Hydrocarbons in Icelandic volcanic-hydrothermal discharges: An inventory of concentrations and preliminary bulk carbon, radiocarbon and clumped isotopic data

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Several criteria have been proposed to be indicative for abiogenic hydrocarbon production in natural systems. Amongst these are i) carbon isotope distribution patterns between n-alkanes and ii) apparent attainment of equilibrium between CH4 and CO2. However, a more detailed knowledge about the parameters exerting control on the extent of C-isotope fractionation between CO2, CH4 and higher chain n-alkanes is necessary to more critically evaluate the suitability of these criteria as indicators of hydrocarbon origin. In several Mediterranean volcanic-hydrothermal systems, CH4 seems to be in equilibrium with CO2. All these investigated systems have in common that the associated hydrothermal reservoirs at depth occur more saline than seawater and that temperatures are always close to the critical point of the corresponding saline waters. We request funding to extend our work to volcanic-hydrothermal discharges on Iceland. The diversity of Icelandic volcanic-hydrothermal systems represents a unique opportunity to further explore hydrocarbon formation processes in volcanic environments. In contrast to the Mediterranean systems, many volcanic-hydrothermal reservoirs on Iceland i) host dilute meteoric waters, ii) exhibit temperatures well beyond the critical point of water and iii) are partially fed by gases deriving from the lower mantle. A comparison of chemical and isotopic data for Icelandic and Mediterranean discharges will improve our knowledge to what extent salinity, temperature and contributions from the lower mantle governs mass exchange between CO2 and CH4.Furthermore, we intend to acquire preliminary carbon isotope data on n-alkanes higher than methane, radiocarbon and clumped isotope (13C-D) data on methane to gain additional information on the origin of hydrocarbons in volcanic-hydrothermal systems. This study aims at improving existing sampling techniques so that bulk carbon isotope analysis on n-alkanes as well as radiocarbon and clumped isotope analysis on methane contained in Icelandic discharges becomes possible.