10.5 Organic Matter Preservation in Marine Sediments
Table 10.2. Primary produetion, new produetion,
export production (organie earbon flux to the sea
floor), and organie earbon aeeumulation in sediments
from various,gresent-day oeean regions (all values in
g/m 2 /a = tIkm ja).
Open
oeean
Primary production 50
N ew produetion
5
Export produetion
at water depth of
250m
5000 m
0.5
Organie earbon aeeumulation in sediment,
when sedimentation
rate 1 ernlka
0.01
10 ernlka
20 ernlka
Coastal
nonupweHing
upwelling
150
250
50
110
15
30
3
13
Values from Stein 1991 (based on Romankevich 1984;
Betzer et al. 1984; Berger et al. 1989; for additional data
see Deuser 1986; Martin et al. 1987; Knauer et al. 1990).
The contribution of terrestrial organic matter is not included.
The results obtained in the modem oeeans, summarized in Fig. 10.5b, agree with the geologie reeord, in
whieh most of the organie matter preserved in ancient sediments aeeumulated in shallow seas. However, in eertain regions and during speeifie periods
organie earbon flux to the sea floor inereased as a
result of widespread anoxie deep-water environments
(cf. Seets. 5.2 and 7.5). In addition, organie matter of
slope sediments was transported by turbidity eurrents
into deeper water.
The late Quatemary sediments of the Arnazon shelf and
deep-sea fan markedly differ in their organic matter content
(Schlünz 1988). During sea-level highstand, the shelf accumulates most of the incoming mud rich in terrestrial TOC
while the fan receives very limited amounts of sediment in
which marine organic matter is dominatinge The fan sediments of glacial lowstands, however, contain mainly terrestrial organic matter which amounts to about 10% of the
present-day global riverine TOC discharge. An estimate for
the global organic carbon accumulation in the Neogene has
been carried out by Perry and France-Lanord (1996)
10.5 Organic Matter Preservation in
Marine Sediments
10.5.1 General Aspects
469
Present-day deep-sea sediments are generally poor in
organie matter, beeause the vertieal earbon flux originating from primary produetion is eontinuously redueed by remineralization in the water eolurnn as
weH as by the aetivity of benthie organisms (Fig.
10.6). Most of the land-derived organie matter entering the oeean is mineralized, used up by heterotrophie organisms, or deposited in eoastal and
shallow-water zones. Here, the already fairly high
autoehthonous vertieal earbon flux ean be augmented, partieularly in estuarine and prodelta environments. However, gravity" mass movements ean
transport organic-rieh sediments from the outer shelf
or slope into deep water.
Fine-grained mud turbidites, in particular, often contain
relatively high amounts of organic carbon (Degens et al.
1986; Morris 1987; Stein 1991; cf. Sect. 5.4.5). For that
reason, the accumulation rate of organic matter can be
fairly high in some deep water sediments, even when the
vertical carbon flux from the overlying photic zone is negligible. In addition, some smalI, deep ocean basins with
restricted water circulation (cf. Chap. 4) can store relatively
large arnounts of organic matter.
10.5.2 Organic Carbon Loss on the Sea Floor
Principal Processes
The export produetion, reaehing the sea floor as particulate matter, first enters the "benthie boundary
layer" (Fig. 10.6). This layer of bottom water has a
slightly higher eoneentration of suspended material
and somewhat deviates in its chemie al eharaeteristies
from thm.e of the overlying water body. Inereased
activity by planktonic miero- and maero-organisms in
this Iayer ean reduee" the vertieal earbon flux more
rapidly than it is the ease in the higher water eolurnn.
Although this proeess is linked with inereased oxygen eonsumption, the bottom water usually still eontains enough oxygen to support bottom life
(epibenthos, infauna, fungi and baeteria) on top of
and within the upper few eentimeters to deeimeters
of the sediment (Fig. 10.6). Miero-organisms, growing rapid1y in the uppermost millimeters or eentimeters of the sediment, aeeomplish further drastie reduetion of the vertieal earbon flux and thus release
eonsiderable quantities of CO/HC0 3 and nutrients.
