Microstructural modifications associated to basaltic glass dissolution: Towards biosignatures of microbially-mediated silicate weathering?

Quantifying the contribution of microbes to silicate dissolution rates is one of the main challenges to improve numerical models of silicate weathering, a process that partly controls atmospheric CO2 uptake and Earth’s climate over geologic timescales. Addressing this challenge will require the definition of biosignatures of bioweathering, for which current definition is controversial. Here we propose to use X-ray reflectivity to characterize the physical properties of nm-thick silica-rich layers formed on basaltic glass weathered in biotic and abiotic conditions, taken as a simplified model relevant for basaltic environments that act as major sink of CO2 on Earth. Since our previous works conducted on altered silicate minerals showed that the properties of such Si-rich layers were inherited from the chemical composition of the fluid medium, we expect to get unprecedented data to identify imprints resulting from bioweathering, a necessary step for quantifying bioweathering fluxes.