Reply to “Methane origin in the Samail ophiolite: Comment on ‘Modern water/rock reactions in Oman hyperalkaline peridotite aquifers and implications for microbial habitability’” [Geochim. Cosmochim. Acta 179 (2016) 217–241]
We thank Dr. Giuseppe Etiope for his comment and the opportunity to further discuss why we consider the origin of the methane detected in subsurface fluids obtained from a peridotite aquifer in Oman to be enigmatic. The central focus of Miller et al. (2016) was the characterization of the fluids and dissolved gases recovered from 300 meter wells drilled into peridotite at two locations near Ibra. Microscale geochemical analyses of rock chips recovered during drilling gave further insight into the aqueous geochemistry measurements. These samples allowed us to analyze the extent of modern peridotite hydration and secondary mineralization in light of potential hydrogen-generating reactions. Additionally, biomass was recovered from the fluids, and 16S rRNA showed the presence of methanogens and methanotrophs. These methane-cycling microbes may be modulating the isotopic signature of CH 4 found in the wells; thus, we do not feel comfortable rejecting the hypothesis that microbial activity contributes to the unusual isotopic signature of CH 4 in the wells without further investigation.