Oxygen isotope behavior in the Sulfate-Water System

Abstract

Fundamental data on oxygen isotope behavior in the sulfate-water system are given. Oxygen exchange rates between sulfate ions and water are very slow and show a marked pH dependence. Of the order of 10/sup +3/ to 10/sup +5/ years are required to closely approach isotopic equilibrium at earth surface conditions. Oxygen isotope fractionation experiments yielded the following relationships: Ln alpha = 3878/(t+2) -0.0034 anhydrite water (and) Ln alpha = 3251/(t+2) -0.0056 dissolved sulfate water. During progressive evaporation of saturated CaSO/sub 4/ solution the gypsum formed tends to concentrate oxygen-18 relative to dissolved sulfate by 2%. Sulfate reducing bacteria preferentially metabolize oxygen-16 by about 4.6% in both pure and natural cultures. Oxidation of sulfide to sulfate in natural environments is a complex process making use of both water oxygen and molecular oxygen.