Microbial Life of Karst systems: how subsurface ecosystems ActiVity may impact the functioning of the (dEep) Critical ZoNe? – MiKroAVEN

The MiKroAVEN project aims at deciphering the impact of the activity of subsurface microbial ecosystems on the functioning and habitability of the Critical Zone. This superficial pellicule of the Earth, whose dynamics are based on the coupling between hydrological, geological and biological processes, is facing many pressures, both of anthropogenic or natural origin, which makes it fragile in a general context of global change. However, its deepest compartment remains poorly studied and the impact on its functioning of the activity of endemic subsurface microorganisms, which are now recognized to constitute the majority of terrestrial prokaryotes, is still under-constrained. The MiKroAVEN project proposes to face this challenge by investigating the crossed-links between geobiology, physicochemistry and geomorphology of cave systems. These latter, being transfer zones between the subsurface and the surface, are considered as natural laboratories for characterizing the impact of interaterrestrial life activity on the external envelopes of the Earth. Through a multidisciplinary approach, bringing together specialists from various disciplines, the MiKroAVEN project will try to decipher the impact of subsurface life activity on rock weathering and groundwater chemistry, notably through (re)mobilization of metal trace elements. The project will focus on the Larzac karst system, of which hydro-physicochemistry has been monitored for years in the framework of the Larzac observatory (OZCAR). This monitoring will be continued and complemented by a thorough study of the microbial ecology of the system and by in situ (in various avens of the system) and in vitro experiments of microbial alteration of rocks. This will allow characterizing the impact of microbial activity on rock weathering, remobilization of trace metals and on the geochemistry of groundwaters, and consequently on the composition of external envelopes of Earth.