Monitoring of selected caves as a prerequisite for the speleothem-based reconstruction of the Quaternary environment in Croatia.

Abstract Quaternary palaeo-environmental changes that have taken place in Croatia are likely to be recorded in speleothems – secondary carbonate deposits precipitated in caves. Confident interpretation of well dated speleothem proxy records relies on modern monitoring programs, which we provided in three regionally different caves. Parallel monitoring of the surface and cave air temperature and relative humidity, precipitation and cave drip intensity, as well as stable isotope modification of meteoric and drip water was carried out in order to estimate the most reliable stalagmites for the interpretation of Quaternary landscape history. In all three caves, Nova Grgosova (239 m a.s.l.; T cave = 11.2 °C) in central Croatia, Lokvarka (780 m a.s.l.; T cave = 7.5 °C) in the mountainous part of Croatia, and Modrič (32 m a.s.l.; T cave = 16.6 °C) in coastal Croatia, we selected the parts of the caves where the ambient cave conditions appeared to be appropriate for equilibrium deposition of calcite in terms of constant air temperature (seasonal amplitudes of 0.73, 0.38 and 0.45 °C, respectively) and relative humidity (100%). Both Atlantic and Mediterranean moisture influences were detected in all three caves, but of different intensities. Cave hydrological settings governed by karst aquifer properties were resolved by the comparison of the precipitation intensities and drip site responses to the rain events, and generally, seasonal rainwater isotopic signal was almost completely attenuated, except for one drip site. Such homogenized drip water and stable cave environmental settings give confidence for calcite deposition under equilibrium conditions, especially for Modrič and Nova Grgosova caves where speleothems' inner structures also look promising for potentially quality dating results and stable isotopic profiles. The fracture-flow drip regime of selected drip sites in Lokvarka Cave, and uncompleted homogenization of the water in the epikarst might point to speleothem samples that are unsuitable for resolving multi-annual Quaternary climate changes. This view is supported by the high porosity internal structure of some Lokvarka speleothems, so further monitoring, sampling and the thorough speleothem examination is therefore necessary for adequate interpretations of palaeo-environmental changes. [ABSTRACT FROM AUTHOR]