Source, timing, frequency and flux of ice-rafted detritus to the Northeast Atlantic margin, 30-12 ka; testing the Heinrich precursor hypothesis
pollen, alkanes, mammoths, Holocene
Alkane biomarker and pollen data were obtained from a 15-m-high and probably c. 240-kyr-old loess-like permafrost palaeosol sequence (‘Tumara Palaeosol Sequence’, TPS) in northeast Siberia. The alkane results were corrected for degradation effects by applying an end-member model and were evaluated by comparing them with the palynological results. The two data sets are generally in good agreement and suggest that the lower part of the TPS developed mainly under larch forests, whereas the upper part of the sequence reflects the expansion of mammoth steppes during the Weichselian glaciation and finally reforestation during the Lateglacial and the early Holocene. For the lower part of the TPS, the palaeoclimatic interpretation according to modern analogue methods would indicate warm, interglacial conditions, but this is at odds with the climate chronostratigraphy based on a multi-proxy palaeopedological approach and numeric dating. Provided that the correlation of the discussed stratigraphic unit with the Late Saalian glaciation and the Marine Oxygen Isotope Stage 6 is correct, our results suggest that temperature was not a limiting factor for tree growth at that time. Furthermore, it seems very likely that it was not mainly temperature changes but rather increasing aridity and continentality during the course of the last glacial that favoured the expansion of the mammoth steppe.
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