7° 



DISCOVERY REPORTS 



Phytoplankton Group 2. This group comprises a series of stations to the west of South 

 Georgia where Bellingshausen and Weddell Sea water are mixing over the continental 

 shelf. The samples are characterized by very large quantities of the small diatom 

 Chaetoceros socialis, which was all but absent in Group i of pure Bellingshausen Sea 

 water, and by moderate quantities of Corethron valdiviae and Chaetoceros criophilum. 

 Rhizosolenia styliformis, so abundant in Group i, is here almost absent, whereas 

 Thalassiothrix antarctica is present in small numbers but was absent in Group i . 



O Melosira hyalina 



+ Rhizosolenia obtusa 

 X Rh simplex 



• COSCINODISCUSS^™^ 



® Asteromphalus challengerensis A Chaetoceros castracanei 



ED A. parvulus 



— Synedra spathulata 



1 



Fig. 36. Chart showing the distribution of a number of the less common species of diatoms confined to 



water of Weddell Sea origin. 



Phytoplankton Group 3. This group represents a number of stations to the north and 

 on the north-east side of South Georgia ; it includes the area shown by Mr Clowes in his 

 water-movement chart to be that of a mixing of the two currents, but also includes 

 stations on the A line which should be Bellingshausen water and on the C and D lines 

 which should be of Weddell Sea water. Yet, as will be seen on reference to Appendix I, 

 all the stations in this group have a definite character as compared with other groups. 

 This suggests that the area of mixture is greater than is indicated by some of the 

 hydrological data, and it is actually supported by the temperature chart shown in 

 Fig. 41. As in Group 2, Chaetoceros criophilum is present in moderate numbers and 



