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Influence of different physical conditions on stable isotopes of water and carbonates in Postojna Cave, Slovenia

Investigations of speleothems and cave environment can provide insights into climate and environmental changes. Postojna cave (Slovenia) is one of the most famous karst caves in South Eastern Europe. Numerous carbonate deposits (flowstone, speleothem) formed during last 50 ka can be used to investigate climate changes during the last Glacial and Holocene because variations in their growth rate and isotopic composition reflect climate changes on the land surface above the cave. There is also evidence that vegetation above the cave was changing during the past. Currently, the land area is covered by forest but 150 years ago there was a bare pasture, meadow. These recent changes in land use may additionally effect the cave environment. In planned work we will asses to which extent these changes can be reflected in isotopic composition of flowstone in the cave system. Additionally, there was also a change in cave structure itself through time. Some parts of the recent cave system were isolated at about 30 ka before present. These changes can be detected by isotopic investigations of speleothems also. We will test the hypothesis that changes in isotopic composition of speleothems on the path from the cave entrance to the deep and stable cave environment are related to seasonal changes in air circulation. There are pronounced winter and summer types of circulations with condensation of water in summer and evaporation in winter time. These seasonal variations should cause distinct differences in the isotopic composition of recent precipitated carbonates in young speleothem formation.

Postojna Cave; Isotopic composition; Stable isotopes; Carbonates; water

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