Triple oxygen isotope signatures in evaporated water bodies from the Sistan Oasis, Iran

Abstract

Natural samples from water bodies in the arid and semiarid environment of the Sistan Oasis, Iran, demonstrate a systematic evolution of 17O-excess and δ18O as a result of nonequilibrium fractionation during extreme evaporation. Residual water samples exhibit a significant and systematic decrease of 17O-excess with progressive evaporation loss, reaching values of -160 per meg over a 35‰ range of δ18O. Waters from heavily evaporated volume-limited natural bodies with limited or no recharge fall on the theoretically predicted isotopic evolution curve in agreement with ambient relative humidity of 30 to 35%. Recharged water bodies appear to follow a different trend. These new results demonstrate the potential of 17O-excess for the estimation of evaporation loss and ambient conditions in an arid environment. Key Points Triple oxygen isotope evaporation trend demonstrated for the Sistan Oasis, Iran 17O-excess modeled from rH and δ18O of initial water and ambient vapor 17O-excess in naturally evaporated waters reflects mean rH and evaporation loss