Emission of CO2 and its related carbonate system dynamics in a hotspot area during winter and summer: The Changjiang River estuary

Bing-Han Li; Hai-Long Zhao; Jiang-Chen Gong; Xi Wu; Chun-Ying Liu; Jing-Wen Hu; Gui-Peng Yang

doi:10.1016/j.marenvres.2024.106496

Emission of CO₂ and its related carbonate system dynamics in a hotspot area during winter and summer: The Changjiang River estuary

Mar Environ Res. 2024 Apr 10:198:106496. doi: 10.1016/j.marenvres.2024.106496. Online ahead of print.

Authors

Bing-Han Li¹, Hai-Long Zhao², Jiang-Chen Gong¹, Xi Wu³, Chun-Ying Liu⁴, Jing-Wen Hu⁵, Gui-Peng Yang¹

Affiliations

¹ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China; Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao, 266237, China.
² Ocean University of China, Research Vessel Centre, Qingdao, 266100, China.
³ Institute for Advanced Marine Research, China University of Geosciences, Guangzhou, 511462, China; Tianjin Key Laboratory of Marine Resources and Chemistry, Tianjin University of Science & Technology, Tianjin, 300457, China.
⁴ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China; Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao, 266237, China. Electronic address: roseliu@ouc.edu.cn.
⁵ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China.

PMID: 38640691
DOI: 10.1016/j.marenvres.2024.106496

Abstract

The carbonate chemistry in river-dominated marginal seas is highly heterogeneous, and there is ongoing debate regarding the definition of atmospheric CO₂ source or sink. On this basis, we investigated the carbonate chemistry and air-sea CO₂ fluxes in a hotspot estuarine area: the Changjiang Estuary during winter and summer. The spatial characteristics of the carbonate system were influenced by water mixing of three end-members in winter, including the Changjiang freshwater with low total alkalinity (TA) concentration, the less saline Yellow Sea Surface Water with high TA, and the saline East China Sea (ECS) offshore water with moderate TA. While in summer with increased river discharge, the carbonate system was regulated by simplified two end-member mixing between the Changjiang freshwater and the ECS offshore water. By performing the end-member mixing model on DIC variations in the river plume region, significant biological addition of DIC was found in winter with an estimation of -120 ± 113 μmol kg^-1 caused by wintertime organic matter remineralization from terrestrial source. While this biological addition of DIC shifted to DIC removal due to biological production in summer supported by the increased nutrient loading from Changjiang River. The pCO₂ dynamics in the river plume and the ECS offshore were both subjected to physical mixing of freshwater and seawater, whether in winter and summer. In the inner estuary without horizontal mixing, the pCO₂ dynamics were mainly influenced by biological uptake in winter and temperature in summer. The inner estuary, the river plume, and the ECS offshore were sources of atmospheric CO₂, with their contributions varying seasonally. The Changjiang runoff enhanced the inner estuary's role as a CO₂ source in summer, while intensive biological uptake reduced the river plume's contribution.

Keywords: CO(2) flux; Carbonate system; Changjiang River; Control mechanisms; East China sea.