Hydrogen and oxygen isotopic composition of aqueous salt solutions by gas–water equilibration method

This study deals with the so-called isotope salt effect associated with the presence of salts in oceanic and other natural waters. We have estimated this effect both for deuterium and oxygen-18, taking advantage of accurate gas–water equilibration methods. Solutions composed of either monovalent or divalent salts and of a mixture of these different salts with a composition similar to seawater have been studied for concentrations of 0.5, 1 and 2 times that of seawater. We confirm that the deuterium salt-effect varies linearly with the molality of the solution and we have checked that this relation applies to low molalities. This result is of direct use for the measurement of δD in saline waters by the H2–H2O equilibration method. There is no significant oxygen-18 salt effect for this range of concentrations.