Environmental changes during early-middle Holocene from the sediment record of the Chaohu Lake,Anhui Province

A typical lake sediment core is obtained from the Chaohu Lake in the lower reaches of the Yangtze River,Anhui Province,China.The timing scale is constrained by AMS 14 C dating method.Climate proxies such as pollen and grain size in the core are analyzed to reconstruct the environment changes at this site approximately between 9870 and 2170 cal.a BP.The results indicate that at the research area, the climate in the early-middle Holocene had evolved through 3 stages.From 9870 to 6040 cal.a BP, proxy records show a warm and dry climate with low water levels after the late-glacial period.During this stage,cool and dry events occurred at about 8910 and 6060-6030 cal.a BP.Then,between 6040 and 4860 cal.a BP,the climate was humid and vegetation was more flourishing in the Chaohu Lake Valley.The Holocene Optimum occurred at 5840-5500 cal.a BP in the Chaohu Lake,showing the best condition of water and heat.Elm Decline occurred at the period of 5380-4930 cal.a BP.Since 4860 cal.a BP,the climate was warm and dry through 2170 cal.a BP as shown in both pollen spectrum and grain-size histories.Two obvious dry events occurred in 3760 and 2170 cal.a BP,respectively.At 2170 cal.a BP,the water level of the Chaohu Lake reached the lowest as the lakebed possibly exposed. Such lake sediment observations are consistent with the historical records in this area.

Possible obliquity-forced warmth in southern Asia during the last glacial stage

Orbital-scale global climatic changes during the late Quaternary are dominated by high-latitude influenced~100,000-year global ice-age cycles and monsoon influenced~23,000-year low-latitude hydroclimate variations.However,the shortage of highly-resolved land temperature records remains a limiting factor for achieving a comprehensive understanding of long-term low-latitude terrestrial climatic changes.Here,we report paired mean annual air temperature(MAAT)and monsoon intensity proxy records over the past 88,000 years from Lake Tengchongqinghai in southwestern China.While summer monsoon intensity follows the~23,000-year precession beat found also in previous studies,we identify previously unrecognized warm periods at 88,000-71,000 and 45,000-22,000 years ago,with 2-3℃amplitudes that are close to our recorded full glacial-interglacial range.Using advanced transient climate simulations and comparing with forcing factors,we find that these warm periods in our MAAT record probably depends on local annual mean insolation,which is controlled by Earth’s~41,000-year obliquity cycles and is anti-phased to annual mean insolation at high latitudes.The coincidence of our identified warm periods and intervals of high-frequent dated archaeological evidence highlights the importance of temperature on anatomically modern humans in Asia during the last glacial stage.

One century sedimentary record of lead and zinc pollution in Yangzong Lake, a highland lake in southwestern China

Reconstruction of trace metal pollution histories and sources may help us to regulate current pollutant discharge. This is especially important for the highland lakes in southwestern China, which are facing trace metals pollution. We present sedimentary records of 11 metals accumulated in Yangzong Lake since the 1870＇s, a highland lake in southwestern China. Pollution of lead and zinc （Pb and Zn） was differentiated based on principal component analysis, geochemical normalization, and lead isotope ratios. Nearly all the metals as well as grain size composition show generally constant values before the mid-1980＇s, denoting stable detrital input in the catchment. Fluctuations in the concentrations of the metals as well as grain size composition since the mid-1980＇s indicate an increase in soil erosion with strengthened human disturbance in the catchment. After geochemical normalization, Pb and Zn showed constant values before 1990 AD and then a gradual increase in parallel with the variations in 2~spb/~~6pb and 2~7pb/2~6pb ratios, indicating that Pb and Zn pollution occurred. Combining the data of 20PPb/206Ppb and 207Pb/206Pb ratios in the sediments of Yangzong Lake, leaded gasoline, Pb-Zn ore and coal, and consumption or production historical trends, we deduced that the enhanced Pb and Zn pollution in Yangzong Lake is caused primarily by ore mining and refining.

Black carbon record of the wildfire history of western Sichuan Province in China over the last 12.8 ka

Wildfire is recognized as a critical Earth system process which affects the global carbon cycle, atmospheric chemistry, and ecosystem dynamics. Estimat- ing the potential impact of future climate change on the incidence of fire requires an understanding of the long-term interactions of fire, climate, vegetation, and human activity. Accordingly, we analyzed the black carbon content and the pollen stratigraphy of sediments spanning the past 12.8 ka from Lake Muge Co, an alpine lake in western Sichuan Province, in order to determine the main factors influen- cing regional fire regimes. The resuks demonstrate that wildfires occurred frequently and intensively during the late deglaciation and the early Holocene when the regional vegetation was dominated by deciduous forests. Wildfire occurrence decreased significantly during the Holocene climatic optimum between 9.2 and 5.6 cal ka BP. Overall, the wildfire history of western Sichuan Province is similar to that of the Chinese Loess Plateau and of East Asia as a whole, suggesting that regional-scale fires depended mainly on changes in the intensity of the Asian summer monsoon. In addition, the fire regime of western Sichuan Province may have been influenced by the establishment of human settlement and agriculture in western Sicbuan Province and the southeastern Tibetan Plateau after about 5.5 cal ka BP, and by an intensification of cereal cultivation coupled with population expansion in southwestern China during the last two millennia.