The oceanic CO₂ System and Carbon Budget in the Great Barrier Reef, Australia

The Great Barrier Reef (GBR) is the largest reef system in the world. During winter (dry season), a relative increase of CO 2 fugacity, together with a depletion in total alkalinity, was evident in the GBR lagoon water. This suggests the release of CO 2 due to CaCO 3 production in the lagoon. But, in detail, significant contribution from organic matter oxidation was also identified. Despite the dissolved carbon losses as carbonate, total dissolved inorganic carbon (DIC) concentration normalized at constant salinity was relatively uniform throughout the study area. This indicates the presence of external carbon input to the lagoon. The most likely source is river discharge, which carries sizeable amounts of dissolved and particulate organic carbon as well as DIC. The marine CO 2 system of the GBR lagoon highlights the nature of tropical carbonate shelves as a strong alkalinity sink and a net oxidation site of land‐derived organic carbon.