This aetivity takes plaee under both aerobic and
anaerobie eonditions. In the ease of oxic bottom waters, oxygen flux from the water into the sediment is
faeilitated by burrowing organisms, but at some
depth below the sediment/water interface (usually
Table 10.2. Primary produetion, new produetion,
export production (organie earbon flux to the sea
floor), and organie earbon aeeumulation in sediments
from various,gresent-day oeean regions (all values in
g/m 2 /a = tIkm ja).
Open
oeean
Primary production 50
N ew produetion
5
Export produetion
at water depth of
250m
5000 m
0.5
Organie earbon aeeumulation in sediment,
when sedimentation
rate 1 ernlka
0.01
10 ernlka
20 ernlka
Coastal
nonupweHing
upwelling
150
250
50
110
15
30
3
13
Values from Stein 1991 (based on Romankevich 1984;
Betzer et al. 1984; Berger et al. 1989; for additional data
see Deuser 1986; Martin et al. 1987; Knauer et al. 1990).
The contribution of terrestrial organic matter is not included.
The results obtained in the modem oeeans, summarized in Fig. 10.5b, agree with the geologie reeord, in
whieh most of the organie matter preserved in ancient sediments aeeumulated in shallow seas. However, in eertain regions and during speeifie periods
organie earbon flux to the sea floor inereased as a
result of widespread anoxie deep-water environments
(cf. Seets. 5.2 and 7.5). In addition, organie matter of
slope sediments was transported by turbidity eurrents
into deeper water.
The late Quatemary sediments of the Arnazon shelf and
deep-sea fan markedly differ in their organic matter content
(Schlünz 1988). During sea-level highstand, the shelf accumulates most of the incoming mud rich in terrestrial TOC
while the fan receives very limited amounts of sediment in
which marine organic matter is dominatinge The fan sediments of glacial lowstands, however, contain mainly terrestrial organic matter which amounts to about 10% of the
present-day global riverine TOC discharge. An estimate for
the global organic carbon accumulation in the Neogene has
been carried out by Perry and France-Lanord (1996)
10.5 Organic Matter Preservation in
Marine Sediments
10.5.1 General Aspects
469
Present-day deep-sea sediments are generally poor in
organie matter, beeause the vertieal earbon flux originating from primary produetion is eontinuously redueed by remineralization in the water eolurnn as
weH as by the aetivity of benthie organisms (Fig.
10.6). Most of the land-derived organie matter entering the oeean is mineralized, used up by heterotrophie organisms, or deposited in eoastal and
shallow-water zones. Here, the already fairly high
autoehthonous vertieal earbon flux ean be augmented, partieularly in estuarine and prodelta environments. However, gravity" mass movements ean
transport organic-rieh sediments from the outer shelf
or slope into deep water.
Fine-grained mud turbidites, in particular, often contain
relatively high amounts of organic carbon (Degens et al.
1986; Morris 1987; Stein 1991; cf. Sect. 5.4.5). For that
reason, the accumulation rate of organic matter can be
fairly high in some deep water sediments, even when the
vertical carbon flux from the overlying photic zone is negligible. In addition, some smalI, deep ocean basins with
restricted water circulation (cf. Chap. 4) can store relatively
large arnounts of organic matter.
10.5.2 Organic Carbon Loss on the Sea Floor
Principal Processes
The export produetion, reaehing the sea floor as particulate matter, first enters the "benthie boundary
layer" (Fig. 10.6). This layer of bottom water has a
slightly higher eoneentration of suspended material
and somewhat deviates in its chemie al eharaeteristies
from thm.e of the overlying water body. Inereased
activity by planktonic miero- and maero-organisms in
this Iayer ean reduee" the vertieal earbon flux more
rapidly than it is the ease in the higher water eolurnn.
Although this proeess is linked with inereased oxygen eonsumption, the bottom water usually still eontains enough oxygen to support bottom life
(epibenthos, infauna, fungi and baeteria) on top of
and within the upper few eentimeters to deeimeters
of the sediment (Fig. 10.6). Miero-organisms, growing rapid1y in the uppermost millimeters or eentimeters of the sediment, aeeomplish further drastie reduetion of the vertieal earbon flux and thus release
eonsiderable quantities of CO/HC0 3 and nutrients.
This aetivity takes plaee under both aerobic and
anaerobie eonditions. In the ease of oxic bottom waters, oxygen flux from the water into the sediment is
faeilitated by burrowing organisms, but at some
depth below the sediment/water interface (usually