particulate, dissolved, and colloid forms. Sequence of
these forms in the synthesis–destruction system constitutes the biogeochemical cycling of matter in the ocean
and the biosphere as a whole.
Forms of organic matter
Organic matter (OM) occurs in marine and oceanic water
as dissolved compounds (DOM), colloids, and particulate
OM. The colloidal and dissolved fractions can be separated from each other with methods such as ultrafiltration
and ion exchange, but in practice, they are usually treated
together. Hence, DOM includes the truly dissolved compounds (particles <1 nm) and colloids, including
1–10 nm and 10–450 nm structures. Large particles
(>0.1–1.0 mm), which can be collected by filtration
through a variety of filters, such as glass fiber Whatman
GF/F (~0.6–0.7 mm pores), separators, and sediment traps,
refer to particulate matter. OM of living beings producing
and degrading the bulk of OM in the ocean represents only
a small part of the total amount of OM. The three forms of
OM in the World Ocean, i.e., living, particulate, and
dissolved OM, make up the pyramid of mass 1: 13: 250
(4 · 10
15
, 50 · 10
15
, and 1,000 · 10
15 g C org ), which reflects
the dynamic equilibrium existing in the biogeochemical
cycle. These forms are combined into an interconnected
heterogeneous system that includes organic nitrogen,
phosphorus, sulfur, and organometallic compounds of natural and anthropogenic origin. Since most of OM in the
ocean is produced during photosynthesis, N- and
P-containing compounds of OM are predominantly of natural origin, while among S-containing compounds, the
fraction of anthropogenous substances increases.
Sedimentation of particulate matter leads to the fact that
all sediments include OM: the maximum concentration is
typical for muds of near-continental areas, especially for
upwelling and high productive waters, and the minimum
one is observed in coarse-grained deposits and red clay,
common in areas where OM supply is scarce. Annually,
160–250 · 10
12 g C org are buried in sediments of the World
Ocean, including about 95 % of near-continental and 5 %
of pelagic oceanic sediments (Hedges and Keil, 1995;
Eglinton and Repeta, 2003; Romankevich and Vetrov,
2013).
Sources of organic matter
The main primary source of OM in the ocean is
phytoplankton (Figure 1). Its average net production,
including lifetime excretions, is ~60 · 10
15 g C org year
À1
.
Another source of OM is the production of ice algae (0.2
10
15 g C org annually) and phytobenthos (3 10
15 g C org )
created by macrophytes and diatoms living in sediments,
as well as a part of OM produced by chemolithotrophs in
the rift zones of the ocean and cold seeps, widely developed
in seas and on the periphery of all oceans. Assessment of the
extent of bacterial chemosynthesis that proceeds through
the oxidation of reduced compounds coming from
the Earth’s interior suggests its small contribution
(<0.6 % of photosynthesis products) to OM balance
(Romankevich, 1984).
To the autochthonous (marine) sources of OM more resistant to degradation, allochthonous (terrigenous) OM coming
from the land is added (~0.7 · 10
15 g C org year
À1
). The
most important terrigenous source of OM in the ocean is
the river runoff, which supplies ~0.6 · 10
15 g C org year
–1
in the dissolved and particulate forms (~30 % and 70 %,
respectively). There are also unevenly distributed organic
compounds in the troposphere; its contribution to the
ocean is estimated as <0.1 · 10
15 g C org year
À1
. Finally,
we should mention such minor, sometimes
underestimated, sources of OM such as coastal erosion,
thermoabrasion, and underground runoff giving in total
~0.4 · 10
12 g C org year
À1
.
Living OM produced on land and in the ocean differs in
ash contents (5 % and 44 %, respectively), proteins (5 and
62 %), carbohydrates (62 and 25 %), lipids (6 and 13 %),
and lignin (27 % and traces). Marine OM contains about
five times more nitrogen and sulfur, more trace elements,
and less oxygen. The d
13
С value varies from À19 to
À24 % in the ocean and differs from the same parameter
for land plants of C 3 type (from À27 to À28 %) and C 4
type (~ À12 %) of carbon fixation.
Dissolved organic matter
In the World Ocean, dissolved OM represents ~94 % of
the total OM and its mass is estimated as 750–1,000 ·
10
15 g C. This is roughly equal to the carbon amount in
the atmosphere.
With the exception of viruses and small non-aggregated
bacteria, DOM is mainly represented by nonliving OM,
which is extremely small and cannot sink in water at
appreciable rates. Seawater DOM affects light transmission in the ocean. Approximately 25–35 % of marine
DOM occurs in molecules with masses of 1 kDa that correspond to nominal molecular sizes of 1 nm or more. Seawater DOM has numerous sources and sinks and a range
of different reactions.
In the active surface layer, DOM concentrations vary
over space and time within two orders of magnitude from
5–10 to 1,000 mМ C (1 mM C ¼ 0.012 mg Cl
À1
). The
main DOM pool is found in the deep ocean where concentrations vary little (mostly within 35–45 mМ, Figure 2).
General patterns of DOM distribution are expressed in
reducing concentration from coastal areas with high productivity of plankton, including the areas of allochthonous
supply from rivers to oligotrophic regions of the ocean, as
well as decreasing concentration with depth in the pelagic
areas. A typical depth profile of DOM concentration in the
ocean shows that the presence of labile DOM is associated
with only the upper part of the water column.
About 30 % of the DOM (sometimes up to 80 %) is
represented by colloids scattering light (size >1 nm) and
containing bioactive and bioavailable organic compounds. Submicron DOM components include liquid
excretions of phytoplankton, phytobenthos, protozoa,
ORGANIC MATTER
597
these forms in the synthesis–destruction system constitutes the biogeochemical cycling of matter in the ocean
and the biosphere as a whole.
