415
Primary Production in the Oceans
liquid chromatography) to determine low molecular weight organic compounds in seawater. The organic compounds are reacted with fluorescence compounds that react with
specific functional groups (acids, aldehydes, amines, etc.) and are detected using a fluorescence detector.
The DOM in seawater consists largely of humic substances and more labile compounds
from the major biochemically important compound classes such as carbohydrates, steroids,
alcohols, amino acids, hydrocarbons, and fatty acids (as well as fatty acid esters and waxes).
9.4.2.2 Particulate Organic Matter
Of the TOC in the oceans, it has been estimated that POC constitutes only 1 to 10%.
Frequently, POM is evaluated from measurements of POC made by carbon analyses or
organic- free glass fiber filters (0.45-μm pore size) used to separate POM and DOM. POM is
obtained by multiplying POC by a factor of two, based on the approximation that carbon
constitutes roughly 50% by weight of marine organic matter. PON and particulate organic
phosphorus (POP) compounds are much less than the POC (see Table 9.9).
POM consists of a mixture of living and dead phytoplankton and zooplankton, and
bacteria and their degradation and exudation products and macroscopic aggregates often
termed “marine snow.” The distribution and nature of POM have been found to be quite
variable geographically, vertically, diurnally, and seasonally and are influenced by a complex set of equilibria between sources, sinks, and circulation patterns. In the euphotic
zone, the major portion of the POM comes from phytoplankton, the chemical composition
of which will vary with species as well as with environmental conditions, hence leading to
significant variations in the nature of the POM. The metabolic products of phytoplankton
can vary with changes in temperature, light intensity, and nutrient availability. Much less
is known about the chemical content and biogeochemistry of POM than is known about
DOM. In the euphotic zone, the majority (90%) of POC comes from living matter, while at
depths of 2400 m and more, less than 1% of the POC comes from living organisms.
Much research activity has focused on the vertical flux of POM from the surface waters of
the ocean to the seafloor (Lee and Wakeham, 1989). The chemical and biochemical changes
that occur as particles sink through the water column significantly affect the composition
of both the sediments and the overlying water. Thus, the physical and biogeochemical
processes that affect the composition of sinking particulate matter also affect biological productivity in the water column as well as modify the organic matter that reaches the ocean
floor and serve in turn as a major source of nutrition for benthic organisms and as a source
of precursors to marine- derived fossil fuels.
Sediment trap experiments conducted at various depths have recently yielded valuable
information on the chemical content and fluxes of marine POM. Sediment traps are large
cones fitted with a number of baffles, and they collect the particulate material in bottles
containing brine and sodium azide to retard the growth of bacteria. The downward flux of
POC appears to be dominated by rapidly sinking particles, that is, particles with diameters
greater than 62 μm. The organic components of these particles consist largely of zooplankton fecal pellets, zooplankton and phytoplankton remains, and humic substances. The
chemical content of these particles is affected by a very complex set of reactions, including
degradation and transformation processes that result in the increased removal of some
labile organic compounds with depth, while other labile organic compounds (often unsaturated), as reported by Wakeham et al. (1984), were found at depths as great as 5068 m (see
Figure 9.43 and Figure 9.44). The feeding activity of meso- and bathypelagic zooplankton
on these rapidly sinking particles was invoked by Wakeham et al. to explain the selective
Primary Production in the Oceans
liquid chromatography) to determine low molecular weight organic compounds in seawater. The organic compounds are reacted with fluorescence compounds that react with
specific functional groups (acids, aldehydes, amines, etc.) and are detected using a fluorescence detector.
The DOM in seawater consists largely of humic substances and more labile compounds
from the major biochemically important compound classes such as carbohydrates, steroids,
alcohols, amino acids, hydrocarbons, and fatty acids (as well as fatty acid esters and waxes).
9.4.2.2 Particulate Organic Matter
Of the TOC in the oceans, it has been estimated that POC constitutes only 1 to 10%.
Frequently, POM is evaluated from measurements of POC made by carbon analyses or
organic- free glass fiber filters (0.45-μm pore size) used to separate POM and DOM. POM is
obtained by multiplying POC by a factor of two, based on the approximation that carbon
constitutes roughly 50% by weight of marine organic matter. PON and particulate organic
phosphorus (POP) compounds are much less than the POC (see Table 9.9).
POM consists of a mixture of living and dead phytoplankton and zooplankton, and
bacteria and their degradation and exudation products and macroscopic aggregates often
termed “marine snow.” The distribution and nature of POM have been found to be quite
variable geographically, vertically, diurnally, and seasonally and are influenced by a complex set of equilibria between sources, sinks, and circulation patterns. In the euphotic
zone, the major portion of the POM comes from phytoplankton, the chemical composition
of which will vary with species as well as with environmental conditions, hence leading to
significant variations in the nature of the POM. The metabolic products of phytoplankton
can vary with changes in temperature, light intensity, and nutrient availability. Much less
is known about the chemical content and biogeochemistry of POM than is known about
DOM. In the euphotic zone, the majority (90%) of POC comes from living matter, while at
depths of 2400 m and more, less than 1% of the POC comes from living organisms.
Much research activity has focused on the vertical flux of POM from the surface waters of
the ocean to the seafloor (Lee and Wakeham, 1989). The chemical and biochemical changes
that occur as particles sink through the water column significantly affect the composition
of both the sediments and the overlying water. Thus, the physical and biogeochemical
processes that affect the composition of sinking particulate matter also affect biological productivity in the water column as well as modify the organic matter that reaches the ocean
floor and serve in turn as a major source of nutrition for benthic organisms and as a source
of precursors to marine- derived fossil fuels.
Sediment trap experiments conducted at various depths have recently yielded valuable
information on the chemical content and fluxes of marine POM. Sediment traps are large
cones fitted with a number of baffles, and they collect the particulate material in bottles
containing brine and sodium azide to retard the growth of bacteria. The downward flux of
POC appears to be dominated by rapidly sinking particles, that is, particles with diameters
greater than 62 μm. The organic components of these particles consist largely of zooplankton fecal pellets, zooplankton and phytoplankton remains, and humic substances. The
chemical content of these particles is affected by a very complex set of reactions, including
degradation and transformation processes that result in the increased removal of some
labile organic compounds with depth, while other labile organic compounds (often unsaturated), as reported by Wakeham et al. (1984), were found at depths as great as 5068 m (see
Figure 9.43 and Figure 9.44). The feeding activity of meso- and bathypelagic zooplankton
on these rapidly sinking particles was invoked by Wakeham et al. to explain the selective