ZOOPLANKTON IN THE SOUTHERN OCEAN 207 



at least, outstanding, and if the 1932 October data had been used in the 1933-34 8o° W series it would 

 not have affected the general conclusions for that meridian. This is of some importance, because the 

 lack of data has made it necessary to select the monthly series of stations in other regions, from 

 different years, in an attempt to show that the vertical movement of the plankton is a general pheno- 

 menon in the whole of the sub-Antarctic and Antarctic regions and is not just peculiar to 8o° W, o° 

 or 20 E. As previously mentioned (p. 196), the number of observations in other areas is very small, 

 but they are sufficient to allow for a comparison with observations from 8o°, o° and 20 in similar 



months. 



Observations in other areas (Fig. 5) 



20 W. The observations in 20 W were not extended into sub-Antarctic waters, but they are of 

 particular interest because they sampled an area of the Southern Ocean greatly influenced by the 

 Weddell Drift. This current of surface water originating in the Weddell Sea has been found to play 

 an important part in the biology of Eiiphausia superba, an animal in which it is immensely rich (Marr, 

 personal communication). Except in its young stages this animal is too large and active to be caught 

 regularly by the N70V, so that the volumes from stations in this region represent the standing crop 

 of zooplankton other than the older krill. 



The January 1932 volumes were similar to those from other regions, and showed a rather irregular 

 vertical distribution of plankton but with the bulk concentrated in the top 100 m. of water at most 

 stations. The March 1937 volumes seem typical of that month in other areas, with very large concen- 

 trations of plankton in the Antarctic surface water. 



110 E. These stations cover an area south of Australia from Fremantle, and they sample sub- 

 tropic, sub-Antarctic and Antarctic waters. The May 1932 results indicated late autumnal conditions, 

 with larger hauls below 250 m., particularly at stations just north and south of the Antarctic con- 

 vergence, while the northernmost sub-Antarctic and the southernmost Antarctic stations show large 

 shallow hauls. On the whole the conditions were not so advanced as in June in other areas. 



March-April 1936 and January 1938 compare well with the same months in other areas. 



160° E. The stations cover an area south of New Zealand. In June 1932 the volumes were small 

 at all depths, with some indication of greater concentration in deeper water at St. 919 in the Antarctic. 

 The volumes in February 1936 and January 1938 were typical of summer months in other regions, 

 with most of the plankton concentrated in the surface waters. Of particular note are the exceptionally 

 large 50-0 and 100-50 m. catches in February. 



These rather fragmentary observations in the region of 20 W, 1 10° E and 160 E are not sufficient 

 to give a seasonal picture of the variations of standing crop in each particular area, but when compared 

 with results from o°, 20 E and 8o° W, they do show that in comparable months the general pattern 

 of vertical distribution throughout those regions of the Southern Ocean which have been examined is 

 the same. 



The meridian of 90 E, 195 1 (Fig. 6) 



The Indian Ocean results are considered separately because they are the only available meridional 

 line of observations in tropical waters, and while a seasonal comparison is impossible they are yet of 

 special interest in relation to the sub-Antarctic and Antarctic data. 



The volume measurements (corrected for difference in net dimension (see p. 195)) show that the 

 bulk of the plankton was in the upper 100 m. of water at all stations. There appeared to be little 

 difference between the catches at sub-tropical and tropical stations, but compared to October volumes 

 in sub-Antarctic and Antarctic waters the volumes of hauls at all depths were small. Of particular 

 note is the uniformity of the results — the vertical distribution of the plankton and the catch at each 

 depth being about the same from station to station. 



