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| Titel |
Lithosphere-biosphere interaction at a shallow-sea hydrothermal vent site; Hot Lake, Panarea, Italy |
| VerfasserIn |
Chia-I Huang, Rudolf Amann, Jan P. Amend, Wolfgang Bach, Benjamin Brunner, Anke Meyerdierks, Roy E. Price, Florence Schubotz, Roger Summons, Frank Wenzhöfer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043997
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| Zusammenfassung |
| Deep-Sea hydrothermal systems are unique habitats for microbial life with primary
production based on chemosynthesis and are considered to be windows to the subsurface
biosphere. It is often overlooked, however, that their far more accessible shallow-sea
counterparts are also valuable targets to study the effects of hydrothermal activity on geology,
seawater chemistry and finally, on microbial life. Such an area of shallow marine
hydrothermal venting is observed approximately 2.5 km east of Panarea Island (Sicily, Italy).
This system is characterized by fluid temperatures of up to 135Ë C, gas emissions dominated
by CO2 and precipitation of elemental sulfur on the seafloor. In an interdisciplinary project to
investigate the influence of geofuels on marine microbiota, sediment cores and
pore fluids were sampled for geological and geochemical analyses. An attempt
was made to link these geochemical data with a characterization of the microbial
community.
One of the investigated sites (Lago Caldo, Hot Lake) is an oval-shaped (~10 by 6 meters)
shallow (~2.5 m deep) depression covered by elemental sulfur. The sediments in this
depression are strongly affected by hydrothermal activity: the pH of pore fluids is in a range
between 5 and 6; the salinity is approximately two times higher than seawater. In situ
temperatures of 36Ë C and 74Ë C (10 cm sediment depth) at two different locations within
Hot Lake indicate variability in hydrothermal flux. The sediment surface layer is anoxic, and
with increasing depth from the sediment-water interface, sulfate concentrations decrease from
~30 mM to less than 10 mM, whereas sulfide concentrations increase from less than 50
μM to ~1000 μM at 25 cm sediment depth, thus suggesting a higher potential
for energy gain based on sulfur disequilibrium. As indicated by the variability in
the sediment temperatures at 10 cm, fluid fluxes and mixing with seawater is not
found to be uniform at Hot Lake. This is reflected in variability of the pore fluids
geochemistry (anions, cations and stable isotope composition of water and sulfate) of depth
profiles.
DNA-fingerprinting techniques (DGGE, ARISA) revealed distinctly different bacterial
16S rRNA gene patterns for three separate sediment cores taken at Hot Lake. Intact polar
lipid (IPL) biomarker analysis revealed a dominance of bacterial over archaeal biomass. The
bacterial IPLs were mainly comprised of diether and diester phospholipids and ornithine
lipids, indicative of viable thermophilic sulfate-reducing and acidophilic sulfide-oxidizing
bacteria. Bacterial IPL abundance was highest in the sediment surface layer. Fluorescence in
situ hybridization showed that with increasing depth and temperature, the abundance of
archaea increased relative to that of bacteria. Comparative 16S rRNA gene analysis revealed a
moderate diversity of bacteria, and a dominance of epsilonproteobacterial sequences.
Cultured representatives of the detected epsilonproteobacterial classes are known
to catalyze elemental sulfur reduction and oxidation reactions and to mediate the
formation of iron-sulfides, including framboidal pyrite, which was found in sediment
samples.
We conclude that mixing between hydrothermal fluids and seawater leads to distinctly
different temperature gradients and ecological niches in Hot Lake sediments. From the
geochemical profiles and a preliminary characterization of the microbiological community,
we found strong evidence of sulfur-related metabolism. Further investigation of certain
clusters of bacteria and archaea as well as gene expression analysis will give us a deeper
understanding of the interaction between geosphere and biosphere at this site in the future. |
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