IS2 DISCOVERY REPORTS 



CONCLUSIONS 



If the above list is compared with that obtained from the results of the stations worked 

 later in the previous year (p. 142), several differences will be remarked. These are in part 

 due to the localization previously noted ; thus the increased importance of forms like 

 Frogilaria antarctica, Nitzschia seriata and Thalassiothrix antarctica, was obviously due 

 to the rich association met with in the far south-west. The greater number and more even 

 distribution of the stations are also partly responsible — if more stations had been worked 

 in the localized Corethron — Rhizosolenia gracillima patch north of Adelaide Island these 

 two forms would doubtless have formed a higher proportion of the whole. Nevertheless 

 when full allowance has been made for these factors, the seasonal differences indicated 

 in the description were very evident. The average number of organisms per station 

 works out at 5,897,000 as against 8,264,900 for the previous survey, a difference suf- 

 ficiently great to indicate a real comparative poverty despite the enormous errors to 

 which such estimations are subject. 



It seems, then, that the spring increase in the Bellingshausen Sea itself takes place 

 very late in the year, and probably merges imperceptibly with the autumnal increase. 

 So far as the evidence goes there is probably no minimum in March, as would appear to 

 be the case in the Weddell Sea and in the older water farther north. In old water of 

 Bellingshausen Sea origin farther north a spring increase undoubtedly occurs, though 

 we have little evidence of that as yet.^ The Corethron — Rhizosolenia gracillima associa- 

 tion which was such a feature of the north-eastern portion of the Bellingshausen Sea, 

 and has been observed to invade the western end of Bransfield Strait late in the season, 

 very evidently develops late in the year in comparatively open water. In fact the re- 

 tardation of the usual cycle in the Bellingshausen Sea would seem to be due chiefly to 

 the persistence of the pack-ice up to comparatively low latitudes until the summer is far 

 advanced. In the Weddell Sea pack-ice is equally abundant, but it appears to break up 

 somewhat earlier in most years and passes away to the north-east in dense belts, traces 

 of which often persist throughout the season round the South Orkney and the South 

 Sandwich Islands. This is due to the more definite circulation induced by the north- 

 ward prolongation of Graham Land. As a result comparatively open water is left behind 

 the ice, thus permitting phytoplankton production to begin earlier in the higher lati- 

 tudes, at any rate in the south-eastern portion of the Weddell Sea. 



Further comparison between the Bellingshausen and Weddell Seas reveals striking 

 differences in both the quality and quantity of the phytoplankton, though this is due in 

 part to the fact that some of the observations from the Weddell Sea area were obtained 

 in comparatively low latitudes. If all the sixty-seven analyses from the Bellingshausen 

 Sea over the two seasons are lumped together, and compared with the sixty-one from 

 the Weddell Sea area over the same period, it will be found that the average estimated 

 number of organisms in the Bellingshausen Sea was only 8,475,000 against some 

 15,695,000, a sufficiently striking difference despite the many obvious factors that tend 



1 See however p. 72. 



