inshore surface waters were occupied by the highly saline return current ; beyond 

 this came still more highly saline subtropical water. In this lay a wedge of even more 

 saline water (> 35-25 %„) which may be identified with the warm-water wedge (see 



