2o 4 DISCOVERY REPORTS 



There were no observations in September, but in October, as in o°, there was a marked increase 

 in the volumes at all stations, particularly in the sub-Antarctic region where there was a large con- 

 centration of plankton in the surface layer. At the Antarctic stations there was no indication of this, 

 and the highest concentrations were in deep water though at a shallower level than they were in August. 



In November most of the plankton appeared to be between ioo and o m. except for the exceptionally 

 large 250-100 m. haul of 8-9 cc, due to a large number of small euphausians, at St. 2484. In the sub- 

 Antarctic the plankton appeared to be concentrated nearer the surface (i.e. between 50 and o m.) than 

 in the Antarctic, which contrasts with the vertical distribution in o° where the reverse was the case. 



In December at all stations except St. 2521 the bulk of the plankton was above 100 m. On the whole 

 the 100-50 m. level had the highest concentration in both sub- Antarctic and Antarctic regions. 



In late January and early February the standing crop of plankton was similar in vertical distribution 

 to that in December when there was very little plankton below 250 m. 



In March large concentrations in the surface layer were still evident, but at St. 2620 there was a 

 marked increase in the volume of the deeper hauls. 



The meridian of 8o° W, 1933-34 season (Fig- 3) 

 Although the observations in 8o° W do not present such a complete series as do those in o° and 20 E 

 they are of particular interest because an analysis of the same samples has formed the basis of a paper 

 by Mackintosh (1937) which described the seasonal circulation of the macroplankton of the area. It is 

 thus possible, in this case only, to compare the volume of a particular haul with its animal composition, 

 and brief reference will be made to these results in the description of the volume measurements that 

 follows. 



In December 1933 the results show that the standing crop of plankton was concentrated in the sub- 

 Antarctic and the northernmost Antarctic surface waters. The volumes at three stations, 1222, 1221 

 and 1220, suggest that in the southern part of the Antarctic region the plankton was still concentrated 

 in deeper water (between 750 and 500 m.). The distribution of the volumes shows there to be a 

 greater quantity of plankton in the sub-Antarctic than in the Antarctic zone, which is the same as the 

 distribution of the total numbers of organisms (Mackintosh, 1937, p. 380). 



In March 1934 the concentration of plankton in the surface waters had increased, and as Mackintosh 

 (ibid) observed for the total numbers, the largest volumes were nearer the surface than in December. 

 The two Antarctic stations nearest the ice edge were relatively poor in surface plankton, as in the 

 previous month, although there is evidence that at these and the stations just north of the convergence 

 the plankton was concentrated in deep water. The September results are rather unsatisfactory owing 

 to the loss of part of the samples at some depths, and the volumes of these samples, which are shown 

 in brackets in Table 1 1 c, are thus minimal values. In spite of this, however, it is obvious that the 

 surface layer in the sub-Antarctic and the Antarctic zones was very poor in plankton except at St. 1421, 

 while the largest concentrations were at the 750-500 m. level. 



In October there is definite indication that in the sub-Antarctic zone the plankton was concentrated 

 at the 250-100 m. level. This was true also of the two northernmost Antarctic stations, in particular 

 St. 1447. At Sts. 1449 and 1450, however, the plankton had not risen above 250 m. It is interesting 

 to note that Mackintosh (ibid) observed that in this month the 250-100 m. horizon provided the 

 greatest number of organisms. 



In November there was still much plankton between 250 and 100 m., but at the Antarctic stations 

 the 250-100 m. level was the richest. 



The monthly results in 8o° W compare well with those for similar months in o° and 20 E. In each 

 meridian the greatest concentrations of zooplankton were in the surface water during summer and 



