UPWELLING AND SUBSI DENCE— ANTOFAGASTA 



145 



with the deflecting force of the earth's rotation, and so drawing up to the surface a mass 

 of heavy cold water from below. It becomes a system charged with potential energy.^ 

 We may imagine the ship taking observations on the outward journey at the height of 

 this process, and that her drift was in the path of the deflected waters. But as soon as 

 the wind force relaxes from force 5 to 3-2, as it did after St. WS 629, the deflecting 

 force and so the pull of the warm offshore water is also relaxed, the cool inshore waters 

 subside, and eventually the former warm surface waters flow back, and we have the 

 conditions met on the return journey. In this way the north-easterly drift of the ship 

 from Sts. WS 630-632 on her return journey, might indicate the influence of the 

 returning waters. The displacement of the surface isotherms with the changing wind 

 conditions is illustrated in Table II. The first section (Fig. 26) may illustrate upwelling 

 and the second (Fig. 27) subsidence." The question is discussed further on pp. 206, 

 208 and 213. 



Table III. Change in position of surface isotherms ojf Antofagasta 



With a change in the wind from south to nortii, the isotherms of 15, 16 and 17'' C. shifted towards 

 the shore. 



In the Bight of Arica it was interesting that a strong inshore current and upwelling 

 should occur in the absence of any wind. The weather was calm and the high tempera- 

 ture of 19-1 ' C. was found unexpectedly close to the coast, a well-marked thermocline 

 existing close to the surface. The absence of any sign of an earlier disturbance suggests 

 that upwelling was probably at its height. The possibility that these high tempera- 

 tures were related to a wedge of warm highly saline water off Peru is suggested in Figs. 

 16 and 17, and that they might have been due to a counter-current is discussed on 

 pp. 192-3. 



1 Sandstrom uses the term "Archimedean forces". 



^ The possible influence of the land contour upon the extent of upwelling and consequently upon the 

 amount of cold water to be found inshore, and the possibility that the water mass off Baia Herradura is of 

 different origin to that off Punta Tetas should not be lost sight of ; they are discussed on p. 208. 



