EARLy AND MID-HOLOCENE ENVIRONMENTAL CONDITIONS IN THE EASTERN ADRIATIC RECORDED IN SPELEOTHEMS FROM MALA ŠPILJA CAVE AND VELIKA ŠPILJA CAVE (MLJET ISLAND, CROATIA) REKONSTRUKCIJA OKOLIJSKIH RAZMER V ZGODNJEM IN SREDNJEM HOLOCENU NA PODLAGI ZAPISA V SIGI JAM MALA ŠPILJA IN VELIKA ŠPILJA (OTOK MLJET, HRVAŠKA) Nina LONčAR1,*, Miryam BAR-MATTHEWS2, Avner AyALON2, Maša SURIć1 & Sanja FAIVRE3 1 Department of Geography, Center for Karst and Coastal Research, University of Zadar, Trg Kneza Višeslava 9, 23000 Zadar, Croatia, e-mail: nloncar@unizd.hr, msuric@unizd.hr 2 Geological Survey of Israel, Malkei Israel St 30, Jerusalem 95501, Israel, e-mail: matthews@gsi.gov.il, ayalon@gsi.gov.il 3 Department of Geography, Faculty of Science, University of Zagreb, Marulićev trg 19/2, 10000 Zagreb, Croatia, e-mail: sfaivre@geog.pmf.hr * Corresponding author Received/Prejeto: 13.02.2017 COBISS: 1.01 ACTA CARSOLOGICA 46/2−3, 229–249, POSTOJNA 2017 Abstract UDC 551.435.8:551.583(497.584)"628.64" Nina Lončar, Miryam Bar-Matthews, Avner Ayalon, Maša Surić & Sanja Faivre: Early and mid-holocene environmental conditions in the eastern Adriatic recorded in speleotherms from Mala Špilja cave and Velika Špilja cave (Mljet island, Croatia) This study presents high resolution oxygen and carbon iso- topic record of two U-Th dated stalagmites from the Eastern Adriatic caves. The stalagmites were collected from Mala špilja and Velika špilja caves situated on Mljet Island in the south- ern part of the Croatian Adriatic. Dripwater samples were collected from Medvjeđa špilja, Strašna peć, Špilja u Vrdolje, Kraljicina spilja, Velika špilja and Mala špilja caves. All caves formed in well-stratified Cretaceous limestones. The average value of deuterium excess of the dripwater is 9.3 ‰, indicat- ing that the atmospheric conditions over the Atlantic Ocean have greater influence on the isotopic composition precipita- tion in the Adriatic region than the Eastern Mediterranean Sea. The longest isotopic record of the speleothems is of sta- lagmite MSM-1 from Mala špilja Cave dated from 119.2 ±3.3 ka to 5.6±0.6 ka, although deposition was not continu- ous. During the Holocene the speleothem grew between 7 ka and 4 ka. That interval is characterized by several δ18Oc and δ13Cc fluctuations reflecting changes in the environment. Su- perimposed on these fluctuations, there is an increasing trend in the 7.0−6.5 ka interval, evident in elevated δ18O values, which primarily refers the trend to drier conditions in the eastern Adriatic, which were occasionally interrupted by wet intervals. Humid conditions are particularly pronounced by low δ18Oc and δ 13Cc values of speleothem MSM-1 between 7.3 and 6 ka, as a reflection of increased precipitation and lower Izvleček UDK 551.435.8:551.583(497.584)"628.64" Nina Lončar, Miryam Bar-Matthews, Avner Ayalon, Maša Surić & Sanja Faivre: Rekonstrukcija okoljskih razmer v zgodnjem in poznem Holocenu na podlagi zapisa v sigi jam Mala Špilja in Velika Špilja (otok Mljet, Hrvaška) Raziskava temelji na visoko ločljivih zapisih kisikovih in oglji- kovih izotopov, pridobljenih iz dveh stalagmitov, datiranih z uran-torijevo metodo. Kapnika sta bila vzorčena v jamah Mala špilja in Velika špilja na otoku Mljet, v južnem delu hrvaškega Jadrana. Vzorčena je bila tudi prenikla voda v jamah Medvjeđa špilja, Strašna peć, Špilja u Vrdolje, Kraljicina spilja, Velika špilja in Mala špilja. Vse omenjene jame so v plastovitem kre- dnem apnencu. Povprečna vrednost presežka devterija v pre- nikli vodi je 9,3 ‰, kar kaže na prevladujoč podnebni vpliv Atlantskega oceana v primerjavi z vplivom vzhodnega Sre- dozemlja. Najdaljši izotopski zapis smo pridobili iz kapnika MSM-1 iz Male špilje, katerega starost je med 119,2 ±3,3 ka in 5,6±0,6 ka. Za kapnik je značilnih več prekinitev izločanja. V holocenu je kapnik rastel v obdobju med 7 ka in 4 ka. V tem obdobju je več izrazitih nihanj δ18Oc in δ 13Cc, kar kaže na spre- membe okolja. Med 7,0 in 6,5 ka je v zapisu trend naraščanja δ18O, kar kaže na relativno suhe razmere v vzhodnem Jadra- nu, ki so jih občasno prekinila vlažna obdobja. Med 7,3 in 6 ka je več obdobij z nizkim vrednostmi δ18Oc in δ 13Cc v vzo- rcu MSM-1, kar kaže na veliko padavin in nizke temperature. Prehod v današnjo sredozemsko klimo (Cs) se je zgodil med 6 ka in 5 ka, najbolj suha obdobja smo zabeležili med 4,7 ka in 4,2 ka. Primerjava izotopskih zapisov δ18Oc on δ 13Cc iz Male špilje (MSM-1) in Velike špilje (Mljet) z zapisi v jami Soreq (Iz- rael) in v sistemu Corchia (Italija) ter drugimi kazalci nekda- njih okolij, npr. jezerskimi sedimenti, kažejo, da sige vzhodne- ACTA CARSOLOGICA 46/2–3 – 2017230 NINA LONčAR, MIRyAM BAR-MATTHEWS, AVNER AyALON, MAŠA SURIć & SANJA FAIVRE INTRODUCTION Croatia encompasses a large part of the Eastern Adri- atic region and therefore has an important role in understanding the paleoenvironmental changes in the Adriatic and the Mediterranean region. Karst oc- cupies 43.7 % of the Croatian territory (Bognar et al. 2012) and it is often referred to as Dinaric or classical karst. Studies on the paleoclimate and palaeoenviron- mental changes based on speleothems from the region are mostly limited to submerged speleothems from the eastern Adriatic Sea. Based on U-Th and 14C dating, and X-ray diffraction of submerged speleothems, Surić and Juračić (2010) have partially constructed curve of relative sea-level changes during the last 220 ka for the Eastern Adriatic coast which generally corresponds to the global sea-level curve. Their studies proposed that environmental settings along eastern Adriatic varied due to climate changes, and that environmental condi- tions were favorable for karstification and speleothem deposition even during the Last Glacial Maximum, as in the Eastern Mediterranean region (Bar-Matthews et al. 2003) and unlike in large part of northern Europe (Gascoyne 1992; Lowe & Walker 1998; Genty et al. 2006; temperatures. The transition to today's Mediterranean climate (Cs) occurred between 6 ka and 5 ka, while the driest con- ditions are recorded at ~4.7 − 4.2 ka. Comparisons between the eastern Adriatic δ18Oc and δ 13Cc records of the speleothem from Mala špilja Cave (MSM-1) and Velika špilja Cave (Mljet Island) with Soreq Cave (Israel) and Corchia Cave (Italy) to- gether with other proxies such as lake sediments demonstrate that the speleothems from the Eastern Adriatic caves record the local and the regional climatic changes. Key words: Holocene, speleothem; stable isotopes; Eastern Adriatic, Croatia. ga Jadrana hranijo pomembne zapise o lokalnih in regionalnih podnebnih spremembah. Ključne besede: Holocen, siga, stabilni izotopi, vzhodni Jad- ran, Hrvaška. fig. 1: Location of islands and caves included in this study. ACTA CARSOLOGICA 46/2–3 – 2017 231 EARLy AND MID-HOLOCENE ENVIRONMENTAL CONDITIONS IN THE EASTERN ADRIATIC RECORDED IN SPELEOTHEMS ... Moreno et al. 2010). The recent studies of