Decorated caves under climate changes: Redefining an effective conservation strategy

Objectives: In view of the effects of global climate change already recorded in many decorated caves, the current conservation strategy of cultural heritage that tries to maintain a stable underground microclimate cannot be sustained any longer. In the DECACLIM project, we propose: (i) to establish a comprehensive monitoring system in three decorated caves that will enable the identification of the minimum sensor network needed for conservation in a changing climate. We hypothesize that a single monitoring station which is the rule in most touristic sites, cannot address the current climatic changes in caves, especially those regarding the cave internal aerology. New observational techniques recently developed by our team (measurement of the thin water film thickness at the air/rock interface, assessment of intensity and direction of slow air motions from flag sensors) will be deployed to assess such effects. (ii) To provide a combined model of cave microclimate including the internal aerology and heat/fluids transfer (water, CO2) through the soil/epikarst/karst that will be fed from projections of regional climate downscaling models. Such approach will provide a longer-term perspective of cave climatology under various climate scenarios. More specifically, it will allow the identification of physical tipping points beyond which the conservation of rock art heritage is at risk. Caves show strongly irregular surfaces at various length scales, and the main technical barrier faced by aerology modelling will be to generate the appropriate surface mesh of cave walls. (iii) To assess the nature, amount, and fate within the cave, of microorganisms suspended in the cave air, in the dripping water, and present on the walls, to detect any change of the structure and dynamics of these microbial ecosystems in response to aerology and climatic changes in the caves. Anticipating microorganism crises in caves is particularly challenging but essential since increases of both temperature and CO2 concentration facilitate the development of heterotrophic bacteria and, change the aerological circulation in caves.