deepOASES

Few processes on Earth have the potential to awake the interest of so many different scientific disciplines as the serpentinization of the mantle-derived rocks along the Mid Ocean Ridges. This region of the oceanic crust represents in fact the boundary between the deep geosphere and the outer shells of the Earth, the hydrosphere and atmosphere, moderating the bulk mass transfer between the Earth’s mantle and the exosphere directly affecting the climate, the composition of the oceans and atmosphere, along with the availability of nutrients on which relies the biological activity and ultimately the habitability of our planet. At the same time this environment represents a powerful reactor where the fundaments molecules of life are naturally synthesized at the planetary scale, outlined the need to consider the serpentinizing oceanic lithosphere as a powerful carbon-fixation and -recycling engine with, nonetheless, very-poorly known sources, sinks, mechanisms and rates. This furthermore suggests that in these environments, viable microbial ecosystems might be only operating by geochemical energy input, regardless of photosynthesis and primary production at Earth’s surface, with far reaching implications for a comprehensive understanding of subsurface environments on our planet and the search of present-day analogs of the early Earth leading to consider, owing to the large concerned volumes, the oceanic lithosphere as the largest microbial habitat on Earth. The key point here is the capacity of serpentinization reactions that affects the first kilometers of the crust to continuously produce molecular hydrogen over a wide range of temperatures. This lets us suspect carbon reduction to occur from deep levels where solely abiotic reactions (i.e. pure chemical processes) can account for the generation of organic compounds of putative prebiotic interest, up to colonizable depths where this hydrogen represents an invaluable source of energy for the inhabitating chemolithoautotrophic microbial communities. This deep life has indeed the ability to capitalize on the steady stream of serpentinization byproducts, converting the available carbon into biomass and then competing against abiotic reactions, thus leadig to consider the oceanic lithosphere as the largest habitat on Earth. Taken as a whole, elemental fluxes between oceanic crust, oceans and mantle can obviously be mediated by the presence of deep rock-hosted ecosystems largely unknown at present. The net amount of this contribution, the magnitude of its impact, as well as the interplay between alteration, abiotic carbon reduction and microbial activity has not yet been estimated by the scientific community and represents a frontier to be explored in the Earth and Life Sciences. Based on our capability to reveal chemical, mineralogical, genetic and metabolic diversity in subsurface environments, we aim here, through an interdisciplinary approach, to bring a qualitative jump in the understanding of the deep organic carbon and nitrogen cycles in the serpentinizing oceanic lithosphere and to shed light on its potential to abiotically generate organic molecules and sustain the development of a microbial life independent from the photosynthesis. By integrating diverse tools from geobiology, mineralogy, geochemistry, microbiology, microbial ecology on field samples along with analogical experiments, and thermodynamical modeling, this project will provide a detailed picture of the progressive abiotic and biological carbon reduction in the oceanic mantle-derived lithosphere and subsequently assess the retroactive impact of this organic carbon pool on the serpentinization reactions and associated elemental fluxes in the oceanic lithosphere, from ridges up to the oceans and subduction zones