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| Titel |
A new 14C groundwater dating approach, applied to an aquifer in North-West India |
| VerfasserIn |
M. Wieser, J. Fohlmeister, R. D. Deshpande, I. Hajdas, W. Aeschbach-Hertig, S. K. Gupta |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063437
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| Zusammenfassung |
| 14C is the only dating tracer to estimate groundwater ages ranging from several
hundred years up to 40 ka. However, radiocarbon dating of dissolved inorganic
carbon in groundwater implies some major complications due to open or closed
system equilibration with soil CO2 and related isotope fractionation, as well as
calcite dissolution during infiltration or later. Numerous models exist to estimate the
resulting so-called hardwater effect using different physical perspectives. Some models
constrain open or closed system situations, while others neglect crucial effects such as
carbonate exchange with the aquifer matrix. These influences, when considered
incorrectly, may lead to misinterpretation of older radiocarbon ages by several thousand
years.
Here we introduce a new correction approach for the hardwater effect in groundwater, by
transferring a model that has been developed for the study of cave dripwater [1]. It is applied
along with several established models to account for the hardwater effect to a multitracer
palaeoclimate study of a groundwater aquifer in North-West India. The new model simulates
a mixed open and closed system equilibration based on hydrogeochemical correlations.
Advantages and shortcomings of the used models are compared and discussed.
Furthermore, a quantitative method to consider matrix exchange for the new as well as for
traditional models is applied. Finally, the resulting 14C ages are calibrated with the
IntCal09 database to obtain calibrated ages also for the groundwater archive. Thus, the
variable input curve of 14C in the atmosphere is considered, which is not the case in
most hydrologic age records, misinterpreting old radiocarbon ages by up to 3000
years.
Applying this approach to the example from India, a groundwater age scale is established. Its
age reaches from recent to late Pleistocene times, enabling palaeoclimatic reconstruction of
the information contained in the archive.
[1] Fohlmeister, J., et al. (2011), Modelling Carbon Isotopes of Carbonates in
Cave Drip Water, Geochimica et Cosmochimica Acta, 75(18), 5219 – 5228,
doi:10.1016/j.gca.2011.06.023. |
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