WARM DEEP WATER 



9' 



2500 m. until a latitude of 54 S was attained. South of 54 S the depth increased to about 

 5000 m. until the gradual rise to the Ross Sea began. The silicate content in this section 

 is shown in Plate XVIII. At the deep station in 47 41-6' S the warm deep water had a 

 content of 3150 mg. at the depth of maximum salinity. South of this latitude where 

 the depth was great enough for the existence of warm deep water of a maximum 

 salinity of 3475 °/ 00 in the north and of 3472 °/ 00 in the south, the silicate content 

 at this depth increased slowly to 4300 mg. just north of the ice. At the actual ice-edge 

 station the corresponding content was rather surprisingly low at 3550 mg., but the 

 phosphate content was also considerably lower, giving the impression that the warm deep 

 water had been mixed with water of a lower nutrient salt content. It is difficult to say 

 what admixture had occurred, since the salinity of the layer had not been greatly affected 

 and the maximum was 3472 °/ 00 compared with 3473 °/ 00 at the station immediately 

 to the north. The content in the upper part of the current increased southwards from 

 a value of 1400 mg. at St. 949 just north of the Antarctic convergence to 3150 mg. at 

 the ice-edge. 



In a somewhat similar section (13) in January 1934 from the ice-edge in 69 49-4' S, 

 north of the Ross Sea, to Auckland, New Zealand, shown in Plate XX, the warm 

 deep water contained much more silicate than in September 1932. Thus at the ice-edge 

 in January the upper layers of the current contained 4650 mg., while at the depth of 

 maximum salinity the content was 5000 mg., these amounts decreasing northwards, 

 particularly in the upper part of the current. Since the two sections were made at different 

 seasons of the year the latitude of the ice-edge was very different. In September 1932 the 

 ice-edge was as far north as 62 12-8' S. The following table gives a comparison with 

 a January station near this position : 



The increased amount of silicate in the observations of January 1934 was continued 

 throughout the section, and at St. 1281, which was situated closest to New Zealand, 

 the content at the depth of the lowest observation, at 2500 m., was as great as 5300 mg. 

 The difference between the amounts in the two years cannot be explained at present ; 

 in the absence of more knowledge of the seasonal and annual variations in the constitu- 

 tion of the warm deep water in this part of the ocean, no definite conclusion can be 

 reached. It is obvious, however, that something of the nature of a seasonal or an annual 

 variation does exist, since the maximum salinity of the warm deep water near New 

 Zealand was 3475 % in September 1932 and 3478 °/ 00 in January 1934; this difference 

 of 0-03 °/ 00 is a very significant one in such a deep layer. 



In the South Pacific Ocean, owing to the low latitude attained by the subtropical 



