DISTRIBUTION OF PHYTOPLANKTON 



75 



Fig. 40. Contour chart showing the total quantity of phytoplankton in the South Georgia December- 

 January 1926-7 survey measured by settled volumes of samples collected in hauls with the N 50 V net from 

 100 m. to the surface and expressed in cc. (cf. Fig. 38). 



In late May 1927, when the R.R.S. 'William Scoresby' revisited South Georgia, the 

 C line was repeated. There was more phytoplankton than in March 1926, but a marked 

 decrease from the summer months of December and January. Chaetoceros criophihun, 

 Ch. socialis, Nitzschia seriata, Corethron valdiviae, Rhizosolenia styliformis and Coscino- 

 discas spp. were the prominent forms. Their numbers are shown in Appendix I, Sts. 

 WS 1 10-1 14. The nature of this plankton resembled that of our phytoplankton Group 4. 



South Georgia to the Falkland Islands 



In passing east to west, from South Georgia to the Falkland Islands, we pass from 

 the Antarctic to the sub-Antarctic Zone; see p. 6. The boundary separating the two 

 masses of surface water — the Antarctic Convergence — lies close against WS 67, and WS 

 68-70 are beyond it in the sub-Antarctic Zone. The set of samples taken across these two 

 water masses is perhaps the most interesting in the present survey. We sec a diminution 

 of the phytoplankton both in numbers and in species as we approach the sub-Antarctic 

 area and pass into it. One after another of the Antarctic species is left behind and 

 Rhizosolenia cnrva, a sub-Antarctic species, increases in numbers. This is shown in 

 Table V, where the stations are arranged in geographical order from west to east (in 

 the reverse order to which they were taken) together with St. 161 which lies well in 

 the Antarctic Zone to the south-west of South Georgia (see Fig. 14). All these stations 



