 |
| Titel |
Monitoring of Bunker Cave (NW Germany): Assessing the complexity of cave environmental parameters |
| VerfasserIn |
Dana F. C. Riechelmann, Andrea Schröder-Ritzrau, Denis Scholz, Christoph Spötl, Detlev K. Richter, Augusto Mangini |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039715
|
|
|
|
|
|
| Zusammenfassung |
| Bunker Cave (N 51Ë 22’03”, E 7Ë 39’53”) is located in the Rhenish Slate Mountains in the
western part of Germany and is part of a giant cave system in the area of Iserlohn
(Hammerschmidt et al., 1995).As part of the DAPHNE (Dated Speleothems - archives of
the paleoenvironment) project Bunker Cave is being monitored since the end of
2006.
The ongoing monitoring program is performed on a monthly base. Surface climate
parameters are measured and samples of rain water, cave air, drip water at eight different drip
sites and modern calcite precipitates from watch glasses placed beneath drip sites are
collected.
Data sets include temperature, precipitation, calculated infiltration, drip rates, electric
conductivity, pH, alkalinity, cations, anions and stable isotopes.
Bunker Cave shows a constant temperature throughout the year. Active calcite
precipitation is higher in winter than in summer, which is due to lower cave pCO2 in winter.
The generally low pCO2 values, however, support almost continuous calcite precipitation
throughout the whole year.
Drip water δ18O values reflect the mean annual isotopic composition of the rainfall in this
area with no or less contribution of the summer rain. The slope of the MWL for local
precipitation is close to the slope of both the global MWL and the local MWL at the nearby
station Bad Salzuflen. The karst aquifer is well mixed as shown by the uniform drip water
δ18O values. Hence, the site is well suited to detect multi-annual climate trends using
stalagmite stable isotope records.
In order to test the potential influence of kinetic isotope fractionation on the stable isotope
signals at Bunker Cave, stable isotope data of modern calcite precipitated on watch glasses
were compared to predicted values. Comparison of the δ18O values of in situ modern calcite
precipitates with the δ18O values expected from equilibrium isotope fractionation suggests a
small kinetic influence, which is probably related to the variability in drip rate (Mühlinghaus
et al., 2009).
The coefficient of variation of discharge versus the mean discharge for each drip
site, allows distinguishing between different discharge behaviours (Baker et al.,
1997). Seasonal drips with up to 15 ml/min as well as seepage flow with 0.002
ml/min are monitored. Most of the eight drip sites show a consistent annual drip-rate
pattern with a delay of several months compared to the main infiltration events. An
instantaneous response to precipitation (i.e., piston-flow) is not observed at any drip
site pointing towards a specific water capacity threshold in the soil and the karst
aquifer.
The dominant aqueous species in the drip water are [Ca2+] and [HCO3-]. However,
[SO42-] also shows high concentrations. The temporal variability in the chemical
composition of the drip-water indicates different processes. Dilution and the influence of
prior calcite precipitation are clearly distinguishable, especially during times of lower
discharge.
Baker, A., Barnes, W.L. , Smart, P.L., 1997. Stalagmite drip discharge and organic matter
variation in Lower Cave, Bristol. Hydrological Processes 11, 1541-1556.
Hammerschmidt, E., Niggemann, S., Grebe, W., Oelze, R., Brix, M.R., Richter,D. K.,
1995. Höhlen in Iserlohn. Schriften zur Karst- und Höhlenkunde in Westfalen Heft 1, 153
S.
Mühlinghaus, C., Scholz, D., Mangini, A., 2009. Modeling fractionation of
stable isotopes in stalagmites. Geochimica et Cosmochimica Acta, 73, 7275-7289. |
|
|
|
|
|
|