WARM DEEP WATER 



79 



also varies from year to year, as, for example, at Sts. 1 154 and 1525 which were situated 

 at the ice-edge in about io° E and made in 1933 and 1935. The following data were 

 obtained : 



The data shown in the above table are typical of the differing contents of the warm 

 deep water at the same position in different years. 



The phosphate content of the warm deep water is always large, and in the Antarctic 

 zone the actual maximum in the water column usually occurs in this layer. 



In the Drake Passage (section i, Plate III), maximum phosphate occurs in the warm 

 deep water in both the Antarctic and sub-Antarctic zones. In the Antarctic zone the 

 maximum is of the order of 140-150 mg. and is situated in the upper part of the warm 

 deep water, whilst in the sub-Antarctic zone the maximum, though still in the warm 

 deep layer, is at a greater depth and is of the order of 130-140 mg. 



In the Antarctic zone of the South Atlantic Ocean the phosphate content increases 

 rapidly across the discontinuity layer which separates the Antarctic surface water and 

 the warm deep layer. In the Scotia Sea and around South Georgia the phosphate 

 content of the whole column is a maximum in the upper layers of the warm deep current ; 

 this maximum is usually of the order of 140-160 mg., the content falling off slightly 

 through the remainder of the layer and sometimes increasing again in the bottom water. 

 Some stations worked in 193 1 and 1934 gave a maximum phosphate content in the 

 bottom water in the region between Elephant Island and the South Shetland Islands. 

 This region is one in which Deacon (1937, p. 108) says there is evidence for the formation 

 of Antarctic bottom water on a small scale, by the complete vertical mixing of the whole 

 water column during winter so that the cold surface water finds its way directly into the 

 bottom layer. 



The distribution of phosphate at the depth of maximum temperature and salinity of 

 the warm deep water in the Scotia Sea northwards from the South Orkney Islands to 

 the Antarctic convergence on three occasions in the season 1934-5 * s shown in Fig. 22. 

 The greatest variation at both depths in the current occurred in April, when the content 

 varied between 127 mg. and 174 mg. at the upper level and between 135 mg. and 

 165 mg. at the depth of maximum salinity. In January and October the variation 

 between the two levels and from north to south was much less. 



To the east of the South Sandwich Islands the warm deep water, though possessing 

 a high phosphate concentration, was not in 1934 the seat of the maximum which was 

 found in the bottom water in this locality. 



The phosphate distribution along section 2 in the western part of the South Atlantic 

 Ocean in 193 1 is given in Plate IV, which shows a vertical section in 30 W from 57 36' S, 

 to i4°27|'N (Sts. 661-699). The warm deep water is of North Atlantic origin, and 



