Deep carbon cycling in subduction zones: 2. Moderate thermal parameter favors carbonate dissolution

Summary Carbonate dissolution represents a key mechanism for slab carbon release in oceanic subduction zones. However, the magnitude and controlling factors of carbonate dissolution remain unclear. Here, we develop a coupled thermo-petrological modeling method that integrates slab dehydration, carbonate mineral abundances and their solubilities into subduction-zone thermal models. Systematic model results establish a quantitative relationship between the dissolved CO2 outflux and the subduction-zone thermal parameter (here defined as φ = slab age × subduction velocity/100 in kilometers), which reveals a peak outflux at φ ≈ 13 km, corresponding to warm subduction zones. The dissolved CO2 outflux exhibits a sublinear increase at φ < 13 km and an exponential decline at higher φ. This indicates that warm subduction zones with moderate thermal parameters provide the favorable thermal conditions for carbonate dissolution. The style of aqueous fluid migration strongly influences both the pattern and magnitude of carbonate dissolution. In the pervasive-flow system, fluid infiltration substantially enhances the dissolved CO2 outflux, producing magnitudes approximately three times higher than those in the channelized-flow system. The specific model results for three representative subduction zones—hot Cascadia, warm Nicaragua, and cold Hokkaido—confirm that warm Nicaragua exhibits higher dissolved CO2 outflux, potentially explaining its high arc CO2 degassing outflux.