25th International Meeting on Organic Geochemistry IMOG 2011

P-221
Differences in distribution of core lipids amongst intact polar
tetraether lipids and its implications for the TEX86
paleothermometer
Sabine K. Lengger 1 , Ellen C. Hopmans 1 , Angela Pitcher 1 , Gert-Jan Reichart 2 , 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 (corresponding author:sabine.lengger@nioz.nl)
The TEX86 is an increasingly used paleotemperature
proxy and relies on the fact that temperature affects
the number of cyclopentane moieties in
thaumarchaeal membrane lipids (glycerol dibiphytanyl
glycerol tetraether lipids, GDGTs). In living Archaea,
these lipids are present as intact polar lipids (IPLs)
with sugar- and/or phosphate-containing groups
attached to the core lipids (CL). IPL-GDGTs are often
seen as diagnostic for living Archaea. It has been
shown that IPL-derived GDGTs often have TEX86values
higher than those of CL-GDGTs (e.g. Peru
Margin [1]), suggesting that the distribution of in situ
produced GDGTs differs from that of fossil GDGTs.
In this study, we examined the underlying causes for
observed differences between TEX86-values of CL
and IPL-GDGTs. We isolated IPL-GDGTs, from
Arabian Sea sediments from different water depths
and bottom water oxygen concentrations, according
to head groups, by preparative HPLC. Monohexose-,
dihexose- and hexose, phosphohexose-GDGTs were
subjected to hydrolysis. Ring distributions and TEX86
of the resulting IPL-derived GDGTs were measured
by HPLC/APCI-MS. We observed large differences in
GDGT-composition amongst head groups: the CLs
GDGT-2 and -3 (numbers indicate the number of
cyclopentane moieties) are predominantly associated
with glycolipids, while CL GDGT-1 is associated
predominantly with a phosphoglycolipid. This
observation is in agreement with results from the
thaumarchaeotal culture Nitrosopumilus maritimus,
where acid hydrolysis of the dihexose-GDGTs did not
yield GDGT-1, contrary to the phosphohexose-
GDGTs [2].
We also investigated IPL-GDGTs of recently enriched
Thaumarchaeota and found strikingly similar results to
those of N. maritimus, i.e. GDGT-0, -1 and
crenarchaeol predominantly occurring as CL of a
hexose-phosphohexose GDGT-IPL, and GDGT-2, -3
and -4 as CLs of dihexose GDGT-IPLs. As a
consequence, the TEX86 shows a relation with the
relative amount of dihexose GDGT-IPLs, i.e.
increasing TEX86 with increasing amount of dihexose-
IPLs. Analysis of suspended particulate matter from
the Arabian Sea also showed a strong relation
between TEX86 values and the relative amount of
dihexose GDGT-IPLs.
Our results thus show that TEX86-values generated by
GDGTs derived from glycolipids are substantially
higher than those generated from the phospholipidderived
GDTGs. Consequently, the substantial
differences in preservation potential between
phosphoglycolipids and glycolipids [3], and perhaps
even within the class of glycolipids, will lead to
changes in TEX86 of IPL-GDGTs with progressing
degradation. Therefore, differences in TEX86 between
IPL-derived and CL-GDGTs do not necessarily
indicate differences in origin (e.g. synthesis
temperature or thaumarchaeal community).
Furthermore, the non-random distribution we find
implies the existence of mechanisms for linking
specific GDGTs to specific headgroups. A systematic
distribution of GDGTs amongst headgroups, in
conjunction with the dissimilar degradation rates of
the latter, is complicating TEX86 calibration with water
column SPM and rendering in-situ calibration with
culture-material difficult. In contrast, IPLs are already
mainly degraded to CL-GDGTs in core-top sediments
and therefore core-top calibrations are likely to be
more reliable.
References: [1] Lipp J. S., Hinrichs K. U. (2009)
Geochim Cosmochim Acta 73, 6816-6833.
[2] Schouten S., Hopmans E. C., Baas M., Boumann
H., Standfest S., Könneke M., Stahl D. A., Sinninghe
Damsté J. S. (2008) Appl Env Microbiol 74, 2433-
2440.
[3] Schouten S., Middelburg J. J., Hopmans E. C.,
Sinninghe Damsté J. S. (2010) Geochim Cosmochim
Acta 74, 3806-3814.
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