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 d−1; range: 0−1111 mmol m2 d−1) were up to ∼300-fold larger than evasion of CO2 to the atmosphere. The reef seawater pCO2 (493 μatm; range: 421−680 μatm) remained above atmospheric values and spanned the upper end of the range of atmospheric levels (400−500 μatm) 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

Submarine Groundwater and Vent Discharge in a Volcanic Area Associated With Coastal Acidification

We investigated submarine groundwater discharge (SGD) in a volcanic coastal area that hosts the world\u27s most biodiverse reefs. Measurements of 222Rn activity in coastal seawater, a tracer for groundwater, indicated prevalent SGD. In areas where seawater 222Rn activity was generally higher, we discovered hydrothermal springs emitting acidic waters (pH ~5.4–6.0) and venting magmatic CO2 that brought local pCO2 levels up to 95,000 ppm. The collection of vents raised CO2 and lowered pH over 1–2 km of coastline. The hydrogen and oxygen isotope compositions of water and chloride concentration revealed that the springs discharge recirculated seawater mixed variably with terrestrial groundwater. Shallower springs and pore water have a higher proportion of terrestrial groundwater than deeper springs, which emit mostly recirculated seawater. This suggests that different SGD mechanisms are present. The SGD could be contributing to the evolution and function of the biodiverse ecosystem, but it also represents myriad pathways for contamination