Calcium isotopic variations produced by biological, kinetic, radiogenic and nucleosynthetic processes

The research summarized here demonstrates that there are significant and systematic variations in the Ca isotopic composition of geological and biological materials. Most if not all of the natural isotopic fractionation has been interpreted in terms of kinetically controlled processes, but there has not yet been any measurement of the equilibrium isotopic partitioning. Laboratory studies demonstrate that some inorganic processes - diffusive transport in silicate liquids and precipitation of aragonite from aqueous solution - can fractionate Ca isotopes. In nature the effects of inorganic fractionation of Ca isotopes have not been demonstrated. Organic processes, however, clearly do fractionate Ca isotopes and hence the Ca isotope system may have its greatest geochemical value as a tracer of organic processes in the geologic record. There also appears to be a role for Ca isotopes in studies of the metabolism of higher organisms and for intracellular ion transport. The research to date suggests that Ca isotopes are fractionated within organisms mainly in the process of formation of mineral matter in bone or shell material. Copyright © Mineralogical Society of America.