engleski

Reconstruction of the karst Quaternary environment in Croatia based on radiocarbon results

Interdisciplinary multi-proxy study of paleoclimate and paleoenvironment in the Croatian karst region was performed within the project “Reconstruction of the Quaternary environment in Croatia using isotope methods”. Dinaric karst occupies about half of the Croatian territory, encompassing continental and coastal areas and different climate zones, and is characterized by intensive carbonate precipitation in form of tufa, speleothem, lake sediment and algal rims. Various carbonate sediments were studied (speleothems from 3 caves, lake sediments from the Plitvice Lakes, tufa deposits from the Zrmanja River area, marine algal rims from several locations along the eastern Adriatic coast) with the aim of estimation of the regional response of the karst environment to global changes during the Quaternary, and to determine specificities of each carbonate system. A summary of the project results will be presented here. Radiocarbon dating revealed two groups with the ¹⁴C ages <11, 000 BP (all types of sediments) and >30, 000 BP (speleothem and tufa). The speleothem and tufa samples from the latter group were dated by the U-Th series method up to MIS 10 and MIS 5 stages, respectively. The Holocene ages ranged from about 11, 000 BP (speleothems) to the Anthropocene (top lake sediments). The response of carbon isotope composition of lake sediments to the global ¹⁴C variation was observed by a¹⁴C peaks in both organic matter and carbonates. Variations in composition of sediments from shallow, coastal lake areas enabled identification of extreme hydrological events. Monitoring of modern environmental settings in three caves revealed variable atmospheric influences and specific hydrological behaviour of each drip site. However, homogenized stable isotope composition of drip water and stable cave environmental settings give confidence for calcite deposition under isotope equilibrium conditions enabling retrieval of paleoclimate and paleoenvironmental information. Algal rims (Lithophyllum byssoides) are good and precise sea-level indicators and their morphology, age and stable isotope composition could be linked to climate changes. Two main goals of algal rims study were to determine the marine reservoir effect essential for accurate calculation of the algal rim ¹⁴C ages, and to reconstruct relative sea-level changes along the eastern Adriatic coast beginning at 5th century. Similarly, study of freshwater reservoir effect along the Zrmanja and Krupa rivers included water chemistry analyses and isotope analyses of DIC and active freshwater carbonates. Mosses are important fragments in the karst environment and they play an active role in tufa formation. Submerged mosses use carbon from two sources: atmospheric CO₂ and dissolved inorganic carbon (DIC). It was found that certain species of mosses incorporate carbon only from dissolved inorganic carbon (DIC), while certain aquatic moss species show higher ¹³C fractionation if the share of atmospheric CO₂ is higher or if the flow velocity is higher. Understanding the source partition can help understanding formation of secondary carbonates that constitute tufa barriers. Project HRZZ-IP-2013-11-1623 “Reconstruction of the Quaternary environment in Croatia using isotope methods” – REQUENCRIM was financed by Croatian Scientific Council, 2014 – 2018.

14C ; Quaternary ; karst ; Croatia ; lake sediments ; tufa ; speleothem ; algal rims

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