Evolution of Reactive Interfaces and Microbial Diversity Associated to Silicate Weathering in the Critical Zone
IPGP - Îlot Cuvier
Chemical weathering of silicate minerals is central to numerous environmental and societal challenges, such as atmospheric CO2 drawdown, long-term management of soil systems or geological storage of CO2. This study addresses the long-standing question of the inconsistency between field and laboratory estimates of dissolution kinetics, by revisiting current approaches of mineral reactivity. It is first demonstrated that the evolution of feldspar reaction rates are inaccurately described by current rate laws, due to intrinsic textural and structural changes occurring at the fluid-mineral interface over the course of the dissolution process. Then, a novel method is developed and implemented to enable in situ probing of biogeochemical weathering rates in the field. Absolute mineral weathering rates derived from this method highlight the significant contribution of extrinsic factors to the field-laboratory discrepancy. Combining these data with a metagenomic analysis of bacterial and fungal community diversity reveals that subtle reciprocal relationships are established between microorganisms and mineral substrates within the mineralosphere. Finally, this thesis emphasizes the impact of passivation phenomena— engendered by the long-term aging of mineral surfaces—on dissolution rates, under field-relevant reacting conditions. These results suggest the incapacity of microorganisms to overcome the passivation barrier.