25th International Meeting on Organic Geochemistry IMOG 2011

O-15
Differential degradation of intact polar lipid GDGTs upon
oxidation of a turbidite sediment
Sabine K. Lengger 1 , Mariska Kraaij 1,3 , Marianne Baas 1 , Ellen C. Hopmans 1 , Jaap S.
Sinninghe Damsté 1,2 , Stefan Schouten 1,2
1 NIOZ Royal Netherlands Institute for Sea Research, 't Horntje, Netherlands, 2 Utrecht University, Utrecht,
Netherlands, 3 University of Applied Sciences Utrecht, Utrecht, Netherlands (corresponding
author:sabine.lengger@nioz.nl)
Lipid biomarkers are widely used in ecology for
studying the diversity and activity of communities.
Archaeal membranes contain glycerol diphytanyl
diether- and glycerol dibiphytanyl glycerol tetraetherlipids
(GDGT) as core lipids (CL) with a variety of
headgroups (intact polar GDGTs; IPL-GDGTs),
including sugars (glyco-GDGTs) and phosphates
(phospho-GDGTs). IPL-GDGTs are being used as
biomarkers for live Archaea as they are thought to
degrade quickly after cell lysis [1]. Theoretical
modeling, however, suggests that glyco-GDGTs might
be preserved over geological timescales and may not
represent living Archaea [2].
Here, we tried to determine the preservation potential
of glyco- and phospho-GDGTs and their applicability
as biomarkers for live archaeal communities. To this
end, we compared lipid concentrations and
composition of the organic-rich sections with the
oxidized ones of the f-turbidite from the Madeira
Abyssal Plain (MAP). This turbidite is a layer of
sediment which was transported by a turbidity current
from its anoxic depositional environment on the
continental slope to the abyssal plain. As the organic
matter was completely mixed during transport, it is
homogenous while, due to the exposure to oxygen in
the bottom waters, it was gradually oxidized by a
downwards moving oxidation front. This makes it ideal
for studying the impact of oxygen on the degradation
of biomarkers [e.g. 3]. We determined CL- and total
IPL-GDGT concentrations by HPLC/APCI-MS and the
abundance of individual crenarchaeol-based IPLs by
HPLC/ESI-MS 2 . Total CL- and IPL-GDGT
concentrations were two orders of magnitude lower in
the oxidized part of the turbidite compared to the
unoxidized part. No phospho-crenarchaeol was
detected in either the oxidized or unoxidized part of
the turbidite, suggesting that phospho-crenarchaeol, if
present before, was degraded very fast. However, in
the unoxidized part, at least three different types of
glyco-GDGTs (monohexose, dihexose and an
unknown hexose+ 180 Da) were detected (Fig. 1). In
the oxidized section, concentrations of the glyco-
GDGTs with the dihexose- and the unknown
Depth [cm]
headgroup had decreased by three orders of
magnitude. In contrast, GDGTs with a monohexose
headgroup seemed to be more persistent and only
decreased by 2 orders of magnitude, similar to CL-
GDGTs. This suggests that this IPL is relatively better
preserved, a degradation product of the other lipids or
that it was biologically produced in the sediment after
oxidation, though no other indications for in situproduction
were found. Our results suggest that
degradation rates among IPL-GDGTs vary strongly, in
decreasing order: phospho-GDGTs >> dihexose-
GDGTs > monohexose GDGTs. IPL-GDGTs can
hence, depending on the type of headgroup, remain
in sediments longer than expected, especially when
deposited in low-oxygen environments, and are only
strongly degraded upon long-term exposure to
oxygen.
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160
180
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220
240
1
10 1 10 2 10 3 10 4 10 5 10 6 10 7
Rel. Abundance
D i h e x o s e
U n k n o w n ( m / z 1 8 0 ) M o n o h e x o s e
Figure 1. Relative
abundances for IPLcrenarchaeol
species unknown
(hexose + 180 Da),
dihexose and
monohexose, in the
unoxidized (below,
grey) and oxidized
(above, white)
sections of the
turbidite.
References:
[1] 260 Biddle J. et al. (2006) Proc Natl Acad Sci USA
103, 3846-3851.
[2] Schouten S. et al. (2008) Appl Env Microbiol 74,
2433-2440.
[3] Huguet C. et al. (2008) Geochim. Cosmochim.
Acta 72, 6061-6068.
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