Igneous and Metamorphic CO₂ Sources: How Large and How Variable?

Igneous and metamorphic processes play a critical role in the geological carbon cycle and Earth’s long-term habitability by transferring carbon between rocks and the ocean–atmosphere system. The magnitude of these carbon fluxes, both in the present day and throughout Earth’s history, remains poorly constrained. Traditional models link carbon degassing to riverine bicarbonate fluxes, but these approaches rely on the questionable assumption that the modern system is in steady-state. Here, we summarize the current state of research on quantifying igneous and metamorphic carbon fluxes using direct measurements, geochemical proxies, and ancient rock records. We also examine the spatial and temporal variability of these processes, which is crucial for understanding their influence on Earth’s carbon cycle over geological timescales.