Carbonate buffering system and the story of CO₂ absorption and emission along the Northeastern coast
Research team conducting field surveys in Ha Long Bay
In the context of continuously rising atmospheric CO₂ concentrations, the ocean is expected to contribute to climate regulation. However, its capacity to absorb CO₂ is uneven, particularly in coastal waters, which are strongly influenced by river discharge, monsoons and biogeochemical processes. The key controlling factor is the carbonate buffering system – the chemical mechanism that determines the ability of seawater to absorb, store or release CO₂.
Although widely studied globally, the carbonate buffering system in Viet Nam’s coastal regions still lacks comprehensive observational data, especially on a seasonal basis. From this reality, Dr. Cao Thi Thu Trang and the research team from the Institute of Science and Technology for Energy and Environment conducted a study in Ha Long Bay and the Bach Dang estuary – two representative water bodies of the Northeastern coastal region.
Dr. Cao Thi Thu Trang at her office
According to Dr. Cao Thi Thu Trang, the carbonate buffering system helps maintain stable pH levels, enabling the ocean to absorb CO₂ without causing abrupt changes to ecosystems. However, in sensitive coastal areas, this role can shift rapidly depending on environmental conditions, even switching from absorption to emission within a single season.
Dr. Cao Thi Thu Trang organises the implementation of the research project
Large-scale surveys establish seasonal datasets for the first time
The research team conducted surveys during both the rainy and dry seasons, collecting hundreds of water samples from surface and bottom layers in Ha Long Bay and the Bach Dang estuary. By combining field observations, chemical analysis and modelling, the team constructed an overall picture of the carbonate buffering system in the area.
Sampling station map, (Left) Bach Dang estuary area (Hai Phong); (Right) Ha Long Bay
The results show that Ha Long Bay maintains relatively stable conditions, with high salinity and pH, enabling it to function as a CO₂ sink in both seasons. In contrast, the Bach Dang estuary exhibits marked variability: it absorbs CO₂ during the dry season but shifts to emitting CO₂ in the rainy season when inputs of water and materials from land increase.
Research team surveys the Bach Dang estuary area
This “reversal” indicates that coastal waters can act both as CO₂ sinks and sources, depending on natural conditions. The findings are consistent with international research trends while also reflecting the specific characteristics of Viet Nam’s coastal zones.
Through simulations of climate change scenarios, the research team observed that dissolved CO₂ and inorganic carbon concentrations tend to increase, accompanied by a slight decline in pH in the Ha Long – Hai Phong area, signalling a potential risk of acidification in the future.
Dr. Cao Thi Thu Trang presenting at a scientific workshop marking the 50th anniversary of the Vietnam Academy of Science and Technology
The study has established a systematic dataset on the carbonate buffering system and CO₂ exchange in coastal waters, providing a foundation for further research on climate change and the carbon cycle. These data can be used to develop CO₂ models and marine environmental monitoring systems.
The project also contributes to human resource development, with scientific publications both domestically and internationally, and was highly evaluated by the appraisal council, receiving an A rating.
Translated by Phuong Huyen
Link to Vietnamese version
