E. Chongyi

Aquatic species dominate organic matter in Qinghai Lake during the Holocene: Evidence from eolian deposits around the lake

Total organic carbon (TOC) in lake sediments and its stable carbon isotope (δ13Corg) are widely applied to investigate paleoenvironmental changes even though their implications are complicated and multi-explanatory. Organic geochemistry studies of lake sediments from Qinghai Lake have been investigated, but some interpretations are controversial. In this study, TOC of one Holocene eolian section and δ13Corg of three eolian sections were studied around Qinghai Lake. Results indicate that the TOC content in eolian deposits was low during the Early Holocene, and gradually increased to high values during the Middle and Late Holocene. The variation in TOC content of eolian deposits is different from that in the lacustrine sequence from Qinghai Lake during the Holocene. The δ13Corg values in the eolian sections were relatively stable, with oscillation amplitudes of ~4‰ (ranging from -25.8‰ to -22.1‰), in contrast to ~10‰ variations in δ13Corg values (varying from -30‰ to -20‰) in lacustrine sediments. Through comparison of TOC and δ13Corg values between eolian deposits and lacustrine sediments, we can confirm indications that the organic matter in Qinghai Lake sediments during the Holocene was primarily a contribution of the aquatic species in the lake. This is significant for understanding the origin of organic matter in lake sediments on the northeastern Qinghai-Tibetan Plateau and for paleoenvironmental inferences using such proxies.

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.

Reconstruction of cultivated land during mid- Holocene in the middle and lower reaches of Yellow River and human impact on vegetations

Yangshao culture is the most important mid-Holocene Neolithic culture in the Yellow River catchment, and thus, a study on the impact of human activities on the environment is important. In the current study, the distribution pattern of the cultivated land in late Yangshao culture is reconstructed using GIS tool and site domain analysis (SDA). The results show that the cultivated land during 5.5–5.0 ka BP was mainly distributed in the Weihe River valley, Luohe River valley, northwestern Henan Plain, Fenhe River valley and eastern Gansu region, especially concentrated in the Xi’an-Baoji line of the Weihe River valley. At that time, at least 37,000 km2 of lands were reclaimed in the middle and lower reaches of the Yellow River, and 132,000 km2 of lands were affected by agricultural activities. Human activities had become the driving force of land use/land coverage. Charcoal records indicate that the ancestors of Yangshao culture burnt forests for reclamation, leading to the decrease of arbor pollen at 5 ka BP in core areas of the Yangshao culture. The areas that were significantly affected by human activities accounted for 3.2% of the Yangshao culture influenced area, while the moderately affected areas accounted for 20.1% of Yangshao culture influenced area. Meanwhile, 92% of the land areas on the edge and outside of the Yangshao culture influenced area were not affected by human activities. The arbor pollen in these areas did not decrease until 4.0 ka BP.