EPSS Colloquium fall-2019

Earth’s biosphere is thought to exert a substantial influence on regolith evolution and chemical weathering rates. However, ecosystems are also highly efficient at retaining and recycling nutrients. Thus, although the ecological demand for rock-derived nutrients (e.g., P, Ca, K) may exceed the rates of regolith supply, ecosystems use a variety of retention and recycling strategies to armor themselves against nutrient limitations. To evaluate the balance between nutrient recycling and new nutrient input, we combined a plant model with a weathering model that accounts for erosion, water flow, regolith thickness, mineral solubilization rates, secondary minerals, and nutrient storage in organic and mineral phases. Although the model predicts strong correlations between weathering and plant growth, the relationship is due to the underlying dependence of both on nutrient rejuvenation from erosion. Collectively, model results suggest that plant productivity is not an unmitigated driver of weathering rates but is instead a commensal partner in regolith evolution. The model results also place constraints on how the biosphere may have influenced the relationship between silicate weathering rates and atmospheric carbon dioxide through Earth history.