10.4 Organic Matter in the Oceans
in the photic (or euphotic) zone where sunlight enables photosynthesis. As soon as the autotrophie organisms sink or are carried by currents into deeper
water, their growth ceases or they die. The depth of
the photic zone usually extends to between 50 and
100 m. At mid-Iatitudes, surface waters cool in winter, and the penetration of sunlight is limited. Consequently, primary production is low. As insolation
increases with the onset of spring, the phytoplankton
begins to grow and reproduce more rapidly, also developing in deeper water, and thus forming "plankton
blooms". Such blooms, however, are restricted to
areas with abundant nutrient supplies either from
rivers or from deeper upwelling waters (Sect. 5.3.3).
About one half to two thirds of the present-day
global oceanic primary production is derived from
these fertile areas of the ocean (Table 10.1; cf. Fig.
10.11), although these make up only approximately
one third of the ocean surface. Such an unbalanced
regional distribution of organie production is even
more pronounced when new production and export
production are considered (see below).
The present-day oeeanie primary produetion amounts to
about 36 x 10 15 gC/a = 36 x 10 9 tC/a; e.g. Berger et al.
1989; Sehlünz 1998). Related to the entire oeean surface,
this mass eorresponds to an average speeifie primary produetion rate of -100 tlkm 2 /a (also see Table 10.1).
In open oeean eonditions, primary produetion is -50
glm 2 /a, whereas in eoastal, non-upwelling regions about
150 glm 2 /a are typieal (Table 10.2). Oeean regions with
oligotrophie waters (e.g., areas of subtropieal gyres sueh as
the Sargasso Sea) eontribute less than 5% ofthe global new
produetion (see below), although they constitute as much
as 40% of the ocean surfaee.
Tbe Food Cbain
The primary production by phytoplankton is used by
heterotrophie organisms as food. In the present
oceans we can observe the following food chain, or
food web:
Phytoplankton (primary producers)
Zooplankton (herbivores, i.e., plant eaters).
Zooplankton (camivores, i.e., eaters of other zooplankton).
Fish (plankton-eaters.or fish-eaters).
Phytoplankton are eaten mainly by herbivorous zooplankton; they in turn are eaten by camivorous zooplankton or fish. At each "tropic level" in the food
chain, dissolved and suspended, dead örganic matter
is released from living organisms into the water. Part
of this organic detritus is used up by other
heterotrophie organisms living in the surface water,
but some dead plant and animal matter sinks into
deeper water, thereby supportirig life at all depths,
including on the sea floor (Fig. 10.6).
467
Most of the energy the animals gain from their
food is used for locomotion and other activities, and
only a small part for growth and reproduction. In
other words, the population at a higher trophic level
must be much larger (often five to six times by
weight) than the population at the lower trophic level
which feeds on the higher one. Thus, the amount of
organic matter produced by phytoplankton is reduced
drastically from one trophic level to the next, and the
biomass of the standing crop in the entire ecological
system represents only a small fraction of the primary
plant production. The organic matter, which is
needed as energy by organisms in the food chain, is
transformed into compounds with lower energy contents (through metabolism) and fmally by bacterial
activity into carbon dioxide and water.
At the same time, inorganic nutrients are released
into the water. If these salts remain in the trophic
zone or are recycled by currents into surface waters,
they allow high primary production to be maintained.
10.4.3 New Production and Export Production
General Aspects
Primary productivity and life processes in the photic
zone are not commonly a focus of geologie al and
sedimentological studies. Geologists are more interested in the burial and preservation of organic matter
below the sea floor. For this reason, marine biologists and sedimentologists have introduced the terms
new production and export production (e.g., Berger
et al. 1989). New production is the vertical organic
carbon flux below the photic zone (at about 100 m
below sea level, Figs. 10.5d and 10.6). Most new
production occurs in narrow, high-fertility belts
along the equator, the subpolar divergence zones, and
in regions of coastal upwelling (cf. Figs. 5.1 and 5.2,
Sects. 5.2.3 and 5.3.3).
The vertical particle flux between 100 m and the
sea floor is further reduced by organisms living in the
deeper water. The remaining proportion of organie
matter (OM) at a given depth, as on the sea floor, is
called .export production. Thus, the vertical carbon
flux fina!ly reaching the sediment surface is often
only a small fraction of the new production. However, settling of OM to the sea floor can only occur if
the organic compounds form organic particles or are
adsorbed to inorganic particles. Dissolved organie
matter per se does not settle.
