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| Titel |
Microbial life in continental salt pan sediments and their response to climate variability in Northern South Africa |
| VerfasserIn |
Steffi Genderjahn, Kai Mangelsdorf, Mashal Alawi, Lukas Belz, Jens Kallmeyer, Dirk Wagner |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250123372
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| Publikation (Nr.) |
 EGU/EGU2016-2608.pdf |
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| Zusammenfassung |
| The environmental history of southwestern African mainland is largely unknown.
Since there are no lacustrine systems with constant water coverage in this area, we
investigated a continental salt pan as a terrestrial geoarchive with the potential to preserve
climate signals. Within the frame of the research project “GeoArchives” (part of the
SPACES program, funded by the German Federal Ministry of Education and Research,
BMBF) we aimed to reconstruct climate variabilities during the late Pleistocene to
Holocene.
The presented study is focused on variations within the microbial community structure
and abundance of key organisms in a salt pan with special regards to sediment age and
geochemical parameters. A combined approach of a 16S rDNA-based quantification method
and lipid biomarker analysis was used to demonstrate the response of the microbial
communities with respect to environmental changes. The phospholipid derived fatty acids
(PLFAs) in sedimentary deposits are characteristic markers for living Bacteria, whereby their
side chain represents a fingerprint of the community structure on a broad taxonomic level.
Archaeol and isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) were used as
characteristic makers for Archaea whereas branched GDGTs (brGDGTs) are typical
biomarkers for Bacteria. In contrast to PLFAs, they represent dead microbial biomass and
thus the past microbial communities in older sediments, since they are already partly
degraded.
Samples from the Witpan, located in the northwest of South Africa and representing a
depths profile from the Late Pleistocene to Holocene, were gathered. Despite the extreme
environment with rather low TOC values, restricted availability of water and high salt
concentration markers for Bacteria and Archaea were observed. A series of saturated,
branched and unsaturated PLFAs were identified. The diversity and concentration of PLFAs
were highest in the top layers (up to 30000 ng gsed−1, 0-10 cm) and characteristic markers
for cyanobacteria were most abundant. The community composition changed with depths and
both the copy numbers of 16S rDNA genes of bacteria (varied from 102 to 105 cell gsed−1)
and the amount of PLFAs (up to 3000 ng gsed−1) reflected a low abundance of
microorganisms despite increasing feedstock in deeper sediments. Thus, the actual salt pan
microbial community is mainly located in the top layers and decreases with depth. In
contrast archaeol and GDGTs increased at the transition from Holocene to deeper Late
Pleistocene sediments (from 40 up to 3400 ng gsed−1) indicating a higher past microbial
abundance during the Late Pleistocene. The increase of GDGTs, TOC, acetate and
formate suggested a higher supply of organic matter and a higher microbial activity
in this period. Therefore, we assumed an increased precipitation during the Late
Pleistocene compared to the arid Holocene in southwestern Africa. We could show the
potential of continental salt pans to preserve climate signals during deposition and we
demonstrated their potential as a Late Quaternary geoarchive by means of lipid biomarker
studies.
To describe the environmental habitat, a detailed analysis of diversity and abundance of
microorganisms using Next Generation Sequencing is planned. |
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