Croatian spe- leothems (Lončar 2012) have showed that their isotopic composition records the period from the Upper Pleis- tocene (MIS 5) to the Upper Holocene (MIS 1), show- ing frequent fluctuations and abrupt changes in stable isotope values along with numerous interruptions in growth. Late Holocene stalagmites from Modrič Cave (Croatia) studied by Rudzka et al. (2012) showed alter- nating δ18Oc and δ 13Cc variations and changes in the sta- lagmite diameters which were linked to periods of drier and wetter conditions. Tufa and speleothems deposition in Croatia depos- ited 6000 years ago were described by Krajcar Bronić et al. (2006), Horvatinčić et al. (1989, 2000, 2003, 2008) and Surić and Juračić (2010). Precipitation and fresh wa- ter studies from several continental and coastal meteoro- logical stations (Horvatinčić et al. 2005; Vreča et al. 2006; Surić et al. 2010; Barešić et al. 2011; Rudzka et al. 2012; Roller-Lutz et al. 2013; Hunjak et al. 2013) revealed good correlations between δ18Op of monthly precipitation and mean monthly air temperature, with lower seasonal variations in δ18Op at the maritime stations while Local Meteoric Water Lines (LMWL) are close to the Global Meteoric Water Line (GMWL) with a decreasing trend of slope for the south-Adriatic stations. Recent study of Surić et al. (2017) provided comprehensive study of pre- cipitation and cave dripwater isotopic composition, drip rates and modern calcite stable isotope content based on two year monitoring and confirmed mutual influences of Atlantic and Mediterranean air masses on precipitation evident at study sites in the north Dalmatian islands, coast and mountain range. Here we present speleothem δ18Oc and δ 13Cc varia- tions and δ18Ow variations of rain and dripwater collect- ed from Mala špilja and Velika špilja caves, situated on Mljet Island and dripwater collected in four caves along the Eastern Adriatic coast (Medvjeđa špilja Cave (Lošinj Island), Strašna peć Cave (Dugi otok Island), Špilja u Vrdolje Cave (Brač Island), Kraljicina spilja Cave (Vis Island) (Fig. 1), with the aim of reconstructing of Holo- cene climate changes in a region. As it is already shown by numerous researches (e.g. Bar-Matthews et al. 1997, 1999, 2000; Magny et al. 2009; Bar-Matthews & Ayalon 2011; Brayshaw et al. 2011; Giraudi et al. 2011; Peyron et al. 2011; Roberts et al. 2011; Zanchetta et al. 2011, 2014, 2016; Rudzka et al. 2012; Combourieu-Nebout et al. 2013; Finné et al. 2014) the Adriatic and Mediter- ranean basins are highly sensitive to climate changes and significant differences between the eastern and western basins are evident. Although stalagmites MSM-1 and VSM-1 have longer depositional period, the purpose of this paper is to give preliminary results for the Holocene environmental settings. Namely, Holocene environmen- tal change records for Croatia are scarce but unlike the older depositional periods, can be reliably compared with other research results. The interpretation of MSM-1 and VSM-1 records are made in terms of local, regional and larger scale cli- mate dynamics, in order to provide new insights to local and regional Holocene climate settings and links between the eastern and western Mediterranean sub-basins. GEOGRAPHICAL, GEOLOGICAL AND CLIMATE SETTINGS The Adriatic, as well as the rest of the Mediterrenean is influenced by air masses of different origin, causing noticeable spatial and seasonal variability of the mete- orological parameters over the basin (Vreča et al. 2006; Lionello et al. 2006). Croatia is situated in the northern part of the temperate zone (Fig. 1) where air masses from the northwest Atlantic Ocean and dry and hot air from North Africa (Šegota & Filipčić 2003) meet mainly in the southeast. According to the Köppen-Geiger climate clas- sification (Peel et al. 2007), the northern part of the Adri- atic is classified as humid subtropical climate (Cfa), with wetter summers and colder and drier winters while the southern Adriatic is classified as hot summer Mediterra- nean climate (Csa). The air temperature can fluctuate by about 20 °C during a season (Artegiani et al. 1997). The eastern part of the basin is much wetter than the west- ern part and maximum precipitation occurs along the southeastern coast (Cushman-Roisin et al. 2001). High air pressure zone prevails over the Croatian Adriatic in the summer months, while the rest of the year is marked by frequent changes of cyclones and anticyclones which move eastward. Climate settings during the summer months are determined mainly by the Azores High which brings stable weather, particularly in the southern part of the Adriatic (Penzar et al. 2001) region. Winter months are determined by the Icelandic and Siberian High. The predominant winter winds are bora gusty downslope windstorm characteristic for the eastern Adriatic coast (Grisogono & Belušić 2009) which brings cold and dry continental air and sirocco that brings humid and warm ACTA CARSOLOGICA 46/2–3 – 2017232 air and occasionally Saharan sand causing the rain dust (Cushman-Roisin et al. 2001). Croatian Eastern Adriatic coast encompasses north and middle Adriatic region and it can be divided into the northern part i.e. Kvarner region, and Dalma- tia region which is in the middle and southern part. The coast, including the islands, is composed mainly of carbonate rocks deposited in a shallow marine en- vironment, with occasional emerging (Jelaska 2002). Pliocene and Pleistocene sea level fluctuations caused primarily by cyclic growth and decay of ice sheets (Lambeck & Chappell 2001) lead to the emersions of carbonate areas which together with tectonics and fa- vourable climatic conditions enabled the karstification of today's eastern Adriatic coast (Surić et al. 2014). Pleistocene-Holocene transgression raised sea level by about 135 m (Church et al. 2004) and flooded to- day's North Adriatic area submerging the lower zones forming numerous islands. The present geomorpho- logical features of the eastern Adriatic coast are a re- flection of fault tectonics, in the general NW-SE direc- tion (Prelogović et al. 1995). Therefore, the littoral is characterised by the parallelism of the coastline, island chains and major geological and geomorphological structures known as Dalmatian type (Fairbridge 1968). Relief of all islands is characterized by typical macro and micro karst forms which are predetermined by the geologic structure and the alteration of limestone and dolostones (Bognar & Curić 1995). Lošinj Island is located in the southernmost part of Kvarner region between 44° 42 'N, 14° 24' E and 44° 28' N, 14° 32' E, stretching for 31 km in a NW−SE di- rection with surface area of 74.37 km2 (Duplančić Leder et al. 2004). The Lošinj Island (Fig. 1) makes the transi- tion area between Mediterranean climate with hot sum- mers (Csa) and moderately warm and humid climate in winter (Cfa) (Filipčić 2000). According to the Croatian