Temperature, pressure and carbon dioxide trends in karst environment: Bossea cave study.

Karst constitutes only 13% of the earth's surface, yet it holds fundamental importance in current matters such as climate change. As the world's population increases, water supply, whether for drinking or irrigation purposes, is a current problem not only in areas considered "arid". Stefanovic (2019) estimates that karst-fed springs supply 9.2% of water demand. In the panorama of Italian karst, Bossea represents a key spot, not only because it is one of the largest tourist caves in Italy but also because it hosts one of the most complete and active laboratories at European level. The cave is situated in the N-W of Italy, in the province of Cuneo. It is constituted by three main parts: the shallowest part – the corridor – represents the touristic entrance. It is followed by the main salon area, the biggest part of the cave, with large volumes and heights up to 40 m. The cave ends in a canyon of moderate cross-section, over the base of which the main collector – The Mora River – flows. Through a dense network of probes both inside and outside the cave, temperature, pressure and carbon dioxide levels were analysed with the aim of determining the dynamics of air flows inside the cave. Analysis of air temperatures revealed the presence of two convective cells. The first, which circulates in the entrance corridor (a fossil branch about 80 meters in length through which tourist entry occurs) reverses its direction between cold and warm seasons. The second, deeper and more uniform overall, circulates in the large halls and undergoes the dragging effect of the main collector. It is, in fact, the latter that causes large decreases in temperature during floods. An attempt was also made to separate, in the temperature and CO2 datasets, the two types of effects acting on the cave: short-term and long-term. The former, with shorter frequencies than daytime, consists mainly of heat exchange due to the passage and respiration of people. The latter, on the other hand, consists of seasonal trends and the effect of floods. Separation was performed by the moving average and Fourier transform methods, which provided similar results. The intricate subject of heat exchange in a cave as big and varied as Bossea is not fully covered in this paper. The knowledge of the air velocity and sections (known from the laser scanner survey carried out in 2019) could allow a quantitative assessment of the volumes of air exchange not only between the interior and exterior but also between the shallower and deeper convective cells. A more in-depth analysis of rock temperatures at various depths, whose probes are installed at numerous points in the cave, would also allow for a more precise assessment of another very important heat exchange: between the cave environment and the rock surrounding it.