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| Titel |
In situ Raman-based detections of the hydrothermal vent and cold seep fluids |
| VerfasserIn |
Xin Zhang, Zengfeng Du, Ronger Zheng, Zhendong Luan, Fujun Qi, Kai Cheng, Bing Wang, Wangquan Ye, Xiaorui Liu, Changan Chen, Jinjia Guo, Ying Li, Jun Yan |
| 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 |
250124060
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| Publikation (Nr.) |
 EGU/EGU2016-3428.pdf |
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| Zusammenfassung |
| Hydrothermal vents and cold seeps, and their associated biological communities play an
important role in global carbon and sulphur biogeochemical cycles. Most of the
studies of fluid composition geochemistry are based on recovered samples, both with
gas-tight samplers and as open specimens, but the in situ conditions are difficult to
maintain in recovered samples. Determination in situ of the chemical signals of
the emerging fluids are challenging due to the high pressure, often strongly acidic
and temperature in which few sensors can survive. Most of those sensors used so
far are based on electrochemistry, and can typically detect only a few chemical
species.
Here we show that direct measurement of critical chemical species of hydrothermal
vents and cold seeps can be made rapidly and in situ by means of a new hybrid
version of earlier deep-sea pore water Raman probe carried on the ROV (Remote
Operated Vehicle) Faxian. The fluid was drawn through the probe by actuating a
hydraulic pump on the ROV, and measured at the probe optical cell through a sapphire
window.
We have observed the concentrations of H2S, HS−, SO42−, HSO4−, CO2, and
H2 in hydrothermal vent fluids from the Pacmanus and Desmos vent systems in
the Manus back-arc basin, Papua New Guinea. Two black smokers (279˚ C and
186˚ C) at the Pacmanus site showed the characteristic loss of SO42−, and the
increase of CO2 and well resolved H2S and HS− peaks. At the white smoker of Onsen
site the strong HSO4−peak observed at high temperature quickly dropped with
strong accompanying increase of SO42−and H2 peaks when the sample contained
in the Raman sensing cell was removed from the hot fluid due to rapid thermal
deprotonation. We report here also the finding of a new lower temperature (88˚ C)
white smoker “Kexue” field at the Desmos site with strong H2S, HS− and CO2
signals.
We also have detected the concentrations of CH4,H2S, HS−, SO42−, and S8 in
cold seep fluids and the surrounding sediment pore water from the northern South
China Sea. Several sediment pore water profiles nearly at the cold seep vent showed
the characteristic loss of SO42−, and the increase of CH4, H2S and HS− peaks.
Dissolved S8 and CH4had been first found at the fluids under the lush biological
communities of the cold seep. This may indicate some bacteria mats at the lush
biological communities oxidize hydrogen sulfide and produce elemental sulfur as a
byproduct.
Our research suggests that the in situ observed H2S:HS−, and HSO4−:SO42− ratios
provide elegant pH sensitive “dyes” with which to diagnose the geochemical reactions
occurring. |
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