25th International Meeting on Organic Geochemistry IMOG 2011

P-414
European lake sediment calibration of long chain n-alkane δD
values
Gert-Jan Reichart 1 , Cornelia Blaga 1 , Jaap S. Sinninghe Damste 1,2
1 Department of Earth Sciences - Geochemistry Faculty of Geosciences, Utrecht University, Utrecht,
Netherlands, 2 Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea
Research, Den Burg, Netherlands (corresponding author:reichart@geo.uu.nl)
Lacustrine sediments provide high-resolution records
of past climatic and environmental change. The, often
laminated, sediments are rich in organics and hence
excellently suited for the application of biomarker
proxies. Compound specific stable hydrogen isotope
(δD) analyses can be used to reconstruct past
changes in the hydrological cycle and thus climate.
Especially long chain n-alkanes, which predominantly
originate from plant leaf-waxes, have the potential to
unravel changes in moisture supply and evaporation
in the lakes‘ catchment area. The application of
compound specific δD analyses in lake sediments,
however, critically depends on a robust calibration.
Different plant communities, changes in local
precipitation over evaporation and differences in
biomarker transport all potentially affect δD values in
n-alkanes and should, therefore, be included in such
a calibration.
In the present study we determined the compound
specific δD ratios of long-chain n-alkanes from
surface sediments of 20 lakes from Europe. The lakes
are situated along a north–south transect (from
Sweden to Italy) and encompass a large temperature
and moisture gradient, as well as contrasting local
settings, allowing for a robust test of the application of
δD values of sedimentary n-alkanes as paleoclimatic
and paleoenvironmental proxies.
δD ratios were measured on C25, C27, C29 and C31 nalkanes,
the most abundant n-alkanes present. From
some sediments also the C23 n-alkane was abundant
enough to allow δD analyses. We observed a large
latitudinal δD change of more than 50‰, which is in
line with the change observed in the precipitation as a
consequence of hydrological cycle. Even though
between individual n-alkanes a large offset was
observed, spanning from -108 to -209‰ for n- C25, -
130 to -209‰ for C27, -162 to -214‰ for C29, and from
-164 to -210‰ for C31, all n-alkanes show a close
correspondence to the analyzed lake water stable
isotopic values, which integrates the catchments area
hydrological cycle. This is in line with previous studies
that showed that the δD of plant leaf wax tracks the
decreasing trend of precipitation δD with increasing
latitude.
δD stable isotopic values of the most abundant nalkanes
in lacustrine sediment are strongly correlated
with the isotopic values of the lake water, collected at
the same time as the sediment samples (r 2 between
0.5 for C31 and 0.75 for C27). This implies that
although several complicating factors potentially offset
the δD values as proxy for the hydrological cycle, the
organic compounds integrate hydrological changes in
the lakes‘ catchment area similarly as the lake water
itself.
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