Forms of organic matter
Organic matter (OM) occurs in marine and oceanic water
as dissolved compounds (DOM), colloids, and particulate
OM. The colloidal and dissolved fractions can be separated from each other with methods such as ultrafiltration
and ion exchange, but in practice, they are usually treated
together. Hence, DOM includes the truly dissolved compounds (particles <1 nm) and colloids, including
1–10 nm and 10–450 nm structures. Large particles
(>0.1–1.0 mm), which can be collected by filtration
through a variety of filters, such as glass fiber Whatman
GF/F (~0.6–0.7 mm pores), separators, and sediment traps,
refer to particulate matter. OM of living beings producing
and degrading the bulk of OM in the ocean represents only
a small part of the total amount of OM. The three forms of
OM in the World Ocean, i.e., living, particulate, and
dissolved OM, make up the pyramid of mass 1: 13: 250
(4 · 10
15
, 50 · 10
15
, and 1,000 · 10
15 g C org ), which reflects
the dynamic equilibrium existing in the biogeochemical
cycle. These forms are combined into an interconnected
heterogeneous system that includes organic nitrogen,
phosphorus, sulfur, and organometallic compounds of natural and anthropogenic origin. Since most of OM in the
ocean is produced during photosynthesis, N- and
P-containing compounds of OM are predominantly of natural origin, while among S-containing compounds, the
fraction of anthropogenous substances increases.
Sedimentation of particulate matter leads to the fact that
all sediments include OM: the maximum concentration is
typical for muds of near-continental areas, especially for
upwelling and high productive waters, and the minimum
one is observed in coarse-grained deposits and red clay,
common in areas where OM supply is scarce. Annually,
160–250 · 10
12 g C org are buried in sediments of the World
Ocean, including about 95 % of near-continental and 5 %
of pelagic oceanic sediments (Hedges and Keil, 1995;
Eglinton and Repeta, 2003; Romankevich and Vetrov,
2013).
Sources of organic matter
The main primary source of OM in the ocean is
phytoplankton (Figure 1). Its average net production,
including lifetime excretions, is ~60 · 10
15 g C org year
À1
.
Another source of OM is the production of ice algae (0.2
10
15 g C org annually) and phytobenthos (3 10
15 g C org )
created by macrophytes and diatoms living in sediments,
as well as a part of OM produced by chemolithotrophs in
the rift zones of the ocean and cold seeps, widely developed
in seas and on the periphery of all oceans. Assessment of the
extent of bacterial chemosynthesis that proceeds through
the oxidation of reduced compounds coming from
the Earth’s interior suggests its small contribution
(<0.6 % of photosynthesis products) to OM balance
(Romankevich, 1984).
To the autochthonous (marine) sources of OM more resistant to degradation, allochthonous (terrigenous) OM coming
from the land is added (~0.7 · 10
15 g C org year
À1
). The
most important terrigenous source of OM in the ocean is
the river runoff, which supplies ~0.6 · 10
15 g C org year
–1
in the dissolved and particulate forms (~30 % and 70 %,
respectively). There are also unevenly distributed organic
compounds in the troposphere; its contribution to the
ocean is estimated as <0.1 · 10
15 g C org year
À1
. Finally,
we should mention such minor, sometimes
underestimated, sources of OM such as coastal erosion,
thermoabrasion, and underground runoff giving in total
~0.4 · 10
12 g C org year
À1
.
Living OM produced on land and in the ocean differs in
ash contents (5 % and 44 %, respectively), proteins (5 and
62 %), carbohydrates (62 and 25 %), lipids (6 and 13 %),
and lignin (27 % and traces). Marine OM contains about
five times more nitrogen and sulfur, more trace elements,
and less oxygen. The d
13
С value varies from À19 to
À24 % in the ocean and differs from the same parameter
for land plants of C 3 type (from À27 to À28 %) and C 4
type (~ À12 %) of carbon fixation.
Dissolved organic matter
In the World Ocean, dissolved OM represents ~94 % of
the total OM and its mass is estimated as 750–1,000 ·
10
15 g C. This is roughly equal to the carbon amount in
the atmosphere.
With the exception of viruses and small non-aggregated
bacteria, DOM is mainly represented by nonliving OM,
which is extremely small and cannot sink in water at
appreciable rates. Seawater DOM affects light transmission in the ocean. Approximately 25–35 % of marine
DOM occurs in molecules with masses of 1 kDa that correspond to nominal molecular sizes of 1 nm or more. Seawater DOM has numerous sources and sinks and a range
of different reactions.
In the active surface layer, DOM concentrations vary
over space and time within two orders of magnitude from
5–10 to 1,000 mМ C (1 mM C ¼ 0.012 mg Cl
À1
). The
main DOM pool is found in the deep ocean where concentrations vary little (mostly within 35–45 mМ, Figure 2).
General patterns of DOM distribution are expressed in
reducing concentration from coastal areas with high productivity of plankton, including the areas of allochthonous
supply from rivers to oligotrophic regions of the ocean, as
well as decreasing concentration with depth in the pelagic
areas. A typical depth profile of DOM concentration in the
ocean shows that the presence of labile DOM is associated
with only the upper part of the water column.
About 30 % of the DOM (sometimes up to 80 %) is
represented by colloids scattering light (size >1 nm) and
containing bioactive and bioavailable organic compounds. Submicron DOM components include liquid
excretions of phytoplankton, phytobenthos, protozoa,
ORGANIC MATTER
597