The coprecipitation of cadmium with aragonite in seawater was experimentally investigated via the constant addition system. It was observed that Cd was weakly partitioned into aragonite. Partition coefficients of Cd (D_(Cd)) were restricted within the range of 0. 2 to 0. 9. Cadmium thus could be regarded as an incompatible element to aragonite. The values of D_(Cd) tend to increase with aragonite precipitation rates. The partition behavior of Cd in the aragonite-seawater system shows remarkable differences to what observed in the calcite-seawater system. It suggests that the coprecipitation of Cd with CaCO_3 would be fundamentally affected by the crystal structure of relative minerals. For the application of Cd/Ca ratios in marine calcium carbonates as proxies of paleo-oceanography, it should cautious to distinguish the mineralogy of relative proxy carriers.
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