Influence of precipitation rate and temperature on the partitioning of magnesium and strontium in calcite overgrowths

To study the incorporation of magnesium (Mg) and strontium (Sr) in calcite precipitated over synthetic calcite seeds (overgrowths) as a function of the precipitation rate (R*, mu mol/m(2) h), we performed precipitation experiments wherein temperature and precipitation rates were decoupled at intervals of approximately 3.63-5.22 mu mol/m(2) h. In most sample reactions, high-magnesium calcite (HMC) overgrowths co-precipitated with aragonite from the stirred solutions exposed to an atmosphere of NH3 and CO2 gases throughout the spontaneous decomposition of (NH4)(2)CO3. The percentage of aragonite in the solid CaCO3 increased with both temperature and dissolved inorganic carbon (DIC). The order of reaction with respect to the [DIC] is temperature dependent and is 1.9, 2.4, and 2.9 at temperatures of 12.5, 25.0, and 37.5 degrees C, respectively. The magnesium distribution coefficient (D-Mg) increases significantly with increasing R*, temperature, and Mg/Ca ratio in the fluid. The strontium distribution coefficient (D-Sr) increases with R* and with increasing MgCO3 concentrations in the calcite overgrowths. However, it is independent of temperature.

Automated summary

This study investigates the incorporation of magnesium (Mg) and strontium (Sr) in calcite precipitates under different precipitation rates, temperatures, and dissolved inorganic carbon concentrations. The results show that the percentage of Mg and Sr in calcite increases with increasing temperature and dissolved inorganic carbon concentration. Additionally, the precipitation rate and Mg/Ca ratio in the fluid also influence the distribution of Mg and Sr in calcite.