Whereas primary production is difficult to quantify, new
produetion, i.e., the downward flux of particulate organic
matter, can be measured by free-floating particle traps (e.g.
lahn 1990; Berger and Wefer 1992). It mainly eonsists of
various dead organisms, mostly micro-organisms, and their
fragments as weil as fecal pellets, peloids, floes and aggregates. The quantity of this downward flux mayaiso reflect
the seasonal variation in primary production.
in the photic (or euphotic) zone where sunlight enables photosynthesis. As soon as the autotrophie organisms sink or are carried by currents into deeper
water, their growth ceases or they die. The depth of
the photic zone usually extends to between 50 and
100 m. At mid-Iatitudes, surface waters cool in winter, and the penetration of sunlight is limited. Consequently, primary production is low. As insolation
increases with the onset of spring, the phytoplankton
begins to grow and reproduce more rapidly, also developing in deeper water, and thus forming "plankton
blooms". Such blooms, however, are restricted to
areas with abundant nutrient supplies either from
rivers or from deeper upwelling waters (Sect. 5.3.3).
About one half to two thirds of the present-day
global oceanic primary production is derived from
these fertile areas of the ocean (Table 10.1; cf. Fig.
10.11), although these make up only approximately
one third of the ocean surface. Such an unbalanced
regional distribution of organie production is even
more pronounced when new production and export
production are considered (see below).
The present-day oeeanie primary produetion amounts to
about 36 x 10 15 gC/a = 36 x 10 9 tC/a; e.g. Berger et al.
1989; Sehlünz 1998). Related to the entire oeean surface,
this mass eorresponds to an average speeifie primary produetion rate of -100 tlkm 2 /a (also see Table 10.1).
In open oeean eonditions, primary produetion is -50
glm 2 /a, whereas in eoastal, non-upwelling regions about
150 glm 2 /a are typieal (Table 10.2). Oeean regions with
oligotrophie waters (e.g., areas of subtropieal gyres sueh as
the Sargasso Sea) eontribute less than 5% ofthe global new
produetion (see below), although they constitute as much
as 40% of the ocean surfaee.
Tbe Food Cbain
The primary production by phytoplankton is used by
heterotrophie organisms as food. In the present
oceans we can observe the following food chain, or
food web:
Phytoplankton (primary producers)
Zooplankton (herbivores, i.e., plant eaters).
Zooplankton (camivores, i.e., eaters of other zooplankton).
Fish (plankton-eaters.or fish-eaters).
Phytoplankton are eaten mainly by herbivorous zooplankton; they in turn are eaten by camivorous zooplankton or fish. At each "tropic level" in the food
chain, dissolved and suspended, dead örganic matter
is released from living organisms into the water. Part
of this organic detritus is used up by other
heterotrophie organisms living in the surface water,
but some dead plant and animal matter sinks into
deeper water, thereby supportirig life at all depths,
including on the sea floor (Fig. 10.6).
467
Most of the energy the animals gain from their
food is used for locomotion and other activities, and
only a small part for growth and reproduction. In
other words, the population at a higher trophic level
must be much larger (often five to six times by
weight) than the population at the lower trophic level
which feeds on the higher one. Thus, the amount of
organic matter produced by phytoplankton is reduced
drastically from one trophic level to the next, and the
biomass of the standing crop in the entire ecological
system represents only a small fraction of the primary
plant production. The organic matter, which is
needed as energy by organisms in the food chain, is
transformed into compounds with lower energy contents (through metabolism) and fmally by bacterial
activity into carbon dioxide and water.
At the same time, inorganic nutrients are released
into the water. If these salts remain in the trophic
zone or are recycled by currents into surface waters,
they allow high primary production to be maintained.
10.4.3 New Production and Export Production
General Aspects
Primary productivity and life processes in the photic
zone are not commonly a focus of geologie al and
sedimentological studies. Geologists are more interested in the burial and preservation of organic matter
below the sea floor. For this reason, marine biologists and sedimentologists have introduced the terms
new production and export production (e.g., Berger
et al. 1989). New production is the vertical organic
carbon flux below the photic zone (at about 100 m
below sea level, Figs. 10.5d and 10.6). Most new
production occurs in narrow, high-fertility belts
along the equator, the subpolar divergence zones, and
in regions of coastal upwelling (cf. Figs. 5.1 and 5.2,
Sects. 5.2.3 and 5.3.3).
The vertical particle flux between 100 m and the
sea floor is further reduced by organisms living in the
deeper water. The remaining proportion of organie
matter (OM) at a given depth, as on the sea floor, is
called .export production. Thus, the vertical carbon
flux fina!ly reaching the sediment surface is often
only a small fraction of the new production. However, settling of OM to the sea floor can only occur if
the organic compounds form organic particles or are
adsorbed to inorganic particles. Dissolved organie
matter per se does not settle.
Whereas primary production is difficult to quantify, new
produetion, i.e., the downward flux of particulate organic
matter, can be measured by free-floating particle traps (e.g.
lahn 1990; Berger and Wefer 1992). It mainly eonsists of
various dead organisms, mostly micro-organisms, and their
fragments as weil as fecal pellets, peloids, floes and aggregates. The quantity of this downward flux mayaiso reflect
the seasonal variation in primary production.