44 



DISCOVERY REPORTS 



SEASONAL VARIATION OF PHOSPHATE IN THE SURFACE LAYER 



AROUND SOUTH GEORGIA 



Although samples for phosphate analysis were taken in the hydrological surveys of 

 December 1926-January 1927, August-September 1928 and December 1928-January 

 1929, it is not considered that an accurate account of the seasonal variation of phosphate 

 in the surface layer at South Georgia can be obtained from a study of these figures. 

 The objection is that these results were obtained from samples which had been stored 

 for varying amounts of time before analysis, and the results are therefore liable to be affected 

 by phyloplankton and bacteria. We are therefore left with five sets of observations on 

 which analysis was made immediately the samples had attained laboratory temperature. 

 The average dates of these observations, the average contents for the surface and 

 0-100 m. layer are given in Table IV. 



Table IV 



Unfortunately, in addition to the material being collected in different years, only three 

 months are represented, and although these are such that they represent an approach 

 to maximum and minimum amounts of phosphate content, no complete graph of the 

 seasonal variation can be drawn. It is interesting to note that the 0-100 m. averages 

 are nearly the same as the surface values in all the sets of observations. This is an 

 indication of the thorough mixing to which the surface layer is subjected at South 

 Georgia. The average surface value of 120 mg. at the end of August 1934 must be 

 very close to the maximum content in this vicinity. 



The February observations were taken at times which were well past those of the 

 peak concentrations of phytoplankton, and thus the two surface averages in 1930 and 

 1935 of 79 and 74 mg. respectively, are probably higher than the average for December, 

 i.e. just after the maximum concentration is reached. In 1930 and 1935 the averages 

 for the 0-100 m. layer had the same value. Exceptionally, the surface value has fallen 

 to figures of 53 and 40 mg. 1 in early February, but it is obvious that a more usual value 

 is of the order of 75-80 mg. This would seem to indicate that the average minimum 

 surface value around South Georgia in late December or early January is probably 

 of the order 65-70 mg., as opposed to a mid-winter figure of about 120-130 mg., the 

 maximum surface content recorded in August 1934 being 130 mg. If the order of 



1 See also footnote on p. 112. 



