Within stalactites from Barbados caves, progressively younger calcite conical growth layers and central canal void-filling calcites contain smaller amounts of Sr and Mg. The observed distribution of Sr and Mg in the stalactites is in agreement with a solution-reprecipitation model in which calcite-to-calcite transitions within a low-Mg calcite vadose zone yield amounts of Sr and Mg decreasing with time to vadose water seeping into ventilated cavern macropores. Within the overall trend of decreasing Sr and Mg content, vadose seepage and speleothem calcites may become locally enriched in Sr and Mg when (1) the groundwater temperature decreases, thus affecting the temperature dependence of the calcite-water distribution coefficients for Sr (0.14 ± 0.02 at 25°C) and Mg (0.062 ± 0.015 at 27°C), or (2) meteoric waters bypass the upper vadose zone to dissolve low-Mg calcites of higher Sr and Mg content in the

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deeper parts of the vadose environment. As determined from radiocarbon dating, the stalactites have vertical growth rates of from 0.013 to 0.22 mm/yr and an average rate of lateral conical growth layer accretion of 0.006 mm/yr.

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