ANTARCTIC BOTTOM WATER 103 



station and ranged from 50 to 1700 mg. In general the content of the bottom water in 

 this area varied from 5500 to 7500 mg. being greater at the more northerly stations in 

 the basin, and less at the ice-edge stations. There are some indications of a cyclonic 

 circulation of the bottom water, with an easterly movement towards the north of the 

 basin and a southerly movement at approximately 30° E. A considerable variation in 

 silicate content of the bottom water exists in this basin, particularly in the eastern part 

 where in May 1934 (section 6, Plate XI) silicate of the order of 7500 mg. was found 

 in the bottom water of o° C. whilst in February-March 1935 only 5500-6000 mg. was 

 recorded (section 4, Plate VIII). 



In May 1932 the deepest observations in the Antarctic zone (section 8, Plate XIII) 

 south of Australia, had a silicate content of 6000-6500 mg. which slowly decreased 

 north of the convergence. In the south Australian basin where the bottom water is 

 clearly mixed with a considerable amount of warm deep water from the Atlantic and 

 Indian Oceans the bottom water had a content of 5400 mg. 



Two sets of observations south-east of New Zealand are shown in Plates XVIII 

 and XX. In 1932 (Plate XVIII) the content of the bottom water was between 4500 mg. 

 and 5000 mg. at the deepest observations at the southern end of the section as compared 

 with over 6000 mg. in a comparable latitude in 1934 (Plate XX). Actually more than 

 7000 mg. was recorded in 67^° S in 1934 at a depth of 2500 m. The bottom water south- 

 east of New Zealand consists of a mixture of the eastward flowing bottom water from 

 the Weddell Sea and warm deep water of mixed origin. The fact that the silicate 

 contents of the bottom water were so different in the two years must be due to the 

 seasonal and probable annual variations in the constituent waters. In 1932 at the deep 

 stations south of the shallow water near New Zealand, the silicate content increased 

 continuously with depth in the bottom current to values of 4200-4400 mg. at a depth 

 of 4500 m. In 1934 the observations did not extend below 3500 m., at which depth the 

 content was of the order of 5300 mg. 



In September 1932 from the ice-edge north of the Ross Sea to 41 03' S, 126 04' W 

 in the central part of the South Pacific (section 14, Plate XXII), the Antarctic 

 bottom water between 160 and I30°W was warmer and more saline than it was 

 north of the Ross Sea; it also advanced more towards the north. Deacon (1937, 

 p. 115) has shown that this advance was not caused by an increase in the current 

 due to sinking of shelf water, but is rather due to the influence of the Cape Adare- 

 Easter Island ridge which causes the bottom current to bend towards the north in the 

 shallower water between 160 and 150 W and to bend back towards the south between 

 150 and 140 W on the other side in the deeper water. The silicate content of the bottom 

 water in this section shows that on the actual ridge, which is about 3000 m. from the 

 surface, there was about 4500-5500 mg. at a depth of 2500 m., whilst in the deeper 

 water between 150 and 140 W there was a content of 4300 mg. at a depth of 4500 m. 



The remainder of the 1932 cruise across the South Pacific (Plates XXIV and XXV), 

 showed that in the deep stations in both the Antarctic and the southern part of the 

 sub-Antarctic zones the bottom water had a content of the order of 5000 mg. 



