TRANSITIONAL PHYTOPLANKTON 



79 



vergence in the Scotia Sea are shown in Fig. 32, along with those worked in the northern 

 part of the Weddell Sea area. 



The total abundance of the phytoplankton on three lines of stations worked across 

 the Antarctic convergence in March-April 1930 is indicated in Fig. 37, where the 

 probable position of the convergence is also shown. The conditions on the line worked 

 in the spring of the year (November 1929) have not been charted with the autumnal 

 results as this would confuse the issue. In Fig. 38 the distribution of the typically sub- 

 Antarctic species Rhizosolenia polydactyla has been plotted separately, along with the 

 probable position of the convergence, and from this figure it will readily be seen how 

 the curve in the convergence to the west of the Shag Rocks helps to account for the un- 

 expected occurrence of this species at the eastern stations on the Falkland Islands-South 

 Georgia line. 



40° 



35° 



SCALE 

 I 0-10,000 

 I 10.000-100.000 



I looDOO- looaooo 



Fig. 38. Chart showing the distribution of Rhizosolenia polydactyla, February-April 1930. 



Summing up the points raised by the lines crossing the Antarctic convergence in 

 1929-30, it will at once be seen that they indicate that in early March the phytoplankton 

 in the old Antarctic surface water to the south was at a minimum, but that at that time 

 a fairly rich Rhizosolenia plankton was to be found immediately to the north of the 

 Antarctic convergence. In spring there was very little phytoplankton at the station 

 worked just to the north of the convergence, and the hauls showed a large but irregular 

 increase as one proceeded southwards, production in the Antarctic surface water having 

 just begun. The April (late autumn) line showed somewhat similar conditions, from 

 which it seems fairly certain that there is a slight autumnal increase very late in the 

 year in the older Antarctic surface water. At the northernmost stations on this line 



