Constraining Holocene hydrological changes in the Carpathian–Balkan region using speleothem δ<sup>18</sup>O and pollen-based temperature reconstructions

Abstract

Abstract.Here we present a speleothem isotope record (POM2) from Ascunsȃ Cave (Romania) that provides new data on past climate changes in the Carpathian-Balkan region from 8.2 ka until the present. This paper describes an approach to constrain the effect of temperature changes on calcite δ 18 O values in stalagmite POM2 over the course of the middle Holocene (6-4 ka), and across the 8.2 and 3.2 ka rapid climate change events. Independent pollen temperature reconstructions are used to this purpose. The approach combines the temperature-dependent isotope fractionation of rain water during condensation and fractionation resulting from calcite precipitation at the given cave temperature. The only prior assumptions are that pollen-derived average annual temperature reflects average cave temperature, and that pollen-derived coldest and warmest month temperatures reflect the range of condensation temperatures of rain above the cave site. This approach constrains a range of values between which speleothem δ 18 O changes should be found if controlled only by surface temperature variations at the cave site. Deviations of the change in δ 18 O c_spel values from the calculated temperature-constrained range of change are interpreted towards large-scale variability of climate-hydrology.Following this approach, we show that an additional ∼ 0.6 ‰ enrichment of δ 18 O c in the POM2 stalagmite was caused by changing hydrological patterns in SW Romania across the middle Holocene, most likely comprising local evaporation from the soil and an increase in Mediterranean moisture δ 18 O. Further, by extending the calculations to other speleothem records from around the entire Mediterranean basin, it appears that all eastern Mediterranean speleothems recorded a similar isotopic enrichment due to changing hydrology, whereas all changes recorded in speleothems from the western Mediterranean are fully explained by temperature variation alone. This highlights a different hydrological evolution between the two sides of the Mediterranean.Our results also demonstrate that during the 8.2 ka event, POM2 stable isotope data essentially fit the temperatureconstrained isotopic variability. In the case of the 3.2 ka event, an additional climate-related hydrological factor is more evident. This implies a different rainfall pattern in the Southern Carpathian region during this event at the end of the Bronze Age.Published by Copernicus Publications on behalf of the European Geosciences Union.

Kinetic processes and stable isotopes in cave dripwaters as indicators of winter severity

“…Consequently, climate reconstructions using δ 18 O-climate relationships in various sedimentary archives (e.g., speleothems) have difficulties distinguishing between changes in local climate and/or shifts in climatic influences that could be interpreted as changes in climate variables. Romania has a very diverse karst landscape, offering a great potential for reconstructing past climate based on cave deposits (Constantin, Bojar, Lauritzen, & Lundberg, 2007;Drăguşin et al, 2014;Onac et al, 2015;Onac, Constantin, Lundberg, & Lauritzen, 2002;Tămaş, Onac, & Bojar, 2005). However, there are only a few studies available which documented the rainwater δ 18 O variability and corresponding cave dripwater changes in the region (Drăguşin et al, 2017;Perşoiu, Onac, Wynn, Bojar, & Holmgren, 2011), making the climatic interpretation of speleothem δ 18 O from this region ambiguous.…”

Palaeohydrological changes during the mid and late Holocene in the Carpathian area, central-eastern Europe

“…Summer and autumn thermal anomalies seem to be connected to decadal-scale variability known as Atlantic Meridional Oscillation (AMO) (Ionita et al, 2013). Therefore, CE Europe and especially the Carpathian region are considered sensitive to hydrological forcing (Drăguşin et al, 2014;Finsinger et al, 2014;Gałka et al, 2016). Providing additional palaeoenvironmental data from this region will lead to better constraining the spatial and temporal variability in hydroclimatic gradients between west-east and north-south Europe at the Holocene scale (Davis and Brewer, 2009;Davis et al, 2003;Magny et al, 2013;McDermott et al, 2011;Roberts et al, 2012;Drăguşin et al, 2014).…”

Transfer of environmental signals from the surface to the underground at Ascunsă Cave, Romania

“…Results for the period prior to April 2013 were reported by Drȃguşin et al (2014). Calcite farmed after this period was measured at CEA-CNRS-LSCE (France) on a VG-OPTIMA mass spectrometer.…”

“…Nevertheless, by analyzing δ 18 O data from stalagmite POM 2, Drȃguşin et al (2014) demonstrated that this stalagmite recorded during the Holocene millennial scale hydrological changes that took place in the eastern Mediterranean. This suggests that calcite at Ascunsȃ Cave is continuously deposited under different climate settings, thus making speleothems from this cave useful for the study of past atmospheric circulation (Cruz et al, 2006;Lachniet, 2009 (Baldini et al, 2006;Dreybrodt and Scholz, 2011).…”

“…Modern calcite was precipitated on glass plates and analyzed for O and C stable isotopes at the site of the published POM 2 stalagmite (Drȃguşin et al, 2014) and on the top of the actively growing POM X stalagmite. Results for the period prior to April 2013 were reported by Drȃguşin et al (2014).…”