COLOUR OF THE SEA 173 



COLOUR OF THE CURRENT 



Buchanan (1910) has observed that surface water of the open ocean is to be referred 

 to one of three colour types, ultramarine, indigo and olive green, characteristic re- 

 spectively of tropical, temperate and polar regions. The colour of coastal waters is, of 

 course, modified by a variety of causes, and the commonly occurring green in the 

 Peru Current, like the olive green of the Antarctic, is attributable to an abundance of 

 diatoms. Since colour is an accepted characteristic of the Coastal Current, it is well 

 to consider how far our own observations uphold the records already made. 



In the neighbourhood of Chiloe, which should be classed as temperate, the water was 

 definitely green (Plate XVI, fig. i) at least as far as 60-70 miles from land, and continued 

 so well to the north of Cape Carranza. Farther up the coast in 25° S, the sea was bluer: 

 but it had a more greenish look at 6 miles from land where the temperature was low 

 (i4-20-i4-45°C.)^ than at 10 miles where the temperature was higher (16-79° C.) (Plate 

 XVI, figs. 2 and 3). But at Antofagasta conspicuous greenness of the water was note- 

 worthy (Plate XVI, fig. 4) : this persisted as far as 7 miles from shore and then seemed to 

 shade off slightly, but the onset of night prevented our recording the change into 

 ultramarine, the colour observed on the following day at 46 miles from land (Plate 

 XVI, fig. 5). A gradual change from green inshore to blue in the open ocean continued 

 the normal state until the arrival of the ship at Pisco, where water of an almost un- 

 believable bright salmon colour was found at midday : the vividness somewhat abated 

 after noon (Plate XVI, fig. 6). The plankton in this region included quantities of a 

 flagellate pigmented with red, and many of the other organisms such as the Foraminifera 

 and the smaller Crustacea had oil globules strongly coloured orange. We believe that the 

 explanation of colour in the sea water lies in these organisms, and it seems probable that 

 the altering of tone in the afternoon may be due in some measure to vertical migration. 

 The hydrology of the water is referred to on p. 216 and a possible connection with the 

 virazon is noted on pp. 210, 232 and 233. Large Medusae, which were noted at other 

 localities also, attracted attention at Pisco by blocking the ship's condenser intake; 

 their numbers made it impossible to keep the intake clear, and the engine-room 

 machinery was closed down until the moment of departure. Medusae were similarly 

 abundant at Sts. WS 712 and 713, where they choked the nets and prevented collection 

 of plankton samples. Their swarming on the borders of water having a high and low 

 temperature is noteworthy. 



At some 50 miles off San Juan streaks of a reddish discoloration were met with, they 

 were just under the surface of a grey sea and in the fading light of dusk had a brick red 

 and scum-like appearance.^ Individual organisms could not be distinguished in the sea, 

 but our nets took up an almost incredible quantity of Euphausian cyrtopias in the 

 course of 5-10 min., affording a parallel to the swarms of Euphmisia stiperba which 

 sometimes colour the Antarctic with patches varying from ochre to brick red. 



On passage from Pisco to Callao the ship encountered changes of colour for which it 

 is less easy to account. At a point 1 5 miles off the coast she entered a zone of brownish 



1 This record is not illustrated. 



9-2 