Meteorological and Hydrological Service (CMHS 2010), the average annual air temperature for the years 1981- 2008 on Lošinj Island is 15.3 °C. Medvjeđa špilja Cave is situated in the central part of the island ~55 m from the sea (Fig. 1, Tab. 1). The entrance to the cave is through a narrow shaft formed along NNE-SSW direction cracks (Malez & Božićević 1965). It is 245 meters long cave which from the entrance descends for 25 m forming a bell shaped chamber and continues in channel mostly submerged by the sea (Jalžić, 2007). The cave is rich in mostly submerged speleothems with few dry parts in the entrance covered with clastic material (so-called Beach) and several walls and rocks covered with speleothem. Dugi otok Island is located in the middle part of the Croatian Adriatic (north Dalmatia) (Fig. 1; Tab.1), situ- ated between 44° 09' N, 14° 49' E and 43° 52' N, 15° 12' E, extending 44.4 km with surface area of 113.31 km2. The climate is Mediterranean with hot summers and wet winters (Csa). Mean annual air temperature (MAAT) is 16.4 °C (CHMS 2010). Strašna peć Cave is situated in the middle of the Island (Fig. 1; Tab. 1) on the west sea- tab. 1: Summary of cave characteristics and sampling location. Cave Position(WGS 84) Alt. (m.) Lenght/ depth (m) Vegetation and average overburden (m) Cave air temp. (°C) Cave air relative humidity (%) Sample location (m from the entrance) Sample* Medvjeđa špilja (Lošinj Island) 44° 36' 22.4'' N 14° 24' 44.6'' E 17.5 245/-25 scarce Medit. maquis 19 ± 5 15 100 20 WMS-1 Strašna peć (Dugi otok Island) 44° 0' 16'' N 15 °2' 19'' E 72 110/-14 scarce Medit. maquis 27 ± 5 11.5 100 6065 WSPD-1 WSPD-2 Špilja u Vrdolje (Brač Island) 43° 21' 10''N 16° 36' 22'' E 310 87/0 dense Medit. maquis 30 ± 5 13.5 - 75 WSUV-1 Kraljicina spilja (Vis Island) 44°04'18.9'' N 16°06'02.6'' E 70 60/0 scarce Medit. maquis 30 ± 5 14.1 - 55 WVKS-1 Mala Špilja (Mljet Island) 42°45'51.6" N 17°28'33.5" E 60 25/-9 scarce Medit. maquis 12 ± 5 13 96.3 4040 WMSa MSM-1 Velika špilja (Mljet Island) 42° 45' 53'' N 17° 28' 19'' E 90 40/0 scarce Medit. maquis 8 ± 1 14 95 13 13 13 WNVSa-1 WNVSb VSM-1 *regular letters for water sample, bold for stalagmite samples NINA LONčAR, MIRyAM BAR-MATTHEWS, AVNER AyALON, MAŠA SURIć & SANJA FAIVRE ACTA CARSOLOGICA 46/2–3 – 2017 233 ward side (Fig. 1). The cave formed in Upper Cretaceous limestone. Average limestone thickness above the cave is 27±5 m. The cave is divided into two chambers 25×20 m and 30×15 m size ending with steep, 14 m deep shaft filled with collapsed material. It is rich with speleothems, many of which are large inactive stalagmites and pillars at the entrance, corroded due to their exposure to the at- mosphere. Active speleothems prevail around the edges of the shaft. Brač Island with total area of 395.44 km2 (Duplančić Leder et al. 2004) is the largest Dalmatian island, situated between 43° 23' N and 16° 25' E and 43° 17' N, 16° 53' E. From the mainland it is separated by the channel 6-13 km Brač Channel. Climatically it belongs to Csa region with MAAT 16.4 °C (CHMS 2010) with typical Medi- terranean vegetation. Špilja u Vrdolje Cave is located in Vrdolje area in the NW part of the Island (Fig. 1; Tab. 1). The entrance to the cave is small (~0.90 m wide), located along the road and overgrown with thick scrub. This is a channel cave formed in Cretaceous limestones. The channel stretches horizontally ~2 m in width, but in some parts it narrows up to 0.5 m. In most parts the cave floor is covered with clay and mud, while at the end of channel there are many stalagmite and pillars. Vis Island is also a part of middle Dalmatia domi- nated by Csa climate. It is 17 km long and 8 km wide with an area of 89.72 km2 it is Situated between 43° 03' N, 16° 02' E and 43° 01' N, 16° 13' E is the most maritime island with the highest MAAT of 17 °C. Kraljicina spilja Cave is situated on the northern coast of the island (Fig. 1; Tab. 1) and so far is the largest known cave on the Vis Island. Morphological it is branched cave consists of five chambers and several smaller channels separated by massive stalagmites, pillars and curtains (facets) (Kaiser & Forenbacher 2002). Mljet Island is the eighth largest (98.02 km2) island in Croatia with an average width of only 3 km. It is elon- gated in shape, and stretches in NW−SE direction for 37 km. The island is located between 42° 48' N, 17° 19' E and 42° 41' N, 17° 45' E and is the southernmost and easternmost island among the large Croatian islands. The MAAT is 16.6 °C. Mala špilja Cave is located on a steep northern slope in the middle of the Island (Fig. 1; Tab. 1). The cave is formed in well-stratified Cretaceous limestone. The entrance is small (0.5×0.5 m) and verti- cal (9 m deep), followed by a 40 m long channel, which forms the main chamber (Jalžić et al. 2007). The cave is rich in speleothems, especially stalactites, stalagmites and columns. Velika špilja Cave is located in the vicinity of the Mala špilja Cave (Fig. 1; Tab. 1). The entrance to the cave is horizontal, probably due to a collapse, as evi- dent by the many collapsed blocks in the front and inside the cave. From the entrance, the cave is descending and opens to an 8 m high chamber. The cave is rich in spe- leothems and the entire left wall of the main chamber is covered by a thick flowstone layer. Among these islands, the highest annual rainfall is in northern Adriatic (Kvarner region) on the Lošinj Is- land (942 mm). The wettest months on the island are Sep- tember, October and November, while the driest month is July (Fig. 3). On the southern islands (Dugi otok, Brač, Vis and Mljet) the rainiest month are November and De- cember and the driest is July. For instance, in July Mljet receives only 16.1 mm (CMHS 2010). fig. 2: Comparison of yearly and monthly average amount of rainfall (1981-2008) on studied islands (CMhS, for the 1981- 2008 period). MATERIALS AND METHODS Dripwater samples were collected during 2010 in Medvjeđa špilja, Strašna peć, Špilja u Vrdolje, Kraljicina spilja, Velika špilja and Mala špilja cave. The location and timing of collecting the, cave dripwater, tempera- ture, relative humidity and other parameters are given in Tab. 1 and 2. Cave dripwater samples have been col- lected using 300 ml bottles with a plastic funnel near the location from which the stalagmite samples were taken. The relative humidity and cave temperature were measured on site with HOBO U23 Pro v2 Temperature/ EARLy AND MID-HOLOCENE ENVIRONMENTAL CONDITIONS IN THE EASTERN ADRIATIC RECORDED IN SPELEOTHEMS ... ACTA CARSOLOGICA 46/2–3 – 2017234 Relative Humidity Data Logger during the dripwater collection. Stable hydrogen and oxygen isotope compositions of water samples were measured at the geochemical lab of the Geological Survey of Israel (GSI), and they are expressed as δD and δ18O values (in ‰) relative to V- SMOW (Tab. 2). Hydrogen isotope composition was measured by ThermoFinnigan