A late-Holocene climate record in stalagmites from Modrič Cave (Croatia)

Few terrestrial Holocene climate records exist from Southeastern Europe despite its important geographic position as a transitional climatic zone between the Mediterranean and mainland continental Europe. In this study we present new petrographic and stable isotope data for two Holocene speleothems from Modrič Cave, Croatia (44o15’N, 15o32’E), a coastal Adriatic site (120 metres inland). Modern meteorological and cave conditions have been monitored for two years to understand the links between the climate variability and the stable isotope time-series records in speleothems. Typical of a Mediterranean-type climate, a negative water balance exists between April and September, so that recharge of the aquifer is restricted to the winter months. The weighted mean δ18O of the rainfall is -5.96‰ (2σ =2.83), and the weighted mean D/H rainfall value is -36.83‰ (2σ = 19.95), slightly above the Global Meteoric Water Line (GMWL), but well below the Mediterranean Meteoric Water Line (MMWL). Modern calcite from the tops of each stalagmite exhibits δ18O values that are close to isotopic equilibrium with their respective drip water values. Unfortunately, the relatively young ages and low uranium contents (c. 50 ppb) of both stalagmites hamper the use of U-series dating. Radiocarbon dates have been used instead to constrain their chronology using a dead carbon correction. Aside from some Isotope Stage 3 material (c. 55 ka), both stalagmites were deposited during the late Holocene. Climatic conditions during the late Holocene are inferred to have been sufficiently wet to maintain stalagmite growth and any hiatuses appear to be relatively short lived. Inferred changes in the stalagmite diameters during deposition are linked to δ13C and δ18O variations, indicating alternating periods of drier and wetter conditions. Drier conditions are inferred for the late Roman Ages warm period and the mid-Medieval Warm Period (MWP). Wetter conditions are associated with the Little Ice Age period.Science Foundation Irelan