Natural abundance of radioactive isotopes of C and H

Abstract

This chapter is concerned with the natural concentrations of the stable isotopes of hydrogen, carbon and oxygen, with particular attention paid to those compounds relevant in the hydrological cycle. For each isotope separately, we discuss the natural fractionation effects, internationally agreed definitions, standards, and reference materials, and variations in the natural abundances. In order to help the reader to appreciate isotopic abundance values as they occur in nature, Fig.7.1 shows some actual isotope ratios and fractionations in a choice of equilibrium systems. Surveys of some practical data of all isotopes concerned are given in the respective Sections. 18 R = 0.00200520 H 2 O (liquid) at 20 o C 18 e s/l = +30.42‰ CaCO 3 (solid calcite) 18 R = 0.00206620 13 R = 0.0111421 CO 2 (gas) 13 e g/b = -8.46‰ HCO 3 -(bicarbonate) at 20 o C 13 R = 0.0112372 18 R = 0.00198567 H 2 O (vapour) 18 e v/l = -9.74‰ H 2 O (liquid) at 20 o C 18 R = 0.00200520 2 R = 0.00014354 H 2 O (vapour) 2 e v/l = -78.4‰ H 2 O (liquid) at 20 o C 2 R = 0.00015575 Fig.7.1 Examples of isotope ratios of compounds in isotopic equilibrium and the respective isotope fractionations, as defined in Sect.3.3. As an example may serve the calculation of 13 e g/b as 13 a g/b -1 with 13 a g/b = 0.0111421/0.0112372 = 0.99154. 89