66 



Pamela G. Jenkins 



March, due to sinking. The thermoclines for the year were found on September 22nd, 

 1952, 15 m, 14-6° C; April 27th, 1953, 15 m, 12-5" C; June 22nd, 20 m, 13-0° C; 

 August 10th, 15 m, 17-2° C. 



In both 1951 and 1952 the autumn maximum (Fig. 5) was in September, the 

 amounts being respectively 0-59 and 1 -02 g/m^ The spring minimum was in Novem- 

 ber 1951, but was three months later the following winter when it was reached in 

 February 1953. But the values were identical, 0-25 g/m^. The spring maximum in 

 April 1952 was 1-33 g/m^ but this value was obtained on the assumption that the 

 amount of chlorophyll was uniform beyond the last depth examined, 50 m to 70 m, 

 bottom. Later work showed that, on account of sinking of the cells, this was probably 

 an underestimate. The maximum was in May in 1953, 3-68 g/m^ (very much higher) 

 with much Phaeocystis present. Both the summer minima fell in June, 0-15 g/m^ for 

 1952 and 0-35 g/m^ for 1953. 



40 



3 O 



2 O 



g/r 



lO 



oo 



Fig. 5. Variation of chlorophyll in water column, 0-70 m, in grams per square metre for 1951-52 



(broken line) and 1952-53 (full line). See text, p. 66. 



These chlorophyll quantities may be converted into wet weights of phytoplankton 

 as in the paper of 1953. Taking Riley's value 2-9 % of chlorophyll (1941 a), calculated 

 on the dry weight, and taking the dry weight as 20 % of the wet weight, we arrive at 

 a factor 1 72 by which one can multiply the weight of chlorophyll to convert it to wet 

 weights of phytoplankton. It is recognized that these factors are somewhat arbitrary. 



THE BOTANICAL COMPOSITION OF THE PHYTOPLANKTON AT STATION El 



Samples of water, 100 ml, from each depth were poured into conical flasks and 

 enriched with Miquel's solution, 0-2 cc of solution A and OT cc of solution B. 



They were placed in a south window during winter and from spring to autumn were 

 illuminated by a diffuse north light. The enrichment of the culture solution gave a 

 better chance for species originally very sparsely represented to multiply and be 

 detected. This amounts, in fact, to the common bacteriological technique. 



Tables II and III are an attempt to indicate the relative amounts found in the earlier 



