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Detection of trace organic compounds by Stir Bar Sorptive Extraction: application to the evolution of the organic composition of hydrothermal fluids from the Rainbow site (36°N, Mid-Atlantic Ridge) over 3 years
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Laboratoire de géochimie et métallogénie, Ifremer, Brest, France. (Géosciences Marines)
Laboratoire de géochimie et métallogénie, Ifremer, Brest, France. (Géosciences Marines)
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The question of the abiogenic oil has been discussed and hydrothermal reactions have been suggested to abiotically generate hydrocarbons. Besides, ultramafic-hosted hydrothermal systems have been regarded as favourable environment for the emergence of life. Therefore, it is of great importance to investigate the presence of organic compounds in hydrothermal fluids. However, because of the sampling difficulties, the complexity of the matrix, the numerous interferences and the assumed trace level concentrations; it was considered a real challenge. Here we show that Stir Bar Sorptive Extraction (SBSE) coupled to Thermal Desorption – Gas Chromatography – Mass Spectrometry (TD-GC-MS) can be successfully applied to analyses of volatile and semi-volatile organic compounds in hydrothermal fluids. The method exhibited excellent reproducibility and conditioned samples appeared to be really stable for up to 3 years. This innovative and versatile technique was used to study the fluids from the ultramafic-hosted hydrothermal field Rainbow located at 36°14’N on the Mid-Atlantic Ridge (MAR). Despite relative stability for mineral composition and gas content is observed, analyses of fluids samples from 2005, 2007 and 2008 revealed more distinct organic compositions. In addition, results suggest the similarity of the organic content of the fluids regardless of the sampling location within the field, which may indicates the presence of a single reaction zone and that no further chemical reactions occur while fluids are transported to the seafloor.

Keyword [en]
SBSE, organic compounds, hydrothermal, ultramafic, MAR, serpentinisation
National Category
Earth and Related Environmental Sciences Analytical Chemistry Geochemistry
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-29192OAI: oai:DiVA.org:su-29192DiVA: diva2:231454
Projects
MoMARnet
Available from: 2009-08-13 Created: 2009-08-13 Last updated: 2010-01-14Bibliographically approved
In thesis
1. Origin of organic compounds in fluids from ultramafic-hosted hydrothermal vents of the Mid-Atlantic Ridge
Open this publication in new window or tab >>Origin of organic compounds in fluids from ultramafic-hosted hydrothermal vents of the Mid-Atlantic Ridge
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Natural gas, primarily methane (CH4), is produced in substantial amounts in ultramafic-hosted hydrothermal systems. These systems could also generate oil (heavier hydrocarbons) and the first building blocks of life (prebiotic molecules). In the presence of iron bearing minerals, serpentinisation reactions generate H2. Subsequently, CH4 could be synthesised by Fischer-Tropsch Type (FTT) reaction (4H2 + CO2 → CH4 + 2H2O) which is an abiotic process. This has lead to the idea of abiotic formation of larger organic molecules. Both thermodynamics and laboratory work support this idea, yet field data have been lacking. This study focuses on determining the organic content of fluids from ultramafic-hosted hydrothermal systems from the Mid-Atlantic Ridge (MAR) and the origin of the compounds. Fluids were collected from the Lost City, Rainbow, Ashadze and Logatchev vent fields during the EXOMAR (2005), SERPENTINE (2007), MoMARDREAMnaut (2007) and MOMAR08-Leg2 (2008) cruises conducted by IFREMER, France. A SBSE-TD-GC-MS technique was developed and used to extract, concentrate, separate and identify compounds in the fluids. Hydrothermally derived compounds appeared to consist mainly of hydrocarbons and O-bearing molecules. In addition, some amino acids were detected in the fluids by ULPC-ESI-QToF-MS but their origin will need to be determined. The organic content of the Rainbow fluids did not show intra field variability unlike differences could be noted over the years. In order to address the question of the source of the molecules, compound specific carbon isotopic analyses were carried out and completed with a bacterial (Pyrococcus abyssi) hydrothermal degradation experiment. The δ13C data fall in the range of -40 to -30‰ (vs. V-PDB), but individual δ13C values preclude the identification of a biogenic or abiogenic origin of the compounds. The degradation experiment, however, suggests an abiogenic origin of a portion of saturated hydrocarbons whereas carboxylic acids would be biogenic, and aromatic compounds would be thermogenic.

Place, publisher, year, edition, pages
Stockholm: Department of Geology and Geochemistry, Stockholm University, 2009. 51 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 336
Keyword
Serpentinisation, hydrocarbons, organic compounds, ultramafic, hydrothermal, geochemistry, origin of life
National Category
Other Earth and Related Environmental Sciences Other Chemistry Topics Geochemistry
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-29172 (URN)978-91-7155-913-5 (ISBN)
Public defence
2009-09-18, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
MoMARnet
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Submitted. Available from: 2009-08-27 Created: 2009-08-12 Last updated: 2009-08-27Bibliographically approved

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