Neritic carbonate for six submerged coral reefs from northern Australia: Implications for Holocene global carbon dioxide

Abstract

Total contribution of six recently discovered submerged coral reefs in northern Australia to Holocene neritic CaCO 3 and CO 2 is assessed to address a gap in global budgets. CaCO 3 production for the reef framework and inter-reefal deposits is 0.26–0.28 Mt. Holocene CO 2 production is 0.14–0.16 Mt. Coral and coralline algae are the dominant sources of Holocene CaCO 3 although foraminifers and molluscs are the dominant constituents of inter-reefal deposits. The total amount of Holocene neritic CaCO 3 produced by the six submerged coral reefs is several orders of magnitude smaller than that calculated using accepted CaCO 3 production values because of very low production, a ‘give-up’ growth history, and presumed significant dissolution and exports. The contribution of submerged coral reefs to global Holocene neritic CaCO 3 is estimated to be 0.26–0.62 Gt, which yields 0.15–0.37 Gt of CO 2. This amount of CO 2 is 0.02–0.05% of the 780 Gt added to the atmosphere since 18 kyr BP. Contributions from Australian submerged coral reefs are estimated to be 0.05 Gt CaCO 3 and 0.03 Gt CO 2 for an emergent reef area of 47.9 × 10 3 km 2. Based on the growth history of the submerged coral reefs in the Gulf of Carpentaria, maximum global Holocene CaCO 3 fluxes could have attained 0.3 Gt yr − 1 between 11 and 7 ka BP. This additional CaCO 3 would have culminated in a maximum CaCO 3 production from all (emergent and submerged) coral reefs of 1.2 Gt yr − 1 and neritic CaCO 3 production of 2.75 Gt yr − 1 . The dilemma remains that the global area and CaCO 3 mass of submerged coral reefs are currently unknown. It is inevitable that many more submerged coral reefs will be found. Our findings imply that submerged coral reefs are a small but fundamental source of Holocene neritic CaCO 3 and CO 2.