WARM DEEP WATER 85 



in the upper layers of the current ; at the greater number it was situated in the highly 

 saline bottom water in the area between 130 and 170 W in the western part of the 

 deep basin in the Antarctic zone of this ocean. The phosphate content at the depth of 

 maximum temperature, i.e. in the upper part of the current, averaged 130 mg. on the 

 east to west cruise and 146 mg. on the west to east cruise. The two cruises took 18 and 

 16 days respectively and were separated by 37 days from the end of one to the beginning 

 of the other. The return or eastward cruise was at a slightly higher latitude owing to 

 the retreat of the ice-edge during the interval between the sets of observations. The 

 difference in phosphate content at this depth in the current must be ascribed to seasonal 

 variation. In the eastward cruise the content visibly increased from west to east, whilst 

 on the westward journey the corresponding decline was not quite so obvious. 



Along the routine line of stations in 8o° W our observations covered only the Antarctic 

 zone and part of the sub-Antarctic zone. The warm deep water was always the seat 

 of the maximum content which usually occurred in the upper part of the current, ranging 

 from i4omg. to i5omg. in most months ; an exception, however, was recorded in March 

 1934 when considerably higher values of 150-170 mg. were found. 



The preceding observations show that the phosphate content of the warm deep water 

 varies both seasonally and annually, and for this reason the amount of data we possess 

 is not sufficient to give an average content. The amounts of phosphate content given 

 in parenthesis below refer to content at specific dates and may vary at other times ; in the 

 Antarctic zone the content is always large. In the western part of the South Atlantic 

 Ocean maximum phosphate (140-150 mg.) occurs in the upper part of the warm deep 

 current as far north as the Rio Grande ridge (35 S), north of which the Antarctic 

 intermediate current contains more phosphate than the warm deep water (80-100 mg.). 

 Less phosphate was found in the deep current in the eastern side of the South Atlantic 

 than in the west — a maximum of H5-i2omg. in the Antarctic zone in March 1933 

 compared with 140-150 mg. in the west in April 1931. 



South of 6o° S in the Atlantic sector of the Southern Ocean maximum phosphate 

 was found sometimes in the upper part of the warm deep water (135-145 mg.) and 

 sometimes in the bottom water ; the reason for this is at present not understood. 



South of Cape Town maximum phosphate (140-150 mg.) occurred in the warm deep 

 water at stations in the Antarctic and sub-Antarctic zones. North of the subtropical 

 convergence the seat of maximum content was in the Antarctic intermediate current. 

 Similarly, in the western part of the South Indian Ocean maximum phosphate was 

 found in the warm deep water south of the subtropical convergence (155-165 mg. in 

 the Antarctic zone and 135-160 mg. in the sub-Antarctic zone), whilst in the sub- 

 tropical zone the maximum was in the intermediate current. In the tropical zone where 

 the deep water is of North Indian Ocean origin it again occurred in the warm deep 

 waterand increased towards the north (139 mg.at i8-|-° S and 161 mg. at 7 N). The North 

 Indian Ocean deep water has a greater content than the North Atlantic deep water. 



Across the Southern Ocean between Enderby Land and Fremantle, Australia, 

 maximum phosphate was always found in the warm deep layer, but south of Australia 



