The chemistry of hyperalkaline springs in serpentinizing environments: 1. the composition of free gases in New Caledonia compared to other springs worldwide.
|Author(s)||Monnin Christophe1, Quéméneur Marianne2, Price Roy3, Jeanpert Julie4, Maurizot Pierre4, Boulart Cedric5, Donval Jean-Pierre6, Pelletier Bernard7|
|Affiliation(s)||1 : Géosciences Environnement Toulouse (CNRS/UPS/IRD/CNES) 14 Avenue E Belin31400 Toulouse ,France
2 : Aix Marseille Univ. Université de Toulon CNRS IRD MIO Marseille ,France
3 : School of Marine and Atmospheric Sciences Stony Brook NY, USA
4 : DIMENC Direction de l’Industrie, des Mines et de l’Energie Nouméa,Nouvelle‐Calédonie
5 : AD2M UMR 7144 (CNRS Sorbonne Université) Station Biologique de Roscoff Place Georges Tessier, 29680 Roscoff, France
6 : IFREMER Unité Géosciences Marines/Laboratoire Cycles Géochimiques ZI Pointe du Diable. CS 1007029280 Plouzané ,France
7 : Géoazur (UCA, IRD, CNRS, OCA) Centre IRD de Nouméa BP A5 Nouméa, Nouvelle‐Calédonie
|Source||Journal Of Geophysical Research-biogeosciences (2169-8953) (American Geophysical Union (AGU)), 2021-09 , Vol. 126 , N. 9 , P. e2021JG006243 (17p.)|
|WOS© Times Cited||3|
|Note||This article also appears in: Ophiolites and Oceanic Lithosphere, With a Focus on the Samail Ophiolite in Oman|
|Keyword(s)||serpentinization, methane, hydrogen, New Caledonia, Sabatier reaction, Prony Bay|
Serpentinization is a natural process that transforms ferromagnesian minerals such as olivine into serpentine and that produces waters at very high pH and gases enriched in methane (CH4) and hydrogen (H2). We report the composition of gases venting at two springs (Bain des Japonais and Rivière des Kaoris) of the serpentinizing environment of the Prony Bay (New Caledonia) collected eight times between 2011 and 2014, along with in situ measurements (temperature, pH, oxydo-reduction potential, dissolved oxygen content) of on-land alkaline springs of the Southern New Caledonia ophiolite. Venting gases are mainly composed of H2, CH4 and N2 and their composition has slightly varied during the 4-year field survey. An elevated oxygen (O2) content in a high-pH water sample is due to air uptake during surface flow. O2-corrected gas compositions along with those published for gas data obtained at similar serpentinizing environments (Italy, Turkey, Philippines, Oman) show that the H2 and CH4 concentrations display a linear correlation with a slope close to the value corresponding to the CH4 production from carbon dioxide rather from a less oxidized carbon such as carbon monoxide. Although these data are consistent with the stoichiometry of the Sabatier reaction, as such in the gas phase, it is also possible that microbial hydrogenotrophic methanogenesis takes place in the aqueous phase followed by degassing. A diagram is proposed that outlines the partitioning of H2 and CH4 between the gaseous and aqueous phases and the need to consider a two-phase flow in the hydrology of these hyperalkaline environments.