Warm trees during cold glacial periods in NE-Siberia?
2 Geographisches Institut, Universität Bern
P 1.10 in Ecosystem Function
We have recently presented a multi-proxy analytical characterisation and palaeoclimatic interpretation of a loess-like permafrost palaeosol sequence (the Tumara Palaeosol Sequence, TPS) in NE-Siberia (Zech et al., 2008). Accordingly, the TPS developed on a Middle Pleistocene fluvio-glacial terrace, comprises a sequence of glacial and interglacial/-stadial palaeosols and represents the last ~240,000 years. Palaeosols with higher contents of organic matter (TOC up to 2.5%) are correlated with glacial periods, whereas palaeosols with low contents of organic matter (TOC ~0.5%) are correlated with interglacial periods. This TOC pattern is explained with a thinner active permafrost layer, water logging and reduced organic matter degradation during glacials. However, the reconstructed vegetation history based on alkane biomarker and pollen analyses seems to be at odds with the climate history based on the pedologic features (Zech et al., submitted). Namely in the lower part of the TPS, we found evidence for forest vegetation and abundant Larix pollen in the stratigraphic unit correlated with the Late Saalian glaciation (130–160 ka BP) and the Marine Oxygen Isotope Stage (MIS) 6. Similar severe discrepancies have also been described for the sediments from the famous Crater Lake El’gygytgyn (Lozhkin et al., 2007). Furthermore, we found abundant larch pollen in fossil peat deposits radiocarbon-dated to the Younger Dryas in the Dyanuska Valley (Werner et al., to be submitted) and larch pollen are also present in Late Glacial sediments from Lake Billyakh (Müller et al., 2008). We therefore question the traditional paradigm that the occurrence of trees is a straight forward proxy for ‘warm’ climate conditions in NE-Siberia.