HighTemperature Con- version Elemental Analyzer (TC/EA) attached to a Delta V ThermoFinnigan mass spectrometer. The measure- ments were carried out at a reaction temperature of 1450 °C (Nelson 2000). Oxygen isotope composition was measured by ThermoFinnigan GasBenchII attached to a Delta Plus mass spectrometer. The δ18O measurements were carried out using the CO2-water equilibration tech- nique (Epstein & Mayda 1953). The precision of these measurements was ±0.1 ‰ for δ18O and ±1.5 ‰ for δD. Stalagmite samples were collected in all caves but here we present the results only from caves on Mljet Is- land. Sample MSM-1 is a 34 cm long stalagmite (Fig. 3) collected at the end of the Mala špilja Cave (Tab. 1). The speleothem is the top of ~30 cm of an almost 1 m long, calcite stalagmite. Before sampling, the speleothem was actively growing from fast dripping water. After cutting the sample into two halves along the growth axis, it was found that the sample is composed of two well-laminat- ed stalagmites (MSM-1-L and MSM-1-R, Fig. 3). The laminae appear in variable colours: white to light and dark reddish-brown. Sample VSM-1 (Fig. 3) from Velika špilja Cave is a 24 cm long stalagmite, ~6.0 cm in diame- ter, collected at the upper part of a big flowstone, close to the roof (~2 m). It is composed of two parts. The bottom part is compact white and light brown calcite and the top part is brown, porous, grainy, sandy and corroded. The speleothems were dated using the U-Th meth- od. The procedures for extraction and purification of U and Th as well as methodology of U-Th dating followed the procedure described in details by Vaks et al. (2006), Gopher et al. (2010), and Bar-Matthews and Ayalon (2011). Sub-samples of 0.1−1.0 g of speleothem material were drilled using 0.5−4.0 mm diameter diamond drill bits. All samples were completely dissolved in a combi- nation of 7M HNO3 and HF, and spiked with a mixed 229Th/236U spike. The reproducibility of 234U/238U ratio was 0.1 % (2σ). The samples were loaded into mini col- umns containing 2 ml Bio-Rad AG 1X8 200−400 mesh resin. U was eluted by 1 M HBr and Th with 6 M HCl. U and Th solutions was evaporated to dryness and the residue dissolved in 2 ml and 5 ml of 0.1 M HNO3, re- spectively. U-Th dating was performed at the GSI geo- chemical laboratory using a Nu Instruments Ltd (UK) MC-ICP-MS equipped with 12 Faraday cups and 3 ion counters. Each sample was introduced to the MC-ICPMS through an Aridus® micro-concentric desolvating nebu- liser sample introducing system. The instrumental mass bias was corrected (using the exponential equation) by measuring the 235U/238U ratio and correcting with the natural 235U/238U ratio. Calibration of ion-counters rela- tive to Faraday cups was performed using several cycles of measurements with different collector configurations in each particular analysis. The U-Th method assumes that all 230Th present in the calcite speleothem is formed in situ by radioactive decay of uranium that co-precipi- tated with the calcite. However, this component is often present in detrital material such as clays, oxides and hy- droxides (Kaufman et al. 1998; Richards & Dorale 2003). For this correction, a 232Th/238U atomic ratio of 3.8 (the average crustal value, Taylor & McLennan 1985) in the detrital components was used. For δ18Oc and δ 13Cc analyses, speleothem samples of 1−2 mg material were drilled every ~0.5−1.0 mm using a 0.8−1.0 mm diameter drill along the growth axis averag- ing of ~0.8 mm/sample. δ18Oc and δ 13Cc measurements were performed was performed at the geochemical lab- oratory of GSI using a Gas Bench system attached to a Delta Plus ThermoFinnigan mass spectrometer. All δ18Oc and δ13Cc values were calibrated against the international standard NBS-19 and in-house standard Carrara Marble, and are reported in per mille (‰), relative to the V-PDB standard. Analytical reproducibility of duplicates is bet- ter than 0.1 ‰ both for δ18Oc and δ 13Cc. A continuous isotopic record was obtained by as- suming that the measured age represents the center of the drilled area, and that there is a constant growth-rate between two adjacent dated points. RESULTS ISOTOPE RATIOS OF HyDROGEN AND OXyGEN OF CAVE DRIPWATER δ18Ow of cave water vary from −6.32 ‰ to −7.03 ‰ and δD vary from −47.9 ‰ to −39.6 ‰ (Tab. 2). The calculat- ed value of d-excess (d-excess is defined as δD−8*δ18O) in each sample varies from 4.4 ‰ to 12.2 ‰, closely fol- lowing the Meteoric Water Line of 9.3 ‰, apart for sam- ple WMSa with d-excess of 4.4 ‰. NINA LONčAR, MIRyAM BAR-MATTHEWS, AVNER AyALON, MAŠA SURIć & SANJA FAIVRE ACTA CARSOLOGICA 46/2–3 – 2017 235 AGE OF THE SPELEOTHEM SAMPLES Twenty-three U-Th ages were determined on stalagmite MSM-1, and seven on stalagmite VSM-1. Isotope ratios are given in Tab. 3 as activity ratios with 2 sigma uncer- tainties. The reproducibility of 234U/238U ratio was 0.11 % (2σ). The degree of initial contamination of 230Th from detritus was estimated by measuring the 230Th/232Th ac- tivity. Only 13 sub-samples, all extracted from the sam- ple MSM-1, satisfy this criterion, and their age has the smallest correction. All other sub-samples had low 230Th/232Th activity and corrections were much higher. Most dating (23 samples) were performed on the larg- tab. 2: Dripwater isotope values. Sample Cave Collecting period δ 18O ‰ (VSMOW) δD ‰ (VSMOW) d-excess (‰) WMSa Mala špilja 20−22 Feb 2010 −6.54 −47.9 4.4 WNVSb Velika špilja 20−22 Feb 2010 −6.76 −44.2 9.9 WNVSa-1 Velika špilja 20−22 Feb 2010 −6.77 −41.9 12.2 WSUV-1 Špilja u Vrdolju 18−19 May 2010 −7.03 −47.5 8.7 WSPD-2 Strašna peć 20 Jun−29 Sep 2010 −6.82 −44.9 9.7 WVKS-1 Kraljicina spilja 19−20 May 2010 −6.32 −39.6 11 WMS-1 Medvjeđa špilja 13 Dec 2009–10 Jan 2010 −6.65 −43.9 9.3 fig. 3: Longitudinal section of the stalagmite MSM-1 and VSM-1. Black squares mark U-Th dating samples positions (real depth); solid lines indicate growth axes along which the samples for the stable isotopes were taken, red squares mark the subsamples dis- cussed in this paper. fig. 4: Replication test for stalag- mites MSM-1-L and MSM-1-R. EARLy AND MID-HOLOCENE ENVIRONMENTAL CONDITIONS IN THE EASTERN ADRIATIC RECORDED IN SPELEOTHEMS ... ACTA CARSOLOGICA 46/2–3 – 2017236 Stalagmite VSM-1 (Fig. 3) is composed of two parts. The inner white portion grew between ~17 and ~13 ka, while the upper ~5 cm grew between ~10 to ~9 ka (Tab. 3). The outer (younger) brown part was dif- ficult to date since it contains large amount of detrital components. Age model was performed assuming constant growth rate between two dated intervals suggesting that the Holocene portion covered by the two speleothems est sample MSM-1 due to its complex structure and nu- merous hiatus (Fig. 3). It resulted in longer record dated from 119.2±3.3 ka to 5.6±0.6 ka, but deposition was not continuous. Speleothem MSM-1 is composed of two well-lami- nated stalagmites (MSM-1-L and MSM-1-R) (Fig 