[Significance]Calcium(Ca)is a major rock-forming and biological nutrient element,which actively par-ticipates in geochemical cycling processes of the Earth's surface,recording the marine environment and its evolution.Owing to various degrees of fractionation by inorganic and organic processes in Earth's surface environment,calcium isotopes are a powerful tool for tracing marine calcium cycle and interactions between Spheres of the Earth.With the development of analysis techniques,calcium isotopes have become an important research method in the field of geo-chemistry.Given the extensive application of calcium isotopes in paleoceanography,it is necessary to provide a re-view.[Methods]On the basis of previous literature,this comprehensive review first introduced the fundamental prin-ciples and fractionation mechanisms of calcium isotopes,the features of the marine calcium cycle,and its isotopes.Based on the current research progress and trend,the main applications of calcium isotopes for paleoceanography,in-cluding the evaluation of carbonate diagenesis,the determination of seawater calcium isotope compositions,and the reconstruction of marine calcium cycle in deep time,are further summarized.Finally,suggestions for the future de-velopment of calcium isotopes in the field of paleoceanography are proposed,which might help promote studies on the deep-time calcium cycle.[Conclusions and Prospects]As a key in researching marine calcium cycle,calcium iso-topes gradually become an important tool.Knowledge of calcium isotopic fractionation mechanisms for different miner-al systems is established preliminary.Fluxes of marine calcium sources and sinks and their calcium isotopic composi-tions are determined roughly.In the future,it would be effective to enhance the understanding of calcium cycle by im-proving the measurement and analysis technology,optimizing theories of calcium isotopic fractionation mechanisms and calcium isotopic evolution curve of seawater in deep time,and conducting multi-proxy and quantitative research about the change of fluxes,calcium isotopic compositions and controlling factors for different calcium sources and sinks.
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