The processes that govern the incorporation of (trace) elements into speleothems can often be linked to environmental changes. Although element incorporation into speleothem calcite is now reasonably well understood, current knowledge regarding trace element variability in speleothem aragonite is very limited. Of particular interest is whether trace element distribution coefficients are above or below one in order to assess the extent to which prior aragonite precipitation has affected speleothem aragonite trace element records. This study uses nine calcite-to-aragonite transitions in seven speleothems from diverse environmental settings to derive the first quantitative estimates of the distribution coefficients for several elements in speleothem aragonite: DMg(Ar) = 9.7E−5 ± 9.01E−5, DBa(Ar) = 0.91 ± 0.88, DSr(Ar) = 1.38 ± 0.53, and DU(Ar) = 6.26 ± 4.54 (1σ SD). For one speleothem from western Germany, the distribution coefficients are generally higher, which is potentially related to the very low growth rates (<11 μm/year) of this sample. In particular, DSr(Ar) appears to show a negative correlation with growth rate when growth rate is below 20 μm/year. In summary, our results demonstrate that speleothem aragonite DMg(Ar) is below one, DU(Ar) is considerably above one, and DSr(Ar) is above one or close to unity. For DBa(Ar), reaching a similar conclusion is difficult due to the relatively high uncertainty. Enhanced prior aragonite precipitation will thus result in lower U and higher Mg concentrations in speleothem aragonite, although in many cases Mg in speleothem aragonite is most likely dominated by other processes. This result suggests that U concentrations in aragonitic stalagmites could serve as a very effective proxy for palaeo-rainfall.
Bibliographical noteFunding Information:
This work is funded by the DFG ( WA3532/1-1 ) to J.A. Wassenburg and internal funding at the University of Mainz. D. Scholz also acknowledges funding of the DFG ( SCHO1274/9-1 ). J. Baldini acknowledges the funding of ERC Grant 240167 . Ian Fairchild is thanked for providing trace element data from stalagmite CL26, and associated uncertainties of Ba and U data. S. Mischel and Y. Kocot are acknowledged for providing cave air CO 2 concentrations from Hüttenbläserschachthöhle. J. Fietzke and Angela Min are thanked for performing the chemistry and measurements of the U/Th ages of flowstone MO and stalagmite MAW4, respectively. Cecilia Cetti is thanked for earlier work on stalagmite MAW4, whereas C. Myers is thanked for fieldwork assistance and providing sample KRUM11. The Bochum thin section lab is acknowledged for making the thin sections of stalagmites MAW4 and KRUM11. B. Stoll, U. Weis and B. Schwager are gratefully acknowledged for their help with measurements and chemistry performed at the Max-Planck-Institute for Chemistry, while L. Zehnder (ETH Zürich) is thanked for support with XRD analyses. D. Tremaine and three anonymous reviewers are thanked for their constructive comments on earlier versions of the manuscript, and the editorial handling by M. Bar-Matthews is greatly acknowledged.
© 2016 Elsevier Ltd
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- Distribution coefficient
- Trace element