Decomposing tropical Pacific air-sea CO2 flux anomalies during marine heatwaves and cold spells: thermal versus non-thermal drivers

Marine heatwaves (MHWs) and marine cold spells (MCSs) are extreme thermal events that can significantly influence air-sea CO 2 fluxes (FCO 2 ), yet their impacts in the tropical Pacific remain poorly constrained. Using multi-source observations and machine-learning models (Random Forest, XGBoost, LightGBM), we assessed FCO 2 anomalies during MHWs and MCSs from 1990 to 2019. Results show that MHWs enhance oceanic CO 2 uptake by ~0.53 mol C m -2 yr -1 , whereas MCSs reduce uptake by ~0.28 mol C m -2 yr -1 . Taylor decomposition indicates that non-thermal factors, especially dissolved inorganic carbon (DIC), dominate pCO 2sea anomalies. LightGBM provides superior predictive skill and reveals that FCO 2 variability is shaped more strongly by spatial structure than by temporal fluctuations and that wind variability plays a particularly strong role among the physical processes driving the non-temperature-related FCO 2 anomalies. These findings improve our mechanistic understanding of how thermal extremes regulate ocean-atmosphere carbon exchange and inform projections of ocean carbon sinks under climate change.