PARTICULATE ORGANIC MATTER I N SEA WATER
103
includes free amino acids and other substances which should be readily
utilizable by heterotrophs. Thus the general stock of dissolved organic
matter in the deep sea includes materials that have been recently
produced in situ by the local assemblage of bathypelagic animals.
Theoretically, such things as amino acids could either be utilized
directly by heterotrophs or could be adsorbed on particulate matter,
which would make them available either to bacteria or to filter feeders.
The general concept that dissolved organic matter originates at the
surface and has a long residence time in deep water is true as a generalization, but these recent observations suggest that internal recycling of
“ young ” materials could be a significant aspect of the biological
economy of the deep sea. However, measurements of excretory rates
thus far have been limited to zooplankton collections taken in the
surface layer, and the results cannot be extrapolated to a quantitative
estimate of excretion under the semi-starvation conditions of the
bathypelagic zone.
As indicated earlier, most of the nitrogenous material in deep water
is in the form of amino N, yet much of the older material must be
combined in forms that make it resistant to biological attack. The low
concentration occurring in nature cannot be the only reason for its
inability to support active heterotrophic growth. Barber (1968) increased the concentration by pressure dialysis but found no significant
utilization in experiments of 1-2 months’ duration. Of course the
method is not precise enough to detect small changes with certainty.
Rakestraw (1947) reported small but significant reductions in oxygen
in long term B.O.D. experiments. The carbon equivalent of this consumption was of the order of 0.1 mg/litre in experiments lasting
considerably longer than Barber’s. While this amount is small compared with the B.O.D. of surface waters, it is in fact much more rapid
than estimated in situ rates of consumption. Presumably the bacteria
were growing more effectively in the bottles than they do in the sea,
as is usual in this kind of experiment.
Degens (1968) has noted that ratios of C13 to C12 are essentially
similar in living plankton, in non-living particulate organic matter and
in recent marine sediments, and there is a reduction in the ratio in
dissolved organic matter and in ancient marine sediments. Biological
utilization of the organic matter presumably has resulted in isotope
fractionation. For example, Degens quoted evidence that the CO,
released during decarboxylation of amino acids can be significantly
enriched in C13 in relation to the remainder of the molecule, and the
remaining organic matter of course will be correspondingly depleted.
Degens concluded that the sediments were derived primarily from
103
includes free amino acids and other substances which should be readily
utilizable by heterotrophs. Thus the general stock of dissolved organic
matter in the deep sea includes materials that have been recently
produced in situ by the local assemblage of bathypelagic animals.
Theoretically, such things as amino acids could either be utilized
directly by heterotrophs or could be adsorbed on particulate matter,
which would make them available either to bacteria or to filter feeders.
The general concept that dissolved organic matter originates at the
surface and has a long residence time in deep water is true as a generalization, but these recent observations suggest that internal recycling of
“ young ” materials could be a significant aspect of the biological
economy of the deep sea. However, measurements of excretory rates
thus far have been limited to zooplankton collections taken in the
surface layer, and the results cannot be extrapolated to a quantitative
estimate of excretion under the semi-starvation conditions of the
bathypelagic zone.
As indicated earlier, most of the nitrogenous material in deep water
is in the form of amino N, yet much of the older material must be
combined in forms that make it resistant to biological attack. The low
concentration occurring in nature cannot be the only reason for its
inability to support active heterotrophic growth. Barber (1968) increased the concentration by pressure dialysis but found no significant
utilization in experiments of 1-2 months’ duration. Of course the
method is not precise enough to detect small changes with certainty.
Rakestraw (1947) reported small but significant reductions in oxygen
in long term B.O.D. experiments. The carbon equivalent of this consumption was of the order of 0.1 mg/litre in experiments lasting
considerably longer than Barber’s. While this amount is small compared with the B.O.D. of surface waters, it is in fact much more rapid
than estimated in situ rates of consumption. Presumably the bacteria
were growing more effectively in the bottles than they do in the sea,
as is usual in this kind of experiment.
Degens (1968) has noted that ratios of C13 to C12 are essentially
similar in living plankton, in non-living particulate organic matter and
in recent marine sediments, and there is a reduction in the ratio in
dissolved organic matter and in ancient marine sediments. Biological
utilization of the organic matter presumably has resulted in isotope
fractionation. For example, Degens quoted evidence that the CO,
released during decarboxylation of amino acids can be significantly
enriched in C13 in relation to the remainder of the molecule, and the
remaining organic matter of course will be correspondingly depleted.
Degens concluded that the sediments were derived primarily from