25th International Meeting on Organic Geochemistry IMOG 2011

P-190
Large scale cooling in Tertiary Central Europe as inferred by the
MBT/CBT paleothermometer
Thorsten Bauersachs 1 , Stefan Schouten 2 , Lorenz Schwark 1
1 Christian-Albrechts-University, Kiel, Germany, 2 Royal Netherlands Institute for Sea Research, Texel,
Netherlands (corresponding author:thb@gpi.uni-kiel.de)
Earth‘s climate experienced dramatic changes
throughout the last 65 Ma. Starting at the
Paleocene/Eocene thermal maximum, the global
climate underwent a gradual cooling that eventually
resulted in the glaciations in the Neogene [1]. Most
reconstructions of climate variability are derived from
the marine realm using global deep sea oxygen
isotope curves or molecular paleotemperature proxies
[1]. In contrast, only little information on the changes
of the continental climate is available, which is mainly
due to a lack of continuous high resolution records
and suitable quantitative temperature proxies.
The methylation index of branched tetraethers
(MBT) is a novel temperature proxy based on
temperature-driven changes in the membrane-lipid
composition of presumably anaerobic soil bacteria [2].
These changes correlate well with mean annual air
temperature (MAAT) and the MBT proxy has thus
been used to reconstruct paleotemperature records in
terrestrial as well as coastal marine sediments [3].
In this study, we employed the MBT Index on a
number of lacustrine deposits ranging in age from the
Early Eocene to the Late Oligocene in order to
reconstruct climate evolution of the Central European
continent. The Messel oil shale (Germany)
accumulated in a small crater lake during the Eocene
climate optimum and thus allows reconstructing
temperature development in a so-called green house
world. Methylation of the branched glycerol dialkyl
glycerol tetraethers (GDGTs) suggests that the MAAT
at time of oil shale formation ranged from 20-32 °C
over an estimated time period of ca. 1 Ma. This is in
good agreement with temperature estimates based on
paleontological observations suggesting a
paratropical climate in Eocene Central Europe with an
average air temperature of ca. 25-30 °C [4].
In contrast, to the green house period of the Early
Eocene, the climate of the Oligocene was significantly
cooler reflected by low MAAT of 8-15 °C in the
lacustrine deposit of Lake Enspel (Westerwald,
Germany). These MBT-derived air temperatures are
similar to those previously reconstructed using floral
elements of the Enspel deposit [5].
Our results indicate that the paleotemperature
trends of the Central European continent, based on
the distribution of branched GDGTs in Tertiary
lacustrine deposits, resemble those previously
obtained from marine records and that the MBT proxy
might be a valuable tool for reconstructing terrestrial
paleoclimate records.
Fig. 1. Mean annual air temperature (MAAT) reconstructed
from the distribution of branched GDGTs in (a) the Eocene
Messel oil shale and (b) the Oligocene Lake Enspel deposit.
References
[1] Zachos et al. (2001) Science 292, 686-693
[2] Weijers et al. (2007) Geoch Cosmoch Ac 71, 701-703
[3] Donders et al. (2007) EPSL 281, 215-225
[4] Wilde (1989) Cour. Forsch. Senk 115, 1-213
[5] Herrmann (2007) PhD Thesis, Tübingen University
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