152 DISCOVERY REPORTS 



speaking it overlaps a part of the Graham Land area, which is defined on a different 

 basis, for there is probably something of a transition zone everywhere to the south of 

 the northern zone. 



(4) The eastern Scotia Sea. A rough triangle, having at its corners the South Sand- 

 wich Islands, the South Orkney Islands and South Georgia. The area is characterized 

 by a plankton which appears to be uniform but unstable. That is to say, a different type 

 of plankton has been taken on the different lines of stations crossing this area, but the 

 plankton was similar at consecutive stations in each line. The composition of the plankton 

 seems to depend on the time of year, and very likely varies from one year to another. 



(5) The "old" Weddell water. It is difficult at present to give any general definition 

 of the plankton in this area, but it includes the unstable and heterogeneous plankton 

 population found on the east side of the South Sandwich Islands. Its southern limit, 

 at the time it was determined, lay between WS 544 and WS 555 (lat. 6o° 40' S, see p. 69), 

 and north of this it may be temporarily defined as the area occupied by water which has 

 flowed out of the Weddell Sea and passed the Scotia Arc in the vicinity of the South 

 Sandwich Islands. 



(6) The eastern Weddell Sea. The limits of this area are not known, but it lies south 

 of WS 555, and, so far as can be judged from a single line of stations, the plankton is very 

 uniform and characterized by a high proportion of the very cold-water species. It 

 offers a marked contrast to the preceding division. 



(7) The western Bellingshausen Sea. The exact limits of this area are also unknown, 

 but it may be regarded temporarily as that part of the Bellingshausen Sea in which the 

 plankton is rich in comparison with that found in the eastern part near Adelaide Island. 

 The plankton taken here was in many ways comparable to that found in the eastern 

 Weddell Sea, but it was rather more variable and the proportion of cold-water species 

 was not quite so high. 



It must be specially emphasized that these divisions are intended to do no more than 

 represent the conditions as they were found at the time of investigation, and it would in 

 fact be surprising if certain modifications of the scheme were not found to be necessary 

 if the results of subsequent work are brought to bear on the question. It should also be 

 mentioned that the boundaries between the different divisions are not geographically 

 fixed lines. The Antarctic convergence may perhaps shift its position according to the 

 time of year, and it has been seen (p. 121) that the change from the scarce plankton of 

 the Graham Land area to the comparatively rich plankton of the northern zone has been 

 found in quite different positions at different times. The distribution of the plankton 

 should not, in any case, be thought of as a static pattern, but as a number of drifting 

 communities whose formation must depend partly on their origin and the methods of 

 propagation of the various organisms, and partly on the changing conditions through 

 which they are carried. In the northern zone the current runs steadily from west to 

 east with little interruption from islands, shoal waters, and varying ice conditions. This 

 probably explains the regularity in the distribution of its plankton. The water flowing 



