25th International Meeting on Organic Geochemistry IMOG 2011

P-411
Intramolecular Radiocarbon Dating on Archaeal Intact Polar
Lipids
Chun Zhu 1 , Gesine Mollenhauer 2 , Julius Lipp 1 , Yu-shih Lin 1 , Kai-Uwe Hinrichs 1
1 Organic Geochemistry Group, Dept. of Geosciences and MARUM Center for Marine Environmental
Sciences, Bremen, Germany, 2 Alfred Wegener Institute for Polar and Marine Research, Bremerhaven,
Germany (corresponding author:czhu@uni-bremen.de)
Investigations on intact polar lipids (IPLs) and
their δ 13 C values have suggested that vast archaeal
communities characterized by a heterotrophic lifestyle
are prevalent in deep-sea subsurface sediments
(Biddle et al., 2006; Lipp et al., 2008). In situ 13 Ctracer
experiments in surface sediments further
suggested that benthic archaea are capable to build
their membranes partially by recycling fossil archaeal
membranes and detritus (Takano et al., 2010) to
minimize energy expenditures, supporting the
hypothesis that adaptations to chronic energy stress
are a unifying ecological principle of archaea
(Valentine, 2007).
Lipid recycling as proposed by Takano et al.
(2010) involves a mechanism in which the biphytanes
in GDGTs (glycerol dibiphytanyl glycerol tetraethers)
are sourced from a different carbon pool than the
glycerol and by inference, presumably also the polar
headgroups. Disparity of radiocarbon age between
these molecular moieties likely results and may
encode valuable information on metabolic traits of the
benthic archaeal communities and on the fate of
archaeal lipids in sediments. Intramolecular
radiocarbon dating on IPLs in subseafloor sediments
can provide direct evidence for mechanisms of in situ
archaeal lipid synthesis and substantiate the fidelity of
IPLs as molecular tracers for a living deep biosphere.
We therefore developed a new analytical
protocol for intramolecular Δ 14 C dating on specific
IPLs. Individual IPLs (i.e. diglycosyl-GDGTs and
H341-GDGTs) were isolated and purified from the
sediment matrix using orthogonal columns (Fig. 1a,b).
Headgroups and core-GDGTs are cleaved from IPLs.
Subsequently, an improved chromatography of core-
GDGTs with a separation of GDGT-4 (GDGT bearing
four pentacyclic rings) from crenarchaeol was
achieved for the first time through a reverse phase
(RP) HPLC (Fig. 1c). Finally, sample processing
blanks are systematically assessed and corrected.
Sediments were collected from the eastern
Mediterranean Sea, the Marmara Sea and the Black
Sea. These sites are characterized by high
sedimentation rates and pre-aged terrestrial OM and
well-dated sapropel deposition. Down-core analysis of
Δ 14 C ages on headgroups, caldarchaeol and
crenarchaeol cleaved from diglycosyl-GDGTs
and H341-GDGTs, respectively, as well as fossil core
GDGTs and dissolved inorganic carbon (DIC) in pore
water are currently undertaken. Those Δ 14 C values
will be compared to the established age models of the
cores. Finally, the metabolism of benthic archaea and
the fidelity of IPLs as living biomass tracers in deeply
buried sediments will be discussed.
Fig.1. Partial HPLC–ESI–MS density maps showing
the peaks of H341-GDGTs (a) and diglycosyl-GDGTs
(b) purified by orthogonal columns, and partial
reversed phase chromatogram of core-GDGTs
determined by HPLC-APCI-MS (c). (number 0-5 and
5‘ denote GDGT-0, GDGT-1, GDGT-2, GDGT-3,
GDGT-4, crenarchaeol and regioisomer of
crenarchaeol, respectively).
References
Biddle, J.F. et al., 2006. PNAS 103, 3846-3851.
Lipp, J.S. et al., 2008. Nature 454, 991-994.
Takano et al., 2010. Nature Geosciences 5, 316-323
Valentine 2007. Nature Reviews Microbiology 5, 316-
323.
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