DISCOVERY REPORTS 



May to October are unshaded and the positions of stations with an incomplete series of hauls used 

 elsewhere in this paper are marked with a cross. 



Although there are some gaps in the observations, notably in the Pacific sector, the chart shows a 

 number of features, some of which have been dealt with at length in previous sections. The large 

 standing crop of plankton just south of the mean position of the Antarctic Convergence, for instance, 

 is very evident, particularly in the Atlantic sector, and if the actual position of the convergence on each 

 line were considered this would be more accentuated (see p. 219). 



The area of Weddell Sea influence is surprisingly poor in plankton, as also is the East Wind Drift. 

 As explained in the previous section, however, no allowance can be made for the great quantities of 

 Euphausia superba which are known to occur in these regions. If this were possible it would be seen 

 that these two surface-water drifts support perhaps the greatest concentration of plankton in the whole 

 of the Southern Ocean. 



In 



_i 

 o 



> 



I 



2CTE 



20E-I20E 



I20E-I80 



)°- 6C?W 



WEST WIND DRIFT 



16 



~1 



WEDDELL DRIFT 



LONGITUDE 

 Fig. 17. 



LONGITUDE 

 Fig. 18. 



Fig. 17. Comparison of the total volume of zooplankton (1 000-0 m.) in various sectors of the sub- Antarctic and Antarctic. 

 Allowance has been made for the differences in the number of winter and summer observations in each sector. 

 Fig. 18. Comparison of the mean volume of zooplankton in the three principal Antarctic Surface Drifts during the main 

 period of increase (November-April), together with the number of observations in each sector. 



Table 8. The variation in mean total volume (i.e. 1 000-0 m.) between various sectors of the sub- Antarctic 

 and Antarctic zones. Allowance has been made for there being different numbers of summer and winter 

 observations in each sector. Total numbers of winter and summer observations in each sector are given in 

 brackets 



The mean total volume (i.e. 1 000-0 m.) of plankton in different regions of the Antarctic, and also of 

 the sub-Antarctic, are compared in Table 8, the results being represented diagrammatically in Fig. 17 

 (allowance has been made for the different numbers of winter and summer observations). The bulk 

 of the observations are from the Atlantic sector and have been treated in three groups, 6o° W-o°, 

 o° and 20 E. Data from the other areas have had to be treated in groups of larger intervals of longi- 

 tude which correspond roughly to the main geographical divisions of the Southern Ocean, 20-120 E 

 being the Indian Ocean sector, 120-180 the Australian-New Zealand sector, and 180-60 W the 



