SECT. 3] 



EASTERN BOUNDARY CURRENTS 



255 



than those of comparable latitudes in the central region of the ocean. Season- 

 ally, additional cold water is introduced along the coast by upwelling (see 

 page 266), and, as a general rule, surface isotherms run more or less meridionally 

 along eastern coasts in contrast to their zonal configuration farther west 

 (Fig. 1). The manner in which the annual variation of surface temperature is 

 affected by coastal boundary processes is discussed on page 269. 



160° 140° 120° 100" 



(a 



(b) 



Fig. 



1. Average surface temperature (°C) for July. 



(a) Pacific adapted from Meteorological Office (1956); 



(b) Atlantic adapted from Bohnecko (1936). 



In some cases (California Current, Peru Current off Chile) the high latitudes 

 from which these currents flow are regions where precipitation exceeds evapora- 

 tion (see Dietrich and Kalle. 1957, fig. 73) so that surface waters are relatively 

 fresh. Evaporation and mixing downstream then tend to increase surface 

 salinity. In other cases (such as the Canary Current) evaporation exceeds 

 precipitation in the source region, and surface salinities are high. 



Average surface salinities of the various currents are as follows : 



California Current 

 Peru Current (off Peru) 

 Peru Current (off Chile) 

 Benguela Current 

 Canarv Current 



less than 33.0 to 34.0% n 



33.5 to 35.0 % 



less than 34.5 % 



less than 35.0 to 35.5 % 



less than 35.5 to 36.5 °4, 



