692 



C. SKOTTSBERG 



Instead of running parallel with the latitude, the isotherms, when approach- 

 ino- the continent, are deflected NE — N and run almost parallel to the coast. 

 The reason for this apparent anomaly is the upwelling of cold subsurface water 

 from a depth of up to 400 m, due to the deviation of the surface current. 

 The reader is referred to ScilOTT's handbook, p. 310, and to GUNTHER's memoir, 

 from which the following passage may be quoted (p. 113 — 114). »The currents 

 under discussion » — the Mentor Current and the Peruvian Cold Current — 

 »cover the area we recognize to-day as the eastern limb of the South Pacific 

 anticyclonic gyratory movement. In the following pages it is shown that the 

 surface water close against the South American coast is hydrologically different 

 from water which may also share northerly movement hundreds of miles out to 

 sea, and consequently provides a distinct biological environment. There is, 

 however, no sharp boundary between the two waters, the one merging gradually 

 into the other. Moreover, from the dynamic standpoint it appears that the 

 movement of both waters is actuated by similar principles, only in the one the 

 presence of the coast induces upwelling and other modifications. In view of 

 the emphatic difference in the character of the inshore and offshore components, 

 it is desirable to draw a distinction between the two. The cool surface water 

 close against the South American coast will be termed the Peru Coastal Current: 

 and for contrast the adjacent oceanic drift which, lying to the west of this, 

 also seems to share northerly movement, the name Peru Oceanic Current is 

 suggested. As, however, both currents compose the limb of the anticyclonic 

 circulation, and as no sharp boundary exists between them, they may justly be 

 referred to by the name of Peru Current.* 



On pp. 222 — 228 GUNTllER discusses the boundaries of the Coastal Current. 

 The effect of upwelling is that »the water inshore is some 2 — 5° cooler than 

 the outermost of the observations on the same parallel, with the consequence 

 that isotherms run in the same direction as the coast but converge with it 

 slightly towards the lower latitudes* (p. 223). The differences are by no means 

 confined to temperature. A condensation of cloud, lessened illumination, a con- 

 stant supply of nutrient salts and for this reason an increase in the amount of 

 plankton, also a difterence in colour, are characteristic of the inshore upwell- 

 ing region. 



The approximate western boundary of the Coastal Current lies, in Lat. 

 10° S 1000, in 20° 900, in 30° 180 and in 40° o miles from the coast, all ac- 

 cording to GUNTllER, who fixes the limit where the isotherms change direction 

 and start to run SW — Nt^. Even if the influence of upwelling water is felt to 

 the west of this limit, it is evident that the Juan Fernandez Islands are situated 

 about 180 miles west of it, in the Peru Oceanic Current. It shares the general 

 northerly movement. PLATE (1. c. p. 227) remarks that at Juan Fernandez a 

 weak current running SW and S is noticed. He regards it as a counter-current. 

 He tells that, during a calm 230 miles east of Masatierra (130 miles from Val- 

 paraiso), his ship drifted south, and he concluded that he was still outside the 

 Humboldt Current in Bergiiaus' sense (= Peru Coastal Current), that is outside 

 the inshore upwelling region. Its width decreases rather rapidly towards the 



