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High-resolution pollen and charcoal records from Qinghai Lake in south-western China are presented. The records reveal variations in vegetation, fire and climate history since 18 500 cal a BP. The results show that seven significant vegetation changes are recorded, which are responses to climate changes and/or fire events. Frequent and intensive fires occurred during the periods 17 900-15 000, 13 000-11 500 and 4280-980 cal a BP, corresponding to relatively dry climatic conditions. Combined with the climatic record from Tiancai Lake, the regional climatic changes since 18 500 cal a BP in western Yunnan Province are reconstructed. Namely, the Heinrich Event 1, the Bølling-Allerød warm period and the Younger Dryas event during the last deglaciation are ubiquitous in western Yunnan Province. The start of the Holocene is recorded at 11 500 cal a BP. The Holocene climatic optimum occurred between 8450 and 4280 cal a BP. After 4280 cal a BP, the climate deteriorated, accompanied by evidence for human impact. Based on this study, we consider that vegetation and climatic changes since 18 500 cal a BP in south-western Yunnan Province are primarily driven by September and average summer solar insolation, with some associated influence from regional sea-surface temperature and sealevel rise. [ABSTRACT FROM AUTHOR]

Pollen and charcoal records of a 150 cm long lake sediment core from Taibai Lake in the middle reach of the Yangtze River reveal seven major changes in regional vegetation over the last 1500 years. During the period c. ad 480–710, evergreen broadleaved forest dominated by Castanopsis/Lithocarpus and evergreen oaks occurred in the Taibai Lake catchment. From c. ad 710 to 1050, the vegetation shifted to a mixed conifer and broadleaved forest, with Pinus expanding at the expense of Castanopsis/Lithocarpus. Between c. ad 1050 and 1320, evergreen broadleaved forest reoccupied the studied area. From c. ad 1320 to 1650, the area of primary forest decreased markedly with synchronous reduction in broadleaved trees and Pinus. Between c. ad 1650 and 1740, the biomass declined rapidly, while secondary Pinus forest began to expand. During c. ad 1740–1950, forest extent increased slightly compared with the previous stage, but the landscape was still secondary forest with the minimum proportion of broadleaved trees. After c. ad 1950, the biomass in the surrounding area was very low, with vegetation types similar to that at present (secondary Pinus forest and mixed conifer and broadleaved forest). A detrended correspondence analysis (DCA) with 125 samples and 34 main pollen types is used to separate human and climatic impacts on vegetation. Then, the pollen assemblage, DCA, charcoal record, and magnetic susceptibility are combined to discuss the key factors inducing these vegetation changes. The vegetation changes were mainly controlled by the climatic changes, with the weak impacts of human activities before c. ad 1320. Since then, the intensity of human influences on vegetation increased gradually, entering a transitional period of main controlling factors of vegetation changes from nature to human activities. After c. ad 1740, the vegetation changes were chiefly controlled by human activities, and the climatic signal was weak. [ABSTRACT FROM AUTHOR]

The commonality and difference in the variations of temperature and precipitation between the Northern Hemisphere (NH) and Southern Hemispheres (SH) in the last millennium are investigated by analysis of the millennium simulation with the ECHO-G coupled climate model. The NH mean temperature variations are generally consistent with those of the SH counterpart on the interannual, decadal and centennial time scales. But, the transition times between the medieval warm period (MWP), the little ice age (LIA), and the present-day warm period (PWP) in the NH leads that in the SH; and the anomaly amplitude in the NH is significantly larger than the SH counterpart. For the precipitation variations, the NH mean precipitation varies in-phase with the SH mean precipitation on decadal and centennial scales (mainly in the mid-high latitudes) but out-of-phase on the interannual scale (mainly in the low latitudes). During the MWP the warming has comparable amplitude in the NH and SH; however, during the PWP the NH warming is considerably stronger than the SH warming. Further, the present-day temperature rises in the NH high latitudes but decreases in the SH high latitudes, which is very different from the warming pattern during the MWP. Since during the MWP the greenhouse gases (GHG) concentration stayed at a low level, we infer that the present-day opposite temperature tendency in the high latitudes between the two hemispheres may be related to the increase of the GHG concentration. [ABSTRACT FROM AUTHOR]

The reconstructed temperature anomalies in the eastern China were compared with the output from a 1000-year model simulation in an attempt to evaluate the model's regional simulation skills and to understand the causes of climate change in China over the last millennium. The reconstructed data are the winter half-year temperature anomalies in the central region of eastern China (25°–40°N, east of 105°E) for the last 1000 years with a 30-year resolution. The model used is the global atmosphere-ocean coupled climate model, ECHO-G, which was driven by time-varying external forcings including solar radiation, volcanic eruptions, and greenhouse gas concentrations (CO2 and CH4) for the same period. The correlation coefficient between the simulated and reconstructed time series is 0.37, which is statistically significant at a confidence level of 97.5%. The Medieval Warm Period (MWP) during 1000–1300 A.D., the Little Ice Age (LIA) during 1300–1850 A.D. and the modern warming period after 1900 A.D. are all recognizable from both the simulated and reconstructed temperatures. The anomalies associated with the LIA and the modern warming simulated by the model are in good consistency with the reconstructed counterpart. In particular during the Maunder sun-spot minimum (1670–1710 A.D.), both the simulated and reconstructed temperature anomalies reach their minima without any phase difference. But in the earlier MWP, significant discrepancies exist between the simulation and the reconstruction, which might reflect the degrading quality of the reconstruction data. The range of the simulated anomalies (1.62 K) is comparable with that of reconstructed (2.0 K). Diagnosis of the model results indicates that, during the last millennium, variations in solar radiation and volcanic activity are the main controlling factors on regional temperature change, while in the recent 100 years, the change of the concentration of greenhouse gases plays most important role in explaining the rapid temperature rising. [ABSTRACT FROM AUTHOR]

