RHIZOSOLENIA CURVATA 



433 



the point of view of this study. The complications induced by the land masses when the 

 main westerly drift of the Southern Ocean flows through Drake Passage to the eastward 

 are responsible for the great southward extension of the sub-Antarctic surface water in 

 this region. As a result the Antarctic convergence in the eastern South Pacific is found 



64"S. 

 I 



63° 



62" 



I 



2000 

 



so.ooo- 



10,000 







4000 



2.000 





 4,000 



2.000 







8,000 



6.000 



4,000 



2.000 



1 





 4000n 



-O- 



I 



60 

 I 



59 



58" 



Il_& 



J I 



1 



1 



1 



*2 



1_JL 



* 



1 



57" 



I 



56" 

 I 



OCTOBER 1932 



DECEMBER 1933 



1 



MARCH 1934 



SEPTEMBER 1934 



OCTOBER 1934 



NOVEMBER 1934 



2,000- 



oJ-o 



Fig. 5. Observations of Rhisosolenia curvata in longitude 8o° W. The continuous vertical line represents the 

 average position of the Antarctic convergence, and the arrows its probable actual position during each series 

 of observations. 



more than 5 farther to the southward than in any other sector. The great difference in 

 latitude enables true sub-Antarctic surface water to reach much lower temperatures 

 here than elsewhere, and provides the explanation of most of the differences between 

 such data as are recorded in Table VI and those from other areas. Thus at St. 141 7, 

 where R. curvata was found in its maximum numbers in September 1934, the surface 

 temperature was only 1-82° C, which in any other area would immediately lead one to 

 suspect that the water was mainly of Antarctic origin. As indicated in Fig. 5, however, 



