Maturation of Silicate Weathering Pathways Revealed by Germanium-Silicon Ratios

We document the evolution of fresh basalt subject to roughly a decade of chemical weathering through systematic temporal shifts in aqueous germanium-silicon ratios (Ge/Si) in a unique set of meso-scale artificial hillslopes. Elevated dissolved Ge/Si signatures relative to bedrock in this young system are associated with formation of high-Si amorphous phase(s) that preferentially exclude Ge. Over several years, dissolved Ge/Si ratios decrease, approaching those of natural watersheds, consistent with a shift toward formation of Ge-enriched secondary phases. Our study points to the critical control of secondary phase speciation on Ge/Si partitioning, while in contrast, stable silicon isotope ratios (δ³⁰Si) in the same samples show fractionation comparable to natural systems. Paired consideration of Ge/Si and δ³⁰Si tracers may thus offer a previously unrecognized means of interrogating the progression of secondary phase speciation in young landscapes, for example, following deglaciation, volcanism, and landslides, and in engineering applications such as enhanced weathering.