Distribution of the fugacity of carbon dioxide in the surface seawater of the Great Barrier Reef

The CO2 fugacity (fCO2) measurements in offshore and lagoonal surface waters were carried out along a ship track of more than 2000 km in and around the Great Barrier Reef (GBR). The surface water in the lagoon of the GBR exhibited higher fCO2 than oceanic water by about 15 μatm, which was mainly due to the on-going calcification in the reef. The transition zones between the lagoonal and offshore waters varied from less than 10 km to over 100 km in width, which might be related to the development of reef, width of passage, and mesoscale seawater circulation. Estimate of net CO2 flux associated with reef calcification was available from independent data sets: fCO2 measurements of the present study and Kinsey and Hopleyʹs [Palaeogeogr., Palaeoclimatol., Palaeoecol. 89 (1991) 363.] estimate of bulk calcium carbonate deposition. These two estimates were of the same order. Consideration of similar results from coral reefs developed around oceanic islands in the Indo-Pacific region, including Majuro Atoll, South Male Atoll, and Palau Barrier Reef, together with our observations at the GBR allowed us to draw the conclusion that coral reefs are a potential source for atmospheric CO2.