i84 DISCOVERY REPORTS 



increasing plankton yield in Table XIII. The correlation between poor plankton (plant 

 and animal) and poor phosphate, and rich plankton and rich phosphate presumably 

 illustrates the restrictive law of population. ^ 



Table XIII. Correlation between volume of plankton and concentration of phosphate 



STATION NUUBERS-WS6I2 

 MILES FROM COAST_ I 50 



W5GI8 W56I5W56I3 

 KVS6I9 W5620 WS6I7|WSGI6|WS6I4 



I 



Rich= >8o mg., Medium = 40-80 mg., Poor= <40 mg. P2O5 per cubic metre. 



In reviewing the phosphate concentrations on these lines, no reference has yet been 

 made to the minor irregularities such as occur off Cape Carranza, Antofagasta and San 

 Juan, where patches of phosphate reduced to a medium value may be met at or near the 

 surface layers in the midst of higher concentrations ; nor to the fact that rich as may be 

 the phosphates at the surface in the upwelling region they are usually less rich than those 

 in lower layers. The possibility of relating 

 this reduction to the activity of phyto- 

 plankton may now be considered. 



Off Cape Carranza two patches of dense 

 phytoplankton were met : one was situated 

 at 5-15 miles from the coast, the other 

 offshore from 35 to 85 miles, and neither 

 at first sight shows a direct relation to the 

 amount of phosphate in the surface layer 

 and to the patch of medium phosphate 

 illustrated in Fig. 54. We may endeavour, 

 however, to measure the reduction of 

 surface phosphates by comparing these 

 values with those in deeper water, say at 

 100 m. In this comparison the mean of 

 the values at o and 20 m. may be expressed 

 as a percentage of the mean of the values 



^ The low values of phytoplankton off the 

 Guanape Islands and the Lobos Islands may be 

 due to over-cropping of the animal plankton, here 

 in its highest concentration. 



z 2D0- 



SGUNDING IN METRES_ 5861 



3031 I7G6 1132 



Fig. 56. Distribution of phosphate (per m.^). Section 

 off Caldera, June 4-6. Corresponding sections of 

 temperature and salinity are illustrated on p. 142. 



