Vital effect on stable-isotope composition seen in foraminifera and coral skeletons

Stable-isotope composition of carbonate precipitated by hermatypic corals and associated benthonic foraminifera is strongly influenced by photosynthesis of symbiotic algae. In situ ¹⁴C and ⁴⁵Ca uptake experiments show that when photosynthesis increases, more light metabolic CO₂ is incorporated in the skeleton. This mechanism explains the non-equilibrium isotopic compositions previously reported for these organisms (as well as for planktonic foraminifera), and have important implications for palaeoenvironmental determinations based on stable-isotope analysis.