Elucidating modern geochemical cycles at local, regional, and global scales using calcium isotopes

In Earth's surface environment, calcium (Ca) is an important mobile metal that is actively and passively transported in solution and within organic and mineral phases, being cycled and recycled during various biogeochemical processes. With the development of modern mass spectrometric techniques small variations in the stable and radiogenic isotopic compositions of Ca can be measured, revealing insight in these complex biogeochemical cycles and tracing and quantifying components across a range of spatial and temporal scales similar to other more routine isotope systems. More than three decades of work reveal systematic variations in the partitioning of Ca isotopes due to both abiotic and biological processes. An overview of processes that fractionate Ca isotopes at local, regional, and global scales is outlined here. We present detailed examples of instances in which Ca isotopes have provided unique insight into the functioning of Earth surface processes and the cycling of Ca at multiple scales. Future studies should target questions for which Ca isotopic analysis provide unique insight and, when combined with other isotope and trace element mull-proxy studies, better constrain the system of interest. M the same time, we challenge the scientific community to explore new frontiers including polar regions and other extreme environments.