Highlights
- Carbonate weathering and methanogenesis affect DIC production in deep groundwater.
- Deep groundwater discharge serves as a buffer against ocean acidification.
- Neglecting deep groundwater overestimates the effect of TSGD on ocean acidification.
Abstract
Shallow groundwater discharge from unconfined aquifers is known to affect ocean carbon budget and ocean acidification. However, the role of deeper groundwater discharge from confined aquifers in ocean carbonate chemistry was previously overlooked. Here, we characterized dissolved inorganic carbon (DIC) and total alkalinity (TA) concentrations and estimated DIC and TA fluxes from confined aquifers (50 ∼ 520 m depth) in the northern Yangtze River Delta. The results show that deep groundwater generally exhibits high DIC concentrations, primarily influenced by carbonate weathering and methanogenesis. The DIC concentrations in the deep groundwater (50 ∼ 520 m depth) are about 14 % lower than the TA concentrations, indicating that the deep groundwater discharge mitigates ocean acidification. However, the DIC concentrations in shallow groundwater (< 30 m depth) are much higher than the TA concentrations, indicating the strengthening of ocean acidification after discharging to the sea. The mean [TA-DIC] flux from the deep groundwater accounts for approximately 8 % of that from the shallow groundwater, but overlooking the deep groundwater will considerably overestimate the effect of terrestrial groundwater on ocean acidification.
Su J., Liu Y., Xie Y., Gong X., Chen T., Zhang Y., Han D. & Wu J., 2025. Groundwater carbon biogeochemistry of coastal confined aquifers and its implications after discharge. Journal of Hydrology 655: 132970. doi: 10.1016/j.jhydrol.2025.132970. Article.
