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. Durin g winter (dry season), a relative increase of CO2 fugacity, together with a depletion in total alkalinity, was evident in the GBR lagoon water. This s uggests the release of CO2 due to CaCO3 production in the lagoon. But, in d etail, significant contribution from organic matter oxidation was also iden tified. Despite the dissolved carbon losses as carbonate, total dissolved i norganic carbon (DIC) concentration normalized at constant salinity was rel atively uniform throughout the study area. This indicates the presence of e xternal carbon input to the lagoon. The most likely source is river dischar ge: which carries sizeable amounts of dissolved and particulate organic car bon as well as DIC. The marine CO2 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.