2018 年 52 巻 3 号 p. 107-129
By using the hydrogen isotope exchange equilibrium between molecular hydrogen (H2) and water vapor, a new method called HIReTS (Hydrogen Isotopes Remote Temperature Sensing) was proposed for remote sensing of fumarole outlet temperatures. In this method, the hydrogen isotopic composition (δD) of fumarolic H2 is obtained remotely from observation in a volcanic plume, and the outlet temperature is then derived from the obtained δD of fumarolic H2. The HIReTS method can be used to obtain the fumarolic temperature remotely in active volcanoes when the actual fumaroles are inaccessible. Recent advances in using the 17O-excess (Δ17O) of nitrate were summarized as well. Within the possible sources of nitrate in the natural environment, only atmospheric nitrate that is produced from atmospheric NO through photochemical reactions can be characterized by the anomalous enrichment in 17O, reflecting the transfer of an oxygen atom from ozone. In addition, Δ17O is stable during partial metabolism—such as denitrification and assimilation, so by using these characteristics of Δ17O, the author and co-workers were able to trace the fate of atmospheric nitrate deposited onto surface ecosystems. This also allowed the author and co-workers to propose a new method to quantify nitrate dynamics—production rate through nitrification and metabolic rate through assimilation and denitrification—in aquatic environments, using the Δ17O of nitrate. The Δ17O method is considered to offer an alternative to the traditional artificial tracer techniques for the determination of nitrate dynamics, including temporal variations.