Pestera Poleva is a medium-sized cave located in the southern part of Locvei Mts., some 10 km nord of the Danube Gorge. It is entirely carved in the so-called Plopa limestones (Barremian). It is a typical fluvio-karstic network that stretches alon some 950 m as un underground meander of the nearby Poleva creek. The main passage follows the subteranean stream and shows numerous 'suspended' meanders that are located at ~1-2 m above the riverbed. Both these meanders and the side-passages are richly decorated with speleothems and the temperature is constant in the dry areas, slightly varyin around the multiannual mean of 10-11 °C. These circumstances make of Poleva cave an ideally suited cavity for paleoclimate studies.
Many samples have been taken from Poleva Cave during preleiminary researches and for some of them preliminary isotope measurements have been done. We selected stalagmite PP10, which covers the time-range of ca. 61 ka to the Holocen. Part of the measurements were carried out during former research stages and most of the isotope and TIMS dates were done under the CLIMKARST Project.
The stalagmite was cut and dated for various stratigraphically-significant zones (in total, 8 high-resolution datings). The results of the datings are presented in the figure to the left. Subsequently, stable isotope samples were taken at 1 cm resolution and, following peer-reviewers suggestions, this resolution has been improved to 0.5 cm/sample and even 0.25 cm/samples for problematic zones.
|Results and discussion
All datings were carried out by us in the TIMS Laboratory of Bergen University, Norway, and the stable isotope measurements were done at the „Karl Franzens” University, Graz, Austria.
Dating results are presented in the figure above and show that the stalagmite formed between ca. 61,7 ka until ca 2,4 ka, with two remarkable interruptions marked by precipitation hiatuses some 44-42 ka and ~20-11 ka, respectively. Among these, the hiatus at ~44-42 ka may have been trigered by an important torrential event (flash-floods) with regional extension considering the fact that in Pestera cu Oase, some 50 km to the north massive sediment deposits are recorded.
The main results of the d18O si d13C measurements in stalagmite PP10 are shown in figures below compared with the GRIP (SFCP, 2004) record and, partially, with the LFG9 stalagmite(Lauritzen & Onac, 1999).
Analysing the isotope profile we may notice a very-well marked stadial between ~67 and ~58 ka, which can be correlated with similar events known from Villars Cave (France) and also Lithophagus Cave (Padurea Craiului, Romania). We can also note a very well-defined stadial between ~40-35 ka about which, so far, there was no information for the Romanian territory.
The upper part of the stalagmite ha continuously grown between ~11 ka and ~2,4 ka has offered the most detailed paleoclimate record so far for the Holocene in Romania. This is signiphicant for the continuous warming at te end of the last glacial maximum and shows several important oscillations with durations of only a couple of hundreds years about 5,2 ka and 3,3 ka ago, respectively.
The full results and detailed discussions may be found in Constantin et al. (2007), while the raw data are available in NOAA's Paleoclimatology Database.
|Paleoclimate research on speleothems from Poleva Cave|
|Researches carried out under the framework of the CLIMKARST Project - "Rapid climate oscillations recorded in karst deposits from Romania as revealed by isotopic and paleomagnetic proxies" - CEEX Grant 627/2005|
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