Geodynamic controls on long-term carbon cycle: insights from fully integrated virtual planets

Over geological timescales climate is regulated by the long carbon cycle, in which a balance is struck between CO₂ degassing from the solid Earth and CO₂ consumption by continental silicate weathering stabilizing atmospheric CO₂ levels and maintain habitable conditions. Geodynamic processes regulate both CO₂ degassing rates as well as the distribution and elevation of continents, thereby controlling continental weatherability and, ultimately, atmospheric CO₂ and long-term climate.

However, long-term carbon cycle models are often limited by their definition of degassing independently of geodynamics evolution and their inevitable attribution of continental weatherability as the primary driver of long-term climate. Furthermore, the sparsity of the geological record means that models often rely on observations of present-day Earth to simulate past Earth states. All these constrains provide limited insight into how geodynamics interacts with climate, and surface processes to regulate atmospheric CO₂ over geological timescales.

To address these limitations, we use fully integrated "digital siblings” of the Earth: 3D fully virtual planets designed to simulate internally consistent evolution of habitable planets over a several 100~Myr timescales, not necessarily aiming to replicate Earth. We integrate three numerical models in a dynamically interdependent framework: the geodynamic model StagYY (Coltice et al., 2019), the climate model PLASIM-GENIE (Holden et al., 2016), and the surface processes model goSPL (Salles et al., 2023).

From these simulations, we compute time-dependent CO₂ degassing rates, using geodynamic outputs, and weathering fluxes, using the formulation of West (2012). Our results reveal fluctuations in degassing rate over a factor of about three, consistent with reconstruction of Earth (Müller et al., 2024) and correlated with seafloor production rate. Weatherability strongly depends on True Polar Wander during supercontinent aggregation, and on sea level fluctuations controlled by seafloor production. Together, these results highlight how geodynamic evolution may regulate the long-term carbon cycle through its interdependent effects on degassing and continental weatherability.