A new value for the stable oxygen isotope fractionation between dissolved sulfate ion and water |
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| Authors: | Richard E Zeebe |
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| Institution: | School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, 1000 Pope Road, MSB 504, Honolulu, HI 96822, USA |
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| Abstract: | Although the stable oxygen isotope fractionation between dissolved sulfate ion  and H2O (hereafter  ) is of physico-chemical and biogeochemical significance, no experimental value has been established until present. The primary reason being that uncatalyzed oxygen exchange between  and H2O is extremely slow, taking ∼105 years at room temperature. For lack of a better approach, values of 16‰ and 31‰ at 25 °C have been assumed in the past, based on theoretical ‘gas-phase’ calculations and extrapolation of laboratory results obtained at temperatures >75 °C that actually pertain to the bisulfate  system. Here I use novel quantum-chemistry calculations, which take into account detailed solute-water interactions to establish a new value for  of 23‰ at 25 °C. The results of the corresponding calculations for the bisulfate ion are in agreement with observations. The new theoretical values show that sediment  -data, which reflect oxygen isotope equilibration between sulfate and ambient water during microbial sulfate reduction, are consistent with the abiotic equilibrium between  and water. |
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