CARBON FLUXES IN CORAL-REEFS .2. EULERIAN STUDY OF INORGANIC CARBON DYNAMICS AND MEASUREMENT OF AIR-SEA CO2 EXCHANGES

Air-sea CO2 exchanges and the partial pressure of CO2 were measured in surface water overlying 2 coral reefs: Moorea (French Polynesia, aust ral winter, August 1992), where coral diversity and surface cover are low, and Yonge Reef (Great Barrier Reef, austral summer, December 1993 ), where coral diversity and cover are comparatively higher. A procedu re is proposed to estimate the potential CO2 exchange with the atmosph ere by taking into account both the saturation level of oceanic seawat er and the equilibration process occurring after water leaves the reef . It is shown that both sites were net sources of CO2 to the atmospher e as a result of the effect of calcification on the dynamics of the in organic carbon system. The potential global CO2 evasion from the ocean to the atmosphere is about 4 times higher at Yonge Reef than at Moore a. It is also demonstrated that, at both sites, the major exchange of CO2 from sea to air occurs as seawater returns to chemical equilibrium after it has crossed and left the reef. The dynamics of inorganic car bon were studied using the so-called homogeneous buffer factor [beta = dln(pCO(2))/dln(DIC)] (where pCO(2) is the CO2 partial pressure in su rface water and DIC is dissolved inorganic carbon), which gave estimat es that approximately 80% of the change in inorganic carbon was relate d to photosynthesis and respiration. This approach showed that the cal cification rate was proportional to the net organic production during the day and to the respiration rate at night.