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Speleothem-based Quaternary hydroclimate reconstruction – a view from Croatia

After the dominance of ice and deep-sea cores, it is most probable that the future in Quaternary palaeoclimate studies might belong to speleothem science (Henderson, 2006), not only due to their complementary spatial distribution, but also for the many other advantages such as: very precise chronology, resolvable stratigraphy, high-resolution proxy records, precipitation reflecting mean annual climate conditions, simplicity of preservation for future studies etc. (Fairchild and Baker, 2012). Speleothems are secondary carbonate deposits that precipitate in caves from the groundwater supersaturated with respect to CaCO3 which percolates through overlying karstified beds. Within their crystal lattice, speleothems may archive time series of data related to changes in the atmosphere, biosphere, hydrosphere and lithosphere that occurred during their deposition. Namely, on its way from the ocean, via air masses through soil and epikarst into the cave system, water undergoes multiple isotopic fractionations. Due to various causes (temperature, distance from the vapour source, altitude, amount of precipitation), ratios of oxygen (18O/16O) and hydrogen (2H/1H) stable isotopes vary, and remain recorded in precipitated speleothems. In addition, carbon stable isotopes ratio (13C/12C) in spelean carbonate indirectly indicates hydroclimate conditions as it predominantly depends on the vegetation situation above the studied cave/speleothems. Apart from palaeoclimate reconstruction, the most significant Quaternary hydrological changes that are the sea level changes, could also be revealed from the speleothems, particularly those from the submarine caves. Namely, speleothems, as typical subaerial features, found below the present sea level prove the lower sea stands during the cold periods, but are also evidence of favorable regional environmental conditions (biological activity and running water essential for speleothem deposition) in spite of globally deteriorated climate. Croatia, as a part of classical karst, hosts countless speleothems in probably more than 10000 caves (Bočić, 2017) offering extraordinary opportunity to reconstruct palaeo-hydroclimate changes in this bordering region between the western and eastern Mediterranean, deeply indented into the European continent. Thus, several monitoring campaign (e.g. Surić et al. 2017 ; 2018 ; Czuppon et al., 2018) followed by speleothem analyses have been conducted. Up to date, many depositional episodes from MIS 10 to the Recent have been reconstructed, completing wider regional hydroclimate picture. Besides, submerged speleothems partially revealed local palaeoenvironmental history for the last 220 ky (Surić & Juračić, 2010). REFERENCES Bočić N. (2017) - Krš – definicija, svojstva, distribucija (in Croatian). In: Rnjak G. (Ed.), Speleologija. Zagreb, 557–570. Czuppon G., Bočić N., Buzjak N., Óvári M., Molnár M., 2018. Monitoring in the Barać and Lower Cerovačka caves (Croatia) as a basis for the characterization of the climatological and hydrological processes that control speleothem formation. Quaternary International, 494, 52- 65. Fairchild I.J., Baker A. (2012) - Speleothem Science: From Process to Past Environments. Wiley-Blackwell, Chichester, 432 pp. Henderson G.M. (2006) - Caving in to new chronologies. Science, 313, 620–622. Surić M., Juračić M. (2010) - Late Pleistocene – Holocene environmental changes – records from submerged speleothems along the Eastern Adriatic coast (Croatia). Geologia Croatica, 63, 155-169. Surić M., Lončarić R., Lončar N., Buzjak N., Bajo P., Drysdale R.N. (2017) - Isotopic characterization of cave environments at varying altitudes on the eastern Adriatic coast (Croatia) – Implications for future speleothem- based studies. Journal of Hydrology, 545, 367- 380. Surić M., Lončarić R., Bočić N., Lončar N., Buzjak N. (2018) - Monitoring of selected caves as a prerequisite for the speleothem-based reconstruction of the Quaternary environment in Croatia. Quaternary International, 494, 263- 274.

speleothems, stable isotopes, hydroclimate changes,

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