25th International Meeting on Organic Geochemistry IMOG 2011

P-171
Lipid biomarkers and phylogenetic analysis indicating the
variability of methanogenic communities within terrestrial Late
Pleistocene and Holocene permafrost deposits in the central
Lena River delta, Siberia
Juliane Griess 1,2 , Kai Mangelsdorf 1 , Dirk Wagner 2
1 GFZ German Research Centre for Geosciences, Potsdam, Germany, 2 Alfred Wegener Institute for Polar
and Marine Research, Potsdam, Germany (corresponding author:juliane.griess@awi.de)
Permafrost environments of the Northern
hemisphere are suspected to be strongly affected by
the currently observed and predicted global
temperature rise (IPCC, 2007). Given that about one
third of global soil stored carbon is preserved in high
Arctic environments, a degradation of permafrost due
to potential future increases of atmospheric and soil
temperatures might lead to an increased
bioavailability of recent as well as ancient carbon.
Thus, an intensified microbial turnover of these
particular carbon pools, driven by substrate
availability and temperature, might cause the release
of large amounts of greenhouse gases such as
methane.
To predict the risk for future climate and
estimate the global atmospheric carbon budget, it is
important to understand the microbial driven methane
dynamics of the Siberian Arctic and their response to
climate changes in the past. Therefore, a combination
of quantitative and qualitative analyses of recent and
fossil methanogenic communities were performed to
reveal variations in permafrost deposits of the
Siberian Arctic.
The Lena River Delta, northeast Siberia, is the
largest delta within the circum arctic land masses with
approximately 29000 km². Drilling of a 23 m
permafrost core was conducted on Kurungnakh
Island, Central Lena Delta (N 72°20, E 126°17) in
2002. Kurungnakh Island is located in the zone of
continuous permafrost and composed of late
Quaternary sediments. The permafrost sequence is
characterized by Late Holocene deposits of sandy
layers, covered by a huge, second formation called
'Ice complex' (IC), with inclusions of large peat blocks
with less decomposed organic material. Furthermore,
Holocene layers of about 2-3 m thickness on top of
the IC are containing ice-wedges of 3-5m width.
The recovered permafrost sequence is
characterized by strong vertical variations of the total
organic carbon (TOC) and in-situ methane content.
The TOC content varies from 2 to 14%, whereas the
methane concentrations range from 2 to 1600 ppm in
certain layers.
Generally, in-situ methane contents reflect the
TOC profile with depth. In this context the questions
are: Is this methane produced by recently active
methanogenic communities in permanently frozen soil
or was the methane produced and trapped during
times of sediment deposition and permafrost
progression and, thus, originate from fossil
communities?
Lipid biomarkers and amplifiable DNA were
successfully recovered throughout the whole
Kurungnakh permafrost sequence with an age of up
to 42 ka. Analysis on the abundance and distribution
of branched and isoprenoidal glycerol dialkyl glycerol
tetraether (GDGT) core lipids (being indicators for
bacteria and archaea, respectively) revealed
variations within the vertical profile following the
trends outlined by the TOC and methane contents.
At 17 m soil depth an interesting interval is
indicated by a pronounced occurrence of archaeal
GDGTs. Additionally, a variety of intact phospholipid
esters indicate the presence of a viable microbial
community at this depth. Furthermore, the respective
interval is characterized by comparably low
abundance of methane, but high amounts of archaeol
and a high diversity of methanogenic archaea, as
shown by genetic fingerprints obtained from
denaturising gradient gel electrophoresis (DGGE).
This suggests the possibility of recent
methanogenesis in permanently frozen ground,
whereas methane might have diffused through the
soil and been trapped in overlaying TOC-rich layers.
Phylogenetic analysis on the basis of clone
libraries of the respective methanogenic communities
show changes in composition and dominance of the
different genera with depth. This observation is
discussed as an adaption of microorganisms to
substrate quality and quantity of soil organic matter or
sedimentation conditions during times of sediment
deposition.
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