PHYTOPLANKTON PERIODICITY IN 

 ANTARCTIC SURFACE WATERS 



By T. John Hart, D.Sc. 



(Text-figs. 1-19) 

 INTRODUCTION 



AIMS, METHODS AND TERMINOLOGY 



OUR main object in planning the phytoplankton work carried out during the last 

 three commissions of the R.R.S. 'Discovery IT was to gain some knowledge of 

 the broader variations in plant population over the whole of the Antarctic zone of the 

 southern ocean. This great enlargement on the scope of our work during earlier com- 

 missions became very necessary with the enormous expansion of modern pelagic 

 whaling during 1928-31, which has since been maintained. 



In dealing with such a vast sea area it was obviously essential to adopt methods which 

 could be used at as many stations as possible. Although our general knowledge of 

 Antarctic seas made it certain that relatively uniform conditions for plant growth would 

 be found over great distances, it must be remembered that our previous work had been 

 mainly confined to the complicated areas round South Georgia and in the Falkland 

 sector. Further, our detailed knowledge of the hydrological background (Herdman, 

 1932; Deacon, 1933, 1937; Clowes, 1934, 1938) was being obtained concurrently with 

 the phytoplankton observations. It was therefore impossible to judge beforehand where 

 a series of observations typical of conditions over a wide area could be obtained. It 

 was only in the last stages of these investigations that such series of repeated obser- 

 vations in one area could be undertaken, and the earlier more widespread work inter- 

 preted in the light of the results so obtained. The general plan of campaign, therefore, 

 resolved itself into an atten^pt to obtain as many observations as possible over the whole 

 zone and to compare these subsequently with repeated series of similar observations in 

 what seemed the most typical oceanic area. This is necessary in order to determine how 

 far the broader diflferences in quantity and quality of the phytoplankton are to be 

 ascribed to seasonal changes, rather than inherent differences in the conditions from 

 place to place. 



In this way I have tried to draw a picture of the main sequence of events in broad 

 outline, for an 'average' year, for several distinct biogeographical regions or areas 

 within the Antarctic zone, and to present it in a form suitable for comparison with 

 other lines of research, such as work on the variations in nutrient materials in the water, 

 and on the zooplankton. It is hoped that this broad survey may serve as a useful basis 

 for more detailed phytoplankton work in the future. In the present circumstances it is 



