25th International Meeting on Organic Geochemistry IMOG 2011

P-244
Identification and distribution of intact branched tetraether lipids
in peat and soils
Francien Peterse, Ellen Hopmans, Stefan Schouten, Anchelique Mets, Irene Rijpstra,
Jaap Sinninghe Damsté
NIOZ Royal Netherlands Institute for Sea Research, Den Hoorn (Texel), Netherlands
Branched glycerol dialkyl glycerol tetraether
(GDGT) lipids are membrane spanning tetraether
lipids that occur ubiquitously in soils and peats (1,2).
The branched GDGTs form the base of several
proxies, like the BIT index that is used to determine
the relative input of soil organic matter into marine
sediments (2), and the MBT/CBT proxy for the
reconstruction of continental air temperatures and
past soil pH (3).
Most studies so far focused on the
distribution of core lipids (CLs) only, however, by
analyzing just the core lipids, only the pool of fossil
material in a soil is covered. In order to differentiate
between branched GDGTs derived from living cells
and those from the fossil GDGT pool, also their intact
polar precursors need to be analyzed. Here we
directly analyzed, using HPLC/ESI-MS 2 , the
occurrence and distribution of intact polar lipid (IPL)
branched GDGTs throughout a depth profile of a
Swedish peat bog, and quantified CL en IPL-derived
branched GDGTs by HPLC/ APCI-MS for
comparison. Some soils were also analyzed.
In addition to two previously discovered
glycosidic IPL-branched GDGTs (4), we identified
IPL-branched GDGTs with a hexose-glucuronyl,
phospho-hexose, phospho-inositol, or hexosephosphoglycerol
headgroup. A Selected Reaction
Monitoring (SRM) assay was developed to monitor
changes in headgroup distribution with depth. The
abundance of all monitored IPL-branched GDGTs
increases below the water table (Figure). However,
individual IPL trends differ; especially the
phospholipids show a relatively much larger increase
with depth than glycosidic IPLs. The oxic part of the
peat bog contains much less IPL-branched GDGTs,
probably due to rapid oxic degradation of any material
produced at times of high water levels and anaerobic
conditions. It is also in this part that we observe a
higher relative abundance of glycolipids compared to
phospholipids. This observation is in agreement with
the more recalcitrant nature of glycolipids (5). Thus, it
seems that the best marker for in situ production of
branched GDGTs is the phospho-hexose branched
GDGT. Comparison of trends in phospho IPLbranched
GDGTs with changes in absolute amounts
of IPL-derived and CL branched GDGTs with depth
indicates that branched GDGTs are mainly produced
by anaerobic bacteria, possibly from a subdivision of
the phylum Acidobacteria, in the anoxic part of the
peat. Some of the IPL-branched GDGTs are also
present in soils, although their distributions differ from
that in the peat profile.
1. Sinninghe Damsté et al., 2000. Chem. Comm.
17, 1683-1684.
2. Hopmans et al., 2004. EPSL 224, 107-116.
3. Weijers et al., 2007. GCA 71, 703-713.
4. Liu et al., 2001. Org. Geochem. 41, 653-660.
5. Harvey et al., 1986. GCA 50, 795-804.
Depth profiles of the Saxnäs Mosse peat bog showing the IPL-branched GDGTs included in the SRM assay and the
concentrations of CL (blue), IPL-derived (open blue), and phospho-IPL derived (grey triangles) branched GDGTs. The
horizontal dotted lines indicate the level of the water table at the time of sampling (14 cm), and at its lowest point (25 cm ).
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