3). The older white part grew between ~119 and 37 ka. Only the top of ~5 cm of MSM-1-R grew during the Holocene be- tween ~7 ka and ~4 ka. tab. 3: Detailed dating results for the holocene portion of the calcitic stalagmites MSM-1 and VSM-1. sample 238U ppm ± 2σ (234U/238U)A ±2σ (230Th/232Th)A ± 2σ (230Th/234U)A ± 2σ Age (ka) Depth from top (mm) Corr. VSM-1-5 0.1829 0.0001 1.03974 0.0017 2.8 0.08 0.3522 0.0092 47.1±3.1 35.0 7 VSM-1-3 0.2381 0.0001 1.03187 0.0012 3.0 0.02 0.2570 0.0013 32.3±0.4 24.3 50 VSM-1-7 0.1767 0.0002 1.02685 0.0022 4.9 0.14 0.0980 0.0027 11.2±1.0 9.3 53 VSM-1-8 0.2070 0.0002 1.02539 0.0014 2.7 0.06 0.1193 0.0025 13.8±1.0 9.7 82 VSM-1-9 0.2020 0.0003 1.02509 0.0023 11.3 0.27 0.1245 0.0030 14.5±1.0 13.4 97 VSM-1-10 0.1860 0.0002 1.02653 0.0013 7.8 0.17 0.1533 0.0034 18.1±0.9 16.2 126 VSM-1-2 0.2402 0.0002 1.02988 0.0019 6.0 0.16 0.1943 0.0051 23.5±1.4 20.5 146 VSM-1-11 0.2110 0.0001 1.02848 0.0019 8.9 0.22 0.1582 0.0039 18.7±1.0 17.1 178 VSM-1-1 0.2261 0.0074 1.04301 0.0011 7.1 0.14 0.2613 0.0052 32.9±1.6 29.4 219 MSM-1-2 0.1645 0.0000 1.01570 0.0017 1.8 0.01 0.5768 0.0026 93.2±1.5 60.4 7 MSM-1-14 0.1382 0.0001 1.04981 0.0024 23.6 0.34 0.3115 0.0045 40.5±1.5 39.2 12 MSM-1-21 0.1910 0.0002 1.01515 0.0022 3.5 0.09 0.0657 0.0017 7.4±0.6 5.6 16 MSM-1-5 0.3111 0.0002 1.01120 0.0014 1.8 0.02 0.2301 0.0027 28.4±1.0 16.2 22 MSM-1-4 0.2255 0.0001 1.00920 0.0010 2.4 0.02 0.1373 0.0009 16.1±0.5 10.5 27 MSM-1-6 0.1703 0.0001 1.06082 0.0016 39.4 0.25 0.2950 0.0018 37.9±0.6 37.2 37 MSM-1-3 0.1602 0.0001 1.06250 0.0021 16.4 0.11 0.3424 0.0024 45.4±1.0 43.5 37 MSM-1-13 0.2979 0.0002 1.02800 0.0017 14.4 0.32 0.0601 0.0013 6.7±0.8 6.3 43 MSM-1-18 0.1383 0.0002 1.04379 0.0023 97.3 2.74 0.4410 0.0120 63.0±5.0 62.5 57 MSM-1-17 0.2908 0.0003 1.05999 0.0027 77.1 0.84 0.5500 0.0058 86.0±3.0 85.3 69 MSM-1-20 0.1230 0.0001 1.01657 0.0036 8.9 0.34 0.0920 0.0036 10.5±1.0 9.5 75 MSM-1-8 0.3892 0.0003 1.06298 0.0008 56.4 0.38 0.5793 0.0035 93.1±2.0 92.2 80 MSM-1-9 0.5477 0.0004 1.04579 0.0016 16.9 0.09 0.6277 0.0032 106.4±2.5 103.0 85 MSM-1-23 0.2020 0.0002 1.02179 0.0027 11.8 0.29 0.1003 0.0024 11.5±0.7 10.7 99 MSM-1-10 0.3513 0.0052 1.03832 0.0027 46.4 0.17 0.6427 0.0026 110.9±1.8 109.6 102 MSM-1-12 0.2292 0.0015 0.98519 0.0129 11.7 0.42 0.0683 0.0026 7.7±0.1 7.1 105 MSM-1-11 0.1966 0.0002 1.04446 0.0027 66.9 0.89 0.6806 0.0086 122.6±6.0 121.7 107 MSM-1-19 0.1453 0.0002 1.05189 0.0026 37.9 0.96 0.2934 0.0073 37.6±2.3 36.9 117 MSM-1-7 0.1991 0.0001 1.04913 0.0014 116.8 0.67 0.3991 0.0022 55.1±0.8 54.8 143 MSM-1-22 0.2491 0.0004 1.05760 0.0020 47.8 0.33 0.6619 0.0044 116.2±3.0 115.0 162 MSM-1-16 0.2479 0.0002 1.04491 0.0017 53.2 0.42 0.6591 0.0051 115.7±3 114.6 198 MSM-1-1 0.2317 0.0001 1.03750 0.0007 72.3 0.32 0.6226 0.0026 105.1±1.5 104.3 213 MSM-1-15 0.2490 0.0002 1.04353 0.0016 137.3 1.12 0.6716 0.0050 119.7±3.3 119.2 222 NINA LONčAR, MIRyAM BAR-MATTHEWS, AVNER AyALON, MAŠA SURIć & SANJA FAIVRE ACTA CARSOLOGICA 46/2–3 – 2017 237 covers the time intervals between ~10 to 9 ka (VSM-1), and between 7.5 to 4 ka (MSM-1). δ18O AND δ13C PROFILES In order to verify that the speleothems were deposited in isotopic equilibrium a replication test (Bar-Matthews et al. 1997; Dorale & Liu 2009), comparing the δ18Oc and δ13Cc values of the two portions of MSM speleothem, MSM-1-L with MSM-1-R, for the same time interval was performed. The test showed strong relationship (R2=0.77) between δ18Oc MSM-1-L and δ 18Oc MSM-1-L, and some fig. 5: holocene δ18Oc and δ13Cc profile of stalagmite VSM-1 and MSM-1 relationship (R2=0.33) between δ13Cc MSM-1-L and δ13Cc MSM-1-L (Fig. 4). δ18O and δ13C analyses were performed on stalag- mites MSM-1 and VSM-1, for the time period from 9.8 to 4 ka. The age model of VSM-1 suggests that during the Holocene the stalagmite was deposited from 9.8 ka to 9.2 ka. The δ18Oc values fluctuate in amplitude of 1.0 ‰ between ~ −6.0 ‰ and ~ −5.0 ‰, and δ13Cc values vary between −10 ‰ and -6.0 ‰ (Fig. 5). Minimum δ18Oc value is −5.78 ‰ at 9.7 ka and maximum peak of δ18Oc value of −4.8 ‰ is at 9.3 ka, coupled with a maximum δ13Cc peak of −5.7 ‰ at the same time. Given the short deposition period of VSM-1, these fluctuations can be considered significant, especially the increasing trend in both δ18Oc and mainly δ 13Cc between 9.8 ka and 9.4 ka. The δ18Oc and δ 13Cc records during the younger time interval from 7.5 ka to 4 ka (MSM-1) are charac- terized by several modes: a very sharp increase over ~500 years in δ13Cc from ~ −12 ‰ to ~ −7 ‰ from 7.5 to 7 ka negatively correlated with the sharp decrease in δ18Oc values from ~ −6 ‰ to ~ −8 ‰. From ~ 6.8 ka to 5.5 ka δ18Oc show minimum values of ~ −7.5 ‰ to −6.5 ‰ and a sharp increase from 5.5 ka to 5.0 ka from ~ −7.5 ‰ to ~ −5.0 ‰ whereas δ13Cc values are almost constant vary only between −7.0 ‰ and −6.5 ‰. Be- tween 5 and 4 ka, δ18Oc values frequently fluctuate in am- plitude of ~1 ‰, with maximum value of −4.9 ‰ around 4.7−4.2 ka (Fig. 5). DISCUSSION CAVE DRIPWATER All dripwater samples follow closely the GMWL with d- excess of ~10 ‰ and Western Mediterranean Meteoric Water Line (WMMWL) (Fig. 6) indicating that the main source of precipitation are the Atlantic air masses. That is in concordance with previous and recent regional stud- ies which have shown that Croatia receives both Atlantic and Mediterranean moisture (Surić et al. 2017). Comparison between the dripwater isotopic com- position and rain water from several stations in Croatia stations: Malinska (as a reference station for the north- ern Adriatic Sea), Zadar (as a reference station for the central Adriatic) and Dubrovnik and Komiža (as a ref- erence stations for the southern Adriatic), and a station in Zagreb representing continental climate (Horvatinčić et al. 2005; Krajcar Bronić et al. 2006; Vreča et al. 2006), shows that the δ18O-δD relationships of all the cave wa- ter follow closely the GMWL although local lines with lower d-excess characterize the southern Adriatic sta- tions with lower slopes (<7) and intercepts (<5) due to higher temperatures and possible evaporation of rain- drops below the clouds (Krajcar Bronić et al. 2006). The present-day cave water δ18O-δD relations suggest that the main source for cave water is rainfall associated with the Atlantic Ocean water vapour. But, since the dripwaters were collected in several caves along the eastern Adriatic coast line only once and at different seasons, such data are difficult to compare and they can not provide insight to the possible seasonal isotopic variation in the dripwa- ter. For example, Strašna peć Cave dripwater sampled in this study (SPD-2) has δ18O value of −6.82 ‰, which is in very good agreement with mean δ18O value of −6.7 ‰ obtained from two year (2013−2015) cave monitoring in Strašna peć (Surić et al. 2017). Since the first monitoring was performed during the short summer/autumn period δD is 5 ‰ lower than mean 2013−2015 value. EARLy