5 NATURAL ABUNDANCE OF THE STABLE ISOTOPES ... - Falw.vu

Stable Isotopes of Hydrogen, Carbon and OxygenTable 7.2 Carbon isotope fractionation in the equilibrium system CO 2 HCO 3 CO 3 CaCO 3 ;13 y/x represents the fractionation of compound y relative to compound x. Values forintermediate temperatures may be calculated by linear interpolation (see also Fig.7.3).T = t (C) + 273.15 Kg = gaseous CO 2 , a = dissolved CO 2 , b = dissolved HCO 3 , c = dissolved CO 3 2 ions, s = solidcalcite.t13 g/b 1 )13 a/g 2 )13 a/b 3 )13 c/b 4 )13 s/b 5 )13 s/g 6 )(C)(‰)(‰)(‰)(‰)(‰)(‰)0 10.83 1.18 12.00 0.65 0.39 +10.555 10.20 1.16 11.35 0.60 0.11 +10.1910 9.60 1.13 10 72 0.54 + 0.15 + 9.8515 9.02 1.11 10.12 0.49 + 0.41 + 9.5220 8.46 1.09 9.54 0.44 + 0.66 + 9.2025 7.92 1.06 8.97 0.39 + 0.91 + 8.8630 7.39 1.04 8.42 0.34 + 1.14 + 8.6035 6.88 1.02 7.90 0.29 + 1.37 + 8.3140 6.39 1.00 7.39 0.25 + 1.59 + 8.031 ) Mook et al., 1974 : 13 g/b = 9483/T + 23.89‰ (7.1)2 ) Vogel et al., 1970 : 13 a/g = 373/T + 0.19‰ (7.2)3 ) From 1 ) and 2 ) : 13 a/b = 9866/T + 24.12‰ (7.3)4 ) Thode et al., 1965 and 1 ) : 13 c/b = 867/T + 2.52‰ (7.4)5 ) Our evaluation of the original data from Rubinson & Clayton, 1969and Emrich et al., 1970 : 13 s/b = 4232/T + 15.10‰ (7.5)6 ) From 1 ) and 5 ) : 13 s/g = + 5380/T 9.15‰ (7.6)Another kinetic process occurring in the soil is the bacterial decomposition of organic matterto form methane (CH 4 ). Here the largest fractionation amounts to about 55‰. In this processCO 2 is simultaneously produced with a fractionation of +25‰, resulting in a 13 value ofabout 0‰.A special problem is the kinetic fractionation during uptake and release of CO 2 by seawater.This fractionation is included in calculations on global 13 C modelling.First we have to emphasise that the difference in isotopic composition between, for instance,gaseous CO 2 and the dissolved inorganic carbon content of water can not be addressed byisotope fractionation between CO 2 and DIC.93