Calcification in coccolithophorids requires major intracellular fluxes
of inorganic carbon and calcium. This paper summarises the major cell
ular fluxes of substrates and products of calcification described in a
simple four compartment model (cytosol, Golgi, coccolith vesicle and
chloroplast). Measurements of the cytosolic and intra-coccolith vesicl
e pH and electrical potentials across the plasma membrane and coccolit
h vesicle membrane allow calculations of the proton electrochemical gr
adients across these membranes and estimates of the free carbonate and
calcium concentrations in the coccolith vesicle. Calcification may pr
ovide a relatively low cost route for elevating the concentration of c
arbon dioxide in the chloroplast. This may have benefits in terms of t
he nutrient requirements for photosynthesis and growth, In particular,
a close relationship appears to exist between calcification and the a
vailability of phosphorus which may correlate with the occurrence of l
arge scale blooms of Emiliania huxleyi in the North Atlantic.