626 Maririe Microbiology 



Ocean (Canadian Polar Shelf) consisted of 44 diatoms, thirteen 

 dinoflagellates and six flagellates, the majority being Centricaceae. 

 The populations are so small and so irregular in vertical distri- 

 bution that the seasonal sequence of successions is hard to recog- 

 nize. 



The neritic, brackish phytoplankton of the Isachsen area, 

 slightly to the south of the Arctic Ocean in the Canadian Arctic 

 Archipelago, shows a bimodal annual c}cle. In 1960 the spring 

 maximum in this cycle was formed by Pennatae, mostly Nitz- 

 schia pungens, N. lineola, and N. seriate, with one peak on July 

 2 and a second on July 9, after which they declined. The summer 

 Centriceae succession, formed mainly by Chaetoceros ceratos- 

 porum, also had two peaks, the first on July 9, and the second 

 and largest on July 13. All cells by this latter date had formed 

 cysts and their cycle was completed. Lesser cycles included a 

 unimodal succession of freshwater green flagellates with a peak 

 on July 2 and a unimodal dinoflagellate cycle with a peak on July 

 22. The Isachsen cycle, with 48 diatoms, 33 dinoflagellates and 

 20 flagellates also formed larger populations than found in the 

 offshore waters of the Arctic Ocean. The definite maxima of Pen- 

 natae followed by Centriceae were separated by only a few days, 

 but the annual cycle must be considered bimodal, although the 

 area is certainly high arctic by Bogorov's (2) criteria. 



Igloolik, Foxe Basin, 660 miles southward of Isachsen, shows 

 clearly a bimodal cycle caused by the alternation of the spring 

 Pennatae and the summer or open-water Centriceae, with maxima 

 separated by 28 days. The spring maximum occurred in 1956 

 in mid July and the summer maximum on August 11, and the 

 latter was followed by maxima of dinoflagellates and Coccoli- 

 thineae. The phytoplankton cycle in the coastal location of Row- 

 ley Island, 60 miles to the south of Igloolik, was exposed to 

 severe ice effect, which delayed the summer successions of Cen- 

 triceae until mid September. The contrasts between the two 

 environments are also reflected in the numbers of species: 34 

 diatoms, 5 dinoflagellates, 1 Coccolithineae at Rowley Island; 78 

 diatoms, 30 dinoflagellates, 9 Coccolithineae at Igloolik. 



Further to the south in Hudson Bay, 235 jihytoplankton 

 species have been recorded. This marked increase is related to 

 higher temperatures, light, less rigorous ice conditions, and the 



