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Origin of organic compounds in fluids from ultramafic-hosted hydrothermal vents of the Mid-Atlantic Ridge
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
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 [en]
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: urn:nbn:se:su:diva-29172ISBN: 978-91-7155-913-5 (print)OAI: oai:DiVA.org:su-29172DiVA: diva2:229402
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
List of papers
1. Hydrocarbons and oxidized organic compounds in hydrothermal fluids from Rainbow and Lost City ultramafic-hosted vents
Open this publication in new window or tab >>Hydrocarbons and oxidized organic compounds in hydrothermal fluids from Rainbow and Lost City ultramafic-hosted vents
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2009 (English)In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 258, 299-314 p.Article in journal (Refereed) Published
Abstract [en]

The first building blocks of life could be produced in ultramafic-hosted hydrothermal systems considering the large amounts of hydrogen and methane generated by serpentinisation and Fischer-Tropsch-Type synthesis, respectively, in those systems. The purpose of this study was to detect and characterise organic molecules in hydrothermal fluids from ultramafic-hosted hydrothermal systems in the Mid-Atlantic Ridge (MAR) region. During the EXOMAR cruise 2005, fluids from the Rainbow (36°14’N) and the Lost City (30°N) hydrothermal fields were collected and treated by Stir Bar Sorptive Extraction (SBSE) and Solid Phase Extraction (SPE). The extracts were analysed by Thermal Desorption - Gas Chromatography - Mass Spectrometry (TD-GC-MS) and GC-MS, respectively. Compared to nearby deep seawater, hydrothermal fluids were clearly enriched in organic compounds, with a more diverse spectrum of molecules. We observed a very similar range of organic compounds in fluids from both sites, with a dominance of aliphatic hydrocarbons (C9-C14), aromatic compounds (C6-C16) and carboxylic acids (C8-C18). The occurrence of these compounds is supported by other field studies on serpentinites and sulfide deposits. Literature on thermodynamic data and experimental work has suggested the possible abiogenic origin of hydrocarbons and organic acids. In addition, it has been shown elsewhere that catalytic reactions producing hydrocarbons likely occur at both Lost City and Rainbow hydrothermal fields as suggested by the evolution of δ13C with increasing C number for methane, ethane, propane and butane. In order to investigate the origin of the organic molecules in the fluids, compound-specific carbon isotope ratio measurements were performed on n-alkanes and carboxylic acids, for which the δ13C values were in the range of -46 to -20‰ (vs. V-PDB). These preliminary data did not allow conclusive support or rejection of an abiogenic origin of the compounds. Indeed, predicting δ13C signatures in hydrothermal systems is likely to be complicated, due to differences in source δ13C signatures (i.e., of the C building blocks), and a variety of, mostly unknown, fractionation steps which may occur along the synthesis pathways. In addition, even though a fraction of the compounds detected in the fluids is likely abiotically produced, a dominance of biogenic sources and/or processes might hide their characteristic signature.

Keyword
Ultramafic, serpentinization, organic, hydrothermal
Identifiers
urn:nbn:se:su:diva-14831 (URN)10.1016/j.chemgeo.2008.10.034 (DOI)000263400300018 ()
Available from: 2009-02-20 Created: 2009-02-20 Last updated: 2017-12-13Bibliographically approved
2. 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
Open this publication in new window or tab >>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
(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
SBSE, organic compounds, hydrothermal, ultramafic, MAR, serpentinisation
National Category
Earth and Related Environmental Sciences Analytical Chemistry Geochemistry
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-29192 (URN)
Projects
MoMARnet
Available from: 2009-08-13 Created: 2009-08-13 Last updated: 2010-01-14Bibliographically approved
3. New insight on the origin of organic compounds in fluids from ultramafic-hosted hydrothermal systems
Open this publication in new window or tab >>New insight on the origin of organic compounds in fluids from ultramafic-hosted hydrothermal systems
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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
Deep subsurface biosphere, hydrothermal, organic compounds, degradation
National Category
Other Earth and Related Environmental Sciences Other Biological Topics
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-29194 (URN)
Projects
MoMARnet
Available from: 2009-08-13 Created: 2009-08-13 Last updated: 2010-01-14Bibliographically approved
4. Detection of trace concentrations of amino acid in aqueous solutions by Ion-pairing reversed-phase UPLC-ESI-QToF-MS: application to hydrothermal fluids
Open this publication in new window or tab >>Detection of trace concentrations of amino acid in aqueous solutions by Ion-pairing reversed-phase UPLC-ESI-QToF-MS: application to hydrothermal fluids
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Amino acids are the fundamental building blocks of proteins that are required for the initiation of living organism, therefore they are key compounds in the origin of life quest. The abiotic production of amino acids within ultramafic-hosted hydrothermal systems was suggested a few decades ago and is strongly supported by thermodynamic data and experimental work. However, field data were clearly lacking and thus investigation of amino acids in fluids from ultramafic-hosted hydrothermal systems was of major importance. Even though amino acids analysis have been carried out routinely for several decades in various field of application, none of the currently available methods appeared suitable for our purpose because of the complexity of the hydrothermal fluids matrix (salts, minerals, gases) and the extremely low concentrations of amino acids that were expected. We took up the challenge and here we describe a method to detect underivatized amino acids down to the sub-ppb level in aqueous matrix by ion-pairing reverse-phase Ultra-high Performance Liquid Chromatography - Electrospray Ionisation - Quadrupole Time of Flight - Mass Spectrometry (UPLC-ESI-QTOF-MS). Characterisation and separation of 10 chosen proteinogenic amino acids was achieved and excellent linearity in the response was obtained for all amino acids with correlation coefficient > 0.9921. This analytical method was successfully applied to natural hydrothermal fluid samples from ultramafic-hosted vents of the Mid-Atlantic Ridge region. Tryptophan and Phenylalanine were clearly evidenced in the fluids and concentrations of Leucine reached 15-55 ppt. We suggest that other amino acids are present in hydrothermal fluids but occur for the major part as metal and/or clay complexes and could not be detected using current approach. Finally, concentrations of amino acids measured in the deep seawater reference sample were in good agreement with generally accepted background level in the deep ocean.

Keyword
Amino acids, UPLC, QToF, hydrothermal
National Category
Analytical Chemistry Other Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-29195 (URN)
Projects
MoMARnet
Available from: 2009-08-13 Created: 2009-08-13 Last updated: 2010-01-14Bibliographically approved

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