238 DISCOVERY REPORTS 



DEPTH AFFECTED BY UPWELLING 



The trend of isotherms and isohahnes below the surface is shown to be influenced 

 not only by upwelling water but by the structure of the compensating currents. The 

 determination of the depth from which upwelling takes place is confused by this second 

 factor. A minimum value of 40 m., a mean of 133 m., and a maximum of 360 m. are 

 suggested (pp. 200-1). 



ORGANIC PRODUCTION 



An attempt is made to ascertain the major effects of these hydrological processes on the 

 life of the region. Areas of exceptional upwelling are first shown to be exceptionally rich 

 in nutrient salts (p. 180, and Figs. 54, 57 and 58) ; and then to have a high phytoplankton 

 and zooplankton content (Table XIII). A new method of demonstrating the consump- 

 tion of nutrient salts by the phytoplankton is tentatively considered (pp. 184-9). The 

 results are shown to be in accord with what is known of the cycle of organic production 

 in other parts of the world : and they have been used to infer the conditions in the area 

 at periods earlier than the date of our visit (pp. 135, 186, 188, 201, 220). 



Regional fertility 



The permanence of upwelling centres suggests that these are perennially more fertile 

 than other parts of the coast : this and the paucity of phytoplankton in the warm wedges 

 and at their points of convergence with the coast (Callao and Arica, Appendix I), suggest 

 that the fertility of a locality is bound up with the position relative to it of the anti- 

 cyclonic swirls. At the same time the unfailing appearance of upwelling, even at such 

 localities of convergence, suggests that all localities are potentially fertile (pp. 211 and 219). 



COLOUR OF THE CURRENT 



The average bulk of phytoplankton varied at different distances from the shore in a 

 way suggesting that the area has not been adequately sampled. Nevertheless there were 

 signs that on average the yield is no heavier in the upwelling zone than at distances up 

 to 100 miles from the coast (Table XI, pp. 178-9). The green colour of the current, 

 on the other hand, was seldom found to extend beyond 30 miles from the shore. A 

 hypothetical explanation is advanced which relates the green colour to the zone where 

 illumination is lessened by cloud (p. 222). 



Discoloration 

 Discoloration due to colours of purely animal nature appear to be rare. Between 

 Sts. WS 656 and 657 such a patch of brick red was discovered, due to a swarm of 

 euphausian cyrtopias. The yellow off Punta Aguja and the salmon colour at Pisco were 

 attributable to vegetable pigments, the former algal (of a symbiotic colonial radiolarian), 

 the latter directly or indirectly flagellate (pp. 174 and 173). 



