CAUSES OF DISCOLORATION 221 



Although a similar effect might not be expected in the larger anticyclonic swirls, the 

 high temperature of the warm wedge checking perhaps the range of vertical migration, 

 yet an eddy of this type seems to have interesting consequences on the plankton (see 

 pp. 229-33). Attention might also be drawn to the identical observations made by UUoa 

 (Juan and Ulloa, 1748) and Smith (1899), of a patch of green water off the Island of 

 Santa Maria in southern Chile, but in the absence of further data, this is a coincidence 

 which must remain a matter of record. 



COLOUR OF THE CURRENT 



The various colours of the water described on pp. 173-5 ^^^ illustrated in Plate XVI, 

 at first seeming to lack orderly arrangement may be grouped into three classes : 



1. The three basal colour types, to one or other of which all oceanic water may be 

 referred. As shown by Buchanan these are either blue, indigo or green. They have 

 transparency. 



2. Opaque colours occurring near land and at other centres of exceptional phyto- 

 plankton production such as in the polar regions. They are presumably referable to 

 animal or terrigenous origins ; they are usually reddish, muddy or chalky, and often 

 occur in patches of a few hundred yards or a few miles in extent. Intermediate browns, 

 ochres, khaki, etc., might be produced either as the result of abnormal conditions (see 

 below) or by admixture of i and 2. 



3. Colours of holophytic organisms such as Trichodesmium, colonial Radiolaria and 

 flagellates. They are straw-coloured, orange or red, and they, apparently, may occur at 

 any distance from land : these also occur in swarms. 



The normal colour distribution in the eastern South Pacific may be said to consist of 

 a coastal zone of green modified locally by varying concentrations of the colours of 

 classes 2 and 3, and this is flanked in the open ocean by indigo in the temperate and 

 ultramarine in the tropical regions. Indigo and blue being basal colour types in these 

 latitudes, are not understood as being colours peculiar to the Peru Coastal Current. 



While the green colour of the current is evidently attributable to phytoplankton, and 

 while aberrant colours when due to the swarming of holophytic organisms can usually 

 be identified by the predominance of a particular species, so far our knowledge of the 

 nature of the colours of class 2 comes mainly from indirect evidence. 



Near Callao, for example, no specific organism seemed to be associated particularly 

 with the rusty coloured patch; and zooplankton was no more abundant here, at the 

 Guafiape Islands, or at Pisco, where the more unusual discolorations were met with 

 (Plate XVI, figs. 6, 7 and 11), than at other localities where the water was green. 

 Moreover, the great majority of zooplanktonic organisms not only in temperate, but in 

 polar regions, are known to make diurnal migrations, seeking the less illumined layers 

 during the hours of daylight (Russell, 1927, 1928, 1931; Hardy and Gunther, 1935). 

 It is improbable therefore that in normal conditions the colour of the sea surface is much 

 affected by the animal constituents of the plankton. The brick red swarm of euphausian 



15-2 



