PARTICULATE ORGANIC MATTER I N SEA WATER
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of their sustenance is derived directly from noii-living particles. Some
particles must be digestible, but earlier calculations also suggest that
if bacteria were solely responsible for utilization of this material, their
productivity could approximately satisfy animal needs.
Some of the organic matter is of course highly resistant to attack
by either animals or bacteria, so that although most of it is used up
eventually, it takes a long time. Thus the organic content of the sediments declines slowly with depth even in the deep ocean where sedimentation rates are slow.
The foregoing discussion, necessarily long because of the many
problems and uncertainties in this kind of analysis, does not reduce
to a precise balance sheet of production and consumption. A few
concluding generalizations are likely to be more useful than a recapitulation of numerical values.
Primary productivity occurs within the upper 100 m, more or less,
in the Sargasso Sea, and the level of productivity is believed to be
considerably higher than was indicated by so-called standard methods
of measuring C14 fixation. Net production plus extracellular production
ara believed to be of the order of 320-380 mg C.m-2.day-1.
About 75-80% of this production is utilized in the surface layer and
upper mid-depths by zooplankton and ultraplankton. The latter term
as defined by Pomeroy and Johannes (1968) includes bacteria, small
heterotrophic algae, and protista. This is primarily a microcosmic
assemblage within organic aggregates, and its total consumption is
probably slightly greater than that of zooplankton.
Approximately 20% of total Consumption is allocated to zooplankton and heterotrophs in the lower mid-depth region, the bathypelagic
zone, and the bottom. The major part of this consumption occurs at
mid-depths, down to and including the level of the oxygen minimum
layer. Total amounts consumed in the bathypelagic and benthic zones
are probably about equal, but in the one case it is thinly spread through
hundreds of metres and in the other it is concentrated into a small depth
range on and in and just over the bottom. Together they probably
account for less than 5% of the total consumption.
Throughout these deeper waters flakes are numerically more important than amorphous aggregates. They are colonized by bacteria
but do not develop complex microcosms. There are various indications,
although the evidence is not entirely convincing, that heterotrophy is
relatively less important in lower mid-depths and the bathypelagic
zone than it is in upper waters or on the bottom.
Higher carnivores have not been considered in this analysis, and
quantitative assessment of their importance in the whole of the deep
111
of their sustenance is derived directly from noii-living particles. Some
particles must be digestible, but earlier calculations also suggest that
if bacteria were solely responsible for utilization of this material, their
productivity could approximately satisfy animal needs.
Some of the organic matter is of course highly resistant to attack
by either animals or bacteria, so that although most of it is used up
eventually, it takes a long time. Thus the organic content of the sediments declines slowly with depth even in the deep ocean where sedimentation rates are slow.
The foregoing discussion, necessarily long because of the many
problems and uncertainties in this kind of analysis, does not reduce
to a precise balance sheet of production and consumption. A few
concluding generalizations are likely to be more useful than a recapitulation of numerical values.
Primary productivity occurs within the upper 100 m, more or less,
in the Sargasso Sea, and the level of productivity is believed to be
considerably higher than was indicated by so-called standard methods
of measuring C14 fixation. Net production plus extracellular production
ara believed to be of the order of 320-380 mg C.m-2.day-1.
About 75-80% of this production is utilized in the surface layer and
upper mid-depths by zooplankton and ultraplankton. The latter term
as defined by Pomeroy and Johannes (1968) includes bacteria, small
heterotrophic algae, and protista. This is primarily a microcosmic
assemblage within organic aggregates, and its total consumption is
probably slightly greater than that of zooplankton.
Approximately 20% of total Consumption is allocated to zooplankton and heterotrophs in the lower mid-depth region, the bathypelagic
zone, and the bottom. The major part of this consumption occurs at
mid-depths, down to and including the level of the oxygen minimum
layer. Total amounts consumed in the bathypelagic and benthic zones
are probably about equal, but in the one case it is thinly spread through
hundreds of metres and in the other it is concentrated into a small depth
range on and in and just over the bottom. Together they probably
account for less than 5% of the total consumption.
Throughout these deeper waters flakes are numerically more important than amorphous aggregates. They are colonized by bacteria
but do not develop complex microcosms. There are various indications,
although the evidence is not entirely convincing, that heterotrophy is
relatively less important in lower mid-depths and the bathypelagic
zone than it is in upper waters or on the bottom.
Higher carnivores have not been considered in this analysis, and
quantitative assessment of their importance in the whole of the deep