. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. SECT. 2] PRODUCTIVITY, DEFINITION AND MEASUREMENT 149 only to multiply by a factor of 2. In the tropics the effect of very high light intensities is particularly conspicuous, for example the afternoon depression such as that demonstrated by Doty and Oguri (1957). In this case it is important always to use the same period for making experiments. The in situ method is time-consuming even when the experiments last only from noon to sunset. It is, therefore, in most cases too expensive to use on. 0
. The Composition of sea-water : comparative and descriptive oceanography. Seawater -- Composition. SECT. 2] PRODUCTIVITY, DEFINITION AND MEASUREMENT 149 only to multiply by a factor of 2. In the tropics the effect of very high light intensities is particularly conspicuous, for example the afternoon depression such as that demonstrated by Doty and Oguri (1957). In this case it is important always to use the same period for making experiments. The in situ method is time-consuming even when the experiments last only from noon to sunset. It is, therefore, in most cases too expensive to use on. 0 10 20 mg C/m day 0 10 20 30 mg C/m day 0 10 20 mg C/m day Fig. 9. In situ experiments in the Kattegat. Sunshine in all cases. (After Steemami Nielsen.) expeditions with big ships. Instead a simulated in situ method may be used. In experiments using water from the different depths the samples are suspended in a tube with running surface water on the deck. In order to imitate the light conditions at the different depths, plates of neutral glass filters are placed above the bottles containing sub-surface water. These neutral filters are chosen in such a way that they match the light absorption in the sea; since, however, the light quality here changes with the depth the imitation is only approximate. Beige (1958) showed that the results from such simulated in situ experiments. 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, M. N. (Maurice Neville), 1919-. New York : Interscience Pub.
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