Terrestrial Organic Matter in Marine Sediments
551
ofterrigenous andlorreworked, fossil organic carbon in Arctic and Nordic Sea sediments clearly
evidence a persistent basinward sediment transport
either by currents or, probably even more important, by glaciomarine supply.
Tracing Terrigenous OM in the Marine
Environment: a Briefintroduction and
Critical Evaluation of Selected Analytical
Approaches
There is a broad spectrum of organic geochemical
approaches established for the differentiation of
terrigenous and marine OM in marine deposits.
These approaches comprise elemental (CIN, HlC
and OIC), isotopic (o l3 C"g)' pyrolytic (Rock-Eval
Pyrolysis - Hydrogen Index (HI), Oxygen Index
(01) and T m ,,) , microscopic (palynology,
maceral analysis), and gas-chromatographic/mass
spectrometric ("biomarker") methods taking advantage of the fact that the chemical composition of
terrestrial biomass is considerably different from
the one of marine biomass. The following chapter
gives a brief introduction into the most popular
analytical approaches applied to recent marine
sediments (for comprehensive reviews see Engel
and Macko 1993, and Tyson 1995).
Elemental Approaches
One of the most popular although less reliable parameter used for the identification of terrigenous
OM is the ratio ofTOC to total nitrogen (CIN, e.g.
Emerson and Hedges, 1988). The use of the CIN
is based on the premises that land-derived OM has
a significantly lower nitrogen content than marine
OM. Typical terrigenous CIN ratios range
from 20 to 200 showing an average value of 24
(Romankevich 1984), whereas marine ratios range
from 5 to 10 (for more details see Tyson 1995).
Interpretation of CIN in TOC-poor marine
sediments with regard to marine vs. terrigenous
OM, however, is strongly impeded by the preferential diagenetic remineralization of nitrogen compared to organic carbon (Emery and Uchupy 1984),
the amount of inorganic nitrogen bound in clay minerals (Miiller 1977; Calvert and Karlin 1991), and
the preferential uptake of nitrogen by benthic organisms. These processes result in a progressive
masking of the original CIN typically leading to
ratios ranging from 5 up to 15 in pelagic deposits.
Hence, taking CIN ratios exceeding 10-12 alone as
an indicator for terrestrial OM is highly questionable. Minor fluctuations in CIN should therefore
preferentially be attributed to diagenetic
effects (e.g. Westerhausenetal. 1993; Verardoand
McIntyre 1994) unless changes in the composition
of OM are indicated by other geochemical evidence. Some fair correlations have been
reported between CIN and ol3C"g' HI and terrestrial biomarkers (e.g. lignin-derived phenols) in
modern marine settings which are influenced by
strong seaward mixing of terrestrial and marine
OM (e.g. Hedges and Mann 1979; Jasper and
Gagosian 1990; Wagner and Henrich 1994; Miiller
et al. 1994; Gofii et al. 1997, Liickge 1997). Considering the variability of marine and terrestrial
endmember values and the various potential effects
which may considerably obscure the primary CIN
ratio in deep-sea sediments we conclude that
CIN ratios are not suitable for quantitative approaches.
Isotopic Approaches
Bulk geochemical characterization of sedimentary
OM based on the organic carbon isotopic signal
(8I3C,,) is one of the most widely used approach
to determine quantitative proportions of terrigenous
organic carbon in recent environments and has long
been used for paleoceanographic and paleoclimatic
studies (e.g. Hedges and Mann 1979; Miiller et al.
J 983; Fontugne and Duplessy 1986; Jasper and
Gagosian 1989; Rau et al. 1989; Westerhausen et
al.1993;Miilleretal. 1994; Riihlemann etal. 1996;
Schneider et al. 1997; Wagner 1998). Organic matter shows considerable variations in its isotopic
value depending on its composition, the source of
carbon and the metabolic pathway involved in its
formation, the PC0 2 level, and the growth rate of
marine plankton. Terrigenous OM derived from
vascular C3-plants (representing more than 95%
ofthe present terrestrial biomass) reveal low values between -25.5 to -29.3 %0 with an average
endmember signature of -27 %0 (see compilation
in Tyson 1995). This endmember may be shifted
551
ofterrigenous andlorreworked, fossil organic carbon in Arctic and Nordic Sea sediments clearly
evidence a persistent basinward sediment transport
either by currents or, probably even more important, by glaciomarine supply.
