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New insight on the origin of organic compounds in fluids from ultramafic-hosted hydrothermal systems
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Laboratoire de géochimie et métallogénie, Ifremer, Brest, France. (Géosciences Marines)
Institut Néel, Grenoble, France. (dept MCMF)
UMR6197 LM2E, Ifremer, Brest, France.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Hydrocarbons gases (C1-C4) as well as larger organic compounds were reported elsewhere in fluids from the Rainbow and the Lost City ultramafic-hosted hydrothermal fields. Whereas hydrocarbon gases are likely abiogenic (Fischer-Tropsch Type reaction), the origin of larger molecules remains unclear. Our ability to differentiate between biotic and abiotic sources of organic compounds in deep-sea hydrothermal systems may give clues to the understanding of organic geochemistry on the early Earth. Here, we report a series of experiments of hydrothermal degradation (40 MPa / 200, 350 and 450°C) of the piezophile archaea Pyrococcus abyssi biomass, which provides supporting lines of evidence of the abiogenic origin of saturated hydrocarbons as well as of the possible biogenic origin of alkylated aromatic hydrocarbons, Polycyclic Aromatic Hydrocarbons (PAH) and C12:0-C16:0 fatty acids in fluids from ultramafic-hosted hydrothermal systems.

Keyword [en]
Deep subsurface biosphere, hydrothermal, organic compounds, degradation
National Category
Other Earth and Related Environmental Sciences Other Biological Topics
Research subject
URN: urn:nbn:se:su:diva-29194OAI: diva2:231455
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.
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 336
Serpentinisation, hydrocarbons, organic compounds, ultramafic, hydrothermal, geochemistry, origin of life
National Category
Other Earth and Related Environmental Sciences Other Chemistry Topics Geochemistry
Research subject
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)
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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