212 DISCOVERY REPORTS 



different latitudes. It is well known that the deflecting force is a function of latitude, 

 is maximal at the poles and is zero at the equator. It may be a factor of considerable 

 importance contributing to the uniformity of hydrological conditions on the west coast. 



EFFECT OF SEICHE 



The eflFect of seiches in oceanic hydrology has been noted in the Bay of Bengal by 

 Sewell (1928) and in the North Atlantic by Helland-Hansen and Nansen (1926). The 

 possibility that the oscillation in the temperature of the upper layers of the sea at 

 Callao from June 26 to August 20, might be ascribed to a temperature seiche should be 

 considered.^ The data illustrated in Fig. 51 indicate that off Callao a peak maximum 

 temperature and a peak minimum temperature occurred on July 4-8 and August 4-8. 

 These peaks may represent respectively the trough and the crest of a subsurface oceanic 

 wave of cool water at the coast. 



According to these dates, the seiche would have a period of about two months. 

 Wedderburn (191 1) calculates that under certain stated conditions, a temperature seiche 

 in the Atlantic might have a period of 34 days. Hypothetical as this conclusion must be, 

 it does not seem inconsistent with the possibility admitted by our data that in the 

 Pacific a seiche might have a period of double this length. The period of a seiche in so 

 small a basin as the Bay of Bengal was observed to lie between 17 and 19 days (Sewell, 

 p. 168), whereas the North Atlantic seiche showed indications of being diurnal (Harvey, 

 1928). Thus the possibilities are wide. 



Unfortunately observations have not been made during other maxima and minima 

 before and after these dates, and they are therefore insufficient to show periodicity 

 which is an essential feature of the seiche. Such a seiche, if it existed in the South 

 Pacific, would have a decided influence upon upwelling ; on the crest, subsurface water 

 would be closer to the surface and relatively weak forces would be able to bring cool 

 water and abundant nutrient salts to the surface, whereas on the trough, wind and 

 current of considerable magnitude would have comparatively little effect on this water. 

 On pp. 208-9 ^^^ '"is^ ^^ temperature off the Guanape Islands on July 10 and 1 1 has been 

 attributed to change of wind: seiche is probably not operating here, because Fig. 51 

 shows that during this date, if a seiche were working, the temperature would be falling. 

 Until some knowledge has been obtained on seiche action in the Pacific, the full effects 

 on upwelling of the separate factors outlined in the foregoing pages cannot properly be 

 understood. 



SPEED OF UPWELLING 



No calculations have been made to indicate the rate at which water may well up, but 

 the apparent quick response of the temperature at and below the surface to changes of 

 wind supports Schott's view that a speed of 15 m. a month as suggested by McEwen 

 (1929, p. 259) is far too slow. Rate of change in hydrological conditions is also con- 

 sidered on p. 213. 



1 I am indebted to Lt.-Col. R. B. Seymour Sewell for this suggestion. 



