Spatiotemporal Evolution of Air–Sea CO2 Flux in the South China Sea and Its Response to Environmental Factors

Increasing atmospheric carbon dioxide (CO2) from human activities underscores the need to understand air–sea CO2 flux in marine environments, particularly in marginal seas like the South China Sea (SCS). This research analyzes the spatial and temporal patterns of air–sea CO2 flux across four typical regions of the SCS: the northern SCS, western SCS, SCS basin, and northeastern SCS. Our results show that the SCS serves as a carbon source from spring to autumn and shifts to a carbon sink in winter. The northern SCS exhibits strong carbon sink behavior during winter, transitioning to a source in warmer months, while the western SCS and SCS basin consistently act as carbon sources year-round, with summer peaks. The northeastern SCS acts as a source in warmer months, becoming a weak sink in winter. Partial correlation analysis reveals that temperature and wind speed significantly influence air–sea CO2 flux, though regional differences exist. Notably, chlorophyll-a in the northern SCS is negatively correlated with air–sea CO2 flux, indicating that high primary productivity enhances CO2 absorption, whereas other regions show contrasting relationships. These findings provide valuable insights into the complex carbon cycle mechanisms in the SCS.