BIOLOGICAL-CONTROL OF AIR-SEA CO2 FLUXES - EFFECT OF PHOTOSYNTHETIC AND CALCIFYING MARINE ORGANISMS AND ECOSYSTEMS

A simple expression enables prediction of the effect of photosynthetic and calcifying systems on air-sea CO2 exchange at all spatial scales (from organism to ecosystem). Input data are: grass primary production (P-g), respiration (R), net calcification (G) and the ratio of CO2 re leased to CaCO3 precipitated (psi); the output is the amount of dissol ved inorganic carbon (F-CO2) which needs to be exchanged with the atmo sphere to balance biologically mediated changes in the concentration o f dissolved inorganic carbon in an open sea water system: F-CO2 = -P-g + R + psi G. Coral reef data were used in the model to illustrate the relative influence of organic and inorganic carbon metabolism on ocea n-atmosphere CO2 cycling. A coral reef comprised of calcareous and non -calcareous organisms can be shown to act as a sink for atmospheric CO 2 when excess (= net) production is high and CaCO3 precipitation is lo w. These characteristics are not typical of actively developing reef s ystems which typically exhibit a nearly balanced organic carbon metabo lism (P-g/R approximate to 1) and relatively high rates of calcificati on. In these circumstances, reef communities can be expected to cause CO2 evasion to the atmosphere. This prediction is confirmed by the onl y existing measurement of air-sea CO2 flux in a coral reef system.