科研之友
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摘要
We report results of C-13/C-12, O-18/O-16, and C-13-O-18 "clumped'' isotope analyses from a series of calcite precipitation experiments from aqueous solutions under laboratory conditions. Chemo-stat precipitation experiments were performed to synthetically form calcite from aqueous solution onto Ca-43-labeled calcite seed crystals. Formation rate was controlled during the experiments to investigate the effect of precipitation rate and temperature on C-13-O-18 bonding in calcite, where rates ranged from 10(-6.88) to 10(-8.20) mol m(-2) s(-1) at three temperatures (10, 20, and 30 degrees C). No relation was observed between precipitation rate and C-13-O-18 bonding proportion over the range of precipitation rates used. The relation between Delta(47) and temperature produced was comparable to calibration studies which report a relatively high sensitivity of C-13-O-18 bonding to temperature over the range investigated. Comparing solution conditions across multiple experimental data sets indicates an inverse relation between saturation state and C-13-O-18 bonding, where high super-saturation conditions are likely to be furthest from equilibrium C-13-O-18 partitioning. Carbon fractionation between calcite and HCO3(aq)- was found to be a temperature independent value of +1.6 parts per thousand. The temperature-dependent calcite-water O-18/O-16 fractionation relation determined in this study is slightly different (larger alpha(calcite-H2O) value) than those measured in several previous investigations. Significantly, we observe a dependence of the O-18/O-16 isotope fractionation factor on growth rate. Taken together, these findings suggest carbonate growth in our experiments approached equilibrium more closely than previous experiments of this type, yet did not achieve full O isotope equilibrium.
- 出版日期2018-3