AND MID-HOLOCENE ENVIRONMENTAL CONDITIONS IN THE EASTERN ADRIATIC RECORDED IN SPELEOTHEMS ... ACTA CARSOLOGICA 46/2–3 – 2017238 The overall values of cave dripwater from the Medvjeđa špilja (MSL) Strašna peć Cave (SPD-2), Špilja u Vrdolju Cave, (SUV), Kraljicina spilja Cave (KSV), Ve- lika špilja Cave (VSM) and Mala špilja Cave (MSM) are close to each other and to the analytical precision. On the other hand, the lower isotopic composition of the cave water compared with local rainfall values suggests that the cave waters are mainly derived from the massive rain events, characterised by lower δ18O and δD values, and/or because winter precipitation has higher chance to reach the cave, since summer evapotranspiration reduces the effective infiltration. δ18O AND δ13C TIME SERIES Stable isotope analyses conducted on speleothem VSM-1 and MSM-1 revealed frequent fluctuations and abrupt changes in δ18O (δ18Oc) and δ 13C (δ13Cc) values expressed in a number of peak values. Important changes of the stable isotopic composition and positive correlation be- tween δ18Oc and δ 13Cc are evident in different stages of speleothem growth. Replication test for stalagmites MSM-1-L and MSM-1-R shows good correspondence of isotopic sig- nal. Strong correlation (R2=0.77) between δ18Oc (Fig. 4) supports the equilibrium conditions during the deposi- tion of stalagmite. Namely, according to Dorale and Liu (2009) such simultaneous variations can be an indication of changes in both, climate and vegetation productiv- ity. Moreover, stalagmites with diameters of more than 11 cm are considered to reflect isotopic characteristic of drip water, and therefore are reliable for environmental reconstructions (Dreybodt & Scholz 2011; Belli et al., 2013). Assuming that the speleothems were deposited in isotopic equilibrium as demonstrated by the Replica- tion test, the calcite δ18Oc variations reflect variations in the cave water δ18O and cave temperatures. It was found that the isotopic signal derived from the analysed spe- leothems is affected by many factors. Amount effect has a major impact on the δ18Oc and therefore its value pri- marily reflects the amount of moisture in the certain pe- riod. Decrease of δ18Oc indicates wet, and the increase of δ18Oc indicates dry conditions. It can be expected that the δ13Cc values of MSM-1 and VSM-1 primarily reflect biogenic production of soil CO2 associated with the climatic factors since according to van Adel and Tzedakis (1996) there was no significant predominance of C4 vegetation in the eastern Adriatic region during the Holocene. Namely, data obtained from the cave speleothems from the northern Europe show that 80−90 % of the speleothem carbon is of biogenic origin (CO2 from the soil) while speleothem δ 13Cc value is connected with the vegetation cover density and mi- crobial activity of cave overburden (Genty & Massault 1997, 1999; Vogel & Kronfeld 1997; Weiner 2011). Since the soil moisture and temperature are driving factors in soil microbial respiration (Fairchild & Baker, 2012) δ13Cc values of MSM-1 and VSM-1 can be considered as proxy that reflects the athmosperic conditions above the caves. In such cases lamina thickness variations can be related to δ13Cc anomalies (Belli et al., 2013) and can be consid- ered for our samples. We presume that δ13Cc of analysed speleothems primarily reflects the density and/or type of vegetation cover and biogenic activity in the soil. Nega- tive δ13Cc values usually indicate abundance of vegetation and more humid climate conditions, while more positive δ13Cc values point to drought conditions and reduced biogenic activity. Considering abovementioned, low δ18Oc and δ 13Cc of speleothems MSM-1 and VSM-1 are mostly indica- tors of humid climate, while high δ18Ocand δ 13Cc values fig. 6: δD vs. δ18O values of drip cave water from the Medvjeđa špilja (MSL) Strašna peć Cave (SPD-2), špilja u Vrdolju Cave, (SUV), kraljicina spilja Cave (kSV), Velika špilja Cave (VSM) and Mala špilja Cave (MSM) (triangles) and mean annual δD vs. δ18O values of Dubrovnik, komiža, Malinska and zadar gNIP stations (squares) in rela- tion to the global Meteoric Wa- ter Line (gMWL) (Dansgaard 1964), Eastern Mediterranean Water Line (MMWL) (gat & Carmi 1987) and Western Medi- terranean Meteoric Water Line (WMMWL)(Celle-Jeanton et al. 2001). NINA LONčAR, MIRyAM BAR-MATTHEWS, AVNER AyALON, MAŠA SURIć & SANJA FAIVRE ACTA CARSOLOGICA 46/2–3 – 2017 239 indicate relatively dry conditions. In the case of negative correlation between δ18Oc and δ 13Cc, lower δ 18Oc values may be the result of hot and humid conditions, while the dry climate may lead to higher δ13Cc values (McDermott et al. 1999). In the Mediterranean region, speleothem δ18Oc is mainly controlled by precipitation where more negative values indicate wet periods (Bard et al. 2002; Bar-Matthews et al. 1999, 2000). However both δ18Oc and δ13Cc can be interpreted differently, depending on factors that at some point had a decisive influence on the isotopic signal. EARLy HOLOCENE Early Holocene most commonly refers to pre-boreal and boreal period (11.7−8 ka) (McDermott et al. 1999), but sometimes chronologically encompasses 10−7 ka period (Bar-Matthews & Ayalon 2011). Isotopic profile of sta- lagmite VSM-1 from Velika špilja cave covers the period between 9.8 ka and 9.3 ka (Fig. 3 and 5). Low δ13Cc values at 9.8 ka and an increasing trend toward 9.3 ka suggest an environmental change from relatively humid condi- tions to less humid conditions, a change that was most likely associated with a change in the vegetation type. The vegetation cover along the Eastern Adriatic in the early Holocene was characterized by mixed deciduous forests (Adams et al. 1999) (Fig. 7). Low δ13Cc values at 9.8 ka, reflecting humid condi- tions at that time, can be related to increased rainfall in the coastal areas of the Mediterranean, which was typical for the early Holocene, and associated, with changes in the character of cyclonic depression (Roberts et al. 2011). Warm and humid conditions in the Adriatic region were determined also by pollen analysis from boreholes (Zon- neveld 1996). Almost continuous increase of δ13Cc values of sta- lagmite VSM-1 with the high peak of δ18Oc and δ 13Cc values at 9.4 ka (Fig. 5) indicates transition to dryer conditions which probably lead to the changes in veg- etation soil biogenic activity, since between ~9 ka and ~7 ka mixed deciduous oak forest with only a few rep- resentatives of Mediterranean vegetation prevailed on Mljet Island (Jahns & van den Bogaard 1998). Thus, the increase in δ13Cc values cannot be due to change in veg- etation but more likely they reflect reduced moisture due to warming. Warming conditions are also evident from Vransko jezero Lake on Cres Island (North Dalmatia), which recorded increase proportion of evergreen oak (quercus ilex) (Schmidt et al. 2000). This assumption is in concordance with the newest findings