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| Titel |
A microbial “bloom” at the onset of the Messinian Salinity Crisis in the Piedmont Basin (NW Italy) |
| VerfasserIn |
Marcello Natalicchio, Daniel Birgel, Francesco Dela Pierre, Francesca Lozar, Xiaolei Liu, Kai-Uwe Hinrichs, Jörn Peckmann  |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112262
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| Publikation (Nr.) |
 EGU/EGU2015-12412.pdf |
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| Zusammenfassung |
| The Messinian Salinity Crisis (MSC), a severe ecological crisis that occurred in the
Mediterranean Basin about 6 myr ago, had drastic consequences for both freshwater
and marine ecosystems (Roveri et al., 2014). The response of prokaryotes to the
changing conditions at the MSC onset is virtually unknown. In a lipid biomarker
study of sediments straddling the MSC onset from the Pollenzo section (NW Italy),
we aim to evaluate the response of microbial communities at the transition from
normal marine to extreme conditions. In this section, the advent of the MSC does not
coincide with the deposition of gypsum; instead shales and intercalated carbonate-rich
beds deposited. These deposits are considered as the deep water counterparts of
gypsum layers that formed in the shallower parts of the basin (Dela Pierre et al.,
2012).
In both pre-MSC and MSC deposits, the molecular fossil inventory is sourced from all
three domains of life and is mainly represented by isoprenoidal alcohols, fatty acids, sterols,
long chain n-alkanes and n-alcohols. However, after the MSC onset, a sharp increase of the
long chains n-alkanes, n-alcohols and fatty acids occurs, indicating a significant increase of
terrigenous organic matter, most likely sourced by enhanced riverine runoff. Remarkably, this
coincides with an increase of sterols (sitosterol and dinosterol), that are typically interpreted
as markers of phytoplankton. The same strata contain filamentous fossils, which have
been interpreted as remains of sulfide-oxidizing bacteria (cf., Dela Pierre et al.,
2012).
The basal MSC deposits are also typified by an increase of isoprenoidal alcohols,
including glycerol dibiphytanyl glycerol tetraethers (GDGTs) and diphytanyl glycerol
diethers (DGD). Caldarchaeol and crenarchaeol are the overall most abundant GDGTs. Their
almost equal distribution in pre-MSC deposits suggests that they derived from planktic
Thaumarchaeota, which are abundant picoplanktonic organisms in modern oceans. In
contrast, caldarchaeol predominates over crenarchaeol in the MSC deposits, indicating a
change towards harsh environmental conditions. A prominent spread of δ13C values between
caldarchaeol- and crenarchaeol-derived biphytanes (δδ13C: 9) in the MSC deposits agrees
with a profound modification of the archaeal community structure. This is further
confirmed by the sharp increase of the DGD archaeol and the appearance of the DGD
extended archaeol. The latter is only sourced by halophilic archaea, confirming an
increase of seawater salinity after the MSC onset. In conclusion, this study reveals that
lipid biomarkers are excellent recorders of the MSC onset. Moreover, they help to
reconstruct the Messinian microbial ecosystems in the course of changing environmental
conditions.
References
Dela Pierre, F., et al., 2012. Palaeogeography, Palaeoclimatology, Palaeoecology 344/345,
78-93.
Roveri et al., 2014. Marine Geology 352, 25-58. |
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