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| Titel |
Modification of the δ¹⁸O value of meteoric water to cave drip water and speleothem calcite |
| VerfasserIn |
Anne Wackerbarth, Denis Scholz, Jens Fohlmeister, Augusto Mangini |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Datensatznummer |
250035489
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| Zusammenfassung |
| Stable isotope signals of speleothems have proved to be valuable archives for past climate
variability in recent years. They provide the possibility of precise dating using the
Th/U-method and allow high resolution isotope analyses. The stable isotope signal of
stalagmites strongly depends on the isotopic composition of the drip water which is affected
by climate parameters, vegetation parameters and the residence time in the soil and epikarst
layer.
To understand how the δ18O value of drip water and stalagmite calcite is influenced by
climate parameters, we developed the Drip Water Model, where the input parameters are:
temperature, amount of cave infiltration, air humidity, the type of vegetation and the CO2
content of soil air.
The δ18O value of precipitation is determined in dependency on temperature by a linear data
fit. Evapotranspiration modifies both, the isotopic composition and the amount of drip water,
since evaporation is accompanied by kinetic fractionation while transpiration is not. Hence,
depending on the ratio of evaporation to transpiration the soil water is enriched in heavy
oxygen. Evapotranspiration is higher in the warmer months, leading to a larger contribution
of winter precipitation to drip water.
The model establishes a weighting function for the δ18O value of a monthly water parcel and
determines its contribution to the annual mean composition of speleothem calcite. The Ca2+
content decides how much calcite is able to precipitate from the water parcel. The model
shows that despite that the CO2 content of soil air being higher in summer than in
winter, the Ca2+ content of drip water is lower in summer than in winter when
the residence time of the water in the soil and epikarst is in only in the range of
few months. This results in even stronger weight of cooler months on the isotopic
composition of stalagmites from Atta Cave, Bunker Cave and B7 Cave in Central
Europe.
The reversed model enables us to tentatively reconstruct average temperatures of past times
from δ18O record from stalagmites. This model takes into account the correlation between the
amount of winter precipitation and temperature in Central Europe which is attributed to the
North Atlantic Oscillation.
The results show a clear anticorrelation of cave temperature and the δ18O value of
speleothem calcite, as observed in samples throughout North and Central Europe. |
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