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| Titel |
The temperature and precipitation reconstructions on Swiss stalagmites with a special emphasis on altitude gradient using noble-gases, δO-18 and δD of fluid inclusions |
| VerfasserIn |
Elaheh Ghadiri, Matthias Brennwald, Rolf Kipfer |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152856
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| Publikation (Nr.) |
 EGU/EGU2017-17755.pdf |
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| Zusammenfassung |
| We present the results of an application of ‘Combined Vacuum Crushing and Sieving
(CVCS)’ system (e.g., allowing to crush samples to defined grain size in vacuum) for the first
time to stalagmites grown in cold climates during the last glacial-interglacial transition, but at
different altitudes.
Recently, concentrations of dissolved atmospheric noble gases in fluid inclusions of
stalagmites were used to reconstruct past ambient cave temperatures, the annual mean
temperature and hydrological conditions when the water was trapped. To reconstruct
temperatures from noble gases (noble gas temperature: NGT) in water-filled inclusions, we
processed samples from Swiss stalagmites M6 from Milandre cave (400 m.a.s.l) and GEF1
from Grotte aux Fées cave (895 m.a.s.l) covering the climatic transitions Allerød–Younger
Dryas–Holocene.
Water content. The amount of water extracted per unit mass of calcite fabric (e.g., ‘water
yield’: WT) was shown to be a measure of the total water content. The data shows that the
WT systematically changes with δ18Ocalcite of the calcite. We therefore conclude that WT
records can be linked on changes in drip rates and thus can be used to track changes of past
precipitation even in cold regions.
Noble gases. Noble gas analysis shows that the annual mean temperatures in Milandre
cave were 2.2±2.0∘C during the late Allerød and dropped to 0±2∘C at the Younger Dryas.
Such temperatures close 0∘C indicate that drip water supply stopped in response to the
formation of permafrost conditions around the cave preventing further stalagmite growth.
However, one late Holocene sample gave a cave temperature of 8.7±1.4∘C agreeing
generally with present day annual mean temperature. The annual mean temperature of
5.7±1.3∘C from GEF1 was determined for the early Holocene. The observed data show
systematic variations with sample elevation, e.g., higher temperature from lower altitude
and vice versa. Combining the isotopic composition of water in fluid inclusions
(δ18Owater, δDwater) and the NGTs allows determining the δ18O–T relation (‘laps
rate’) in the past as both δ18O and T scale with altitude. This calibration is key as
paleo–temperatures are often reconstructed from δ18O, δD data whereby it is implicitly
assumed that the modern Δ(δ18Owater, δDwater)–ΔT relation is also valid for the past.
Our study makes an argument that noble gas analysis in stalagmites can also be a
new route to address this fundamental hypothesis of past climate reconstruction. |
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