The temperature variation in an epikarstic cave and its impact factors: a case from Velika Pasica Cave,Central Slovenia

In order to reveal the temperature variation mechanism of a small and relatively closed cave, the surface temperature, the cave air temperature and the drip water temperatures were monitored with high-resolution recorders for a 7-year period. The results indicated that the cave temperature is mainly affected by the external seasonal oscillations. The temperature curve of the inner cave area (with standard deviation between 0.59 and 0.87) was much smoother in comparison with that of the surface (with SD as high as 8.46). However, the cave reacted to the temperature drifts with some delay, for example, at VP3 in 2006, the internal temperature increased for additional 49 days after the surface temperature dropped colder than inside of the cave. This seasonal variation and delayed response of the internal temperature were mainly affected by conduction from the epikarst rock mass. Air convection also occurred in the cave, especially when the surface temperature dropped lower than that of the inside cave (during the winter time) and in the outer section (close to the entrance), which caused an abrupt and irregular variation of the outer section. In addition, the influence from the percolating water was ephemeral and depended on its supplementary amount and temperature difference, e.g., there were more apparent responses at VP1 and VP3 when the intensive rain fell. The percolating water temperature could be a good indicator for water flow in epikarst.