PHOSPHATE AND SILICATE IN THE 

 SOUTHERN OCEAN 



By A. J. Clowes, m.Sc, a.r.c.s. 



(Plates I-XXV; Text-figs. 1-29) 



INTRODUCTION 



FOR some years past the Discovery Committee has been collecting hydrological data 

 in southern waters. Amongst these data is a large number of estimations of the 

 phosphate and silicate contents of the various waters encountered in the Southern 

 Ocean. The importance of a knowledge of the distribution and fluctuations of phosphate 

 and silicate in this ocean may clearly be seen when it is realized that these nutrient salts 

 are essential to the life economy of the huge concentrations of plankton found in southern 

 waters. The plankton forms the basic food supply of the whales, and in the production 

 of this food supply enormous quantities of these two nutrient salts are withdrawn from 

 the sea water. This report describes our present knowledge of the distribution, fluctua- 

 tions and cycles of these two important salts. 



Consideration has only been given to those estimations which were obtained by 

 analysis as soon as the samples of sea water had come to laboratory temperature ; only 

 the results of analyses carried out on board R.R.S. 'Discovery II' are included here. 

 It is felt that by excluding all material which had to wait more than about 12 hours before 

 analysis, a more accurate series of results is obtained, since changes in the nutrient salt 

 content of the samples due to phytoplankton and bacteria is minimized. 



So far only part of the data has been published {Discovery Reports, iv, pp. 1-232), 

 but reference to the plates at the end of this report will show that most of the data have 

 been inserted in the vertical sections which have been so carefully drawn by Miss E. C. 

 Humphreys. The data not shown in the vertical sections are usually those between 

 o and 200 m. ; these have been omitted only to prevent confusion in the plates which, 

 however, were constructed with the aid of all the data. At most stations observations 

 were made at o, 10, 20, 30, 40, 50, 60, 80, 100, 150, 200, 300, 400, 600, 800, 1000, 

 1500, 2000, 2500, 3000 m. and at intervals of 500 m. to the bottom. Unprotected 

 thermometers were used with the reversing bottles so that the true depth of the sample 

 could be calculated. 



No attempt has been made to correct the data for salt error. It was considered that 

 the present state of our knowledge on this question was insufficient to warrant the making 

 of such corrections which indeed might have to be recalculated later on. All values of 

 phosphate and silicate contents are given as milligrammes of P 2 5 and Si0 2 respectively 

 per cubic metre of sea water. The coeruleomolybdic method of Deniges as adapted by 

 Atkins (1923 a), was used for the analysis of phosphate, whilst the method of Dienert 

 and Wandenbulcke, introduced into sea-water analysis by Atkins (19236), was used for 



