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.

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.

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Cave speleothems grow from supersaturated dripwaters and store information about various karst processes along the water fl ow path. Anomalous non-saturated waters may occur if (1) rainfall water passes very rapidly through karst profi le or if (2) two saturated waters of diff erent compositions are mixed. Th e low mineralization close to saturation could be reached also as (3) result of calcite precipitating prior the water enters the cave. Th e hydrogeochemistry of four dripwaters in the Punkva Caves (Moravian Karst) was systematically studied for anomalous properties during one-year period. Th e drips are situated in a passage behind Přední Dóm Chamber (CP1 and CP2, 24 samples each), in Tunnel Corridor (TC1, 24 samples), and in Zadní Dóm Chamber (ZD1, 6 samples). Th e dripwaters CP1, CP2, and ZD1 show various fl ow regimes but very similar hydrogeochemical properties: electric conductivity (EC = 550-630 μS/cm), saturation (SI calcite = 0.8-1.2), and Mg/Ca ratio (1000*(Mg/Ca) = 15-20). In contrast, the dripwater TC1 shows stable drip rate and EC = 275-350 μS/cm, SI =-0.1 to 0.3, and almost thrice as high Mg/Ca ratios as other drips. High and stable discharge of the drip TC1, combined with low EC, SI close to zero, and high Mg/Ca ratio indicate that a prior precipitation of calcite is responsible for the anomalous composition of the dripwater. Th e slightly negative SI values that were occasionally observed indicate that further minor processes probably participate on the water formation.