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Reconstruction of the Quaternary environment in Croatia using isotope methods

The research within the framework of the project Reconstruction of the Quaternary environment in Croatia using isotope methods (acronym REQUENCRIM) will be presented. The project is financed by the Croatian Science Foundation for the period 2014-2018 and it focuses on palaeoclimate and palaeoenvironment study of different carbonate sediments from different climate zones using isotope methods. Croatian karst offers exquisite potential for researches of Quaternary paleoclimate and paleoenvironment, having the wide range of karstic forms already proven as good (paleo)environmental archives, such as terrestrial and submerged speleothems, tufa deposits, karstic lake sediments, karstic water and marine algal rims. Isotope composition of carbonate deposits has an important application in paleoclimate and paleoenvironmental studies. In the Project we consider the stable isotope ratios 13C/12C and 18O/16O as well as radioactive isotope 14C and isotopes of U-Th series. Assuming isotopic equilibrium during carbonate precipitation, terrestrial carbonates such as speleothems, tufa or lacustrine sediments can provide a record of environmental and climatic information while marine algal rims are good indicator of sea level change. Tufa, lake sediments, speleothems and algal rims from Croatia were studied using isotope methods, but not systematically and in much less extent than worldwide. Previous research indicated that speleothems and tufa from Dinaric karst may contain valuable paleotemperature and/or paleoenvironmental records (Surić et al, 2005, 2009, Horvatinčić et al, 2000), that lake sediments reflect environmental changes and anthropogenic influence (Horvatinčić et al, 2008), and that algal rims can help in establishing relative sea-level change (Faivre et al, 2013). Since the Dinaric karst is the region where all kind of mentioned sediments can be found, this research is aimed towards integrating knowledge obtained by studies of individual types of deposits from the same area, searching for new conclusions on the reconstruction of the Quaternary environment and climate. The proposed interdisciplinary project of natural sciences encompasses three groups from three scientific institutions: 1) Laboratory for Low-level Radioactivity, Department of Experimental Physics, Ruđer Bošković Institute (14C team), 2) Department of Geography and Department of Biology, Faculty of Science, University of Zagreb (Algal rims team), and 3) Department of Geography, University of Zadar and Department of Geography, Faculty of Science, University of Zagreb (Speleo team). The whole project team consists of 12 scientists: 4 geographers, 3 chemists, 2 geographers/geologists, 1 geologist, 1 physicist and 1 biologist. The planned activities are grouped to following objectives to ensure efficient project implementation: 1. Reconstruction of the paleoenviromental/paleoclimate settings from the speleothems. The activities are focused on the three caves from the different regions and altitudes and encompass cave monitoring (microclimate and drip rate), sampling of stalagmites, modern calcite samples, rain and drip water, U-Th and 14C dating, stable isotope (SI) analyses, data evaluation, interpretation and preparation of data for synthesis. 2. Reconstruction of paleoenviromental/paleoclimate settings from fresh-water carbonates (lake sediments and tufa). The activities include: sampling of water and tufa in the Zrmanja River, 14C and U-Th dating of tufa, data evaluation ; subsampling of archived lake sediment cores from several locations in Lakes Prošće and Kaluđerovac, measurement of 14C and SI in carbonate and organic fractions, CHN and mineralogical analyses, interpretation of data. 3. Reconstruction of relative sea-level changes from algal rims. The activities are focused on studying the connection between sea level changes and climate changes: algal rim monitoring, measurement and sampling of already found and new algal rims, 14C dating (LSC and AMS) and SI analyses. The prospection of new sections of the coast in term of new biological and geomorphological markers is planned also. Evaluation and interpretation of results based on algal rims. 4. Synthesis of results and common interpretation. All the results obtained under Objectives 1 - 3 will be compared and related to each other. Expected outcome: determined differences in reconstructed paleoclimate / paleoenvironmental conditions in various regions ; how various carbonates record/reflect conditions in time of deposition ; relation between isotopic composition of water and modern carbonate deposits. In the frame of the Project the carbonate samples will be collected in the area of the Dinaric karst in Croatia as follows: a) Speleothems as the most suitable calcite deposits for reconstruction of paleoclimate changes are collected from three caves from the different regions and altitudes: Modrič Cave (32 m a.s.l.) in littoral Croatia, Lokvarka Cave (760 m a.s.l.) in Gorski kotar region, and Grgosova Cave (239 m a.s.l.) in Samobor region. Monthly sampling and monitoring in all three caves started in November 2014. b) Tufa samples will be collected in the Zrmanja River: fossil tufa deposit from the dry tufa barriers from several locations (for paleoenvironmental reconstruction), as well as recent tufa deposits and water seasonally at several locations. Several tufa samples from the dry tufa deposit Gazin Kuk have been dated by the 14C method. c) Lake sediments as good recorders of environmental changes within lake ecosystem and regional catchment are studied at the Plitvice Lakes. For this purpose we use the sediments from archive collection (sediments, top ~40 cm, taken in 2011-2012, frozen and stored at RBI) from two lakes, Lake Prošće and Kaluđerovac at several sampling points of different water depths. 14C and δ13C analyses of the carbonate and organic fractions from the two sediment cores at the Prošće Lake, as well as CHN analyses of sediment have been performed. d) Algal rims as an important marker for sea-level change will be sampled at ~8 locations from northern, central and southern Adriatic. Their vertical position in relation to recent sea level will be meticulously recorded. Collected samples will be carefully examined and subsamples will be mechanically isolated for dating. The analyses of 14C dating, stable isotope 13C/12C and 18O/16O will be used. In order to record the present state of algal rims, monitoring will be performed twice a year on two locations. The monitoring of the algal rims has started on the Vis Island. Recent investigations have been centered on the determination of the marine radiocarbon reservoir effect of the Eastern Adriatic Sea and particularly of the algal rims as it is the basis for further accurate sea-level and climate reconstructions. Acknowledgment The work was performed within the project 1623 Reconstruction of the Quaternary environment in Croatia using isotope methods financed by the Croatian Science Foundation. References: Faivre S., Bakran-Petricioli T., Horvatinčić N., Sironić A. (2013) Distinct phases of relative sea level changes in the central Adriatic during the last 1500 years – influence of climatic variations? Palaeogeography Palaeoclimatology Palaeoecology, 369, 163-174. Horvatinčić N., Barešić J., Babinka S., Obelić, B., Krajcar Bronić I., Vreča P., A. Suckow (2008) Towards a deeper understanding how carbonate isotopes (14C, 13C, 18O) reflect environmental changes: A study with recent 210Pb-dated sediments of the Plitvice Lakes, Croatia. Radiocarbon, 50, 233-253. Horvatinčić N., Čalić R., Geyh M. (2000) Interglacial growth of tufa in Croatia ; Quaternary Research, 53, 185-195. Surić M., Juračić M., Horvatinčić N., Krajcar Bronić I. (2005) Late Pleistocene - Holocene sea-level rise and the pattern of coastal karst inundation - records from submerged speleothems along the Eastern Adriatic Coast (Croatia). Marine Geology, 214, 1-3, 163-175. Surić, M., Richards, D.A., Hoffmann, D.L., Tibljaš, D., Juračić, M. (2009) Sea level change during MIS 5a based on submerged speleothems from the eastern Adriatic Sea (Croatia). Marine Geology, 262, 62-67.

Quaternary; karst; speleothem; algal rims; lake sediments; tufa; izotope methods

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