25th International Meeting on Organic Geochemistry IMOG 2011

P-248
Comparison of soil organic matter tracers (branched GDGTs and
soil-specific BHPs): A study of the NW Mediterranean shelfslope
region
Jung-Hyun Kim 1 , Helen M. Talbot 2 , Roselyne Buscail 3 , Thomas Wagner 2 , Jaap S.
Sinninghe Damsté 1
1 NIOZ, ‘t Horntje (Texel), Netherlands, 2 Newcastle University, Newcastle, United Kingdom, 3 CEFREM,
Perpignan, France (corresponding author:Jung-Hyun.Kim@nioz.nl)
The transport of terrestrial organic matter (OM) to
coastal sediments represents a significant flux in the
global carbon cycle. Although a large range of bulk
and molecular proxies for terrestrial OM is available,
quantification of the relative inputs of terrestrial OM to
marine sediments is still difficult due to large
variations in concentrations of compounds in various
higher plants and different degradation rates. The
incomplete understanding of the transfer of terrestrial
OM from land to the ocean is probably due to the lack
of diagnostic (geochemical) proxies especially for soil
OM, which accounts for two third of the total terrestrial
carbon budget.
Recently, several developments have led to
new insights into the recognition of soil OM in marine
environments. The Branched and Isoprenoid
Tetraether (BIT) index has been introduced as a
proxy to trace soil OM input from land to the marine
environments [1]. This index is based on the relative
abundance of branched glycerol dialkyl glycerol
tetraethers (GDGTs) versus a structurally related
isoprenoid GDGT ―crenarchaeol‖. More recently, four
bacteriohopanepolyols (BHPs, adenosylhopane
adenosylhopane-type 1, 2-methyl adenosylhopane,
and 2-methyl adenosylhopane-type 1), have been
suggested to be characteristic of soil microbial
communities [2] and potentially can also serve as
molecular markers for soil OM supply in river, lake,
and marine sediments [3,4].
In this study, we compared both soil OM
tracers in peats and soils collected in the Rhône and
Têt watersheds (Southern France) and surface
sediments of the Gulf of Lions (NW Mediterranean,
Figure 1). Branched GDGTs and soil-specific BHPs
occur ubiquitously in peats and soils. The comparison
of soil-specific BHP parameters with those of
branched GDGTs shows no clear relationship in the
watersheds. This suggests that these two groups of
soil-specific compounds are synthesized by different
microbial organisms living in different niches and/or
separate depths in the soil profile (oxic top versus
anoxic deep). Nevertheless, marine surface
sediments show that both branched GDGTs and soilspecific
BHPs decrease offshore, indicating the
delivery and preservation of these soil OM tracers in
marine environments.
Our initial results suggest that soil-specific
BHPs are transported from land to the sea via rivers
similar to branched GDGTs and thus soil-specific
BHPs may have potential to also serve as a tracer for
soil OM input from land to marine environments.
However, our study also shows that the current state
of knowledge does not allow for a simple direct
comparison of soil-specific BHP parameters with
branched GDGTs indicating that care must be taken
when comparing both soil OM proxies. More work is
required to extend our limited knowledge on the
production, occurrence and preservation of both
groups of biomarkers in various environmental
settings.
Latitude (N)
44.0
43.5
43.0
42.5
Têt River
42.0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Longitude (E)
Rhône River
Figure 1. Sampling locations in the Gulf of Lions
considered in this study.
References:
[1] Hopmans et al., 2004, Earth Planet. Sci. Lett., 224,
107-116.
[2] Cooke et al., 2008a, Org. Geochem., 39, 1347-
1358.
[3] Talbot et al., 2007, Org. Geochem., 38, 1212–
1225.
[4] Cooke et al., 2008b, Org. Geochem., 39, 965-971.
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