Calcium is a major dissolved species in seawater with a residence time of about a million years. Its sources include rivers and hydrothermal fluids, as well as small amounts via sediment diagenesis. Ca is also tied to the carbon cycle via carbonate precipitation in the oceans. The PI proposes that detailed measurements of Ca isotopic variations in present day Ca sources and sinks will shed light on the details of the oceanic Ca cycle. Such data could then be used to interpret past changes in Ca isotopic abundances, which would ultimately be related to climatic variability and changes in global carbonate preservation and temperature fluctuations. The PI has demonstrated the ability to make these unique measurements with the high precision necessary to study Ca cycling, and he proposes to make new measurements in existing samples of river water, hydrothermal fluids and marine sediments and basalts. These data, together with existing seawater results, would provide a signifcant advance in our understanding of the oceanic Ca cycle.
