PERU CURRENT 



is reduced in width. A marked similarity or uniformity of temperature 

 exists from north to south. Temperature observations at Valparaiso 

 and Paita with a difference of latitude of 28° show a temperature 

 difference of less than 5° F. A comparison of temperatures between 

 places on the shore and those a short distance inland also reveal the 

 effect of the ocean on the climate. 



The morning mists are the product of the abrupt cooling of air 

 in contact with the sea at an hour when the land breeze still holds. 

 These mists, or Garuas as they are known locally, extend all along the 

 coast of Peru and northern Chile. The inability of the air to bring 

 rain is explained by a lack of evaporation from cool water to cool air 

 and also by the fact that the onshore breezes, which would be expected 

 to bring rain, are deflected upward by the coastal mountains but suf- 

 ficient change in temperature to cause condensation does not occur. 

 It is estimated that air in this area at 65° F. may be warmed 25° F. by 

 the land it is blown against. It would then take an ascent of nearly a 

 mile to cool the air 25° F. thus leaving it at the same temperature at 

 which it started and with no progress toward condensation. This 

 arid condition persists for decades, with an appearance of rain, but 

 no rain. It is amazing to encounter a pall of low cloud or an overcast 

 sky, with ports hidden in fog, but at the same time encountering ex- 

 treme evidences of aridity in the coastal areas. The coast appears 

 like a desert under a humid sky. The fog forms over the upwelling 

 stream of cold water and gathers on the seaward slopes of the coastal 

 hills. 



sea water. Groups of birds retreat or advance with a change of con- 

 ditions and areas are invaded by a different species. 



ZONE OF SUBDUED COASTAL MOUNTAINS 

 ZONE OF COASTAL TERRACES VVET SEAWARD DRY LANDWARD 



DRY UNDERNEATH FOG-BANK ASPECT ^ ASPECT 



>;~^, ^SERT ZONE^ 



FOG BANK, .2000 



GARUAS 



Morning garuas are produced by the abrupt cooling of air in contact with the 

 sea at an hour when the land breeze stilt holds. The air drifts landward with 

 the onshore wind and mist gathers on the seaward slopes of the coastal hills. 

 The garuas descend at night nearly to the surface and all but disappear dur- 

 ing the day, or they may extend indefinitely westward. 



The rain making conditions in this area are in such fine balance 

 that only a slight interference with the existing conditions might cause 

 a deluge that could lay the coast in ruins. Mud-walled houses and 

 sun-dried brick buildings would crumble in a heavy rain and the dry 

 alluvial valley lands would become mighty rivers. Fertile tracts 

 would be washed into the sea or be covered by sand. 



Fortunately these conditions are infrequent and take place only 

 in a small area along the north coast of Peru where tropical conditions 

 temporarily blanket the area during the seasonal invasion by the 

 countercurrent. 



MARINE LIFE 



The divisions controlling the distribution of animals in land areas 

 are mountains, deserts, broad rivers and other abrupt lines govern- 

 ing changes in temperature or rainfall. The ranges of fish and marine 

 invertebrates can likewise be correlated with the temperature and 

 chemical content of the sea water. Ocean birds, like land birds, are 

 bound in the same way to their own type of conditions, if not for their 

 whole life then for at least a part of it. Few sea birds can long survive 

 a marked change in sea temperatures and salinity. The unique and 

 limited areas of change in the oceans provide barriers and invisible 

 walls controlling bird existence. 



Water temperature appears to be the principal limiting factor 

 governing the distribution of sea birds. The control is bound up with 

 a long sequence of conditions related to temperature, rather than a 

 simple direct relationship. Temperature range is an important event 

 in the life cycle beginning with the phenomena of sunlight and photo- 

 synthesis and ending with the nature and quantity of organisms upon 

 which birds feed. Temperature is the most important factor of sea 

 water in relation to sea life. Salinity and density factors as controlled 

 by current and climate are only further complications in the relation- 

 ships. Studies of conditions at the north end of the Peru Current have 

 revealed some of the secrets in these relationships in which birds are 

 adjusted and respond quickly to periodic changes in the character of 



SEA-LIFE CIRCUIT 



The ultimate source of food for all marine life is the microscopic 

 plant life obtaining sustenance from the nutrient elements in the sea 

 water. Tissue thus built up then becomes food for small crustaceans 

 and certain fishes which are in turn consumed by birds and other ani- 

 mals. Microscopic plants number tens and hundreds of thousands 

 per quart of sea water. Existing principally within 50 fathoms of the 

 surface, the dead remains settle and decompose in the lightless depths. 

 The enriched water from the decomposition is then recirculated to the 

 surface and made available for further profuse development. 



Decomposition of animal and plant remains by bacteria brings 

 derivatives of the body substances to a soluble condition in water, 

 from which some may be removed for use by other advanced forms. 

 An ordinary circuit in this chain of events would be: diatom — cope- 

 pod — herring — cod (or bird) — bacterium — sea water — diatom. The 

 diatoms are one of the basic connecting links and surpass a thousand- 

 fold in bulk the productiveness of all other aquatic plants. They may 

 be likened to a pasture in the sea and, although available everywhere, 

 are most profuse in waters of low temperature. They are an abundant 

 source of food for all marine animals. 



Low temperatiu-e and low salinity, usually associated with the 

 southern oceans, create an abundance of life far in excess of that in 

 warm sea water. The food substances of ocean life such as carbonic 

 acid, nitrites and nitrates of calcium and magnesium, phosphates, 

 silica and other elements, all exist in very small quantities everywhere. 

 The living substances incessantly use up the elements. Sea water of 

 low temperature, being more favorable to a high gas content and 

 richer in mineral compounds, support a more abundant plankton 

 growth. Co-existing generations in these low temperature areas assist 

 in the creation of a more generous growth and aid in factors tending 

 toward a longer life span leading to complete development. 



Zones of distinctive conditions, each with a typical amplitude of 

 temperature, salinity, and condition for the support of plant and 

 animal life are defined geographically. These zones succeed one an- 

 other from polar latitudes and are named Antarctic, Sub-Antarctic, 

 Sub-Tropical, and Tropical. Hydrological circumstances within each 

 zone bear an interesting relationship to the distribution of sea birds. 

 The relationship of phosphate to plankton abundance, the distribu- 

 tion of plankton in general, and the color of sea water in relation to 

 the contained life, are indicated by the number of sea birds. 



Discontinuities of temperature and salinity in the open ocean 

 behave more or less as though separated by a wall and are the physi- 

 cal basis for the zones of convergence. Surface layers of water are 

 inhabited by organisms not characteristic of near-by zones. Parts of 

 these convergencies are shaped and stretched as though by pressure, 

 and although influenced by surface topography, these boundaries are 

 seldom controlled by relationship to latitude alone. Such a diversion 

 can be observed in the South Pacific where the Sub-Tropical conver- 

 gence shapes northward in the vicinity of latitude 30°S., longitude 



63 



