. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. 146 NIELSEN [chap. 7 estimating the rate of respiration to 8% of the rate of light-saturated photo- synthesis, as was done by Steemann Nielsen (1952). The rate of the true net production is thus obtained by multiplying the experimentally found value by a factor of 96. In order to obtain a value of true gross production we must- multiply by a factor of ft 1,000 2,000 3,000 4,000 Lux Fig. 7. Experiments for measuring the rate of respiration (see text). (After Steemann Nielsen and Hansen, 195
. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. 146 NIELSEN [chap. 7 estimating the rate of respiration to 8% of the rate of light-saturated photo- synthesis, as was done by Steemann Nielsen (1952). The rate of the true net production is thus obtained by multiplying the experimentally found value by a factor of 96. In order to obtain a value of true gross production we must- multiply by a factor of ft 1,000 2,000 3,000 4,000 Lux Fig. 7. Experiments for measuring the rate of respiration (see text). (After Steemann Nielsen and Hansen, 1959.) G. The Influence of Dark Fixation and Isotope Discrimination It is generally known that, in animals as well as in plants, a dark exchange of CO2 takes place which has nothing to do with photosynthesis. In this way labelled CO2 may be introduced into the organic matter of both plants and animals. In a culture of algae the dark fixation of 14C02 is negligible compared to the fixation due to photosynthesis at light saturation, as was first shown by Brown, Fager and Gaffron (1949). In ordinary 14C-experiments for measuring organic production in the sea other organisms are present in addition to the autotrophic algae. Nevertheless, in experiments lasting 4 h, the dark fixation in water from the photic layer is usually only a few (1-3) per cent of the fixation at light saturation. In water with a very low production, preferably from the lower boundary of the photic layer, dark fixation may be relatively higher (Fig. 8). The same is true in polluted water with a high stock of bacteria. Whenever possible, dark bottles should be employed in addition to the ordinary clear bottles and the dark fixation rates should be subtracted from the ordinary Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hill,
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