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Quaternary palaeoenvironmental records in secondary carbonate deposits from Croatian karst

Project Reconstruction of the Quaternary environment in Croatia using isotope methods studies regional response of the karst environment in Croatia to global changes during the Quaternary, and especially the response of various carbonates to palaeoenvironmental changes and relations among them. Various carbonate sediments from different climate zones are studied: speleothems from 3 locations in littoral Croatia (Modrič Cave), mountainous Gorski Kotar region (Lokvarka Cave) and central Croatia (Nova Grgosova Cave), lake sediments from the Plitvice Lakes, tufa deposits from the Zrmanja River, and marine algal rims from several locations along the eastern Adriatic coast. Speleothems were collected in the 3 caves combined with 2-year monitoring of environmental conditions in the caves in order to determine stability of cave atmosphere vital for palaeoclimate studies. Additionally, stable isotopes (δ2H and δ18O) in rainwater and drip water as well as stable isotopes (δ13C and δ18O) in speleothems from Modrič and Lokvarka caves were analysed. Stable microclimate conditions were identified in all caves, which, together with significantly attenuated seasonal variations of stable isotopes in drip water, make all three caves suitable for palaeoclimatic studies. Age of the speleothems from Nova Grgosova Cave and Modrič Cave was determined by U-Th method, while radiocarbon dating was applied to the Lokvarka Cave speleothems. Study of algal rims along the eastern coast of the Adriatic Sea included monitoring, sampling and isotope measurements. Additionally, radiocarbon analyses of modern, pre-bomb marine organisms collected along the eastern Adriatic coast were performed in order to calculate and compare marine 14C reservoir ages (R) and regional offsets (∆R). The marine reservoir ages of shells and algae significantly differ, even though both inhabit the hard substrate from the intertidal zone to shallow sea. Lake sediment cores, the top 30 - 40 cm, were taken from various locations in two lakes of the Plitvice Lakes system and isotope, CHN and mineralogical analyses were completed. Isotope analyses included a14C and 13C in carbonate and organic fractions of the sediment. It was demonstrated that both fractions analysed simultaneously give a good overview of the processes in the lakes. It was established that the geochemical and isotopic composition of sediments is determined by lake's environmental conditions. 14C dating of tufa deposits from the Zrmanja River was also performed combined with the water chemistry. Holocene origin of the tufa deposits was proven and conditions of tufa deposition along the Zrmanja River were also determined. Further researches are aimed at identifying tufa deposits from older interglacial periods. Project Reconstruction of the Quaternary environment in Croatia using isotope methods (HRZZ-IP-11-2013-1623) was funded by the Croatian Science Foundation.

Palaeoenvironmental changes, Quaternary, karst, Croatia

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