Temporal Succession Of Ancient Phytoplankton Community In Northeastern Tibetan Lakessince The Late Pleistocene And Implication For Paleo-environmental Change

Climate change is a topic that naturally piques our curiosity. The uplift of Qinghai-Tibetan Plateau(QTP) plays an important role in the evolution of Asian climate systems. Nowadays, QTP lies at a critical and sensitive junction of four climatic systems: the Westerlies, the Siberian High, the East Asian Monsoon and the Indian monsoon. A wide variety of lakes on QTP are sensitive to these climate systems and can provide continuous archives(sediments) of past environmental conditions.Microscopic analysis of fossil plankton preserved in lake sediments is a widely used approach in paleo-climate studies, but the majority of plankton does not have fossilizing microscopic features and are thus excluded from micro-paleontological observations. However, these non-fossilizing plankton are sensitive to environmental changes and can be useful for paleo-climate studies. Fortunately, recent studies have shown that temporal changes in plankton ecology, including microscopically nonfossilizing plankton, can be reconstructed from Holocene and Pleistocene marine and lake sediments using sedimentary DNA. We obtained 5.78 m lacustrine sediment core of the Qinghai Lake on QTP and investigated the temporal succession of ancient phytoplankton community of past 18.5 k yr in Qinghai Lake, using the sedimentary ancient DNA approach. This succession was the correlated with the paleoenvironmental and paleo-climatic changes of the lake region from the late Pleistocene to the present. Our results showed that seven classes and sixteen genera of phytoplankton in the lake underwent major temporal changes, in correlation with known climatic events. Trebouxiophyceae and Eustigmatophyceae were predominant during the cold periods, whereas Chlorophyceae, Phaeophyceae, Xanthophyceae, Bacillariophyceae, and Cyanophyceae were abundant during the warm periods.Based on these correlations, a potentially useful proxy, phytoplankton index, is proposed to provide a qualitative estimate of paleo-temperature at present(such as stadial vs. interstadial climates).We also obtained an 80 m sediment core in Qarhan Lake and presented highresolution geochemical records of terrestrial input, paleo-salinity, and air temperature spanning the last 72.4 kyr. Apparent Dansgaard-Oeschger(D-O) and Heinrich events were wellpreserved in the Qarhan Lake sediments. The Qarhan region was dominated by a humid and wet climate before the H5 event(46 kyr B.P.), likely because of a strong Asian summer monsoon. However, after H5 climate in the region became dry and temperature became more variable, possibly because of a stronger regional influence of the Westerlies and Siberian High. A similar abrupt drying event was observed in a low-latitude lake, Towuti Lake, Indonesia, which happened after H3 event. We infer that the abrupt drying of these two lakes was a response to a combination of gradual intensification of high-latitude glacial forcing(or Heinrich events) and low orbital insolation in the region. Both ice sheet expansion in high latitude(or Heinrich cold events) and local precessional insolation variability controlled the regional climate change in East and Southeast Asia.