312 • DISCOVERY REPORTS 



restriction of Rhincalanus to Antarctic water at the end of the season which we have 

 already noticed (pp. 298-9). It may be regarded as the winter condition and as a 

 regularly occurring process. 



The line between the South Shetlands and the Falklands also shows a feature to which 

 Mackintosh (1934, p. 121) has already drawn attention. This is the sharp division be- 

 tween the moderately rich catches at the two northerly Antarctic Stations ( 1 1 1 6 and 1 1 1 7) 

 and the comparatively very poor catch at the most southerly station ( 1 1 1 5 ). Mackintosh 

 has already shown that this line of demarcation can be drawn in the southern Drake 

 Passage for the plankton as a whole, and from comparisons of its positions at different 

 dates in different years he suggested that the line moves southward during the season. 

 At the beginning of the season 1 93 2-3 , at the end of October and beginning of November, 

 there was a similar line of demarcation so far as the distribution of R. gigas is concerned 

 between Sts. 992 and 994 and between Sts. 1014 and 1015 (Fig. 14), but these stations 

 are too far apart for the exact position of the line to be fixed. Its position in February 

 between Sts. 11 15 and 11 16 does not, however, suggest that it has moved appreciably 

 between the beginning and the end of the season. Mackintosh (1934, p. 121) further 

 suggested that there is a rich plankton in the central part of the Drake Passage which 

 spreads farther southwards towards the end of the summer. We have seen, however, 

 that so far as R. gigas is concerned, there is a diminution in quantity towards the end of 

 the summer in the Drake Passage, and the largest catches on the February line, taken 

 at Sts. 1 1 16 and 11 17, do not suggest any marked southward movement of the area of 

 abundance. In fact the indications are that the area of abundance moves away north- 

 eastwards towards South Georgia — as indeed one might expect in view of the general 

 direction of flow of the surface waters. Thus, while reduction in numbers takes place in 

 the Drake Passage, the species still remains fairly abundant around South Georgia 

 (Sts. 1 125 and 1127) at the end of the summer. 



The line from South Georgia to the pack-ice edge in 69° 22' S, 9° 37-5' E, taken in 

 March, passes throughout its length through Weddell Sea water. As already explained the 

 western stations on this line (Sts. 1 138-47 ; Fig. 2b) were taken in water flowing north- 

 eastwards out of the Weddell Sea, while the more easterly stations (i 148-53) were taken 

 in the East Wind Drift current flowing westwards into the Weddell Sea. St. 1 148 lies in 

 the area of divergence between these two masses of water. At St. 1142, as already 

 explained (p. 307), there appears to be a tongue of warmer water moving southwards, 

 since at this station the average temperature between o and 100 m. is above i-o°C. (Fig. 7), 

 while at all the stations south of it it is less than 0° C. All the catches on this line were 

 small, less than 500 individuals, as is usual in Weddell Sea water, except at the warmer 

 station (1142) at which over 1000 individuals were taken. This station corresponds in 

 position with St. 807 (Fig. la), taken in mid-January in the preceding season. The 

 catch in the two hauls combined at that station was 520 individuals. In January 1932, 

 however, the southward movement of warm water in this area was less pronounced than 

 in March 1933 and extended only to St. 806 at which 11 04 individuals were taken. 



Fig. 1 5 shows the distribution of R. gigas based on its percentage of the copepods in 



