Origin of organic compounds in fluids from ultramafic-hosted hydrothermal vents of the Mid-Atlantic Ridge

Other titles Origine des composés organiques dans les fluides provenant de systèmes hydrothermaux ultrabasiques situés sur la dorsale médio-Atlantique
Type Thesis
Date 2009-09-18
Language English
Author(s) Konn Cécile
University Stockholm University
Discipline Géochimie
Thesis supervisor Nils HOLM
Thesis co-supervisor CHARLOU Jean-Luc
Financement Europe (projet Marie-Curie)
Mot-Clé(s) origine de la vie, géochimie, systèmes hydrothermaux, ultrabasique, composés organiques, hydrocarbures, serpentinisation
Keyword(s) origin of life, geochemistry, hydrothermal, ultramafic, organic compounds, hydrocarbons, serpentinisation
Abstract 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 that 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 S13C data fall in the range of -40 to -30 0/00(vs. V-PDB), but individual S13C 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.
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Konn Cécile (2009). Origin of organic compounds in fluids from ultramafic-hosted hydrothermal vents of the Mid-Atlantic Ridge. PhD Thesis, Stockholm University. https://archimer.ifremer.fr/doc/00000/6939/