2 DISCOVERY REPORTS 



tions than anywhere else, we know there is an annual variation of temperature, salinity 

 and phosphate, and it can be assumed that there are corresponding variations in the 

 open ocean. 



In March 1933 the surface phosphate content at the ice-edge south of the South 

 Atlantic Ocean in c.-|-° E (St. 1154) was 104 mg., whilst about 250 miles north of this 

 position the surface value was 74 mg. ; this latter value was, however, accompanied by a 

 much heavier phytoplankton. 



We have no actual ice-edge figures south of Australia, but at St. 889 in 6i° 44-6' S, 

 13 1° 38-4' E at the end of May 1932 the surface value was 135 mg., a high winter value. 

 The position of this station was north of the ice-edge, which was in the extremely low 

 latitude of 63 41-4' S at this time of the year. The value of 135 mg. is very high, and 

 together with a content of 141 recorded at the ice-edge in 153 57-2' W in September 

 1932 probably represents the extreme value for surface phosphate at the ice-edge in 

 winter; a more usual figure is 130 mg. 



South of the Tasman Sea in mid-June 1932 the ice-edge surface value at St. 906 

 (6i° 247' S, 154 26-2' E) was 130 mg., but a short distance east at St. 912 (6i° 05' S, 

 158 24-5' E) the corresponding content was only 92 mg. St. 912 was situated in very 

 much shallower water than was St. 906, the respective depths being 991 and 3041 m. 

 The chemical and physical data for the water columns at these stations were very 

 different, and in particular the warm deep water at St. 912 was markedly less saline 

 and had a lower phosphate content and yet was much warmer than at St. 906. 



In September 1932 the ice-edge surface value north of the Ross Sea was 127 mg. at 

 St. 956 in 62 12-8' S, 158 n-o' W. In mid-January 1934 the corresponding station 

 was situated at a much higher latitude owing to the difference of season. The surface 

 phosphate at this station, 1267, in 69 49-4' S, 159 12-6' W was 82 mg. at a date when 

 phytoplankton production was in full activity and responsible for a large withdrawal 

 of nutrient salt. 



In January, February, March and November a large number of observations were 

 made along the Pacific ice-edge from the Ross Sea to 8o° W in which longitude there 

 are also data for September and October. In the first half of January 1934 from 77 to 

 i59°W the average ice-edge value of phosphate in the surface was 87 mg., which was 

 also the average of some eighteen stations within 200-250 miles of the ice-edge. In late 

 February to mid-March on the return voyage from west to east at an average latitude 

 slightly higher than the westward cruise, six ice-edge stations gave an average surface 

 phosphate of 88-5 mg., whilst all the stations within 200-250 miles from the ice gave an 

 average value of 88 mg. In the interval between the westward and eastward cruises it is 

 probable that the phyto-plankton of the southern region reached its maximum concen- 

 tration, but it is doubtful whether the average value for the surface phosphate dropped 

 much below 87 mg., which may represent an average minimum surface value for this 

 region. A comparison of this value with figures for the lower part of the Antarctic 

 surface layer shows that about 30 per cent of the available phosphate is withdrawn by 

 the phytoplankton at the ice-edge of the South Pacific sector of the Southern Ocean. 



