Hydrocarbons and oxidized organic compounds in hydrothermal fluids from Rainbow and Lost City ultramafic-hosted vents

Abstract

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 δ 13 C 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 δ 13 C 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 δ 13 C signatures in hydrothermal systems is likely to be complicated, due to differences in source δ 13 C 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

Organic, Gas, and Element Geochemistry of Hydrothermal Fluids of the Newly Discovered Extensive Hydrothermal Area in the Wallis and Futuna Region (SW Pacific)

“…Conversely, some other studies reported the absence of organic compounds in hydrothermal fluids except at the Lost City alkaline vent field which is theoretically more favourable for abiotic synthesis [36]. Nevertheless, we report here the presence of semivolatile organic compounds in hydrothermal fluids from the Wallis and Futuna area and provide concentrations of a selection of extractable compounds that have been identified elsewhere as hydrothermally derived [27,37]: n-alkanes, n-fatty acids (n-FAs), mono-, and polyaromatic hydrocarbons (BTEXs and PAHs). These very first quantitative field data might feed thermodynamic models of abiotic synthesis, guide the design of experiments to better understand hydrothermal organic geochemistry, and help assessing the importance of hydrothermally derived organic compounds in metal complexation and, as a nutrient for microorganisms, complete fluxes calculation and enter in the carbon cycle budget calculations.…”

“…Notably numbers of studies agree on the major ligand role of organics in metal stabilisation, transportation, bioavailability, and ore-forming but there are hardly any clues on the nature of these ligands in hydrothermal environments [16][17][18][19][20][21][22][23][24][25]. Organic compounds in hydrothermal fluids may come from marine dissolved organic matter (DOM) recycling [12,13], subsurface biomass degradation [26], entrainment of organic detritus from local recharge zones, and subsequent degradation, or abiotic formation in the deep subsurface [27][28][29][30]. The latter is supported by many theoretical [31][32][33] and experimental work summarised in two reviews [34,35].…”

Ideas and perspectives: Hydrothermally driven redistribution and sequestration of early Archaean biomass – the hydrothermal pump hypothesis

“…In recent hydrothermal fields, however, organic matter becomes thermally altered and redistributed (Simoneit, 1993;Delacour et al, 2008;Konn et al, 2009). Laboratory experiments using marine DOM indicate that thermal alteration 10 already occurs at temperatures >68-100°C, and efficient removal of organic molecules at 212-401°C (Hawkes et al, 2015(Hawkes et al, , 2016.…”

Asbestiform sepiolite coated by aliphatic hydrocarbons from Perletoa, Aosta Valley Region (Western Alps, Italy): characterization, genesis and possible hazards

“…Serpentinite-hosted hydrothermal systems -analogous to those of the Combin Zone where the investigated sepiolite was collected -are ideal sites for the production of abiogenic hydrocarbons via the FT-t reaction, by means of progressive polymerization and polycondensation reactions (Konn et al, 2009;Taran et al, 2007). Since a widely accepted hypothesis for sepiolite genesis involves direct precipitation from an aqueous solution saturated with Mg and silica (Jones and Galán, 1988;Galán and Pozo, 2011) and with an insignificant Al activity (Birsoy, 2002), the Perletoa sepiolite probably originated from a similar process.…”