Groundwater occurrence and discharge at coral atoll and barrier reef systems

This project will, for the first time, assess the role of the reef flat plate - a lithified carbonate unit ubiquitously present in coral reef systems - on the distribution and rate of submarine groundwater discharge. Focusing our studies on a high-island barrier reef (Moorea, French Polynesia) and a low-island coral atoll (Tetiaroa, French Polynesia) with the same tidal and climate forcing, we will apply multiple methods including thermal infrared mapping, electric resistivity, distributed temperature sensing and 222Rn surveying as well as coring and dye transport studies to (1) trace groundwater flow to and through the reef, (2) develop a numerical model of reef hydraulics in the context of head, temperature and salinity gradients, (3) quantify rates of SGD across 4 distinct reef transects; and (4) discern the impact of SGD on reef water total alkalinity and dissolved inorganic carbon geochemistry. The results may improve our ability to identify SGD in reefs and to gage the role of SGD in sustaining reef ecosystem functioning in an acidifying ocean.