Are microbes the ultimate drivers of subsurface weathering? rates, actors, mechanisms and nanoscale imprints of the bioweathering of fresh and aged silicates
The ambition of this proposal is to provide the very first realistic assessment of the contribution of microbes to subsurface silicate weathering rates. The motivation is simple: ~70% of Earth’s bacteria and archaea live underground, and microbes have long been suspected to impact silicate weathering rates, which affect the Earth’s climate. However, the rates and mechanisms of silicate bioweathering essentially remain a terra incognita, particularly in basalt settings. Such environments are suggested to be a potential host for early life and represent prime targets for massive injections of CO2 to fight against global warming, whose success strongly relies on silicate reactivity. Having a deep insight on the respective biotic and abiotic contributions to subsurface silicate weathering rates is therefore fundamental and urgent.
Providing such estimates requires to overcome a twofold challenge: 1) to quantify dissolution rates in aqueous fluids that sustain endemic microbial communities and at the same time 2) to supersede the classical use of freshly ground substrates, whose reactivity is orders of magnitude greater than that of aged silicates long altered in natural settings.
This proposal offers a solution: An interdisciplinary and non-conventional approach to assess the contribution of microbes to silicate weathering rates in complex environmental media. It consists in measuring dissolution rates using non-invasive nanotopography measurements of the silicate substrates reacted in natural solutions. These substrates will be treated beforehand to get surface properties that mimic various stages of aging. These measurements will be combined with studies of the microbial diversity associated with the substrates, innovative nanoscale characterizations of the reacted surfaces, and modeling of the dissolution process based on first principles. This strategy will provide an unprecedented and timely picture of the functioning and rates of subsurface silicate bioweathering.