Open CO 2-underground water system in the West Carpathians (south Poland) — Chemical and isotopic evidence

Abstract

In the open CO 2-water system δ 13C of the total dissolved carbonate, i.e. δ 13C(TDC) is P CO 2 and δ 13C-(CO 2,g) dependent as TDC is P CO 2 dependent. The variation of δ 13C(TDC) in such a system is described by the following equilibrium equation: σ 13C(TDC) = (σ 13C(CO 2,g) + 1000) α 0 γH 2CO 0 3 + α 0K 1 γHCO - 3{H} + α 0K 1K 2 γCO 2- 3{H} 2 1 γH 2CO 0 3 + K 1 γHCO - 3{H} + K 1K 2 γCO 2- 3{H} 2 × 1000 Chemical and isotopic data of waters in the West Carpathians (south Poland) when subjected to the necessary computation reflect properties of a system open to CO 2. P CO 2 of the waters of interest at the Earth's surface is close to 1.2 atm. Their initial chemical speciation has been assigned to this value using program PHREEQE. Then δ 13C-values of dissolved carbonate species in the waters were calculated according to the Wigley-Plummer-Pearson procedure to obtain the value for δ 13C f(TDC) which corresponds to P CO 2 = 1.2 atm. Resulting δ 13C f(TDC)-values when plotted as a function of TDC f and pH f fall well between two curves independently derived for δ 13 C(CO 2, g) = −1‰ and −3‰, and P CO 2 = 1.2 atm., t = 10°C and I = 0.1. This implies that waters from the West Carpathians are under almost constant CO 2 pressure and constant δ 13C(CO 2,g). Moreover, it suggests that a single origin of CO 2 is quite possible.