Gattuso J.-P., Pichon M., Jaubert J., Marchioretti M. & Frankignoulle M., 1996. Primary production, calcification and air-sea CO2 fluxes in coral reefs: organism, ecosystem and global scales. Bulletin de l'Institut Océanographique n° spec. 14(4): 39-46.




Abstract

We summarize here data on primary productivity, calcification and air-sea CO2 fluxes collected from a reef coral, a reef flat and a reef mesocosm and present a discussion on the global effect of marine calcification on atmospheric CO2. The respective effects of CO2 uptake by photosynthesis and CO2 release by respiration and calcification on the carbon budget of a zooxanthellate scleractinian coral were investigated in the laboratory. The air-sea CO2 flux was inferred by modelling the CO2 system. Its integration showed that the direction of the net daily flux is from sea to air (evasion). Measurements of gross production and respiration of the 'Tiahura barrier reef' (Moorea, French Polynesia) showed that the reef displayed a very small excess production. Net calcification was positive both during the day and at night. The measured air-sea CO2 fluxes were close to zero in the open ocean but displayed a strong daily pattern at the reef front and the back reef. Integration of the fluxes over 24-h showed that the reef ecosystem was a source of CO2 to the atmosphere. Other investigations include a comparison of the main metabolic features of a 40 m3 reef mesocosm set up in Monaco to those of a Red Sea coral patch enclosed in situ in a 6 m3 chamber. The budget of organic production/consumption of the mesocosm reef was slightly negative while that of the coral patch was slightly positive. The captive reef and the coral patch exhibited high rates of precipitation and dissolution of CaCO3 but the 24 h budgets of both systems were positive (net CaCO3 deposition). The role of marine calcification as a source of dissolved CO2 is due to chemical equilibria and is therefore a function of the partial pressure of CO2 in seawater (pCO2). The present ratio of released CO2/precipitated carbonate is 0.6 and calculations show that it will rise up to 0.76 for a doubling of the pre-industrial pCO2. This would result in a net CO2 source of approximately 2% of the present day fossil fuel flux.


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