Interpreting silicon isotopes in the Critical Zone

Silicon isotopes serve as powerful proxies for weathering and element cycling, with their interpretation hinging on three key parameters: parent mineral isotope ratios, partitioning between solute and secondary phases, and fractionation factors tied to clay formation. This study reveals that these parameters vary systematically along an erosion gradient, from the kinetically limited Rhone Valley in the Swiss Alps to tectonically inactive highlands of Sri Lanka. Differential weathering of primary minerals leads to distinct silicon isotope signatures in solubilized rock, while clay mineralogy and composition—particularly Si-poor clays—control mass balance and fractionation factors. Larger fractionation factors correlate with Al availability, suggesting a mechanistic link. These findings provide a quantitative framework for using silicon isotopes to reconstruct past and present weathering processes.

Frings, P. J., Oelze, M., Schubring, F., Frick, D. A., & von Blanckenburg, F. (2021). Interpreting silicon isotopes in the Critical Zone. American Journal of Science, 321(8), 1164–1203. https://doi.org/10.2475/08.2021.02