Abstract
This study investigates the carbonate system in the northern South China Sea shelf off the Pearl River estuary during the spring of 2023. Contrary to the typical distribution pattern observed in river-dominated coast where dissolved inorganic carbon (DIC) increases offshore, field observations revealed higher DIC in inshore waters (> 1980 µmol kg− 1) than in offshore seawaters (< 1970 µmol kg− 1), with DIC in the coastal zone being 20.9±8.8 µmol kg− 1 higher than that offshore. An end-member mixing model indicated that the high DIC coastal water was primarily attributed to mixing with the remnant high-DIC southward winter China Coastal Current water. In addition, biological processes and air-sea CO2 exchange also played important roles. Two representative regions were examined: the inshore high-DIC region and the offshore low-DIC region. In the inshore high-DIC region, biological processes and air-sea CO₂ exchange increased DIC by 11.6 ± 3.0 (relative to air-sea CO2 equilibrium) and 1.1 ± 7.0 µmol kg− 1 (relative to conservative mixing), respectively. In the offshore low-DIC region, biological processes decreased DIC by 5.1 ± 3.5 µmol kg− 1, whereas air-sea CO2 exchange increased DIC by 9.9 ± 2.8 µmol kg− 1. Overall, this study highlights the dominant role of the cross-seasonal influence of the remnant water of the coastal current, as well as the secondary but significant contributions of biological activity and air-sea CO2 exchange to the DIC distribution in coastal regions.
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Acknowledgements
Zhaozhang Chen and Longqi Yang organized the CTD sampling and processed the CTD data. We thank the crews of the R/V Yanping II for their assistance during the cruise. Shuqi An is acknowledged for his help in sampling and TA measurements. We are also grateful to the chief scientist, Dr. Hao Zhang, for the help during the cruise.
Funding
The study was supported by the Natural Science Foundation of China (42141001) and National Key R&D Projects (2022YFC3105302).
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Lei, S., Yang, Y., Bu, D. et al. Cross-seasonal influence of China Coastal Current water on spring carbonate system in the northern South China Sea.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-55237-x
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DOI: https://doi.org/10.1038/s41598-026-55237-x
Keywords
- Pearl River estuary
- Northern South China Sea coast
- Dissolved inorganic carbon
- Water mass mixing
- Biogeochemical processes
- Air-sea CO2 exchange
Source: Ecology - nature.com
