DISTRIBUTION OF ANTARCTIC MACROPLANKTON 121 



These charts are shown primarily as a record for comparison with more recent data 

 or future material, but one interesting point may be mentioned here. In each of the 

 lines of stations between Cape Horn and the South Shetland Islands there is an abrupt 

 change from the rich plankton of the greater part of the Scotia Sea to the thin plankton 

 of the Shetland neighbourhood. The position of the change is indicated by a pecked 

 line in Figs. 32, 34, 37 and 38. If these four figures are compared it will be seen that 

 on the November and February lines (Figs. 32 and 34) the change comes at about 150 

 miles from the South Shetland Islands, that on the March line (Fig. 37) it is about 100 

 miles off, and on the April line (Fig. 38) it is only about 30 miles off. From this it seems 

 possible that there is normally a rich plankton in the central part of the Drake Strait 

 which spreads farther south towards the end of the summer. Here comparison is made 

 between different months in different years, so that the apparent shift may possibly be 

 the effect of a coincidence. The results of future work will no doubt settle the question. 



If there is in fact such a southward trend of the plankton it would not of course imply 

 an actual transport of plankton towards the south. Such a thing would seem impossible 

 in the present state of our knowledge of the hydrology of these regions. All the evidence 

 goes to show that the Antarctic surface water in these latitudes moves towards the east 

 and north, and there seems no possibility of even a local or periodical deflection towards 

 the south. A more likely explanation might lie in the variation of the amount of upwelling 

 of the "new" water on the south side of the Drake Passage. It has been found that the 

 area occupied by this "new" water extends farthest to the north in midsummer and is 

 most contracted in winter. The boundaries of the " new " water and of the thin plankton 

 do not appear quite to coincide, but there is a similarity in the changes of position of 

 these boundaries. A rich plankton has been found in the Bellingshausen Sea in the 

 neighbourhood of Peter 1st Island, and it is to be supposed that this is carried by the 

 easterly drift towards the Drake Passage. A reduction in the upwelling of water and a 

 shrinkage of the area it occupies in the southern part of the Drake Passage might then 

 make way for the plankton from the Bellingshausen Sea and thus produce the effect of 

 a southerly trend of the rich plankton. 



Little can be said of the variations in the quantity of plankton in the more eastern 

 parts of the Scotia Sea. Figs. 32-9 suggest that the plankton may perhaps be a little 

 more patchy in the later than in the earlier part of the summer. 



DISTRIBUTION OF WARM- AND COLD-WATER SPECIES 

 It has been shown that among the Antarctic macroplankton species there are many 

 which prefer, or are confined to, either the warmer or the colder water, but just as there 

 are alterations in the position of the rich and poor plankton, so there are changes in the 

 distribution of the warm- and cold-water species. 



SOUTH GEORGIA 

 Table IV shows, for each species, the average number of specimens per haul for each 

 group of stations off South Georgia. These are the same groups as those listed on p. 1 1 5, 



DIX 



