i 3 o DISCOVERY REPORTS 



Table V, column 8). The plankton here, however, although it contained an element of 

 cold-water species, was not nearly so "cold" as it was in the same region earlier in the 

 season. The conditions were in fact very similar to those which obtained about February 

 and March 1929-30 (Fig. 41). 



It has been seen that the evidence strongly suggests that around South Georgia the 

 cold-water species are prominent in spring, but become reduced as the summer ad- 

 vances, and we now have clear evidence that in the 1 930-1 season, in the area roughly 

 between the South Sandwich and South Orkney Islands, a "cold" plankton in 

 December gave way to a comparatively "warm" plankton in February (compare Figs. 

 43 and 45). There is every reason to suppose that this is a normal process. 1 930-1 is 

 the only single season in which the plankton distribution can be compared in several 

 different months, but the conditions in October 1928-9 and February-March 1929-30 

 fall into place very well. The 1928-9 season was not so cold as the 1 930-1 season, the 

 ice did not reach quite so far north in October, and the area of the South Georgia survey 

 was not invaded by the "cold" plankton, which, however, came very near to it. The 

 1929-30 season was a mild one and there was no sign of ice round the South Sandwich 

 Islands, but the conditions in February-March were very similar to those in February 

 1 930-1, except that the cold-water species had retreated farther to the south-east. 



It is difficult to decide exactly what connection exists between the pack-ice and the 

 presence of the very cold-water species (group (h) in Table III, p. 107). They are rarely 

 if ever found except close to the ice or in places in which there has recently been ice. 

 On the other hand the presence of ice does not necessarily entail the presence of cold- 

 water plankton. 



Fig. 46 shows the changes in the position of the pack-ice during the 1930-1 season, 

 and its tendency to hang around the South Orkney and South Sandwich Islands while 

 farther to the east the sea becomes clear of pack-ice for hundreds of miles to the south- 

 ward. In Fig. 47 the boundaries between the warm- and cold-water plankton shown in 

 Figs. 40, 41, 42 and 45 are superimposed on one chart. This shows again how the cold- 

 water plankton retreats to the south-east of South Georgia. It will be seen that west- 

 ward from the South Sandwich Islands a warmer plankton is always found, and there 

 is evidence of a tendency towards a warmer plankton also to the east of the islands (see 

 Fig. 42). It seems in fact that around the South Sandwich Islands there is a tongue of 

 cold-water plankton reaching up from the south. 



The cyclonic circulation in the Weddell Sea, and the cold water which flows out to- 

 wards the South Orkney and South Sandwich Islands is responsible for the persistent 

 ice and the cold-water plankton in this region, and it is possible that the ridge of the 

 South Sandwich chain temporarily deflects the current towards the north, carrying the 

 cold-water species up in the tongue mentioned above. 



The presence of cold-water species near Bouvet Island suggests that there might be 

 another cyclonic system farther to the east, and Wiist (1928) has published a chart of 

 current systems in the Atlantic which does in fact show such a system. Its centre is 

 given as about 6o° S, 30 E, and its orbit just embraces the stations near Bouvet Island 



