Isotopic analysis (C, N) and species composition of rodent assemblage as a tool for reconstruction of climate and environment evolution during Late Quaternary: A case study from Bisnik Cave (Czestochowa Upland, Poland)

摘要

Rodent remains are potentially a powerful tool in paleoecological reconstructions. Rodents are a worldwide group of mammals inhabiting all climatic zones, from arctic tundra to tropical forests. Some of their representatives have narrow ranges of environmental tolerance, while others have cosmopolitan distributions. Additionally, rodent remains are well preserved and numerous in cave sediments, and are easily identified to the species level. The species composition of rodent assemblage from the specific cave gives valuable data on ecosystem status around the site. Moreover, isotopic composition (C, N) of rodent remains provides information on some environmental factors, e.g. type of vegetation, soil activity, precipitation, and temperature. The material for this study was collected from the sediments of the Bisnik Cave (Poland). The cave is known from its sediment sequence deposited during the middle and late Pleistocene and Holocene, containing a rich collection of the Pleistocene fauna remains and archeological artifacts. The stratigraphy of the sediment sequence previously was based on archeological findings and several radiometric dates. In this study, we applied U-Th dating method to bone collagen, rodent tooth enamel, and cave bear tooth enamel. Finally, we revised the chronology of sediment sequence from the Bisnik Cave based on these new data. We found significantly higher variability of nitrogen and carbon isotopic composition in the lemming than in the common vole. However, both species show the same trends in isotopic composition of nitrogen in time. At the beginning of the record, δ~(15)N values were relatively high, suggesting intensive soil activity and, indirectly, mild climate. After that, from a stratigraphic layer dated to the early Wurm glaciation, lower δ~(15)N values point to lower soil activity. Deterioration of ecosystem productivity and climate conditions were also confirmed by higher δ~(13)C. This indicates lower canopy effect and suggests conversion of vegetation around the cave. The isotopic record suggests high instability of the environmental conditions during the Wurm glaciations, with significantly warmer periods before and after the Last Glacial Maximum.