SUMMARY: GROUPING SYSTEM: NORTHERN REGION 34i 



This leads to a ' telescoping ' of the N-S gradient in the conditions of existence which 

 renders the distinction of three zones as in the typical oceanic regions impracticable. 

 To make the scheme complete one must treat the more oceanic portions of the Weddell 

 Sea, between the Southern Region and the southern limit of the Scotia Sea, as a special 

 area, but we have very few observations there. The special areas have been dealt with as 

 follows : 



The South Georgia area: between 52 and 55" S, 33 and 41° W. 

 The Scotia Sea: between the Antarctic convergence and 62° S, 30 and 70° W, 

 excluding the South Georgia area. 



Other special areas : where our observations are too few for detailed consideration, the 

 best known being the eastern South Pacific. 



The most important phytoplankton species have been grouped on a system which 

 takes into account their general distribution, both seasonal and geographical. The 

 classic concepts of Gran's binary system are difficult to apply, owing mainly to the 

 relatively slight temperature gradient over the whole vast region studied. Other in- 

 dividual environmental features give little help, with the result that while Gran's ideas 

 have been followed as closely as possible the system remains much more arbitrary, and 

 is intended only to facilitate consideration of these results. 

 A very brief outline of this grouping is as follows : 



Group I. Small oceanic pennate diatoms: Fragilariopsis, Nitzschia seriata, etc., with 

 Distephamis. 



Group II. Large oceanic diatom species: Solenoids, large Chaetocerids, etc. 

 Group III. Neritic and ice-edge forms — all diatoms whose restricted distribution 

 warrants this description. 



Group IV. Oceanic Chaetocerids— e.g. Chaetoceros otlanticum, Ch. dichaeta. 

 Group V. Oceanic Discoidae— some small species of Coscinodiscus, Actinocydiis and 

 large Asieromphalus spp. 



The observations summarized in the following paragraphs form the factual basis of 

 this grouping. 



An itinerary of the phytoplankton observations in the Antarctic zone during the last 

 three commissions (1933-9) of the R.R.S. ' Discovery II ' is given. Localities of all the 

 estimations are tabulated in the Appendix. 



The observations within each region or area are then described. In the Northern 

 Region there is a slight increase over the minimal winter values in early spring, followed 

 by the rapid main increase in November-December, when the maximum may be 

 reached, though sometimes not achieved until January. The standing crop shows a 

 marked decline in late summer followed by a secondary increase, small and more 

 irregular than the main, during March-April. During May the decline towards the 

 negligible winter values is probably rapid. 



The qualitative sequence is marked by the close coincidence of the maximum relative 

 importance of neritic/ice-edge diatoms (Group III) and the onset of the main increase. 

 By the time the maximum is reached they are again becoming relatively scarce, and at 



