engleski

Stable isotope study of dripping warer in Postojna cave

Speleothems are secondary carbonate deposits which form often cave systems in karst and consist of several forms such as stalagmites, stalactites and flowstone. They are deposited from groundwaters with increased carbon dioxide concentration. This carbon dioxide is derived from the high partial pressure of CO2 in the soil atmosphere, generated by microbial processes and root respiration. Stalagmites and stalactites are formed by the degassing of ground waters from drip sources within caves, and flowstone is formed by the same mechanism, but in higher-discharge cave steeps and streams. The oxygen isotope composition of cave seepage water depends not only on the average value of precipitation, but also on evaporation processes occurring in the epikarst zone. The d13C values of speleothems can provide important paleoclimatic information because the carbon isotopic composition of seepage water is strongly influenced by the uptake of soil-CO2. The d13C values of the water will depend on whether the soil CO2 is derived from C3 type vegetation with the Calvin-Benson photosynthetic pathway or from C4 type vegetation with a Hatch-Slack photosynthetic pathway. Water samples were collected monthly in three different locations in the Postojna cave. The sampling locations were chosen to cover all types of cave water as well as varying positions relative to the thickness of the rock cover. Samples were collected also from the river Pivka and spring Močilnik. The results of a year-round measurements of d13C and d18O in karst waters will be presented.

karst; stable isotopes; speleothems

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