20 DISCOVERY REPORTS 



the results obtained quite intelligibly. The rich Rhisosolenia plankton, with R. polydactyla 

 dominant, that we have found in sub-Antarctic water on other occasions, was not re- 

 presented, and in the oceanic sub-tropical water the phytoplankton was extremely poor. 

 It is probable that this water would have shown a richer phytoplankton at a more 

 favourable time of year, but not, of course, anything approaching that found off the 

 south-west coast of Africa in a similar latitude. There, with considerable upwelling 

 caused by the offshore winds, the concentration of nutrient ions in the surface layers was 

 at least three times as high as in the oceanic water with which we are immediately con- 

 cerned (30-60 mg. P2O5 per m.^ as against 8-10), and a fairly rich mixed plankton was 

 present. The state of affairs off the south-west coast of Africa may be likened to the con- 

 ditions obtaining off the west coast of South America, in the Humboldt current, but on 

 a much smaller scale. 



The tremendous preponderance of diatoms and comparatively huge bulk of the 

 phytoplankton of Antarctic surface waters is well illustrated by the more southerly 

 stations, despite the fact that, owing to the time of year, production for the season was 

 nearly over, and much phytoplankton had undoubtedly perished and sunk to the lower 

 layers. This disparity between the numbers of organisms in Antarctic, sub-tropical and 

 tropical surface waters is so great that it is not possible to represent it diagrammatically 

 in the same figures, so that recourse must be had to the tabulated results of analyses. 

 The relative proportions of the chief classes of phytoplankton organisms are also shown 

 in tabular form. 



The absence of Coccosphaeriales is to be explained by the method of collection, for 

 vertical hauls with the Gran net were taken in the tropics as in our routine work in the 

 far south. For the successful estimation of Coccosphaeriales prompt examination of 

 centrifuged water samples is essential, and this is very difficult to accomplish on a small 

 ship during a long sojourn at sea. 



The results of the analyses made on the long line of stations in 30° W are given in 

 Table I, which shows the hydrology of the surface waters together with the dates and 

 positions of the stations ; the estimated numbers of diatoms, dinoflagellates, Schizo- 

 phyceae and other organisms follow. The positions of these stations are shown in the 

 Station List (1932, pi. i). 



From time to time in the account which follows mention is made of other work 

 performed in sub-Antarctic waters. The analyses upon which these remarks are based 

 will be found in Tables XVII-XXIII. At one or two points reference is made to 

 the phytoplankton of South African waters. Forty stations were worked there during 

 the winter and early spring of 1 930-1 ; the material was briefly examined on board at 

 the time but has not yet been worked up in detail. 



THE PHYTOPLANKTON OF ANTARCTIC SURFACE WATERS 



As will be seen from the more detailed consideration that forms the body of this paper 



the Antarctic surface water may have quite distinct floras, varying with the major current 



systems within the Antarctic convergence to which the particular tract of water belongs. 



