| Summary: | Against the background of climate warming, marine heatwaves (MHWs) and terrestrial drought events have become increasingly frequent in recent decades. However, the combined effects of MHWs and terrestrial drought on CO<sub>2</sub> uptake in marginal seas are still unclear. The East China Sea (ECS) experienced an intense and long-lasting MHW accompanied by an extreme terrestrial drought in the Changjiang basin in the summer of 2022. In this study, we employed multi-source satellite remote sensing products to reveal the patterns, magnitude, and potential drivers of CO<sub>2</sub> flux changes in the ECS resulting from the compounding MHW and terrestrial drought extremes. The CO<sub>2</sub> uptake of the ECS reduced by 17.0% (1.06 Tg C) in the latter half of 2022 and the Changjiang River plume region shifted from a CO<sub>2</sub> sink to a source (releasing 0.11 Tg C) in July-September. In the majority of the ECS, the positive sea surface temperature (SST) anomaly during the MHW diminished the solubility of CO<sub>2</sub> in seawater, thereby reducing CO<sub>2</sub> uptake. Moreover, the reduction in nutrient input associated with terrestrial drought, which is unfavorable to phytoplankton growth, further reduced the capacity of CO<sub>2</sub> uptake. Meanwhile, the CO<sub>2</sub> sink doubled for the offshore waters of the ECS continental shelf in July-September 2022, indicating the complexity and heterogeneity of the impacts of extreme climatic events in marginal seas. This study is of great significance in improving the estimation results of CO<sub>2</sub> fluxes in marginal seas and understanding sea–air CO<sub>2</sub> exchanges against the background of global climate change.
|
|---|