144 



DISCOVERY REPORTS 



undergoing alteration before reversal of the wind : secondly, after the wind had changed 

 to a north-easterly direction and to force 2, the ship continued to drift in its face to 

 the north-eastward (from Sts. WS 630 to 632). If wind direction alone were to be 

 considered these facts would argue against the wind being a controlling factor; but 

 the strength of the wind is equally important, and the conditions here probably 

 illustrate its influence exceptionally well. 



Fig. 28. Changes in wind and in the distribution of surface isotherms off Antofagasta in the period June 8-10, 

 1931. The sequence of events described in the text may be traced by following the track of the ship (thin 

 line in direction of thin arrows) from Punta Tetas. The position of stations on this line is shown by dots 

 (cf. Fig. 9). Isotherms are indicated by heavy lines, wind direction and force by broad arrows. The dotted 

 lines show the shift of the isotherms of 15, 16 and 17° C. ; the isotherm of 14° C. had disappeared when the 

 site occupied by it on June 8 was revisited on June 10 (see Table III, and compare with Figs. 24-27). 



Comparison of Figs. 26 and 27 shows far more active upwelling and far more cold 

 water at the surface in section 26 of the outward journey than in 27 on the return. The 

 wind data show a similar contrast of strong southerly and easterly winds on the west- 

 ward journey and weak northerly winds during the return (Fig. 28). While the subse- 

 quent rise in surface temperature with change of wind might have been brought about 

 by mixture of the upwelled with off'shore water, the evidence of the ship's drift raises 

 another possibility. We may picture the lighter warm surface water driven away from 

 the coast as a result of these strong southerly and easterly winds acting in conjunction 



