Dimensionless Controls on the Fate of Fluvial Inorganic Carbon

Rivers play a critical role in the global carbon cycle, transporting carbon from land to ocean while emitting significant amounts of CO₂ to the atmosphere. Yet, the processes controlling the partitioning of fluvial inorganic carbon (IC) between atmospheric release and downstream transport remain poorly understood due to complex hydrodynamic and biogeochemical interactions.

Building on Budyko’s hydrological framework, we propose a dimensionless approach to uncover the primary controls on IC partitioning. Two key parameters are introduced: (1) the fraction of IC in equilibrium with atmospheric CO₂ and (2) the ratio of transport to evasion timescales. Our analysis reveals that water chemistry regulates stable IC transport downstream, while water hydrodynamics dictates the fate of out-of-equilibrium IC. River catchment analyses support the dimensionless framework and highlight different IC dynamics depending on the stream order. Overall, this framework provides a predictive tool for river carbon dynamics, with implications for land-to-ocean fluxes and fluvial emissions.