Early and mid-holocene environmental conditions in the eastern Adriatic recorded in speleothems from Mala Špilja cave and Velika Špilja cave (Mljet island, Croatia)
Authors: Lončar Nina , Bar-Matthews Miryam , Avalon Avner , Surić Maša , Faivre Sanja 
Published: January 2018

This study presents high resolutionoxygen and carbon isotopicrecord of two U-Th dated stalagmites from the EasternAdriatic caves. The stalagmites were collected from Mala špiljaand Velika špilja caves situated on Mljet Island in the southernpart of the Croatian Adriatic. Dripwater samples werecollected from Medvjeđa špilja, Strašna peć, Špilja u Vrdolje,Kraljicina spilja, Velika špilja and Mala špilja caves. All cavesformed in well-stratified Cretaceous limestones. The averagevalue of deuterium excess of the dripwater is 9.3 ‰, indicatingthat the atmospheric conditions over the Atlantic Oceanhave greater influence on the isotopic composition precipitationin the Adriatic region than the Eastern MediterraneanSea. The longest isotopic record of the speleothems is of stalagmiteMSM-1 from Mala špilja Cave dated from 119.2±3.3 ka to 5.6±0.6 ka, although deposition was not continuous.During the Holocene the speleothem grew between 7 kaand 4 ka. That interval is characterized by several δ18Oc andδ13Cc fluctuations reflecting changes in the environment. Superimposedon these fluctuations, there is an increasing trendin the 7.0−6.5 ka interval, evident in elevated δ18O values,which primarily refers the trend to drier conditions in theeastern Adriatic, which were occasionally interrupted by wetintervals. Humid conditions are particularly pronounced bylow δ18Oc and δ13Cc values of speleothem MSM-1 between 7.3and 6 ka, as a reflection of increased precipitation and lower temperatures. The transition to today's Mediterranean climate(Cs) occurred between 6 ka and 5 ka, while the driest conditionsare recorded at ~4.7 − 4.2 ka. Comparisons betweenthe eastern Adriatic δ18Oc and δ13Cc records of the speleothemfrom Mala špilja Cave (MSM-1) and Velika špilja Cave (MljetIsland) with Soreq Cave (Israel) and Corchia Cave (Italy) togetherwith other proxies such as lake sediments demonstratethat the speleothems from the Eastern Adriatic caves recordthe local and the regional climatic changes.Key words: Holocene, speleothem; stable isotopes; EasternAdriatic, Croatia.Rekonstrukcija okoljskih razmer vzgodnjem in poznem Holocenu na podlagi zapisa v sigi jamMala Špilja in Velika Špilja (otok Mljet, Hrvaška)Raziskava temelji na visoko ločljivih zapisih kisikovih in ogljikovihizotopov, pridobljenih iz dveh stalagmitov, datiranih zuran-torijevo metodo. Kapnika sta bila vzorčena v jamah Malašpilja in Velika špilja na otoku Mljet, v južnem delu hrvaškegaJadrana. Vzorčena je bila tudi prenikla voda v jamah Medvjeđašpilja, Strašna peć, Špilja u Vrdolje, Kraljicina spilja, Velikašpilja in Mala špilja. Vse omenjene jame so v plastovitem krednemapnencu. Povprečna vrednost presežka devterija v preniklivodi je 9,3 ‰, kar kaže na prevladujoč podnebni vplivAtlantskega oceana v primerjavi z vplivom vzhodnega Sredozemlja.Najdaljši izotopski zapis smo pridobili iz kapnikaMSM-1 iz Male špilje, katerega starost je med 119,2 ±3,3 ka in5,6±0,6 ka. Za kapnik je značilnih več prekinitev izločanja. Vholocenu je kapnik rastel v obdobju med 7 ka in 4 ka. V temobdobju je več izrazitih nihanj δ18Oc in δ13Cc, kar kaže na spremembeokolja. Med 7,0 in 6,5 ka je v zapisu trend naraščanjaδ18O, kar kaže na relativno suhe razmere v vzhodnem Jadranu,ki so jih občasno prekinila vlažna obdobja. Med 7,3 in6 ka je več obdobij z nizkim vrednostmi δ18Oc in δ13Cc v vzorcuMSM-1, kar kaže na veliko padavin in nizke temperature.Prehod v današnjo sredozemsko klimo (Cs) se je zgodil med6 ka in 5 ka, najbolj suha obdobja smo zabeležili med 4,7 kain 4,2 ka. Primerjava izotopskih zapisov δ18Oc on δ13Cc iz Malešpilje (MSM-1) in Velike špilje (Mljet) z zapisi v jami Soreq (Izrael)in v sistemu Corchia (Italija) ter drugimi kazalci nekdanjihokolij, npr. jezerskimi sedimenti, kažejo, da sige vzhodnega Jadrana hranijo pomembne zapise o lokalnih in regionalnihpodnebnih spremembah.Ključne besede: Holocen, siga, stabilni izotopi, vzhodni Jadran,Hrvaška.