Magda Mandić

Modern C, O, and H isotope composition of speleothem and dripwater from Modrič Cave, eastern Adriatic coast (Croatia)

Modric Cave is a shallow horizontal cave situated in the middle of the eastern Adriatic coast (Croatia). The cave entrance is located 120 m from the coast at an altitude of 32 m above sea level, and due to its position on the SW slope of the Dinaridic mountain range, a Mediterranean climatic influence is dominant. Due to the stable environmental conditions [(15.6 ± 0.1) °C] Modric Cave was recognized as a potential site for detailed palaeoclimatic studies. Isotope analyses of modern carbonate speleothems, rain and dripwater were conducted in order to evaluate the isotopic equilibrium conditions. The δ18O composition of rain and cave seepage waters shows an absence of kinetic isotopic fractionation within the epikarst zone, whereas the relation between δ13C and δ18O in modern carbonate samples and dripwater suggests the isotopic equilibrium conditions during the carbonate deposition. These results contribute to a better understanding of the present-day isotopic composition and they provide a basis for interpretation of speleothem- derived palaeoclimatic records.

Note on the spring region of Gacka River (Croatia)

We present the first results of a study of the Gacka River spring area, an important Croatian drinking water resource. Stable isotope data (obtained at the Stable Isotope Laboratory SILab in Rijeka) are used in combination with hydrological and meteorological data. The δ18O values give information on the mean catchment altitudes of the three main springs of Gacka River (Majerovo vrelo, Tonkovića vrelo and Pećina). Hydrological, meteorological and stable isotope data indicate good mixing of infiltrated and ground waters. The precipitation d-excess shows a seasonally varying influence of continental and maritime air masses. †Revised version of a paper presented at the 9th. Symposium of the European Society for Isotope Research (ESIR), 23 to 28 June, Cluj-Napoca, Romania.

Concentration and stable carbon isotopic composition of CO2 in cave air of Postojnska jama, Slovenia

13 C airCO2 lower than in the outside atmosphere. Strong seasonal fluctuations in both parameters were observed at locations deeper in the cave, which are isolated from the cave air circulation. By using a binary mixing model of two sources of CO2, one of them being the atmospheric CO2, we show that the excess of CO 2 in the cave air has a δ 13 C value of -23.3 ± 0.7 ‰, in reasonable agreement with the previously measured soil-CO 2 δ 13 C values. The stable isotope data suggest that soil CO 2 is brought to the cave by drip water. Abstract: