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: gross primary production (P,), respiration (R), net calcification (G) and the ratio of CO? released to C a C 0 3 precipitated (W); the output IS the amount of dissolved inorganic carbon (F,,?) whlch needs to be exchanged with the atmosphere to balance b~ologically m e d ~a t e d changes in the concentration of d~ssolved inorganic carbon In an open sea water system: Fro? = -Pg + R + VG. Coral reef data were used in the model to illustrate the relatlve influence of organic and inorganic carbon metabolism on ocean-atmosphere COZ cycling. A coral reef comprised of calcareous and non-calcareous organisms can be shown to act a s a sink for atmospheric CO2 when excess (= net) production is high and C a C 0 3 precipitation 1s low. These charactenstlcs are not typical of actively developing reef systems whlch typically exhibit a nearly balanced organic carbon metabolism (PgIR = 1) and relatively high rates of calcification. In these circumstances, reef communities can be expected to cause CO2 evasion to the atmosphere. This prediction is confirmed by the only existing measurement of air-sea CO2 flux in a coral reef system.