Submarine Groundwater Discharge Releases CO2 to a Coral Reef

Submarine groundwater discharge (SGD) flows into coral reefs. In volcanically active areas, the incoming groundwater is typically CO2-rich which can alter the carbon balance and views on how coral reefs function at prevailing high CO2. We quantified dynamic hydrothermal SGD and CO2 fluxes to a Philippine coral reef over a spring-neap tidal cycle. SGD rates, with mean of 35 cm d(-1)and 5-95% range of 0-147.8 cm d(-1).The groundwater-CO2 fluxes (266 mmol m(2) d(-1); range: 0-1111 mmol m(2) d(-1)) were up to similar to 300-fold larger than evasion of CO2 to the atmosphere. The reef seawater pCO(2) (493 mu atm; range: 421-680 mu atm) remained above atmospheric values and spanned the upper end of the range of atmospheric levels (400-500 mu atm) expected for the next century. Because of the hydrothermal SGD, the reef has prevailing above-atmospheric CO2 and is a source to the atmosphere and nearby waters.

Automated summary

Submarine groundwater discharge can have significant impacts on coral reefs, especially in volcanically active areas. A study in the Philippines found that hydrothermal SGD led to a substantial increase in CO2 flux from groundwater, making the coral reef a source of CO2 emissions to the atmosphere and nearby waters.