Tracing Terrigenous OM in the Marine
Environment: a Briefintroduction and
Critical Evaluation of Selected Analytical
Approaches
There is a broad spectrum of organic geochemical
approaches established for the differentiation of
terrigenous and marine OM in marine deposits.
These approaches comprise elemental (CIN, HlC
and OIC), isotopic (o l3 C"g)' pyrolytic (Rock-Eval
Pyrolysis - Hydrogen Index (HI), Oxygen Index
(01) and T m ,,) , microscopic (palynology,
maceral analysis), and gas-chromatographic/mass
spectrometric ("biomarker") methods taking advantage of the fact that the chemical composition of
terrestrial biomass is considerably different from
the one of marine biomass. The following chapter
gives a brief introduction into the most popular
analytical approaches applied to recent marine
sediments (for comprehensive reviews see Engel
and Macko 1993, and Tyson 1995).
Elemental Approaches
One of the most popular although less reliable parameter used for the identification of terrigenous
OM is the ratio ofTOC to total nitrogen (CIN, e.g.
Emerson and Hedges, 1988). The use of the CIN
is based on the premises that land-derived OM has
a significantly lower nitrogen content than marine
OM. Typical terrigenous CIN ratios range
from 20 to 200 showing an average value of 24
(Romankevich 1984), whereas marine ratios range
from 5 to 10 (for more details see Tyson 1995).
Interpretation of CIN in TOC-poor marine
sediments with regard to marine vs. terrigenous
OM, however, is strongly impeded by the preferential diagenetic remineralization of nitrogen compared to organic carbon (Emery and Uchupy 1984),
the amount of inorganic nitrogen bound in clay minerals (Miiller 1977; Calvert and Karlin 1991), and
the preferential uptake of nitrogen by benthic organisms. These processes result in a progressive
masking of the original CIN typically leading to
ratios ranging from 5 up to 15 in pelagic deposits.
Hence, taking CIN ratios exceeding 10-12 alone as
an indicator for terrestrial OM is highly questionable. Minor fluctuations in CIN should therefore
preferentially be attributed to diagenetic
effects (e.g. Westerhausenetal. 1993; Verardoand
McIntyre 1994) unless changes in the composition
of OM are indicated by other geochemical evidence. Some fair correlations have been
reported between CIN and ol3C"g' HI and terrestrial biomarkers (e.g. lignin-derived phenols) in
modern marine settings which are influenced by
strong seaward mixing of terrestrial and marine
OM (e.g. Hedges and Mann 1979; Jasper and
Gagosian 1990; Wagner and Henrich 1994; Miiller
et al. 1994; Gofii et al. 1997, Liickge 1997). Considering the variability of marine and terrestrial
endmember values and the various potential effects
which may considerably obscure the primary CIN
ratio in deep-sea sediments we conclude that
CIN ratios are not suitable for quantitative approaches.
Isotopic Approaches
Bulk geochemical characterization of sedimentary
OM based on the organic carbon isotopic signal
(8I3C,,) is one of the most widely used approach
to determine quantitative proportions of terrigenous
organic carbon in recent environments and has long
been used for paleoceanographic and paleoclimatic
studies (e.g. Hedges and Mann 1979; Miiller et al.
J 983; Fontugne and Duplessy 1986; Jasper and
Gagosian 1989; Rau et al. 1989; Westerhausen et
al.1993;Miilleretal. 1994; Riihlemann etal. 1996;
Schneider et al. 1997; Wagner 1998). Organic matter shows considerable variations in its isotopic
value depending on its composition, the source of
carbon and the metabolic pathway involved in its
formation, the PC0 2 level, and the growth rate of
marine plankton. Terrigenous OM derived from
vascular C3-plants (representing more than 95%
ofthe present terrestrial biomass) reveal low values between -25.5 to -29.3 %0 with an average
endmember signature of -27 %0 (see compilation
in Tyson 1995). This endmember may be shifted