Influence of Typhoons in the Western North Pacific on Air-sea CO₂ Flux Variations and Underlying Mechanisms

To investigate how frequent typhoons in the western North Pacific (WNP) regulate air-sea CO₂ flux, this study uses a high-resolution air-sea CO₂ flux dataset based on neural-network inversion, together with a typhoon track density function during 1982–2022, to systematically extract the characteristics of CO₂ flux responses to typhoons at the synoptic scale and to analyze the associated driving mechanisms. The results indicate that under typhoon influence, the gas transfer coefficient and seawater CO₂ solubility increase by 11.52% and 3.11%, respectively, while the air-sea CO₂ partial pressure gradient ( \Delta f\mathrmC\mathrmO_2 ) decreases by 10.10%. Ultimately, these combined alterations lead to an average enhancement in the oceanic CO₂ efflux density of 2.58 (mmol/m²)/d during typhoon events. Spatially, the anomalies in \Delta f\mathrmC\mathrmO_2 exhibit pronounced regional divergence, characterized by positive anomalies in the South China Sea (SCS) and negative anomalies in the WNP. This basin-scale contrast is controlled by the interplay between thermal and non-thermal (dynamic mixing) processes. Typhoon-induced sea surface cooling enhances CO₂ solubility, effectively reducing seawater f\mathrmC\mathrmO_2 by 2.08 µatm in the SCS and 1.97 µatm in the WNP. In contrast, strong vertical mixing and upwelling entrain CO₂-rich subsurface waters into the surface layer, raising seawater pCO₂ by 2.85 µatm in the SCS and 0.99 µatm in the WNP. As a result, thermal processes dominate in the WNP, whereas non-thermal dynamic mixing processes prevails in the SCS, jointly shaping the observed basin-scale \Delta f\mathrmC\mathrmO_2 variations. Mechanism decomposition further reveals that the typhoon-driven CO₂ flux variation is primarily contralled by extreme wind forcing, which account for 52.62% of the total flux change. Regionally, thermal processes dominate in source-sink transition zones, contributing 12.15% to the total variance, while non-thermal dynamic mixing processes dominate in the SCS, contributing 8.83%. These findings highlight the critical role of extreme weather events in regional carbon cycling, providing a robust scientific basis for refining regional carbon budget estimates and for projecting the evolution of oceanic carbon sinks under future climate warming scenarios.