322 DISCOVERY REPORTS 



high values and two in September very low ones. This merely gives slight confirmation 

 of the conclusion that the main increase takes place in December, which was reached as 

 a result of the earlier work mentioned. 



At a single station, 2199, worked on 21 January 1938 close into the Balleney Islands, 

 a value of 57,830 units of pigments was recorded. This is comparable to the highest 

 values recorded in the South Georgia area, and shows that neritic conditions can give 

 rise to intense local concentrations much farther south at the corresponding time of 

 year. This particular concentration was clearly very local, however, for stations worked 

 within some 30 miles were oceanic in character, as regards both quantity and quality 

 of the phytoplankton. At St. 2199 neritic species were strongly dominant, the minute 

 Chaetoceros sociale was by far the most numerous, but there were also large quantities of 

 Thalassiosira spp., Eiicampia balaustium in summer phase, and the large, richly pig- 

 mented Biddulphia striata. 



BIOLOGICAL FEATURES OF SPECIAL INTEREST 

 DISTRIBUTION WITH DEPTH OF THE ANTARCTIC PHYTOPLANKTON 



We have seen that in view of the inaccuracy of the centrifuge method demonstrated 

 by Nielsen, it has not been considered worth while to discuss in detail the resuhs 

 obtained during the third commission. Nevertheless, it is at least probable that, where 

 the quality of the phytoplankton is fairly uniform down to the lowest depths sampled 

 (loom.), the largest count will indicate the neighbourhood of the maximum density of 

 the population. Selecting these uniform stations we have 117 series of observations 

 scattered throughout the Antarctic zone during the productive period, and it appeared 

 to me that by considering the frequency with which the apparent optimum occurred at 

 different depths, one should obtain an idea of the normal type of distribution with depth 

 not far from the truth. 



The frequencies with which maximum numbers of phytoplankton organisms were 

 found at various depths are shown in the following table : 



Table 11 



* Samples from 30 m. were taken at only a few stations, where a marked thermocline between 20 and 

 50 m. suggested that depth might prove critical. 



