Decreased Air-Sea CO 2 ${\mathbf{\text{CO}}}_{\mathbf{2}}$ Flux During the Persistent Marine Heatwaves in the Yellow Sea and East China Sea

Abstract

Marine heatwaves (MHWs) exert a significant influence on marine ecosystem, especially in marginal seas where carbonate processes are intricately linked to temperature variations. However, how MHWs affect the carbonate processes in marginal seas, such as the Yellow Sea (YS) and East China Sea (ECS), remains unclear. Here, we employ a physical-biogeochemical model to simulate marine ecosystem, aiming to systematically quantify impacts of persistent MHWs (PMHWs) on air-sea ${\text{CO}}_2$ flux (${\text{FCO}}_2$) anomaly in YS and ECS. Results reveal that due to reduced wind speed and elevated temperature during PMHWs, ocean ${\text{CO}}_2$ reservoir experiences dramatic decrease. In summer when the ocean releases CO₂ to the atmosphere, suppressed ocean CO₂ outgassing induced by decreased wind speed counteracts elevated ocean CO₂ outgassing resulted from high temperature. In winter, both wind speed and temperature factors suppress ocean CO₂ absorption from the atmosphere to the ocean. In addition, the spatial pattern of ${\text{FCO}}_2$ is dominated by partial pressure of ${\text{CO}}_2$ in the surface water (${\text{pCO}}_2$). While thermal effects have a contribution of 61% and 33% in YS and ECS to positive ${\text{pCO}}_2$ anomaly, non-thermal effects primarily driven by alkalinity anomaly play a more vital role in amplifying ${\text{pCO}}_2$ anomaly (61% and 90% respectively). Furthermore, horizontal advection emerges as a dominant ocean process in modulating ${\text{pCO}}_2$ variations in YS and ECS, with the contribution of 72 ± 17% and 75 ± 60% respectively. These findings underscore the importance of understanding the physical mechanisms behind PMHWs in analyzing its ecological impacts within coastal ocean environments.