form Vransko jezero lake sediments indicating transition from colder to warmer Holocene climate from 9.6−9.3 ka (Bakrač et al. 2015). Warming and dry conditions between 9 ka and 7.8 ka were recorded in the isotopic signal in spe- leothems from the Italian cave Grotta di Ernesto (Mc- Dermott et al. 1999). Average surface temperature of the Mediterranean Sea was up to 2.9 °C higher than today (Marchal et al. 2002) thus it is possible that the dry con- ditions recorded by the δ18Oc and δ 13Cc values of stalag- mite VSM-1 reflect warming in the entire Eastern Adri- atic region. Extremely dry conditions between 9.5 ka and 9 ka were also recorded in the western Mediterranean (SE France − SE Spain) (Jalut et al. 2000) and it is very likely that such conditions prevailed in the wider area of Mljet Island. MIDDLE HOLOCENE Middle Holocene refers in the present study to the time pe- riod between 7 and 4 ka. The paleoenvironmental chang- es along the eastern Adriatic coast can be reconstructed from the isotopic record of stalagmite MSM-1 from Mala špilja Cave (Figs. 3 and 5). During the mid-Holocene, δ13Cc values are more constant and change within ±2 ‰ indicating that during this period the vegetation cover remained rather constant as was proposed by Wunsam fig. 7: Vegetation cover 18000 and 8000 years ago (after tzeda- kis 2005; Adams & faure 1997; Adams et al. 1999 and Adams n.d., modified). EARLy AND MID-HOLOCENE ENVIRONMENTAL CONDITIONS IN THE EASTERN ADRIATIC RECORDED IN SPELEOTHEMS ... ACTA CARSOLOGICA 46/2–3 – 2017240 et al. (1999) and Tzedakis et al. (2005). Consequently, the most important environmental changes are interpreted based on δ18O oscillations. We suggest that changes in the δ18Oc of MSM-1 during the mid-Holocene reflect mainly changes in the rainfall amount (Bar-Matthews et al. 1996, 2000; Drysdale et al. 2004; Belli et al., 2013). Based on the large isotopic fluctuations several short-term climatic events can be observed: The wet- test phase evident from lowest δ18Oc and δ 13Cc values coupled with highest growth rate is between 7.2 ka and 6.4 ka. There is a negative correlation between δ18Oc and δ13Cc before 7.2 ka, i.e. the lowest (−13.1 ‰) δ 13Cc and high (−5.5 ‰) δ18Oc (Fig. 5) accompanied by increased MSM-1 speleothem growth rate. The very low δ13Cc val- ues are indicative for very wet periods as was also sug- gested for other temperate regions including Croatia (Fairchild et al. 2006). The increase of δ13Cc after 7 ka with maximum δ 13Cc value of −7.2‰ at ~6.8 ka and rather low δ18Oc (−6.1 ‰) (Figs. 5 and 8) points to relative dryer climate which lasted 200 years, and ends with extremely wet event at 6.6 ka in the area of Mljet Island and its surroundings. Between 6.5 ka and 5.5 ka there is slight increase in δ13Cc (by ~2 ‰) and decrease of growth rate which are prob- ably connected to the transition to the Mediterranean climate whereas δ18Oc values at that time are still very low ranging between −7.7 ‰ and −6.6 ‰ coupled with relatively low δ13C, and could be linked to a wet period associated with cooling and decrease in winter temper- atures (Mayewski et al. 1997 in Zanchetta et al. 2014). There are two dry events at 6 ka and 5.6 ka, evident from sharp decrease of δ13Cc and growth rate, each followed by wet events at 5.8 and 5.5 ka as evident by the low δ18Oc (−7.2 ‰) coupled with low δ13Cc (~ −11 ‰). This phase is followed by short (~400 years) return to lower values and increased growth rate with two events of reduced rainfall/moisture centered at 5.4 ka and 5.2 ka and two events of increased rainfall amount at 5.3 ka and 5.1 ka. Transition towards drier late Holocene is evident from progressive increase of δ18Oc coupled with relatively high δ13Cc which points to reduction in rainfall. It starts at 5 ka with sharp increase in δ13Cc (−8.8 ‰) and lowest growth rate which continues onwards. High δ18Oc and δ 13Cc and at ~4.8 ka points to reduced moisture, while the driest phase is recorded in high δ18Oc coupled with relatively constant δ13Cc (~ −10 ‰) between 4.5 ka and 4.2 ka. Given the high concordance between the MSM-1 isotopic profile, changes in vegetation cover recorded in sediments from Malo jezero Lake and the Veliko jezero Lake on Mljet Island on the one side, and global warm- ing followed by the maximum transgression on the oth- er, we can conclude that the stable isotope profile of sta- lagmite MSM-1 reliably reflects mid-Holocene climate as fluctuations between relatively wet and relatively dry conditions. THE REGIONAL CONTEXT OF MSM-1 ISOTOPE RECORD Climatic conditions recorded in stalagmite MSM-1, can be linked to changes in the Mediterranean environment recorded in speleothems from wider region (Fig. 8). Since the Adriatic region is bordering area between At- lantic and Mediterranean atmospheric and ocean circu- lation influence (Davis et al. 2003; Roberts et al. 2011), fig. 8: The δ18Oc and δ 13Cc re- cords of MSM-1, compared with the isotopic records of Corchia (Drysdale et al. 2005) and Soreq caves (Bar-Matthews et al. 2003). The age offset between the re- cords (in the order of up to sev- eral hundreds of years) has to be considered in the context of age uncertainties. NINA LONčAR, MIRyAM BAR-MATTHEWS, AVNER AyALON, MAŠA SURIć & SANJA FAIVRE ACTA CARSOLOGICA 46/2–3 – 2017 241 it is suggested that wet conditions have prevailed during deposition of Sapropel (S1), affected also the central part of Eastern Adriatic where Mljet Islands is located. Wet conditions during deposition of S1 have been recorded in the western Mediterranean (Corchia Cave, Italy) (Zan- chetta et al. 2007, 2014). It is most likely that the southern parts of Croatian Adriatic were influenced by the Medi- terranean atmospheric conditions. We suggest that wet- ter conditions associated with the period of sapropel S1 depositions as recorded between 7 ka and 6.8 ka in Soreq cave (Bar-Matthews et al. 2000, 2003) (Fig. 8) and in lake sediments from Vransko jezero Lake (Croatia) (Bakrač et al. 2015) also influenced this part of the Adriatic re- gion. Wet conditions during the period of S1 sapropel deposition is recorded also in alpine caves speleothems (Spötl et al. 2010). The relative dry event at 6.8 ka can be related to transition from wet early Holocene to drier mid Holo- cene, but also marks the end of S1 influence and may be correlated to the 6.8 ka North Atlantic ice-rafting event (Bond et al. 2001) which is also recorded in North Africa (Rashid et al. 2013) and in Swiss Alps as a short-lived glacier re-advance (Luetscher et al. 2011). At ~6.6 ka, a wet event is observed, marked by significant low δ18Oc value of −7.8 ‰ (Figs. 8 and 9), while δ13Cc profile is quite constant. Frisia et al. (2006) suggested that high δ13C variability from 7.5 ka to 6.5 ka is transitional pe- riod from a pluvial early Holocene to the present-day cli- mate conditions interrupted by periods of relatively dry winters. It is possible