25th International Meeting on Organic Geochemistry IMOG 2011

P-435
Impact of lake water pH on the distribution of branched
tetraether membrane lipids: further indication for an aquatic
source
Petra Schoon 1 , Anna de Kluijver 2,3 , Jack Middelburg 2,3 , John Downing 4 , Jaap Sinninghe
Damsté 1 , Stefan Schouten 1
1 NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, 't
Horntje, Texel, Netherlands, 2 NIOO Netherlands Institute of Ecology, Department of Ecosystem Studies,
Yerseke, Netherlands, 3 Department of Earth Sciences - Geochemistry, Faculty of Geosciences, Utrecht
University, Utrecht, Netherlands, 4 Iowa State University, Department of Ecology, Evolution, and Organismal
Biology, Ames, Iowa, United States of America (corresponding author:petra.schoon@nioz.nl)
Recently, the distribution of branched glycerol dialkyl
glycerol tetraethers (GDGTs) in lake sediments have
gained increased interest for their potential use in
reconstructing paleoenvironmental conditions [e.g. 1,
2]. Branched GDGTs are membrane lipids produced
by yet unidentified bacteria that thrive in soils, peat
bogs and likely lake waters or sediments. Branched
GDGTs comprise methylated C28 alkyl chains, which
are ether-linked to a glycerol backbone at either side.
Additionally, some of these alkyl chains contain a
cyclopentyl moiety. Weijers et al. [3] found a
correlation between the relative degree of cyclization
of these branched tetraether lipids with soil pH (CBTindex)
for soils and peats. However, application of this
proxy in lake sediments may be complicated as the
sources of the branched GDGTs can be both
autochtonous and allochtonous [4].
Here we studied the distribution of branched GDGTs
in suspended particulate matter sampled from 23
lakes in Iowa and Minnesota (USA). These lakes
have been selected to encompass a wide range in pH
(6.1 to 9.8) and alkalinity (8 to 237 mg CaCO3/L).
Such a cross-system lake study will allow us to test
the CBT-index on variations in water column pH. The
sampled lakes in Minnesota have an overall lower pH
than the sampled lakes in Iowa (Fig. 1). We find that
branched GDGT concentrations are higher in the (low
pH) Minnesota lake suspended matter, compared to
those in Iowa. This is in agreement with observations
in soils where the amount of branched GDGTs is
higher with lower pH [5], thus suggesting that these
compounds are produced, at least partly, in situ in the
lake. Furthermore, our preliminary results show a
linear correlation between observed lake water pH
and the CBT-index, although lakes with a pH above
8.5 do not seem to fit this correlation. The same kind
of relationship has recently been found in a study of
Chinese lake surface sediments [6]. Our findings
suggest that the CBT proxy may potentially be used
to reconstruct the pH of ancient lakes [cf. 1], although
the application of the CBT-index on high pH lakes
should be performed with care.
Fig. 1. Range in pH and alkalinity of the analyzed lakes in
Iowa and Minnesota, USA.
References
[1] Tyler et al. (2010), J. Geophys. Res. 115, doi: 10.1029/
2009JG001109.
[2] Blaga et al. (2010), Org. Geochem. 41, pp. 1225-1234.
[3] Weijers et al. (2007), GCA 71, pp. 703-713.
[4] Tierney & Russell (2009), Org. Geochem. 40, pp. 1032-
1036.
[5] Peterse et al. (2010), Org. Geochem. 41, pp. 1171-
1175.
[6] Sun et al. (2011), J. Geophys. Res. 115, doi: 10.1029/
2010JG001365.
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