i88 



DISCOVERY REPORTS 



this zone phytoplankton catches were small together suggest that this upwelling is of 

 very recent date. 



At Antofagasta, a patch of phytoplankton having a high concentration was crossed in 

 the area of cool upwelled water rich in phosphate 7-15 miles offshore. The three 

 observations in the phytoplankton patch (Sts. WS 625-627) show a decrease in phos- 

 phate from high to medium values, whereas at the same stations at 80-100 m. 

 phosphate values are high (Table XIV). In the poorer water offshore and in the poorer 

 water of the second Antofagasta line, no phytoplankton patches were recognized. 



In its relation to the distribution of phytoplankton, the percentage reduction in 

 surface phosphates off San Juan conforms with the conditions met with off Cape 

 Carranza and Antofagasta (Table XIV) except for an apparent reduction of 91 per cent 

 at Sts. WS 652-654 in the highly saline warm-water wedge where the phytoplankton was 

 negligible. The anomalous condition at these stations is explained if the water of the 

 wedge has an oceanic origin and unlike surface water closer inshore has not arrived, 

 recently at any rate, by upwelling. This suggestion receives some support from the 

 species composing the phytoplankton: for whereas the inshore stations were rich in 

 Chaetoceros, Thalassiosira and Rhizosolenia, at Sts. WS 652-654, these genera were 

 replaced by Planktoniella. 



In regard to the lines off northern Peru, we have unfortunately no phosphate data off 

 Callao and Punta Aguja where alone exceptional catches of phytoplankton were made. 

 Phytoplankton in the catches off 

 the Guanape Islands, Lobos Islands 

 and Capo Blanco was comparatively 

 poor, but the nets contained a con- 

 sistently rich zooplankton fauna. 



These results may be summarized 

 (Table XV and Fig. 62) by com- 

 bining the data off Cape Carranza, 

 Antofagasta and San Juan and 

 averaging the percentage figures ex- 

 pressing depletion for stations of 

 different phytoplankton concentra- 

 tion. The method and the results 

 are discussed on pp. 218-19. It will 

 have been noted that data from other 

 lines do not lend themselves to pre- 

 liminary treatment in respect of the 

 detailed or more intimate relation 

 between phytoplankton and phos- 

 phate, and that this is because either 

 the phytoplankton is poor and our measurements are not representative or the phosphate 

 data are incomplete. 



60/S 



§40% 



t- 

 u 



3 

 O 

 UJ 



< 



I 



lOOcc SOOcc 



PHYTOPLANKTON —SETTLED VOLUME 



300cc 



Fig. 62. Graph relating phosphate reduction to volume of 

 phytoplankton : off Cape Carranza, Antofagasta, and San Juan. 

 For explanation see text and Tables XIV and XV. 



