The ratio of the activity coefficients of deuterated and light water (Γ) is given in chloridic saline solutions as a function of the molality of the salt components by the expression: 1- 1 Γ × 103 -δγ = 6.1MCaCl2 + 5.1MMgCl2 + 2.4MKCl + 0.4MNaCl. Calculations based on the Craig-Gordon evaporation model show that in the case of evaporating brines, the salt effect on the activity coefficients of the isotopic water species results in deviation of the δ values from a constant slope "evaporation line", when plotted on the conventional δ-diagram, of deuterium concentration versus 18O activity. Conversion of concentration data to activities eliminates these deviations to a large extent, indicating them to be an artifact of the scales employed for measuring the isotope abundance. The origin of Dead Sea waters and other natural brines is discussed in the light of these findings.
ASJC Scopus subject areas
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science