of the light energy than at the same optical depths in richer regions. 

 According to our results, in a mesotrophic region, the attenuation of 

 penetrating radiation by pigments at the surface is 1%, increasing to 5% 

 of the total attenuation at the depth reached by 1% of the light, while 

 in a eutrophic region, the corresponding values are 50% and 80%. Thus, 

 the difference between eutrophic and mesotrophic regions at the surface 

 is a factor of 50, and at the 1% light-penetration depth--a factor of 16 

 (Koblentz-Mishke et al., 1975). This is almost proportional to the mean 

 difference of Q^ in Fig. 7, d: 5.5 times at the surface, 2 times at 

 the depth of 1% light penetration. These simple calculations confirm 

 the fact that the light energy absorbed by phytoplankton pigments in 

 mesotrophic waters is used in photosynthesis with effectiveness equal to 

 that of eutophic waters. 



The values of energetic effectiveness of photosynthesis obtained 

 indicate that, at least in the lower portion of the euphotic layer, the 

 radiocarbon method of measurement of primary production yields quite 

 realistic results. At greater depths, clearly overestimated data are 

 obtained, apparently a result of methodologic measurement errors. 



The possibility of estimating the influence of environmental 

 factors on photosynthesis by means of energetic effectiveness is also 

 quite important. 



Conditions of mineral nutrition . The study of the variation of 

 primary production of the oceans with conditions of mineral nutrition is 

 a significantly more difficult task than the study of its variation with 

 the influence of light, due to the interconnection and interaction of 

 the elements of mineral nutrition, due to the fact that in oceanographic 

 practice their secondary characteristics are determined, and especially 

 due to the existence in certain cases of feedback between the production 

 and concentration of nutrients. 



The demand of phytoplankton for various nutrient elements has been 

 studied to widely varying extents. Phosphorus has been comparatively 

 well studied, silicon to a lesser extent, nitrogen still less, 

 particularly in the ammonia form, and almost no studies of iron demand 

 have been made. As concerns the role of microelements and biologically 

 active substances, the literature contains only a few more or less 

 probable hypotheses. The primary source of nutrient substances is the 

 reserve of the substances, which is accumulated in deeper waters as a 

 result of the decomposition of organisms, then rises into the 

 photosynthetic layer. A second source of supply of nutrient elements 

 for algae is their regeneration in the photosynthetic layer itself in 

 the process of decomposition of organic compounds by bacteria (Dugdale, 

 Goering, 1967) and by zooplankton. The rate of regeneration of various 

 nutrients is not identical, and, in general, depends on the temperature 

 and relationship between the quantities of phytoplankton and 

 zooplankton. In the tropics, it occurs more rapidly than in the 

 temperate regions, due to the high temperature and as a result of the 

 higher relative quantity of zooplankton. A third source is the arrival 

 of nutrients with river runoff from the land (Sutcliffe, 1972) and upon 

 mineralization of organic matter in shelf sediment. This source is 

 important only in the seas and in the inshore areas of the ocean. One 



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