The Great Barrier Reef: A source of CO2 to the atmosphere

Abstract The Great Barrier Reef (GBR) is the largest contiguous coral reef system in the world. Carbonate chemistry studies and flux quantification within the GBR have largely focused on reef calcification and dissolution, with relatively little work on shelf-scale CO 2 dynamics. In this manuscript, we describe the shelf-scale seasonal variability in inorganic carbon and air-sea CO 2 fluxes over the main seasons (wet summer, early dry and late dry seasons) in the GBR. Our large-scale dataset reveals that despite spatial-temporal variations, the GBR as a whole is a net source of CO 2 to the atmosphere, with calculated air–sea fluxes varying between −6.19 and 12.17 mmol m −2 d −1 (average ± standard error: 1.44 ± 0.15 mmol m −2 d −1 ), with the strongest release of CO 2 occurring during the wet season. The release of CO 2 to the atmosphere is likely controlled by mixing of Coral Sea surface water, typically oversaturated in CO 2 , with the warm shelf waters of the GBR. This leads to oversaturation of the GBR system relative to the atmosphere and a consequent net CO 2 release.