@article{oai:nagoya.repo.nii.ac.jp:02001821,
 author = {Sambuichi, Takashi and Tsunogai, Urumu and Kura, Kazushige and Nakagawa, Fumiko and Ohba, Takeshi},
 issue = {6},
 journal = {GEOCHEMICAL JOURNAL},
 month = {},
 note = {Recent studies have reported slight but definite differences in Δ^′17O between the lithosphere and hydrosphere. In the present study, we precisely and accurately quantify the Δ^′17O values of geothermal H2O and mid-ocean ridge basalt (MORB) with normalization on the VSMOW-SLAP scale to further substantiate these differences and to discuss the isotopic evolution of the hydrosphere throughout the geologic time scale. With a Δ^′17O value of -60 ± 13 × 10^-6, the Δ^′17O value of MORB is comparable with that in other silicates reported in previous studies. However, the Δ^′17O value of geothermal H2O tended to decrease from +31 × 10^-6 to -51 × 10^-6, which are the usual Δ^′17O values in meteoric water and silicates, respectively, in accordance with the 18O-enrichment. These results imply an active oxygen isotope exchange between silicates and geothermal H2O under high-temperature conditions at depth. This is supported by previous studies which report the 17O-enrichment of silicate altered by hydrothermal H2O. Considering this direct evidence for depletion of 17O, we conclude that the 17O-depleted H2O has been supplied continuously to the hydrosphere. Additionally, low-temperature interaction between the silicates and H2O besides high-temperature hydrothermal interaction must be assumed to explain the observed Δ^′17O of the terrestrial hydrosphere. We conclude that the Δ^′17O of the terrestrial hydrosphere should have been variable throughout the geologic time scale owing to the various oxygen exchange interaction between the lithosphere and hydrosphere.},
 pages = {e25--e33},
 title = {High-precision Δ^′17O measurements of geothermal H2O and MORB on the VSMOW-SLAP scale: evidence for active oxygen exchange between the lithosphere and hydrosphere},
 volume = {55},
 year = {2021}
}