Experimental studies of oxygen isotope fractionation in the carbonic acid system at 15°, 25°, and 40°C

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• 作者：William Cory Beck ; Ethan L. Grossman and John W. Morse
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2005
• 期刊代码：27_00167037
• 类别：ear
• 出版时间：2005
• 卷：69
• 期：14
• 页码：3493-3503
• 文件大小：392 K

摘要

In light of recent studies that show oxygen isotope fractionation in carbonate minerals to be a function of HCO₃⁻ and CO₃²⁻ concentrations, the oxygen isotope fractionation and exchange between water and components of the carbonic acid system (HCO₃⁻, CO₃²⁻, and CO_2(aq)) were investigated at 15°, 25°, and 40°C. To investigate oxygen isotope exchange between HCO₃⁻, CO₃²⁻, and H₂O, NaHCO₃ solutions were prepared and the pH was adjusted over a range of 2 to 12 by the addition of small amounts of HCl or NaOH. After thermal, chemical, and isotopic equilibrium was attained, BaCl₂ was added to the NaHCO₃ solutions. This resulted in immediate BaCO₃ precipitation; thus, recording the isotopic composition of the dissolved inorganic carbon (DIC). Data from experiments at 15°, 25°, and 40°C (1 atm) show that the oxygen isotope fractionation between HCO₃⁻ and H₂O as a function of temperature is governed by the equation:

where α is the fractionation factor and T is in kelvin. The temperature dependence of oxygen isotope fractionation between CO₃²⁻ and H₂O is

The oxygen isotope fractionation between CO_2(aq) and H₂O was investigated by acid stripping CO_2(aq) from low pH solutions; these data yield the following equation: