25th International Meeting on Organic Geochemistry IMOG 2011

P-227
Terrestrial organic matter in the sediments of the German Bight
– estimate of relative proportions using the BIT index in
comparison to other proxies
Anna Böll, Barbara Scholz-Böttcher, Jörn Logemann, Jürgen Rullkötter
Institut of Chemistry and Biology of the Marine Environment (ICBM), Oldenburg, Germany
The Branched and Isoprenoid Tetraether Index (BIT
index) is a recently developed proxy for estimating the
fluvial transport of soil-derived terrestrial organic
matter into marine sediments. The BIT index is based
on the relative abundance of terrestrially derived
tetraether lipids versus crenarchaeol of marine origin.
In this study, the distribution and sources of terrestrial
organic matter in the surface sediments of the
southeastern part of the North Sea (German Bight)
was investigated. The BIT index (analysed by
HPLC/MS adapted from [1,2]) was compared to wellestablished
proxies such as C/N ratios, stable carbon
isotopes ratios and n-alkane distribution patterns in
order to investigate the applicability of the BIT index in
the German Bight.
To assess the amount of terrestrial organic matter in
the sediments of the German Bight two binary mixing
models and a three end member mixing model were
applied [3]. The binary mixing models were based on
δ 13 C content and BIT index, respectively, and for the
three end-member mixing model δ 13 C values, BIT
index and C/N ratio were used (e.g. see Figure 1).
BIT values ranged from 0.29 to 0.89. The bulk proxies
applied, δ 13 C value and C/N ratio, ranged from -25‰
to -18.15‰, and from 1.71 to 6.91, respectively. Only
a weak correlation was found between BIT index and
other proxies. Overall, all proxies indicate a decrease
of terrestrial organic matter in the surface sediments
with increasing distance from the coast.
In contrast to open marine areas (3%-43%), the
sediments from the Jade Bay and the Elbe river
mouth contain high proportions of terrestrial organic
matter (32% to 77% and 55% to 66%, respectively).
Furthermore, it is shown that the terrestrial organic
matter is mainly derived from soil.
Although the BIT index and the other proxies show a
similar trend, BIT index values indicate higher
fractions of terrestrial organic matter in the surface
sediments than δ 13 C values.
Thus, the BIT index should only be used as a
qualitative proxy for the relative amount of terrestrial
organic matter in the German Bight.
Terrestrial OC [%]
100
90
80
70
60
50
40
30
20
10
0
South of Helgoland
Binary mixing model (BIT index)
Binary mixing model (� 13 C)
Three end-member mixing model
North of
Helgoland
99-101 99-102 99-103 99-104 10697 10685 10689 10691 10693 10695
Sample
40'
20'
54 o N
40'
20'
40'
North of
Helgoland
Helgoland
South of
Helgoland
8 o E
20' 40'
Figure 1: Estimate of the proportions of terrestrial
organic matter in the sediments of the German Bight
based on two end-member mixing models and on a
three end-member mixing model (based on δ 13 C
values, BIT index and C/N ratio).
References
[1] Hopmans, E.C., Schouten, S., Pancost, R.D., van
der Meer, M.T.J., Sinninghe Damsté, J.S., 2000.
Rapid Commun. Mass Spectrom. 14, 585-589.
[2] Hopmans, E.C., Weijers, J.W.H., Schefuß, E.,
Herfort, L., Sinninghe Damsté, J.S., Schouten, S.,
2004. Earth Planet. Sci. Lett. 224, 107-116.
[3] Weijers, J.W.H., Schouten, S., Schefuß, E.,
Schneider, R.R., Sinninghe Damsté. J.S., 2009.
Geochim. Cosmochim. Acta 73, 119-132.
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