PHYTOPLANKTON AND HYDROLOGY 



77 



to be inhibited by lack of phosphates as it is in our home waters. 1 The relatively high 

 phosphate content of these surface layers as compared with that of the surface layers of 

 lower latitudes or even of corresponding latitudes in the northern hemisphere is one of 

 the most N striking characteristics of the Antarctic Zone. This rich supply of phosphates 

 appears to be locked up in the circulation between the deeper layers of the ocean in 

 lower latitudes and the cold surface water of the Antarctic (see p. 8). The change in 

 phosphate content of the surface water from the Equator to the Antarctic was well shown 

 by Ruud's (1930) surface samples taken on the Vikingen Expedition in 1929, and in 

 greater detail for all depths by the ' Discovery II ' in April and May of 1931. The values 

 for depths down to 1000 m. are shown in Table VI, where the figures are taken from 



Table VI 

 Phosphate estimation expressed as mg. per cubic metre made by the ' Discovery IF on a line 

 of stations along the meridian 30 Wfrom latitude 57 36' S to 09 47' S, April-May, 

 1 93 1. Values below 80 in heavy type 



the Station List in vol. IV of the Discovery Reports. Atkins (1923 a) has shown for the 

 English Channel that the changes in the phosphate content of the surface layers from 

 35-40 mg. per cu.m. in mid-winter to 0-5 mg. per cu.m. in summer are correlated with 

 the production of the spring phytoplankton maximum. In 1926 at South Georgia the 

 average phosphate content for the upper 50 m. in December (Antarctic summer) at five 

 stations on the C line off the north-east coast is 95 mg. per cu.m., and at corresponding 

 stations some three weeks earlier it was 1 10 mg. per cu.m. The phosphate values along 

 these lines may be compared in Table VII. To see a change over a longer period and 

 from winter conditions, we must look beyond our present survey to the data obtained 

 in the surveys of 1928 published in the Station List in vol. m of the Discovery Reports. 



1 This is further discussed on pp. 85 and 86. 



