TY - JOUR A1 - Herzschuh, Ulrike A1 - Kürschner, Harald A1 - Mischke, Steffen T1 - Temperature variability and vertical vegetation belt shifts during the last similar to 50,000 yr in the Qilian Mountains (NE margin of the Tibetan Plateau, China) N2 - A 13.94-m-long sediment core, collected from a medium-sized lake in the Qilian Mountains (NE Tibetan Plateau, China), was analysed palynologically at 81 horizons. The interpretation of indicator taxa yielded various vertical shifts of the vegetation belts. These palaeovegetation results have been checked with lake surface pollen spectra from 8 takes representing different altitudinal vegetation belts. Our main findings are the following: A short period of the late Marine Isotope Stage 3 (around similar to 46,000 yr ago) was characterized by interglacial temperature conditions with a tree line above its present-day altitude. During the LGM, the vicinity of the lake was not covered by ice but by sparse alpine vegetation and alpine deserts, indicating that the climate was colder by similar to 4-7 degrees C than today Markedly higher temperatures were inferred from higher arboreal pollen frequencies between similar to 13,000 and similar to 7000 yr ago with a Holocene temperature optimum and a maximal Picea-Betula mixed-forest expansion between similar to 9000 and similar to 7000 yr ago, when temperatures exceeded the present-day conditions by at least 1-2 degrees C. Alpine steppes and meadows and sub-alpine shrub vegetation dominated around the lake since the middle Holocene, suggesting that vegetation and climate conditions were exceptionally stable in comparison to previous periods. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/00335894 U6 - https://doi.org/10.1016/j.yqres.2006.03.001 SN - 0033-5894 ER - TY - JOUR A1 - Tian, Fang A1 - Qin, Wen A1 - Zhang, Ran A1 - Herzschuh, Ulrike A1 - Ni, Jian A1 - Zhang, Chengjun A1 - Mischke, Steffen A1 - Cao, Xianyong T1 - Palynological evidence for the temporal stability of the plant community in the Yellow River Source Area over the last 7,400 years JF - Vegetation history and archaeobotany N2 - The terrestrial ecosystem in the Yellow River Source Area (YRSA) is sensitive to climate change and human impacts, although past vegetation change and the degree of human disturbance are still largely unknown. A 170-cm-long sediment core covering the last 7,400 years was collected from Lake Xingxinghai (XXH) in the YRSA. Pollen, together with a series of other environmental proxies (including grain size, total organic carbon (TOC) and carbonate content), were analysed to explore past vegetation and environmental changes for the YRSA. Dominant and common pollen components-Cyperaceae, Poaceae, Artemisia, Chenopodiaceae and Asteraceae-are stable throughout the last 7,400 years. Slight vegetation change is inferred from an increasing trend of Cyperaceae and decreasing trend of Poaceae, suggesting that alpine steppe was replaced by alpine meadow at ca. 3.5 ka cal bp. The vegetation transformation indicates a generally wetter climate during the middle and late Holocene, which is supported by increased amounts of TOC and Pediastrum (representing high water-level) and is consistent with previous past climate records from the north-eastern Tibetan Plateau. Our results find no evidence of human impact on the regional vegetation surrounding XXH, hence we conclude the vegetation change likely reflects the regional climate signal. KW - Pollen KW - Lake Xingxinghai KW - Tibetan Plateau KW - Holocene KW - Vegetation change KW - Regional climate Y1 - 2022 U6 - https://doi.org/10.1007/s00334-022-00870-5 SN - 0939-6314 SN - 1617-6278 VL - 31 IS - 6 SP - 549 EP - 558 PB - Springer CY - New York ER - TY - JOUR A1 - Saini, Jeetendra A1 - Guenther, Franziska A1 - Aichner, Bernhard A1 - Mischke, Steffen A1 - Herzschuh, Ulrike A1 - Zhang, Chengjun A1 - Maeusbacher, Roland A1 - Gleixner, Gerd T1 - Climate variability in the past similar to 19,000 yr in NE Tibetan Plateau inferred from biomarker and stable isotope records of Lake Donggi Cona JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - We investigated 4.84-m-long sediment record spanning over the Late Glacial and Holocene from Lake Donggi Cona to be able to reconstruct circulation pattern on the Tibetan Plateau (TP). Presently, Lake Donggi Cona is located at the boundaries of Westerlies and Asian monsoon circulations in the northeastern TP. However, the exact timing and stimulating mechanisms for climatic changes and monsoon shifts in this region are still debated. We used a 19-ka-long stable isotope record of sedimentary n-alkanes to address this discrepancy by providing insights into paleohydrological conditions. The SD of nC(23) is influenced by lake water evaporation; the BD. values of sedimentary nC(29) are mainly controlled by moisture source and temperature changes. Long-chain n-alkanes dominate over the core whereas three mean clusters (i.e. microbial, aquatic and terrestrial) can be inferred. Multi-proxies suggest five major episodes in the history of Lake Donggi Cona. The Lake Donggi Cona record indicates that the Late Glacial(18.4-14.8 cal ka BP) was dominated by low productivity of mainly microbial and aquatic organisms. Relatively low delta D values suggest low temperatures and moist conditions eventually caused by stronger Westerlies, winter monsoon and melt-water influence. Likely, the shift (similar to 17.9 cal ka BP) from microbial to enhanced aquatic input suggests either a change from deep to shallow water lake or a break in local stratification. Between 14.8 and 13.0 cal ka BP, variable climatic conditions prevailed. Although the Westerlies weekend, the increase in temperature enhanced the permafrost and snow melting (displayed by a high sedimentary accumulation rate). Higher delta D values indicate increasingly arid conditions with higher temperatures which eventually lead to high evaporative conditions and lowest lake levels. Low vegetation cover and high erosion rates led to high sediment accumulation resulting in stratification followed by anoxia in the terminal lake. From 13.0 to 9.2 cal ka BP, lowered values of 813 along with high contents of terrestrial organic matter marked the early-Holocene warming indicating a further strengthening of summer precipitation and higher lake levels. A cooling trend was observed in the mid-Holocene between 9.2 and 3.0 cal ka BP accompanied by higher moisture availability (displayed by lowered SD values) caused by reduced evaporative conditions due to a drop in temperature and recovering Westerlies. After 3.0 cal ka BP, a decrease in lake productivity and cold and semi-arid conditions prevailed suggesting lower lake levels and reduced moisture from recycled air masses and Westerlies. We propose that the summer monsoon was the predominant moisture source during the Belling-Allered warm complex and early -Holocene followed by Westerlies in mid-to-late Holocene period. Stable carbon isotope values-32%o indicate the absence of C-4 -type vegetation in the region contradicting with their presence in the Lake Qinghai record. The 81) record from lake Donggi Cona highlights the importance of the interplay between Westerlies and summer monsoon circulation at this location, which is highly dynamic in northeastern plateau compared to the North Atlantic circulation and insolation changes. Consequently lake Donggi Cona might be an important anchor point for environmental reconstructions on the Tibetan Plateau. (C) 2017 The Authors. Published by Elsevier Ltd. KW - n-alkanes KW - Hydrogen isotopes (delta D) KW - Carbon isotopes (delta C-13) KW - Carbon preference index (CPI) KW - Westerlies KW - Continental air masses KW - Precipitation KW - Late Glacial and Holocene Y1 - 2017 U6 - https://doi.org/10.1016/j.quascirev.2016.12.023 SN - 0277-3791 VL - 157 SP - 129 EP - 140 PB - Elsevier CY - Oxford ER -