192 WATER MASSES AND CURRENTS OF THE OCEANS 



shift of the tropical rain belt to the south takes place. Thus, in March, 

 1925, the precipitation at Trujillo, in 8°S, amounted to 395 mm, as com- 

 pared to an average precipitation in March of the 8 preceding years of 

 only 4.4 mm. These terrific downpours naturally cause damaging floods 

 and erosion. In the 140 years from 1791 to 1931, 12 years were char- 

 acterized by excessive rainfall at Piura, in lat. 5°S, and 21 years by 

 moderate rainfall which were, however, greatly in excess of the average. 

 During the remaining nearly 100 years the rainfall was close to nil. A 

 greater development of El Nino is therefore not an uncommon phe- 

 nomenon, but on an average the catastrophic developments appear to 

 occur once in 12 years. The records reveal no periodicity, because the 

 interval between two disastrous years varies from 1 year to 34 years. 



The El Nino is not the only current that brings warm water to the 

 coast of Peru with subsequent destruction of the organisms near the coast. 

 High temperatures off the coast appear to be an annual occurrence 

 in the months of April to June in about lat. 9° to 12°S — that is, at and 

 to the north of Callao. These high temperatures are due, as was pointed 

 out by Gunther, to the greater development of the warm branch of the 

 northern swirl, and the water that approaches the coast is in this case 

 offshore oceanic surface water of high temperature and relatively high 

 salinity (p. 190). The disastrous effect on the marine organisms is very 

 much milder than that caused by the El Nino, but is otherwise similar 

 in character. It may lead to the killing of plankton and fish and to the 

 migration of guano birds, but is ordinarily observed mainly by a change 

 in the color of the coastal water and by development of hydrogen sulphide. 

 Locally, these changes are known by the name of ''aguaje," but this name 

 is also used synonymously with "Callao painter." The approach of the 

 oceanic water toward the coast is not accompanied by any disastrous 

 meteorological conditions. 



On leaving the coast, the waters of the Peru Current join the waters 

 of the South Equatorial Current, which flows all the way across the 

 Pacific toward the west, but is known only as far as surface conditions 

 are concerned. The subsurface data are inadequate for computation 

 of velocities and transports, and it is therefore not possible to give any 

 numerical values. Some features of this current will, however, be dealt 

 with when the currents of the equatorial regions of the Pacific are dis- 

 cussed, and it will be shown that the cold water along the Equator does not 

 represent a continuation of the Peru Coastal Current, but is due to a 

 divergence along the Equator within the South Equatorial Current. 



The other currents of the South Pacific Ocean are even less known, but 

 from the character of the water masses it appears that two current 

 systems exist whose nature may be revealed by future exploration. One 

 big gyral appears to be present in the eastern South Pacific, but in the 

 western South Pacific annual variations are so great that in many regions 



