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Carbon dioxide (CO 2 ) 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 CO 2 corresponding to aqueous carbonates, P CO 2 ðWÞ (10 -2.91 -10 -2.35 , i.e., 0.12-0.45 vol%), and those participating in the initial dripwater formation, P CO 2 ðHÞ (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 CO 2 ðairÞ (10 -3.31 -10 -2.49 , i.e., 0.06-0.32 vol%). Both the P CO 2 ðairÞ and P CO 2 ðWÞ showed clear seasonal variations with maxima in summer and minima in winter. In contrast, the P CO 2 ðHÞ 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 CO 2 ðWÞ , P CO 2 ðHÞ , and SI calcite was recognized as a result of prior calcite precipitation. Evolution of dripwater during CO 2 degassing and calcite precipitation is demonstrated in detail in a geochemical model. The study presents new data indicating that the CO 2 source might be deployed in deeper parts of karst profile (epikarst) in addition to karst soils.

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Abstract:The anomalous drip in the Punkva caves (Moravian Karst) shows specific hydrogeochemical properties such as low SI calcite~0 .14 ± 0.11 (standard deviation), low mineralization (4.53 ± 0.42) × 10 À3 mol l À1, and enhanced values of δ 13 C (À7.85 to À8.35‰ VPDB), Mg/Ca × 1000 ratio (45.7 ± 3.3), and Sr/Ca × 1000 ratio (0.65 ± 0.06). By these properties, the anomalous drip significantly differs from other regular drips in the same cave and other caves in the region. The study suggests that the anomalous drip properties are a consequence of prior calcite precipitation or/and water mixing along the water flow path. As the former processes are spatially controlled, the knowledge of dripwater flow path seems to be necessary for correct paleoclimatic/paleoenvironmental reconstructions.