1Section 5.2 Climate Dynamics and Landscape Evolution, GFZ German Research Centre for Geosciences, Potsdam, Germany
2Chair of Climatology, Technische Universität Berlin, Berlin, Germany
3Physical Geography, Institute of Geography, Friedrich-Schiller-Universität Jena, Jena, Germany
4Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Potsdam, Germany
5Institute of Geographical Sciences, EDCA, Freie Universität Berlin, Berlin, Germany
6Institute for Earth and Environmental Sciences, Universität Potsdam, Potsdam, Germany
Abstract. Grain size distributions offer powerful proxies of past environmental conditions that are related to sediment sorting processes. However, they are often of multimodal character because sediments can get mixed during deposition. To facilitate the use of grain size as palaeoenvironmental proxy this study aims to distinguish the main detrital processes that contribute to lacustrine sedimentation across the Tibetan Plateau using grain size end-member modelling analysis.
Between three and five robust grain size end-member subpopulations were distinguished at different sites from similarly-likely end-member model runs. Their main modes were grouped and linked to sediment transport and depositional processes associated with certain climatic background and catchment configurations.
The coarse sands and clays with grain size modes > 250 μm and < 2 μm were probably transported by fluvial processes. Aeolian sands (~ 200 μm) and coarse local dust (~ 60 μm), transported by saltation and in near-surface suspension clouds, are probably related to occasional westerly storms in winter and spring. Coarse regional dust with modes ~ 25 μm may derive from near-by sources that keep in longer-term suspension. The continuous background dust is differentiated into two robust end-members (modes: 5–10 and 2–5 μm) that may represent different sources, wind directions and/or sediment trapping dynamics from long-range, upper-level westerly and episodic northerly wind transport. According to this study grain size end-members of only fluvial origin contribute small amounts to mean Tibetan lake sedimentation (19 ± 5%), whereas local to regional aeolian transport and background dust deposition dominate the clastic sedimentation in Tibetan lakes (contributions: 42 ± 14% and 51 ± 11%). However, fluvial and alluvial reworking of aeolian material from nearby slopes during summer seems to limit end-member interpretation and should be crosschecked with other proxy information. If not considered as a stand-alone proxy, a high transferability to other regions and sediment archives allows helpful reconstructions of past sedimentation history.