Silicon isotopes and continental weathering processes: Assessing controls on Si transfer to the ocean

Knowledge of the weathering processes controlling continental transfer of dissolved silicon (DSi) to the ocean is fundamental to the estimate of the long-term atmospheric CO2-budget. Studies at the soil profile and catchment scales demonstrate that the Si isotopic composition of soil and riverine DSi is a marker of abiotic and/or biotic weathering processes. In this paper, we first review Si isotopic fractionation in the natural environment. We then evaluate the application of Si isotopes to gain new insights into weathering processes on distinct spatial and temporal scales. We suggest that bulk soil δ30Si is inversely correlated to weathering degree, regardless of variability in climate, soil age and lithology. We also posit that the Si isotopic composition of DSi and suspended matter in rivers is indicative of the weathering regime (weathering- vs. transport-limited) prevailing in the area where DSi flux originates. Finally, we propose some future research directions.