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| Titel |
No impact of ionic strength/salinity on divalent cation fractionation during inorganic calcite precipitation |
| VerfasserIn |
J. Tang, A. Niedermayer, S. J. Köhler, M. Dietzel, F. Böhm, B. Kisakurek, A. Eisenhauer |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027931
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| Zusammenfassung |
| In order to apply divalent cation fractionation (44Ca/40Ca, Sr/Ca, etc.) during calcium
carbonate formation as a proxy to reconstruct paleo-environments, it is essential to evaluate
the impact of various environmental factors. In this study, the CO2 Diffusion Technique
(Dietzel et al., 2004) was used to crystallize inorganic calcite from aqueous solutions at
different ionic strength/salinity by the addition of NaCl.
Results show that at 25Ë C the discrimination of Sr/Ca in the precipitated calcite is
controlled by the precipitation rate (R in μmol/m2/h). The apparent Sr distribution
coefficients (log DSr) of calcite are positive linear related to the log R values. However, the
data points of log DSr vs. log R fall in the same line for all experiments done at I = 0.0353,
0.292, and 0.8353, respectively. This indicates that Sr/Ca fractionation during inorganic
calcite formation is not significantly influenced by ionic strength/salinity.
In analogy to Sr/Ca, the 44Ca/40Ca fractionation is not influenced by ionic
strength/salinity either. At 25Ë C the calcium isotope fractionation between calcite and
aqueous calcium ions (Î44-40Cacalcite-aq = δ44-40Cacalcite - δ44-40Caaq) correlates
negatively with log R values for all the experiments, independent of the respective I
value.
Tang et al. (2008) reported a negative linear relationship between Î44-40Cacalcite-aq and
log DSr during calcite formation, which is independent of temperature, precipitation rate, and
aqueous (Sr/Ca)aq ratio. The results of our recent experiments at 25Ë C and various I values
indicate that this general behavior is not affected by ionic strength/salinity.
References
Dietzel M., Gussone N., and Eisenhauer A. (2004) Co-precipitation of Sr2+ and Ba2+
with aragonite by membrane diffusion of CO2 between 10 and 50ºC. Chemical Geology, 203,
139-151.
Tang J., Dietzel M., Böhm F., Köhler S.J., and Eisenhauer A. (2008) Sr2+/Ca2+ and
44Ca/40Ca fractionation during inorganic calcite formation: II. Ca isotopes. Geochim.
Cosmochim. Acta, 72, 3733-3745. |
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