9 6 



DISCOVERY REPORTS 



subject to annual or seasonal variation. Much more silicate was present in 1934 than 

 in 1932. The following table shows this: 



September 1932 



SiO., at maximum salinity 

 t° C. 



3'5° (47° 4 1 ' 6 ' 8 ) 



1400 (just north of Antarctic convergence) 



43°° (355° at ice-edge) 

 3150 (at ice-edge) 



January 1934 



SiO a at maximum salinity 

 f C. 



475° (47° l6 -5' S) 



1450 (just north of Antarctic convergence) 



5000 (at ice-edge) 

 4650 (at ice-edge) 



In the central part of the South Pacific the content decreased northwards across the 

 Antarctic zone from values of 3850 mg. and 4500 mg. at the depths of maximum tem- 

 perature and salinity to values of 1200 mg. and 3600 mg. respectively just north of the 

 Antarctic convergence. The current was at a greater depth in the sub-Antarctic zone 

 and the silicate content increased. 



In the ice-edge region of the South Pacific, except in the extreme east, the silicate 

 content of the warm deep water increased from east to west from 3000-3300 mg. in 

 the east to 4600-4700 mg. in the west in the upper part of the current, and from 3500- 

 4000 mg. in the east to 5000-5300 mg. in the west at the deeper position of the salinity 

 maximum. This increase in silicate content is connected with the general direction of 

 movement of the current which is towards the east and south. Also the increased 

 temperature from west to east in the current indicates that the deep water in its passage 

 from west to east is mixing with other waters and loses silicate in so doing. 



In 8o° W five sets of observations in different months showed that the silicate content 

 in the upper part of the warm deep water decreased from south to north across the 

 Antarctic zone. The content at the ice-edge ranged from 4500 mg. in 68° S, in March, 

 to 3250 mg. in 64 S, in September. There was a further fall to 1500-2500 mg. in 58 - 

 59 S. Approximately 5000 mg. were present at the ice-edge at the depth of maximum 

 salinity, a content which decreased slightly northwards. 



ANTARCTIC BOTTOM WATER 

 PHOSPHATE AND SILICATE CONTENT 



There is no sharp density discontinuity between the warm deep water and the colder 

 bottom water. Evidence for the existence of these two currents is of course supplied 

 by longitudinal sections of temperature, salinity and oxygen content in the South 

 Atlantic, Indian and Pacific Oceans. The phosphate content of the bottom water may 

 best be seen from the sections in the plates at the end of this report. It is not possible 

 to give charts of horizontal distribution in this layer because at present our data are 

 inadequate to make allowances for seasonal or annual variation, i.e. although we have 



