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 SIcalcite 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.