Kinetic isotopic fractionation of argon and neon during air-water gas transfer

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• 作者：Kevin E. Tempest ; ^{ket5@u.washington.edu} ; Steven Emerson
• 关键词：Isotope fractionation ; Argon ; Neon ; Argon isotopes ; Neon isotopes ; Gas exchange
• 刊名：Marine Chemistry
• 出版年：2013
• 出版时间：20 July, 2013
• 年：2013
• 卷：153
• 期：Complete
• 页码：39-47
• 全文大小：798 K

文摘

The use of the noble gas isotope ratios ²²Ne/²⁰Ne and ⁴⁰Ar/³⁶Ar as geochemical tracers of environmental conditions (i.e. continental paleotemperatures from groundwater) and processes (i.e. air-sea gas exchange) requires accurate values for kinetic and equilibrium isotopic fractionations (¦Á_k and ¦Á_eq). Until now, these values have been approximated using different theoretical models. Here we evaluated both the kinetic and equilibrium fractionation factors experimentally by measuring the relative mass transfer rates of the major and secondary isotopes of argon and neon in laboratory experiments at 20 ¡ãC during exchange across the air-water interface as gas saturations evolved from 0 to 100 % . The kinetic isotopic fractionation factors, ¦Á_k, for argon (40/36) and neon (22/20) are determined to be 0.9961 ¡À 0.0001 (¦Å_k = ? 3.9 ¡À 0.1¡ë) and 0.9931 ¡À 0.0004 (¦Å_k = ? 6.9 ¡À 0.4¡ë), respectively. The kinetic isotopic fractionation factors are much closer in agreement to theoretical values determined by molecular dynamics simulations than to values calculated using the square root of molecular reduced masses. The equilibrium fractionation factor for neon (22/20) at 20 ¡ãC is determined to be 1.00104 ¡À 0.00005 (¦Å_eq = 1.04 ¡À 0.05¡ë). An argon equilibrium fractionation factor of 1.00107 ¡À 0.00002 (¦Å_eq = 1.07 ¡À 0.02¡ë) determined at 20 ¡ãC agrees with a linear interpolation of previous measured values at 2 ¡ãC and 25 ¡ãC ().