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Speleothems as archives of Quaternary palaeoenvironmental changes in Croatian karst – isotopic approach

Speleothems, as secondary carbonate deposits precipitated within the caves, record series of data related to the changes in the atmosphere, biosphere, hydrosphere and lithosphere during their deposition. Reconstruction of many of those environmental changes is based on speleothems’ isotopic compositions, particularly on their temporal variations. Both stable and radioactive isotopes are used to provide insight into past events either for chronostratigraphic purposes (U-Th series, 14C), for the interpretation of varying temperature and rainfall composition (δ18O, δD), for the vegetation changes (δ13C) or as palaeothermometer ('clumped isotopes' i.e. Δ47). Speleothems stand out among other archives, e.g. ice cores, deep sea cores, lake sediments etc., due to their: i) very precise chronology ; ii) high-resolution proxy records ; iii) geographical distribution in regions omitted by ice and marine cores ; iv) precipitation reflecting mean annual climate conditions ; v) cave environment well protected from exogenic impacts ; vi) simplicity of preservation for future studies, etc. However, there are still some weaknesses of the dating methods (unknown initial 14C activity or presence of initial 230Th), and of arguable reliability of δ18O and δ13C signals due to their dependence of many different variables. Nevertheless, isotope-based speleothem studies are worldwide accepted and Croatia, with its classical Dinaric karst and thousands of caves, offers exquisite potential for such researches. From the late 1990’s on, speleothems were used for the reconstruction of the palaeoenvironments above and below sea-level. Ten submerged caves (18 speleothems) have been encompassed into the sea-level reconstruction, while 15 subaerial caves (>30 speleothems) have undergone researches aimed to the reconstructions of the palaeoclimate changes. In order to provide insight into contemporary geochemical settings and hydrogeological behaviour of the rain- and dripwater, and modern carbonate deposition, recent studies are complemented with thorough monitoring program. In spite of relatively small surface, Croatia occupies important geographical position in terms of distribution of the air masses between continental Europe and Mediterranean. Thus, the main objectives of these researches are evaluation of dominant influences throughout the Quaternary and estimation of the resulting climate and overall environmental settings which should be starting point for the projections of the changes to come.

speleothems; isotopes; palaeoenvironment; Quaternary; Croatia

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