1 90 WATER MASSES AND CURRENTS OF THE OCEANS 



Owing to the width of the current and the small transport, its velocities 

 are quite small. This must be true particularly in the case of the Peru 

 Oceanic Current, which, however, is little known. Within the better 

 known Peru Coastal Current the upwelling represents a very conspicuous 

 feature. The upwelling is caused by the southerly and south-southeast 

 winds that prevail along the coasts of Chile and Peru and carry the warm 

 and light surface waters away from the coast, resulting in cold water being 

 drawn from moderate depths (40 to 300 m) toward the surface. 



According to Schott and to Gunther, the most active upwelling 

 occurs in certain regions separated by regions in which the upwelling is 

 less intense. Both authors recognize four such regions between lat. 3°S 

 and 33°S, but they do not agree on the extent of the different regions, 

 probably because the regions are not absolutely fixed or because the 

 locations ascribed to the different regions may depend upon the available 

 data. Gunther has particularly examined the two northern regions, 

 where the most intense upwelling occurs in 5°S and 15°S, respectively, 

 and has shown that the surface temperatures in the winter of 1931 (June 

 to August) indicate the existence of two tongues of warm water that 

 approach the coast to the south of the regions of intense upwelling. The 

 upwelled water, on the other hand, leaves the coast as tongues of cold 

 water, and thus the distribution of surface temperatures shows alternate 

 tongues of warm and cold water. Schott's analysis and other observa- 

 tions indicate that the locations of these tongues do not vary much from 

 one year to another, and the tongues must therefore be either permanent 

 or recurrent. Gunther interprets these tongues as demonstrating the 

 existence of swirls off the coast, assuming that within one branch of the 

 swirl upwelled water moves out and that within another branch oceanic 

 water moves toward the coast. 



In early winter, April to June, the shoreward-directed branch of the 

 northern swirl is well developed and carries water of high temperature in 

 toward the coast in latitudes 9° to 12°S. It may even appear as an 

 inshore warm current that brings great destruction to the animal life 

 of the coastal waters. In the discussion of the California Current, it will 

 be shown that this current is similarly characterized by a series of swirls 

 on the coastal side of the current, and that in November to February, 

 when there is practically no upwelling, a warm countercurrent flows to 

 the north along the coast. 



At the northern boundary of the Peru Coastal Current, certain char- 

 acteristic seasonal changes take place. During the northern summer 

 the Peru Coastal Current extends just beyond the Equator, where it con- 

 verges with the Equatorial Countercurrent, the waters of which in summer 

 turn mainly toward the north. In winter the countercurrent is displaced 

 further to the south, and part of the warm but low-salinity water of the 

 countercurrent turns south along the coast of Ecuador, crossing the 



