engleski

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

Few Holocene climate records exist from Southeastern Europe region despite its important geographic position as a transitional climatic zone between the Mediterranean and continental Europe. Previous studies have focused on the use of submerged coastal speleothems from Croatia as palaeo sea-level indicators. In this study we present new petrographic, stable isotope and radiocarbon data for two Holocene speleothems from Modrič Cave (44°15’N, 15°32’E), a coastal Adriatic site (200-300 metres inland). Cave air temperature, drip-rates and rainfall amounts have been monitored at the site for two years. A negative water balance typically exists between April and September so that the recharge of aquifer reservoir above the cave is restricted to the winter months. The δ18O mean weighted value of the rainfall is -5.96 ‰ (2σ =2.83) and the mean weighted 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). Two drip sites c. 60 metres apart show different average δ18O values. At the drip site MODW-21, δ18O is relatively well buffered, indicating a seasonal range of c. 1‰ compared with a range of 5.4‰ in the rainfall, despite showing a more sensitive hydrological response to rainfall events than the second drip site (MODW-22). At the latter site, δ18O is less well buffered and shows a larger seasonal range of c. 2.2‰. At drip site MODW-21 the mean δ18O is similar to the weighted mean δ18O value of the rainfall whereas the other site (MODW-22) shows a 1‰ higher mean δ18O value. Both drips were feeding stalagmites, which exhibit differences in calcite δ18O, consistent with their respective drip-water values implying near-equilibrium deposition at both sites. 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 to constrain the chronology using a dead carbon correction based on the analysis of modern calcites. Aside from some Isotope Stage 3 material (c. 55 ka), both stalagmites were deposited mostly in the late Holocene. Inferred changes in the diameters of the stalagmite during deposition were linked to the time series δ13C and δ18O values indicating alternating periods of drier and wetter conditions. There is no evidence for speleothem deposition in the early- to mid-Holocene at this site, consistent with other published studies from Southeastern Europe. A preliminary age model indicates that climatic conditions during the Holocene were sufficiently wet to maintain stalagmite growth and that any hiatuses were relatively short in duration.

Late-Holocene stalagmite ; palaeoclimate ; Modrič cave ; Croatia

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