Application of radiocarbon to detect a deep source CO2 in soil air

Abstract

A method using carbon isotopes (14C and 13C) for quantifying the proportion of CO2 contribution from deep sources, e.g. magma, subducted materials or mantle, in soil air is established, and discussed in comparison with the conventional methods and errors. A relationship between carbon isotopic ratios (δ14C and δ13C) and CO2 concentration has been used to estimate proportions of CO2 reservoirs in conventional studies. Our study indicates that a relationship between δ14C and δ13C is available to quantify the CO2 derived from deep subsurface, deep CO2 contribution, within low errors (1σ=0.01–0.02). The estimated values of deep CO2 contribution by this method were agree with those estimated by the conventional method, while the estimated results using the relationship between δ13C and CO2 concentration show slightly higher values of deep CO2 contribution than those by the method using the δ14C in several samples. The quantifying errors estimated by δ14C and CO2 concentration are the smallest to be ca. ±0.005, but in case of the CO2 concentration higher than 1% in soil air. With regard to the method using δ13C and concentration, the error of estimated results shows ca. ±0.05 for the sample of which CO2 concentration is over 2%.