Investigations at fixed and spatial stations were conducted during the rainy and dry seasons of 2023–2024 in the Bach Dang Estuary (Hai Phong City, Vietnam) to evaluate the composition of the carbonate chemical system and the air-sea CO2 flux. The results show that, due to significant changes in salinity and pH combined with high water temperatures, the water contains more dissolved CO2 in the rainy season than in the dry season. The partial pressure of CO2 in the water ranges from 49 to 5140 µatm during the rainy season and from 96 to 580 µatm in the dry season. The flux of CO2 exchange across the air-sea interface ranges from − 4.0 to 83.0 mmol m−2 day−1 during the rainy season and from − 4.9 to 3.1 mmol m−2 day−1 in the dry season. Thus, the Bach Dang Estuary acts as a source of CO2 emissions into the atmosphere during the rainy season, whereas it acts as a sink for atmospheric CO2 in the dry season. Strong hydrodynamics in the Estuary lead to pronounced changes in the composition of the carbonate buffer system, especially during the rainy season. It is expected that this study will contribute to a better understanding of the carbonate chemical system in typical tropical coastal estuaries.
Trang C. T. T., Kha P. T., Van Nam L., Ngoc D. H., Long D. T., Huong N. T. A., Mai P. T. N., Minh N. V., Quang P. V. & Ha N. T. T., 2025. CO2 partial pressure and air-sea CO2 flux in the Bach Dang Estuary (Hai Phong City, Vietnam). Ocean Science Journal 60: 20. doi: 10.1007/s12601-025-00215-z. Article.
