Continental and Seafloor Weathering in the Global Carbon Cycle: Inverse Modeling and Implications for the Precambrian

The relative importance of tectonics and continental versus seafloor weathering in controlling the geological carbon cycle are unknown. Here, we present a new open-source, carbon cycle model that explicitly captures the temperature-dependent and pH-dependent kinetics of seafloor weathering to investigate carbon fluxes and the evolution of atmospheric CO2 and ocean pH.We first apply the model to the last 100 Ma and validate model outputs using proxy data. Model parameters are rigorously constrained using Bayesian inverse methods. To fit proxies, the temperature dependence of continental weathering must be much weaker than commonly assumed: we find 14-30°C surface warming is required to double the continental weathering flux, compared to 3-10°C in previous work. Additionally, continental weatherability has approximately doubled since 100 Ma, demanding explanation by uplift and sea level changes. The average Earth system climate sensitivity is also found to be notably higher than fast-feedback estimates. These conclusions are robust to assumptions about outgassing, modern fluxes, and the kinetics of seafloor weathering. Finally, the model is extended to the Precambrian to investigate the relative importance of continental vs. seafloor weathering over Earth history. We contast our results against existing carbon cycle models of the early Earth.