Holocene environmental and climate change on the Tibetan Plateau is intensively studied and discussed with the aim to better understand the factors controlling the hydrology of individual river catchments and especially the availability of water which is of utmost significance for the communities downstream in times of rapid climate change. Thus, a late glacial and Holocene sediment record from Lake Heihai in the Kunlun-Pass region was investigated using ostracod and geochemical analyses. Cold and dry conditions were inferred between ca. 12.9 and 12.3 cal ka BP and higher temperatures before and afterwards. The cold spell probably corresponds to the Younger Dryas (YD) event in the North Atlantic region. Warmer and wetter conditions with highest lake levels and decreased lake-water salinity were recorded from ca. 10.8 to 7.0 cal ka BP when the summer monsoon was strengthened. The cold 8.2 cal ka BP event is not significantly recorded in the region probably due to the predominance of the summer monsoon over the westerlies. A declined lake level and increased lake-water salinity as the result of cold and dry conditions are inferred from ca. 7.0 to 4.5 cal ka BP when the strengthening of the mid-latitude westerly circulation probably triggered glacier advances in the catchment. An even lower lake level existed during cold conditions with glacier advances from ca. 4.5 to 1.2 cal ka BP. The level of Lake Heihai rose again after ca. 1.2 cal ka BP due to warmer conditions, causing the retreat of glaciers and higher runoff. Our record from the Kunlun Pass region provides further evidence for the catchment-specific response of hydrographical systems which are partly controlled by glaciers as major water sources.
Bibliographical noteFunding Information:
The research was supported by The Second Tibetan Plateau Scientific Expedition and Research (STEP) program ( 2019QZKK0704 ), Fundamental Research Funds for the Central Universities, Lanzhou University ( lzujbky-2019-46 ) and the National Natural Science Foundation of China ( 41571177 ).
Continuously high TOC contents in zone 2 suggest relatively high lake productivity and relatively warm conditions. The carbonate content shows a decreasing trend. The sand content decreases mostly apart from the uppermost section of zone 2, whilst the silt content shows the opposite trend (Fig. 5). These changes probably indicate a high lake level and wet conditions. Ostracod shells become abundant and constantly present in the zone. The euryhaline species Limnocythere inopinata dominates, accompanied by low abundances of Eucypris afghanistanensis, Ilyocypris cf. bradyi, Eucypris mareotica and Leucocythere sp. A single shell of Tonnacypris cf. estonica is recorded at 359 cm depth (Fig. 6). Limnocythere inopinata is one of the most widespread species in water bodies of the Tibetan Plateau (Mischke et al., 2002, 2003a, 2003b, 2007; Li et al., 2010). Although it has broad tolerances to important environmental factors such as water temperature, habitat type, water depth and salinity (Meisch, 2000), it is regarded as a summer and a polythermophilic species (Yin and Geiger, 1996; von Grafenstein et al., 1999; Meisch, 2000). It thrived best at 20 °C in laboratory culturing experiments recorded by Yin et al. (1999). Its dominance supports our assumption of relatively warm conditions between ca. 10.8–7.0 cal ka BP. Transfer-function inferred SC values range from 2648 to 4405 μS cm−1, which represents an estimated salinity range from 1.9 to 3.2‰. Thus, Lake Heihai was probably an oligohaline lake during the formation of zone 2.We appreciate Bernd Wünnemann (Southwest Jiaotong University, Chengdu; Freie Universität Berlin) who kindly provided the core samples. We thank Hao Chen, Lianfu Zhou for providing data, and Dada Yan and Yongzhan Zhang for help during fieldwork. Detailed and constructive comments on a first manuscript draft or later versions by David B. Madsen (University of Texas and Lanzhou University), Tomasz Goslar (Poznan Radiocarbon Laboratory, Adam Mickiewicz University), Christian Leipe (Max Planck Institute of Geoanthropology), Gregori Lockot, Pavel E. Tarasov (both Freie Universität Berlin) and three anonymous reviewers were greatly appreciated. We thank Sylvia Pinkerneil (Helmholtz-Centre Potsdam-GFZ German Research Centre for Geosciences) for help with measuring oxygen and carbon stable isotopes of ostracod shells. The research was supported by The Second Tibetan Plateau Scientific Expedition and Research (STEP) program (2019QZKK0704), Fundamental Research Funds for the Central Universities, Lanzhou University (lzujbky-2019-46) and the National Natural Science Foundation of China (41571177).
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- Central Asia
- Summer monsoon