ABSTRACT

The isotopic fractionation factors in evaporation of water at 60° and 80°C were determined from the isotopic ratios of water under steady-state balance between inflow and evaporation. The results at 60° and 80°C are 1.0501 ± 0.0029 and 1.0431 ± 0.0022 for H₂O/HDO and 1.0176 ± 0.0010 and 1.0156 ± 0.0008 for H₂¹⁶O/H₂¹⁸O, respectively. Oyunuma, isotopically the heaviest geothermal pond in Japan, is enriched by 40.3‰ in D/H and by 16.5 ‰ in ¹⁸O/¹⁶O, respectively, relative to its meteoric inflow and may be a natural example of such steady-state evaporation pans.