25th International Meeting on Organic Geochemistry IMOG 2011

P-165
Characterisation of organic acids in geological samples
Jacqueline Mireya Calzada Mendoza, Andrea Vieth-Hillebrand, Heinz Wilkes
Deutsches GeoForschungsZentrum, Potsdam, Germany (corresponding author:mireya@gfz-potsdam.de)
It was long thought that life on Earth is restricted to
the surface and the upper few meters of sediment.
The relatively recent discovery of deep microbial life
brought up an important topic in geobiological
research: the question what the potential carbon and
energy sources sustaining microbial ecosystems in
geological habitats are and how they are generated
[1-3].
Most organic carbon-rich deposits are formed in
sedimentary environments, where the organic matter
suffers biochemical and geochemical processes
which control its preservation and degradation. It is
still not well known, however, which fractions of the
organic matter are available for utilization by
heterotrophic microorganisms. Several studies have
been performed to show that organic carbon rich
lithologies like lignites, coals and kerogen could act as
potential ―feeder‖ lithologies for the deep biosphere
[4-6], leading to the conclusion that abiotically driven
degradation reactions of the buried organic matter
may provide substrates for microbial activity in deep
sediments. It has been proposed that carbonaceous
sediments can supply low molecular weight organic
acids (LMWOA) to the deep biosphere [7], however,
rates and quantities of these processes have not
been elucidated until now.
LMWOA play an important role in biogeochemical
processes as products or reactants of various types of
reactions. They may be formed abiotically through
thermal breakdown of organic matter or by microbial
metabolism of organic components of higher
complexity. It is known since long that many LMWOA
can be utilized by numerous types of microorganisms
as carbon and/or energy sources. Thus their
metabolism by microorganisms plays an active role in
carbon cycling in the geosphere. LMWOA may also
be used as basic building blocks in biosynthesis of
complex lipids with functions as structural
components, in energy storage, and in signalling [8].
This contribution presents the analytical strategy and
first results about the qualitative and quantitative
assessment of the natural variability of LMWOA in
the C2 – C10 range in different organic-rich sediment
and rock samples, e.g. samples representing early
diagenesis, a maturity sequence of coals and a series
of reservoir rocks from biodegraded oil reservoirs. We
applied gas chromatography–mass spectrometry
(GC-MS) using a polar column for the identification
and quantification of underivatized organic acids and
gas chromatography-isotope ratio mass spectrometry
(GC-IRMS) to determine the carbon and hydrogen
isotopic composition of individual LMWOA. The
obtained data will be interpreted in the framework of
comprehensive characterization of the bulk dissolved
organic carbon (DOC) and its different fractions. This
includes also the quantification of inorganic anions
and LMWOA with less than 5 carbon atoms (e.g.
acetate, formate) by ion chromatography (IC) and the
characterization of dissolved organic matter by size
exclusion chromatography (liquid chromatographyorganic
matter detection LC-OCD).
References
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