ii8 DISCOVERY REPORTS 



At the most southerly station on the Hne the high surface sahnity and low temperature 

 show clearly that the surface water was in the main of Weddell Sea origin, and the 

 analyses of the phytoplankton haul revealed notable differences from those obtained 

 farther to the north. C. valdiviae was still dominant in a rather poor catch (the time was 

 early for the spring increase to have got far advanced in Weddell Sea water thus far 

 south), but to nothing like the same extent as over the rest of the Bransfield Strait at this 

 time. Sixteen species of diatoms were recorded as against a maximum of ten (St. 

 WS 476) at any one station in the rest of the strait on this survey. Here also Eiicampia 

 antarctica showed a strong maximum and other species forming a considerable propor- 

 tion of the catch were Thalassiosira antarctica and Fragilaria antarctica. Chaetoceros 

 atlanticus, Ch. dichaeta and the normal form of Rhizosolenia alata made their only ap- 

 pearance of the survey at this station, which also furnished our only records in the 

 Bransfield Strait of the littoral species Melosira sol and Biddulphia (Triceratium) 

 arcticum. The presence of these last-named species indicates the possibility of a strong 

 current flowing northwards through Antarctic Sound. 



The next line of stations on this survey (Sts. WS 483-7) was worked from a point south 

 of Macfarlane Strait to the vicinity of Astrolabe Island. The analyses of the phyto- 

 plankton material then collected are given in Table XXXVII. It will be seen at once 

 that little in the way of detailed description is necessary, as Corethron valdiviae was 

 strongly dominant throughout, very few other species being recorded and these in 

 entirely subordinate numbers. The hauls from the two northernmost stations on the 

 line were moderate in quantity, as also was that from the southernmost station, while 

 those from the two stations in the middle of the strait were considerably richer. The 

 increase in salinity at the two southernmost stations on this line probably indicated 

 some slight degree of mixing with Weddell Sea surface water, but this was apparently 

 without influence on the nature of the phytoplankton on this occasion. 



The analyses of the catches at the various stations worked at the western end of the 

 strait on this survey (Sts. 488-93) are shown in Table XXXVIII. It will be seen that 

 though Corethron was strongly dominant throughout, a much larger number of species 

 was recorded than on the line in the middle of the strait. The occurrence of species 

 other than Corethron was, however, both scattered and scanty, as might be expected 

 from the fact that the surface water in which they were taken was certainly of Bellings- 

 hausen Sea origin, in the course of percolating through the various western openings 

 of the Bransfield Strait proper. The pronounced dominance of Corethron in water of 

 this type occupying the greater part of the strait indicates that some factor in the local 

 conditions must be strongly unfavourable to the development of other forms. 



The most notable of the rarer species at these stations were Rhisosolenia gracillima 

 and Thalassiosira antarctica. Nitzschia seriata was present in considerable numbers at 

 St. WS 489. All these forms have been encountered in much greater abundance in the 

 Bellingshausen Sea somewhat later in the year. 



The phytoplankton hauls obtained at the western end of the strait on this survey were 

 very considerably poorer in quantity than those taken farther to the east, as may be seen 



