THE DISTRIBUTION OF DISCOLORED WATER 



occur by a change in current direction. This may also be 

 seasonal, as it is in cases of El Nino and Aquaje, off the 

 Peruvian coast. 



Before discussing these currents, it would be well to de- 

 cribe briefly the normal currents and temperature distribution 

 off the west coast of Peru from Pisco north to the Gulf of 

 Guayaquil. 



The Peru current, also known as the Humboldt current, 

 which moves from south to north, is a northerly branch of the 

 Pacific Antarctic Drift and is particularly noted for its sus- 

 tained low temperatures (mean annual temperature close to the 

 shore line of central Peru is 10 to 11° C. lower than the 

 theoretical value for that latitude). This low temperature 

 extends from a point somewhere south of 45° S. to Punta Arina, 

 4° 40' S., and is caused by the upwelling of the deeper waters. 

 Along the northern coast of Peru, the current normally swings 

 to the west and converges with the Equatorial Counter Current 

 running East. The line of convergence marked by a "tide 

 rip," runs along irregularly from Punta Aguja to the Galapagos 

 Islands. The Counter Equatorial Current, which normally turns 

 northward along the coasts of Ecuador, Colombia and Central 

 America, seasonally swings to the south during January-March, 

 bringing a counter current of warm water down the coast of 

 Peru, displacing the ordinarily cold water of the Peru Coastal 

 Current. This influx of warm water may reach as far soutli as 

 Salaverry, 8°13'S., and even occasionally Pisco. The drastic 

 temperature reversal causes widespread mortality of littoral 

 invertebrates, fish and even guano birds. The disturbance to 

 Ihe planktonic life commonly results in extensive discoloration. 



A similar current change ocurring farther south during the 

 months of April through June is called Aquaje. High tempera- 

 tures appear off the coast of Peru between the latitudes 9° and 

 12°S., caused by the movement inshore of the outlying oceanic 



Destruction of fish by the "Red Tide" off the Gulf Coast. 



waters of high temperature and relatively high salinity. As is 

 true of El Nino, the surface waters are usually colored blood 

 red. 



Polar waters are often discolored in spring because of the 

 abundance of winter-accumulated nutrients. 



These are regular occurrences whose causes are clearly 

 marked. Discoloration however, can occur locally and un- 

 expectedly even in mid-ocean. Here the causes are obscure. 

 Some meteorological quirk or unusual temperature change may 

 bring it about. In coastal waters, even the addition of trace 

 elements brought down with river runoffs has been considered a 

 possible cause. Thus it would seem that regularity of en- 

 vironmental cycles brings about a regularity in occurrences of 



WORLD DISTRIBUTION 



OF 

 DISCOLORED WATER 





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