科研之友
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摘要
Few terrestrial Holocene climate records exist from south-eastern Europe despite its important geographical position as a transitional climatic zone between the Mediterranean and mainland continental Europe. Here we present new petrographic and stable isotope data for two Holocene speleothems from Modric Cave, Croatia (44 degrees 15%26apos;N, 15 degrees 32%26apos;E), a coastal Adriatic site (120m inland). Modern meteorological and cave conditions have been monitored for 2 years to understand the links between climate variability and 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 delta 18O of the rainfall is -5.96 parts per thousand (2 sigma=2.83), and the weighted mean D/H rainfall value is -36.83 parts per thousand (2 sigma=?19.95), slightly above the Global Meteoric Water Line, but well below the Mediterranean Meteoric Water Line. Modern calcite from the tops of each stalagmite exhibits delta 18O values that are close to isotopic equilibrium with their respective drip water values. Unfortunately, the relatively young ages and low uranium contents (ca. 50 p.p.b.) 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. Apart from some Isotope Stage 3 material (ca. 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 delta 13C and delta 18O 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. Wetter conditions are associated with the Little Ice Age.
- 出版日期2012-8
