194 DISCOVERY REPORTS 



by Raimondi (1891), Lavalle (1924) and Stiglich (1925) might be regarded as due to the 

 same cause and as evidence of the recurrent nature of these swirls. 



Clowes (1933) distinguishes between stationary whirls^ such as may be dependent 

 upon the topographic features of the sea-bottom, and whirls which are not stationary 

 such as the travelling disturbances that may be met with along a convergence. 



The evidence just reviewed suggests that the anticyclonic swirls off the Peruvian coast 

 have a stationary character. While this may be approximately true, data collected during 

 the survey point to the probability that the more northerly wedge was first converging 

 with the coast southwards of Callao, but later northwards of Callao. In this way it is 

 thought that the isolated patch of very warm water of 19-10' C. in Pisco Harbour 

 (Appendix IV) and the changes of temperature off Palominos Island (Fig. 51) and off 

 the Guafiape Islands might be explained (see pp. 208-9). Alterations in the size or 

 position of the swirl would bring about these changes; and as no direct connection with 

 the sea-bottom is apparent, an oscillation in the position of the swirl, possibly with 

 changes in the meteorological conditions, may be expected. 



It remains to refer to the easterly and southerly drift of the Prussian sloop ' Mentor ' 

 in 1823. Mentor's Gegen Drift, as it was distinguished by Berghaus on his chart of 

 1837, is marked as setting towards the Bight of Arica; but since it was recorded in 

 approximately 20° 13' S, 83° 07' W (Berghaus, 1842), which is at some considerable 

 distance from the Peruvian coast, its identity with the wedge met with during the pre- 

 sent survey must remain in doubt. 



Deep Current. Another current of importance proceeding towards the south is the 

 return current off Chile flowing between sub-Antarctic water and the Antarctic inter- 

 mediate water. Having a northerly origin, it is distinguished from these two by a 

 higher salinity, warmth and poor oxygen content: it seems to be derived from both 

 subtropical and sub-Antarctic water. The influence of the earth's rotation may 

 perhaps be seen in its convergence with the coast, and is, moreover, seen in Figs. 18, 

 20, 22, 24 and 45 to be a purely coastal phenomenon. This suggests that it may be, 

 like the extension northward of sub-Antarctic water, a mid-water current compensat- 

 ing for the water which is welling up. But whereas the sub-Antarctic water above 

 it is frequently to be found drawn to the surface, this return current, lying below, 

 was found to be welling up only at San Juan and Antofagasta, areas of exceptional 

 upwelling. 



The various current systems that are shown above to be an adjunct of the Peru Coastal 

 Current, probably each exert an important influence on the fauna and flora. The pos- 

 sible influence of the eddy is discussed on p. 220. The return current just described, 

 whose oxygen has been reduced by the rich life of the inshore waters, may be returning 

 organisms and their spores towards the south after they have been carried away north- 

 ward at the surface. The northward extension of sub-Antarctic water brings water rich 



1 Clowes (1933) refers to a gyratory movement in the Weddell Sea by the term "whirl". The present 

 writer has taken the term "swirl" from Tait (1930). 



