Holocene climatic change and the nomadic Anthropocene in Eastern Tibet: palynological and geomorphological results from the Nianbaoyeze Mountains |
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| Authors: | Frank Schlütz Frank Lehmkuhl |
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| Institution: | 1. Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany;2. Institute for Earth- and Environmental Science, University of Potsdam, Karl-Liebknecht-Straße 24–25, 14476 Potsdam, Germany;3. Indian Institute of Science Education and Research, Kolkata, India;4. Limnology and Fisheries Laboratory, Centre of Research for Development, University of Kashmir, India;5. Universität Hamburg, Institute of Biogeochemistry and Marine Chemistry, Hamburg, Germany;6. UFZ Helmholtz Centre for Environmental Research, Dept. Catchment Hydrology, Halle, Germany |
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| Abstract: | Our study provides detailed information on the Lateglacial landscape and vegetation development of Tibet. Based on a suite of geomorphological and palynological proxy data from the Nianbaoyeze Shan on the eastern margin of the Tibetan Plateau (33°N/101°E, 3300–4500 m asl.), we reconstruct the current state as a function of climate history and the longevity of human influence. Study results constrain several major phases of aeolian sedimentation between 50–15 ka and various glacier advances during the Late Pleistocene, the Holocene and the Little Ice Age. Increased aeolian deposition was primarily associated with periods of more extensive glacial ice extent. Fluvial and alluvial sediment pulses document an increase of erosion starting at 3926 ± 79 cal yr B.P., coinciding with cooling (Neoglacial) and a growing anthropo-zoogenic influence. Evidence for periglacial mass movements indicate that the late Holocene cooling started at around 2000 cal yr B.P., demonstrating increased surface activity under the combined effects of human influence and climate deterioration. The onset of peat growth generally depended on local conditions that include relief, meso-climate and in more recent times also on soil compaction due to animal trampling. We distinguish three initiation periods of peat growth: 12,700–10,400 cal yr B.P. for flat basins inside last glacial terminal moraines; 7000–5000 cal yr B.P. for the main valley floors; and 3000–1000 cal yr B.P. for the higher terrace surfaces.The Holocene vegetation history started with an open landscape dominated by pioneer shrubs along braided rivers (<10,600–9800 cal yr B.P.), followed by the spreading of conifers (Picea, Juniperus, Abies) and Betula-trees accompanied by a successive closing of the vegetation cover by Poaceae, Cyperaceae and herbs (9800–8300 cal yr B.P.). First signs of nomadic presence appear as early as 7200 cal yr B.P., when temperatures were up to 2 °C warmer than today. Forest remained very patchy with strong local contrasts. During the following cooling phase (5900–2750 cal yr B.P.) the natural vegetation was transformed by nomadic grazing to Bistorta-rich Kobresia pygmaea-pastures. Modern nomadic migration routes were established at least 2200 years ago. Overgrazing and trampling led to the shrinking of Bistorta and the spreading of annual weeds. Short-lived cold events (8000, 6200, 3500 cal yr B.P.) impacted on the vegetation only temporarily.As the transformation of the natural Poaceae-rich vegetation into Kobresia-pastures modified the influence of the Tibetan Plateau (“hot plate”) on the monsoon system, our data even point to an early start of a nomadic (!) Anthropocene nearly 6000 years ago. Against the background of a very long grazing history, modern Tibet must be seen as a cultural landscape. |
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