A REPORT ON OCEANOGRAPHICAL 



INVESTIGATIONS IN THE PERU 



COASTAL CURRENT 



By E. R. Gunther, m.a. 



(Plates XIV-XVI; Text-figs. 1-71) 



INTRODUCTION 



THE name Peru Coastal Current has been used to denote that part of the South 

 Pacific anticyclonic circulation in which northerly current is most conspicuous ; and 

 whose physical, chemical and biological characteristics are most aflFected by admixture 

 with water upwelled from the lower layers. 



This report is the outcome of a survey carried out in 193 1 by the R.R.S. 'William 

 Scoresby ' ; it endeavours to bring together in a general description the salient features 

 of the region as a whole, as they appear from a preliminary examination of the data, and 

 to summarize the literature likely to be useful to those later engaged upon the prepara- 

 tion of more detailed reports. 



The first two sections are introductory ; the body of the report is mainly occupied 

 with an analysis of facts ; while hypotheses by which they may be explained are con- 

 sidered among the conclusions on the results obtained. 



The Peru Coastal Current, sometimes called Humboldt's Current, represents a narrow 

 belt of cold water which runs up the west coast of South America roughly from Valparaiso 

 to the Gulf of Guayaquil, the boundary of Peru and Ecuador. The current varies in 

 strength, ships having to reckon seriously with it at some times and in some places, 

 whereas at others it is so weak as to be unnoticed. The waters are generally cooler 

 than those of the adjoining Pacific and are often coloured green, khaki, brown, orange, 

 and even red, by a wealth of marine life which gives rise in the south to a whaling 

 industry and in the north to the richest bird population in the world and its com- 

 mercially valuable deposits of guano (Plates XV and XVI). The interest of the current 

 lies in the problems presented by its phenomena under normal and abnormal conditions 

 and in their underlying causes, in its connection with the Chilean and Peruvian 

 littoral, with the existence of saltpetre beds, and in its effects on the economic life of 

 the inhabitants. 



In his Naturalist's Voyage round the World Darwin (1845, p. 47) has summarized the 

 features of the continent of South America in the following words : 



In the southern part of the continent, where the western gales, charged with moisture from the 

 Pacific, prevail, every island on the broken west coast, from lat. 38° to the extreme point of Tierra 

 del Fuego, is densely covered by impenetrable forest. On the eastern side of the Cordillera, over the 

 same extent of latitude, where a blue sky and a fine climate prove that the atmosphere has been 

 deprived of its moisture by passing over the mountains, the arid plains of Patagonia support a most 

 scanty vegetation. In the more northern parts of the continent, within the limits of the constant 

 south-eastern trade wind, the eastern side is ornamented by magnificent forests; whilst the western 



^0M fl936 



