Calcium isotopes as tracers of biogeochemical processes

The prevalence of calcium as a major cation in surface and oceanic environments, the necessity of calcium in the functioning of living cells and bone growth, and the large spread in mass between calcium isotopes all suggest that calcium isotope biogeochemistry can be an important avenue of insight into past and present biogeochemical cycling processes. In the following chapter, we review the main areas of research where Ca isotope studies have been pursued and detail recent research results in biogeochemical applications. In marine environments, biogenic fractionation of Ca isotopes during biomineralization produces predictable offsets in some organisms, which facilitate the reconstruction of seawater δ^44/40Ca over geologic timescales. In terrestrial studies, observed Ca isotope fractionation between soil and various components of vegetation enables the construction of a local Ca budget and provides a partial explanation for the scale of Ca isotopic variability within a single watershed. The research reviewed in this chapter provides a foundation for future investigations into the macroand microscopic processes and biochemical pathways dictating the distribution of this essential nutrient using stable Ca isotope ratios.