This work tackles the issue of the existence of deep ecosystems hosted in mantle-derived rocks and sustained by the serpentinization process along Mid Ocean Ridges. The progressive hydration of peridotite-forming minerals releases molecular hydrogen, which in turn constitutes a source of metabolic energy for chemiolithoautotrophs microorganisms. State-of-the-art microspectroscopic techniques have been applied to serpentinites-hosted atypical mineralizations potentially induced by microbial activity and preserved in rocks coming from slow-spreading ridges and the Apennine ophiolites.
The oceanic serpentinites present peculiar mineral assemblages constituted by porous hydroandraditic garnets harbouring endogenic organic carbon accumulations. These represent remnants of microbial ecosystems that have played a crucial role in driving hydrogarnet dissolution and precipitating secondary mineralizations. In addition, the biologically-derived organic matter experienced hydrothermal degradation, producing a light oil fraction released to the hydrothermal circuit.
The Apennine ophiolitic serpentinites display instead a mineralization constituted by millerite and serpentine filaments embedded in calcite that has been interpreted as representative of a fossilised fungal colonization held in the rock porosity.
The results of this study support the existence of active microbial ecosystems sustained by the serpentinization by-products in deeply-seated hydrated peridotites. They indicate that a significant part of organic carbon can be stored within the oceanic crust, with the potential to impact the global carbon budget along with the elemental fluxes from the mantle to the oceans.