212 



DISCOVERY REPORTS 



level. The second period of increase is apparently the greatest, although in the sub-Antarctic this 

 may be due to a single very large volume of 10-5 cc. for the 50-0 m. sample at St. 2219. 



Table 4. The monthly variation in the mean total volume of plankton {i.e. the sum of all measure- 

 ments from 1000 to o m.). Numbers of observations are given in brackets 



SUB-ANTARCTIC 



1 1 1 



ANTARCTIC 



~i 1 1 1 1 1 1 1 r 



n m r? v vi th vjh 

 MONTH 



IX 



x xi xn 



Fig. 9. Seasonal variation in the mean total volume of zooplankton in the whole water column sampled*(i.e. 1000-0 m.) 

 in the sub-Antarctic and Antarctic. Numbers on each curve as in Fig. 8. 



It will be remembered that in calculating the monthly mean volumes for each depth interval the 

 actual measurements had to be corrected to give the volume for a standard haul of 50 m. In this way 

 variations in concentration at different levels in the whole water column can be assessed. When, 

 however, the individual measurements at each depth are added together the resultant volume is a 

 measure of the total standing crop of plankton in the whole water column sampled. Table 4 gives the 

 mean monthly total volumes together with the number of observations in each month in the sub- 

 Antarctic and Antarctic zones. It is compiled from all stations with a complete series of measurements 

 from 1000 to o m., and the results are shown in Fig. 9. 



The monthly mean volumes show that, compared to the surface waters, there is relatively little 



