Tidal-Driven Submarine Groundwater Discharge and Its Influences on the Carbonate System of a Coastal Coral Reef in the Northern South China Sea

The driving mechanisms of submarine groundwater discharge (SGD) in Sanya Bay in the northern South China Sea were investigated using a combination of time-series observation and modeling, as well as the influences of SGD on the carbonate system of a coastal coral reef. SGD flux, characterized by high variability on flood-ebb and spring-neap tidal cycles, was found to be mainly driven by tidal pumping. SGD posed more significant impacts on coastal water at the ebb phase during the spring tide (higher SGD flux and extended offshore reach of SGD impact), with nearshore water to be more heavily affected. Under the influence of SGD, the diurnal ranges of the carbonate variables observed in the coral reef system were 124 - 313 mu mol kg(-1) for dissolved inorganic carbon, 29 - 101 mu mol kg(-1) for total alkalinity, 179 - 717 mu atm for partial pressure of CO2, and 0.20 - 0.45 for pH. The variations of the CO2 system were dominated by the enhanced SGD input during the spring tide, while biological metabolism of coral reef played a predominant role during the neap tide. The intensified SGD input resulted in higher diurnal variations of the carbonate variables, enhanced acidification, and oceanic CO2 emission during the spring tide. The SGD-associated inorganic carbon flux is an additional stressor influencing coastal acidification in the context of rising atmospheric carbon dioxide.

Automated summary

The study found that the flux of submarine groundwater discharge in Sanya Bay is mainly driven by tidal pumping, with more significant impacts on coastal water during the spring tide, resulting in higher variability of carbonate variables.