Significant CO₂ emission in the shallow inshore waters of the southeastern Yellow Sea in 2020

This study investigated the carbonate system and air-sea CO₂ exchange in the inshore waters along South Korea's western coastline in 2020. Overlooking these waters might introduce significant errors in estimating air-sea CO₂ fluxes of the southeastern Yellow Sea, given their interaction with land, offshore regions, and sediments. During periods other than summer, seasonal variations in seawater CO₂ partial pressure (pCO₂) could be generally explained by thermal effects. Tidal mixing and shallow depths resulted in weaker stratification-induced carbon export compared to offshore regions. However, during summer, inshore waters exhibited high spatial variability in pCO₂, ranging from approximately 185 to 1000 μatm. In contrast to offshore waters that modestly absorbed CO₂, inshore waters shallower than 20 m emitted ∼100 Gg C yr^-1 to the atmosphere. However, considering the high heterogeneity of the study area, additional observations with high spatial and temporal resolution are required to refine estimates of air-sea CO₂ exchange.