that the short lasting isotopic dry and wet events at 6.8 ka and 6.6 ka respectively, represent seasonality changes and may indicate changes between dryer and wetter winters or storm tracks. Sharp decrease of δ18Oc and δ 13Cc values (Fig. 5) and high growth rate (100 mm/ka) of MSM-1, recorded between 7.3 and 6.5 ka suggests wet period in the eastern Adriatic coast mainly in the wider area of Mljet Island. Wunsam et al. (1999) recorded wet conditions on Mljet Island in Malo jezero and Veliko jezero lake sediments which began before 8.4 ka followed by an increased amount of rainfall with maximum between 7 and 6 ka. Bakrač et al. (2015) recorded wet period in Vransko jeze- ro (near Biograd) lake sediment, where the change in the vegetation cover in north Dalmatia is connected with in- creased river inputs around the Adriatic basin from the central Adriatic borderlands around 7.5−7.0 ka (Com- bourieu-Nebout et al. 2013). Both records are in very good agreement with wet periods recorded in MSM-1 δ18Oc and δ 13Cc values. Mid-Holocene wet conditions were also reported in most parts of central and southern Europe (Harrison et al. 1993). The average surface tem- perature of the Mediterranean Sea was reduced by about 2.5 ºC, and there was a decrease in salinity of Tyrrhenian Sea (Kallel et al. 1997 in Wunsam et al. 1999). Isotope records of stalagmites from Clamouse Cave (southern France) and Ernesto Cave (NW Italy) (McDermott et al. 1999) confirmed an increased amount of precipitation as also evident in Soreq Cave (Bar-Matthews & Ayalon 2011). When comparing MSM record with Soreq and Cor- chia there is very good correlation in isotopic profiles, es- pecially in increase of values from mid to late Holocene which is most evident from 5 ka onwards. In MSM-1 hu- mid period, there is similarity in between Corchia and MSM record around 7 ka. In particular there is good match in intervals with higher values at ~6 ka, 5.6 ka, 5.2 ka, 5 ka and ~4.2 ka, and lower values at ~5.8 ka and ~5.5 ka (Fig. 8) suggesting that at that time all sites were under influence of the same atmospheric circulation. They were probably affected by the North Atlantic cir- culation and changes in SST where higher temperatures increased summer aridity and winter precipitation (San- chez Goni et al. 1999; Drysdale et al. 2009). Wet phase before 5.8 ka evident from in all profiles is recorded also in Sofular Cave (Turkey) (Göktürk et al. 2011). On the other hand, there is negative correlation between MSM and Soreq δ13Cc isotopic profiles between 6.5 ka and 6 ka suggesting that these caves were under different atmo- spheric influence. In the regional context, Wunsam et al. (1999) sug- gest that the transition to modern Mediterranean climate (Cs) occurred between 6.3 ka and 5.5 ka, when condi- tions in the paleoenvironment became drier with most of the rainfall during the winter followed by gradual de- crease during summer. Between ~5 ka and ~4 ka there is noticeable increase in δ13C and δ18Oc values and lower growth rate and gradual narrowing of stalagmite MSM-1. Highest δ18Oc peak (−4.9 ‰) at 4.8 ka and 4.3 ka, and an increase in δ13C to −8.8 ‰ at ~5.0 ka points to a tran- sition to drier late Holocene and reduction in rainfall. The dry phase could be linked to 4.2 ka event known as a very dry Holocene climatic event (De Menocal 2001). There are many supporting evidence of drought condi- tions that began before 4.5 ka and has only moderately recovered (Rashid et al. 2013). In Croatia, dry conditions at 4.0 ka have been observed in the reduced input of fresh water in the Mirna river valley in Istria (Kaniewski et al. 2016). Phase of intense drought ~4.2 ka is recorded across North Africa (Gasse & Van Campo 1994), East- ern Mediterranean and the Red Sea (Bar-Matthews et al. 1997) Italy (Buca della Renello cave) (Drysdale et al. 2006). Furthermore, speleothem record from Belgium for the 5a−3 ka time period suggests a progressive dry- ing with high dry-wet variability and very dry peaks at 5.2 ka and 4.5 ka (Verheyden et al. 2014). EARLy AND MID-HOLOCENE ENVIRONMENTAL CONDITIONS IN THE EASTERN ADRIATIC RECORDED IN SPELEOTHEMS ... ACTA CARSOLOGICA 46/2–3 – 2017242 Despite the lower dating resolution for Holocene period, preliminary results of this study provide valuable new in- formation about the eastern Adriatic paleoenvironmen- tal conditions during the Early and Middle Holocene and are comparable to similar results obtained from other parts of Europe and the world. The average value of d-excess of analysed dripwater of 9.3 ‰ indicates that the atmospheric conditions over the Atlantic Ocean has greater influence on the isotopic value of the precipita- tion from Adriatic than Mediterranean atmospheric con- ditions, which coincides with other similar researches conducted in Croatia. The Holocene is marked by numerous δ18Oc and δ13Cc fluctuations reflecting many and sudden changes in the environment superimposed on a general increasing trend of δ18O values from early to mid-Holocene. Gen- erally, low δ18Oc and δ 13Cc of speleothems MSM-1 and VSM-1 correspond to wetter conditions, while high δ18Oc and δ13Cc values correspond to relatively dry conditions. Mid-Holocene climate is characterized by fluctuations between relatively wet and relatively dry conditions. Hu- mid conditions are particularly pronounced by low δ18Oc and δ13Cc values of speleothem MSM-1 between 7.3 ka and 6 ka and can be related to the deposition of Sapropel (S1). Transition to today's Mediterranean climate (Cs) in the eastern Adriatic which occurred between 6 ka and 5 ka is recorded in MSM-1 between 6.5 ka and 5.5 ka and was occasionally interrupted by wet intervals. Also, there is a general trend towards drier conditions especially after 5 ka. The main dry events are recorded at 6.8 ka, ~6 ka, 4.8 ka and 4.3 ka, and the wettest events are at 7.2 ka, 6.6 ka and 5.5 ka. Reconstruction of past vegetation and climate in the Mljet Island area allowed us to induce a general background for understanding local settings in the con- text of regional change driven by the environmental and climate changes across the Adriatic region. MSM-1 and VSM-1 speleothem records have revealed new ideas and questions about the regional and large scale past climates fluctuation in the research area, emphasizing the need for a more extensive network of paleoclimate records from Croatia to better understand Holocene climate. CONCLUSIONS ACKNOWLEDGEMENT This research was supported by UKF Grant Agreement No. 71/10 and Geological Survey of Israel where all labo- ratory work and analyses were performed. The authors wish to thank to P. Kovač Konrad, N. Buzjak, V. Jalžić, D. Henc, K. Motočić, T. Guščić, V. Šarunić and Nature Park Mljet for assistance during the field work. For the data- sets and useful suggestions we are grateful to R. N. Drys- dale, D. Genty and F. McDermott. 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