The Chemistry of Hyperalkaline Springs in Serpentinizing Environments: 1. The Composition of Free Gases in New Caledonia Compared to Other Springs Worldwide

Serpentinization is a natural process that transforms ferromagnesian minerals such as olivine into serpentine and produces waters at very high pH gases enriched in methane (CH4) hydrogen (H2). We report the composition of venting two springs (Bain des Japonais Rivière Kaoris) serpentinizing environment Prony Bay (New Caledonia) collected eight times between 2011 2014, along with situ measurements (temperature, pH, oxydo-reduction potential, dissolved oxygen content) on-land alkaline Southern New Caledonia ophiolite. Venting are mainly composed H2, CH4, N2 their has slightly varied during 4-year field survey. An elevated (O2) content high-pH water sample due to air uptake surface flow. O2-corrected gas compositions those published for data obtained similar environments (Italy, Turkey, Philippines, Oman) show H2 CH4 concentrations display linear correlation slope close value corresponding production from carbon dioxide rather less oxidized monoxide. Although these consistent stoichiometry Sabatier reaction, phase, it also possible microbial hydrogenotrophic methanogenesis takes place aqueous phase followed by degassing. A diagram proposed outlines partitioning gaseous phases need consider two-phase flow hydrology hyperalkaline environments.