OBSERVATIONS IN THE SOUTHERN REGION 315 



numerous species ; it is known to show greatly increased importance in the Intermediate 

 Region also at this time, so that this observation may be quite typical. 



Among the neritic and ice-edge diatoms (Group III) the increased importance of 

 Nitzschia closterium, Fragilaria spp. and the more truly tychopelagic ice forms is even 

 more pronounced than in the Intermediate Region, as one would expect. Of the oceanic 

 Chaetocerids (Group IV) it need only be said that in the Southern Region C/iaetoceros 



2500-r- 



2000 — 



1500 — 



1000 — 



500 



JuIl| August September October November December Januaru| FebruarLj March April Mai^ June 



Fig. 12. Southern Region. Seasonal variation in plant pigments per m.^, means of all available observations 

 at mean dates. Number of observations shown in brackets. 



dichaeta, and more particularly the minute tenuicornis phase of that species, were by 

 far the most important. The group reached its highest importance during the height of 

 the main increase. 



The other categories of microplankton counted were quite insignificant in the 

 Southern Region, but Phaeocystis bnicei was important, as would be expected. This 

 organism was less frequently dominant over the diatoms and rather more unevenly 

 distributed than it had been in the Intermediate Region, however. It was observed 

 most abundantly in January and February ; fairly frequently, but in appreciably smaller 

 quantities, early in March. 



