Variations of carbon dioxide in the air and dripwaters of Punkva Caves (Moravian Karst, Czech Republic)

Abstract

Carbon dioxide (CO₂) was studied in Punkva Caves in the Moravian Karst (Czech Republic) during a one-year period from February 2012 to March 2013. Partial pressures of the CO₂ corresponding to aqueous carbonates, $P_{{{\text{CO}}_{{2}}({\text{W}}) }}$ (10^−2.91–10^−2.35, i.e., 0.12–0.45 vol%), and those participating in the initial dripwater formation, $P_{{{\text{CO}}_{{2}}({\text{H}})}}$ (10^−1.77–10^−1.49, i.e., 1.7–3.2 vol%), were calculated from dripwater hydrogeochemistry, and compared with the partial pressure in cave air, $P_{{{\text{CO}}_{{2}}({\text{air}})}}$ (10^−3.31–10^−2.49, i.e., 0.06–0.32 vol%). Both the $P_{{{\text{CO}}_{{2}}({\text{air}})}}$ and $P_{{{\text{CO}}_{{2}}({\text{W}})}}$ showed clear seasonal variations with maxima in summer and minima in winter. In contrast, the $P_{{{\text{CO}}_{{2}}({\text{H}})}}$ was very stable without any significant seasonality, which could indicate its independence on surface conditions. As an exception, one anomalous drip with significantly lower and varying $P_{{{\text{CO}}_{{2}}({\text{W}})}}$, $P_{{{\text{CO}}_{{2}}({\text{H}})}}$, and SI_calcite was recognized as a result of prior calcite precipitation. Evolution of dripwater during CO₂ degassing and calcite precipitation is demonstrated in detail in a geochemical model. The study presents new data indicating that the CO₂ source might be deployed in deeper parts of karst profile (epikarst) in addition to karst soils.