296 ■ DISCOVERY REPORTS 



tion was particularly dense. The most evident embraced the two stations 737 and 739, 

 in the coldest water of the Drake Passage along the pack-ice edge (Figs, i a, 8). At 

 St. 737 the estimated number in the combined hauls was 15,590, while at St. 739 it was 

 44,650. These two stations were situated just off the Antarctic continental shelf where 

 warm deep waterwells upwards towards the surface (Deacon, 1933, pp. 180-1). Although 

 this is not evident from the position of the discontinuity layer at these two stations them- 

 selves (Table II a), they are nevertheless sufficiently near the region of upwelling for its 

 effects to be perceptible in the plankton. Other especially large catches were taken in the 

 area of abundance immediately south of the convergence in the South Atlantic west and 

 north of South Georgia, and at St. 803 (Figs, i a, 8) where the estimated number in 

 the combined hauls was 19,948. 



North of the Antarctic convergence in the South Atlantic, in sub-Antarctic water, 

 is an area where Rhincalamis formed 50-75 per cent of the total copepod catch. Here the 

 catches in the combined hauls amounted by estimate to between 5000 and 10,000 

 individuals. This area was missing in the Drake Passage where the Antarctic convergence 

 formed a much more pronounced limit to the region of density of the species. Here the 

 convergence sharply divided the area of maximum abundance from sub- Antarctic water 

 in which Rhincalamis formed 25-50 per cent of the total copepod catch and where 

 between 2500 and 5000 individuals were taken in the combined hauls. In the South 

 Atlantic east of South Georgia there are no observations defining the northern boundary 

 of the 5000-10,000 zone at this time of year, but the 5' C. isotherm may be suggested as 

 its northern boundary. 



This marked abundance of Rhincalamis in Antarctic water of Bellingshausen Sea 

 origin in the Falkland Sector is in striking contrast with the comparative paucity of the 

 species in the cyclonic current originating in the Weddell Sea (Fig. 8). Within this mass 

 of water moving north-eastwards out of the Weddell Sea, having an average tempera- 

 ture less than 0° C, Rhincalanus amounted to less than 15 per cent of the total catch 

 (Fig. 9) and the numbers of individuals taken at each station were less than 500 in the 

 two hauls combined. 



There is thus a pronounced difference, so far as the abundance of R. gigas is con- 

 cerned, between the two main water masses in the Antarctic surface water of the Falk- 

 land Sector. The Bellingshausen Sea current, flowing through the Drake Passage around 

 the western end of South Georgia into the South Atlantic, is characterized by a great 

 abundance of this species, while the Weddell Sea cyclonic current, flowing along the 

 east coast of Graham Land and east of South Georgia towards the South Sandwich 

 Islands, is characterized by a relative scarcity of R. gigas but by a rich copepod fauna of 

 which R. gigas is not an important constituent. 



Between these two masses of water is an area of variable extent where their influences 

 mingle. North of South Georgia, as already mentioned, a tongue of Weddell Sea water 

 pushes westwards and causes the 5000 and 2500 lines of equal numerical distribution of 

 R. gigas to take a bend westwards before turning eastwards again across the South 

 Atlantic. South of South Georgia, where another tongue of Weddell Sea water pushes 



