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| Titel |
StalAge - A new algorithm especially designed for the construction of speleothem age-depth models |
| VerfasserIn |
Denis Scholz, Dirk Hoffmann |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039135
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| Zusammenfassung |
| A standard approach to construct age-depth models for speleothems on the basis of
230Th/U-ages is not available yet. Some studies apply linear interpolation between dated
depths; others use least squares polynomial fits. Other authors, in turn, use various kinds of
splines or even more sophisticated methods based on the general growth mechanisms of
speleothems. A general approach to estimate the uncertainty of stalagmite age models has
neither been developed yet. Since the exact determination of the timing and duration of
climatic events recorded in speleothem calcite depends on the method used to calculate the
age model, a general technique for the calculation of both the age model and its uncertainty is
urgently needed.
Here we present a new algorithm, especially designed for constructing age-depth models
based on speleothem 230Th/U-ages. The algorithm relies on two basic assumptions: (i)
the age model must increase monotonically with increasing distance from top of
the stalagmite, and (ii) if possible within the associated error bars, the simplest
age-depth relationship (i.e., a straight line) is fitted to the age data. Whereas the
first assumption simply arises from the absolute constraint of increasing age with
increasing distance from top, the second assumption avoids over-interpretation of the age
data.
The performance of the algorithm was tested using synthetic speleothem age data. For
this purpose, a numerical model simulating (i) speleothem growth, (ii) incorporation and
temporal evolution of U-series isotopes and (iii) mass spectrometric analysis was developed.
This allows simulation of extreme scenarios, such as stalagmite sections including obvious
outliers, age inversions and pronounced detrital contamination, and also to test the
performance and robustness of the algorithm under these conditions.
The developed algorithm has distinct advantages in comparison with the existing
methods. Firstly, it is very robust. Outliers and age inversions are automatically detected and
taken into account for the calculation of the age model and its uncertainty. The uncertainty in
such sections is appropriately enlarged and, thus, probably more realistic than that calculated
by other methods. Secondly, the inclusion of the monotonicity criterion provides additional
information apart from the 230Th/U-ages and the corresponding errors. This results
in smaller errors than those calculated by other methods in sections without age
inversions.
The algorithm is written in the free statistical software R and will be made available as a
free download to the speleothem community. |
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