YongJuan Sun

THE ENVIRONMENTAL CHANGE RECORDED IN JIANGXIGOU LOESS SECTIONS IN QINGHAI LAKE REGION

The Qinghai Lake area is a hot spot in global change studies,due to its sensitivity to global warming.During the last deglaciation,aeolian deposits were widely distributed in the region,with drastic environmental and climatic changes.In this paper,we studied two loess sections(JXG1and JXG2) near the Jiangxigou town to the south of Qinghai Lake,upon which we reconstructed the regional environmental changes since the last deglaciation.The results show that :(1) During 13～11.5kaBP,the paleolclimate was cold and dry there.Aeolian deposition prevailed and sandy loess formed.In general,the region was changing from a cold and dry to a cool and humid environment;(2) During 11.5～5kaBP,pedogenesis was relatively strong.Maximum moisture levels occurred during the period of 9～5kaBP,and in general,the paleoclimate was warm and wet;(3) After 5kaBP,climate often alternated,dust storm occurred frequently,vegetation coverage decreased,and the climate entered a relatively unstable stage.The environmental changes of the Jiangxigou Loess section are comparable with those revealed by the boreholes in the Qinghai Lake and the Heimahe loess section.The redness of the Jiangxigou loess section is a sensitive index to environmental change.The loess deposition since the last deglaciation in Qinghai Lake area was mainly controlled by the ice volume of the northern hemisphere,which was driven by the summer solar irradiation at the high latitude.The Westerlies played the role as a cold-air conveyer between the North Atlantic and the northeastern Tibetan Plateau.

A comparative study of radiocarbon dating on terrestrial organisms and fish from Qinghai Lake in the northeastern Tibetan Plateau, China

Qinghai Lake is the largest lake on the Tibetan Plateau (TP) and in China and has been a focus of paleoenvironmental and climatic research for decades. However, limited understanding of lake 14C reservoir effects (LRE) has led to inconsistent interpretations among proxies of different sediment cores. As such, the onset of LRE variability during the Holocene is still unclear. 14C dating of archeological samples from four locations (Gangcha, Shaliuheqiaoxi, and Shinaihai sites, and Niaodao section) including naked carp (Gymnocypris przewalskii, Kessler) fish bones, animal bones and teeth, and charcoal was employed to estimate variations in LRE over the last few thousand years. LRE offsets calculated as the difference between LRE of animal bones and fish bones are more reliable than that of charcoal and fish bones due to the ‘old wood’ effect in charcoal. LRE offsets recorded in fish bones were ~0.5, ~0.6, and ~0.7 ka during the periods of 3.0–3.4 cal ka BP, 0.58–0.60 cal ka BP, and modern lake times, respectively, which may indicate a temporal minimum LRE offset. Unlike the wide spatial variations of LRE ages obtained from surface total organic carbon (TOC) samples of the modern Qinghai Lake, LRE offsets from the three contemporaneous locations in Qinghai Lake were all ~0.5 ka, suggesting efficient carbon mixing occurred in naked carp. However, the late-Holocene (~3.1 ka BP) LRE increased slightly with increasing salinity and decreasing lake level.

Variations in Air Temperature during the Last Century Revealed by delta18O in the Chongce Ice Core from the Tibetan Plateau

Through analyzing the isotopic ratio δ18O variation characteristics of Chongce ice core, it exhibited an increase trend in the 20th century, and the temperature near the Chongce Ice Cap rose about 1.1 °C during last century. Through wavelet analysis, the δ18O in Chongce ice core showed three heating periods and two cooling periods. The wavelet variance analysis of the isotopic ratio δ18O variation indicates 13-year, 25-year and qusia-46-year periods. Compared with the ground weather observation stations in the high north Tibetan Plateau and the low Taklimakan Desert, and the June-September mean temperature of the MUT (500hPa and 300hPa) above the whole Asia for 1948-92, the results show that the climatic information on the TP in Chongce ice core is likely very less, and the δ18O of Chongce ice core may represent the summer temperature of Taklimkan Desert and the summer temperature of the middle-upper tropsphere above the middle-high latitude Asia especially the central Asia.