MARINE PLANKTON DIATOMS ON OPERATION HIGHJUMP* 



General . A series of water samples was collected from 

 the USS CACOPAN on Operation HIGHJUMP for investigation 

 of the Diatomaceae. The samples were collected by filling a 

 citrate bottle either with surface water obtained with a bucket 

 or with water obtained from various depths with Nansen 

 bottles. The positions of those samples collected in the 

 antarctic are plotted on figure 3. The species of diatoms 

 found at each station are listed in figure 37 with notations 

 indicating the relative abundance of diatoms at each station. 



According to the hydrographical data available, the Ant- 

 arctic Convergence is not sharply defined in the area from 

 which most of the diatom samples were taken, but lies some- 

 where between latitudes 59°S and 63°S. Sample 42, therefore, 

 was taken from the polar waters south of the convergence and 

 sample 44 was taken north of the convergence. There is a 

 surface water temperature difference of about 10 degrees F. 

 between the two stations, which is a further indication that 

 the convergence has been crossed. It can be seen from table 8 

 that the antarctic circumpolar surface water south of the 

 convergence supports an extremely rich phytoplankton popu- 

 lation which is strikingly absent from the waters to the north 

 of the convergence. The phytoplankton wealth of the antarctic 

 waters has been frequently commented upon before. "» i0 

 Hart 10 has suggested that the diminished population in the 

 subtropical and tropical regions are a result of the almost 

 complete lack of nutrient salts in the surface waters of these 

 regions, while in the polar regions nutrients cannot be re- 

 garded as a limiting factor at any time, since the content 

 never falls below a minimum of about 0.9 mygram-atoms of 

 PO4 per liter which is well above diatom needs. Hart con- 

 siders that the high nutrient content is caused by the fact 

 that the supply released by the spring break-up of the ice- 

 pack is never exhausted. The marked vertical mixing of the 

 antarctic waters, caused by weak thermal stratification, 

 results in the ascent of nutrient-rich deep water. This is un- 

 doubtedly another cause of this nutrient surplus. 



*This section was prepared by Brian Boden of Scripps Insti- 

 tution of Oceanography. 



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