Slow snails and rapid climatic change

Presenting person: Dr. Olivier Moine, Lehrstuhl für Geomorphologie, Universität Bayreuth
Th. 2006-02-02 (16:15), H6

During the last glaciation (~70-20 kyr BP), the occurrence of cyclical millennial timescale temperature increases (1-2 kyr) has been recorded across the whole North Hemisphere. However, their impact on the environment in Europe remains poorly documented due to the lack of high resolution pollen records north of the Mediterranean domain. In this periglacial area, evidences of rapid climatic changes are found in loess deposits alternating with tundra soils, in which numerous shells of terrestrial molluscs were preserved. Between 34 and 20 kyr BP, the high resolution molluscan analysis performed in the Nussloch loess sequence (Rhine Valley, Germany) indicates that humidity increases and vegetation decreases are associated with tundra soils. They are followed by large increases in mollusc populations indicating temperature increases and that we correlated with global climatic warmings recorded in Greenland ice-cores. For the interval 34-20 kyr BP, molluscan populations also show cyclical fluctuations but the lower resolution of the record precludes the definition of such a precise framework.
Another approach in quaternary malacology is the development of transfer functions to quantify climatic parameters. Hence, we adapted the Mutual Climatic Range method to molluscan assemblages. Tests showed that modern distributions of taxa are mainly constrained by temperature parameters. Applied on modern assemblages, the method allowed the reconstruction of the modern European latitudinal temperature gradient. The application of fossil assemblage from Achenheim (Alsace, France) reconstructed major temperature variations for the last climatic cycle. The results are encouraging but ameliorations are still necessary before the method can be fully functional.
For the Nussoch section, we thus decided to combine amino acid racemization and luminescence dating to quantify temperature changes.


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