The concentration of some trace gases in cave is documented to have higher values with respect to the outside atmosphere. Partial pressure of carbon dioxide is one of the main parameter in cave due to its control in speleothem deposition and speleogenesis. Its concentration could depend on soil activity in the cover, or disaggregation of organic matter, but mostly is originated by the karst process itself through the nucleation of calcium carbonate. Recently this gas has been proposed as a key in local carbon cycle at short term scale as sinks and sources for atmospheric CO2. With the purpose to understand the anomalous high concentration observed in the Murge of Apulia, this work reports the preliminary results of the CO2 monitoring performed in the underground atmosphere of 5 caves in this karst region, (Castellana, Salto, Calzino, Torre di Mastro, and Abate Eustasio), monitored in January 2018 Air CO2 concentration was measured as mixing ratio using a Non-Dispersive Infra-Red spectrometer NDIR (Zenith), with a range 0÷10,000 ppm and an accuracy of ±50 ppm. As the concentration of this gas in air masses is dependent of its water vapour content, temperature and relative humidity were also recorded. In the Castellana Cave the monitoring was performed continuously for few days using a NDIR datalogger (Perfect Prime: range 0÷10,000 ppm; accuracy ±50 ppm) which recorded CO2 concentration every 10 minutes.The preliminary results show an increase in CO2 concentration with depth. It ranges from typical value of cave environment to level proximal to soil concentration. The partial pressure of CO2 in Torre di Mastro at 40 m in depth from the surface reaches value >10,000 ppm (temperature 12.5 °C - 100%). In Castellana Cave the monitoring lasted for 1 day in a passage close to the public trail, with concentration around 800 ppm, and some peaks during the night. Here the temperature was 14.0 °C and relative humidity never reached saturation (85%) probably due to the artificial ventilation of the cave. Spot measurements were also performed along the touristic path with values ranging between 1,000 to 1530 ppm. The carbon dioxide content in the Salto Cave had typical cave values (from 2000 to 2800 ppm). Only the final shaft showed CO2 concentration > 10,000 ppm (temperature 18.2 °C - 100 %). The lowest value was recorded at the Abate Eustasio Cave with pCO2 ranging between 900 ppm at the bottom of the entrance and 1,000 ppm in the inner cave passages (temperature 16.2 °C - 100%). On the other hand, the Calzino Cave showed the highest and dangerous CO2 concentration that suddenly rose few meter below the entrance (16.2 °C - 100%), reaching 12,700 ppm in the shaft at -10 m and 36,000 ppm further inside at -20 m in depth (a shaft never explored for this reason). This CO value seems not related to physical parameter such as temperature and relative monitoring. Further investigation could clarify this pattern.
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