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| Titel |
Hydrothermal mixing: Fuel for life in the deep-sea |
| VerfasserIn |
M. Hentscher, W. Bach, J. Amend, T. McCollom |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027199
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| Zusammenfassung |
| Deep-sea hydrothermal vent systems show a wide range of fluid compositions and
temperatures. They reach from highly alkaline and reducing, like the Lost City hydrothermal
field, to acidic and reducing conditions, (e. g., the Logatchev hydrothermal field) to acidic and
oxidizing conditions (e. g., island arc hosted systems). These apparently hostile
vent systems are generally accompanied by high microbial activity forming the
base of a food-web that often includes higher organisms like mussels, snails, or
shrimp.
The primary production is boosted by mixing of chemically reduced hydrothermal vent
fluids with ambient seawater, which generates redox disequilibria that serve as energy source
for chemolithoautotrophic microbial life. We used geochemical reaction path models to
compute the affinities of catabolic (energy-harvesting) and anabolic (biosynthesis) reactions
along trajectories of batch mixing between vent fluids and 2 -C seawater. Geochemical data
of endmember hydrothermal fluids from 12 different vent fields (Lost City, Rainbow,
Logatchev, TAG, EPR 21-N, Manus Basin, Mariana Arc, etc.) were included in this
reconnaissance study of the variability in metabolic energetics in global submarine vent
systems.
The results show a distinction between ultramafic-hosted and basalt-hosted hydrothermal
systems. The highest energy yield for chemolithotrophic catabolism in ultramafic-hosted
hydrothermal systems is reached at low temperature and under slightly aerobic to aerobic
conditions. The dominant reactions, for example at Rainbow or Lost City, are the oxidation of
H2, Fe2+ and methane. At temperatures >60 -C, anaerobic metabolic reactions,
e. g., sulphate reduction and methanogenesis, become more profitable. In contrast,
basalt-hosted systems, such as TAG and 21-N EPR uniformly indicate H2S oxidation to be
the catabolically dominant reaction over the entire microbial-relevant temperature
range.
Affinities were calculated for the formation of individual cellular building blocks from
inorganic reactants (H2, CO2, NH4+, HPO42-, etc.), which include amino acids,
sugars, amines, nucleic acids, and fatty acids. Again, ultramafic-hosted sites are
distinct from their volcanically-hosted counterparts in that biosynthesis reactions are
much less energy-demanding. For a range of biosynthesis reactions, including the
formation of proteins, vent systems like Lost City have a fairly wide window of
temperature (i. e., fluid mixing ratio) in which biosynthesis reactions are actually
endergonic. These favourable energetics of anabolism help microorganisms grow
rapidly when conditions are favourable. These results also have potential implications
for the development of early life, as alkaline and reducing vent fluids generate an
environment that appears to lower the energetic demands of biosynthesis reactions
considerably. |
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