Abstract: The lightness (L*) and concentrations of Rb, Sr and organic carbon (C org) have been measured in the age-constrained lake sediment cores recovered from Co Ngoin in the central Tibetan Plateau. Dissolved Sr flux is a dominant control on the variation of Rb/Sr ratios in the sediments. Variations in color and geochemical proxies of Co Ngoin sediments display a continuous history of late glacial to mid-Holocene chemical versus physical weathering intensity in response to past climatic changes between approximately 13,500 and 4500 cal yr B.P. A lower chemical weathering under a late glacial climate was followed by a higher weathering during the Holocene Optimum. Weathering intensity in the central Tibetan Plateau catchment also responds to well-known climatic events, such as the Younger Dryas (YD), and possibly the Holocene Event 5 (HE-5). Although there are differences in time or duration of the climatic events, many of the well-known late glacial to mid-Holocene events occurred in high-elevation Co Ngoin where atmospheric circulation might play a hemispherical role in climatic forcing. The sediment hiatus since c. 4200 14C yr B.P. in the Co Ngoin indicates a period of desiccation that was probably associated with a sharp decrease in summer monsoon strength. Our lascustrine results not only imply catchment weathering variations in response to late glacial to mid-Holocene climatic conditions in the central plateau, but also provide further evidence for global connections between regional climates. [Copyright &y& Elsevier]

According to high-resolution analyses on multi-proxy of sediment core from the Er-hai Lake, Yunnan Province, the sequence of climatic and environmental change since the Holocene has been reconstructed based on accurate dating. The results show that climate had transited from cold-wet to warm-wet during ca. 12950-8399 aBP in this area, and the transition happened in ca. 10329 aBP. Due to the enhancing southwest Asian monsoon and increasing precipitation, the lake-level of the Erhai Lake began to rise after ca. 10329 a BP. Climate in the catchment was warm and wet during the mid-Holocene, and the warmest stage appeared in ca. 8399-6371 a BP. The lake-level descended in the mid-Holocene because of the decrease of effective moisture in the basin. Human activities appeared in ca. 6371 a BP, and the initial manner mainly focused on deforestation. Up to ca. 2139 a BP, due to the amount of immigration into this area, the cultivation was developed widely, which was followed by mining (coal mine). [ABSTRACT FROM AUTHOR]

New deglacial pollen and conifer stoma records from Tiancai Lake, northwestern Yunnan Province, southwestern China, an alpine lake in the southwest monsoon region, are presented in this study. Based on these records, the lithology of core TCYL1, and PCA analysis of pollen data between ~21 and 11.5kaBP (calibrated 14C years), the deglacial vegetation and climate changes are discussed in detail. The results show that Tiancai Lake was above the upper limit of Picea/Abies forest (a treeline in the study area) between ~21 and 11.5kaBP, and the climate was colder and drier than that of the Holocene. During this period eight significant vegetation changes are recorded that are considered to be responses to changing temperatures and variations in the southwest monsoon in southwestern China. The Heinrich Event 1 (H1), the Bølling/Allerød warm period (BA) and the Younger Dryas cold event (YD) are all clearly detected in this record. In addition, this study finds that the initial late glacial warming in northwestern Yunnan Province was at ~18.7kaBP, which is coincident with the climate records in monsoonal Central Asia, the Indian Ocean, the tropical and subtropical Pacific Ocean, and Antarctica, and is a response to solar insolation changes. A noted temperature increase between 15.8 and 14.4kaBP occurred at the end of the H1 and before the BA, which indicates a strong pre-Bølling warming. Based on the study, we consider that the hypothesis about a slowdown of the ocean's thermohaline circulation is sufficient to explain these late glacial abrupt events. [ABSTRACT FROM AUTHOR]

Abstract: Reconstructing past changes of the summer monsoon in southwestern China is key to understanding the paleoclimatic dynamics of the Indian summer monsoon (southwest monsoon), a major tropical system with impacts beyond the region. High-resolution pollen and conifer stoma data are presented from a sediment core (Tiancai Lake), located just below treeline in the Hengduan Mountains, northwestern Yunnan Province of China. These data record changes in vegetation and climate for the latest Pleistocene and Holocene (c. the last 12,230 cal. yr BP), and by comparing these results with the pollen records from the nearby Erhai Lake and Lugu Lake, a regional climate history in Yunnan Province can be inferred. During the period of 12,230–11,510 cal. yr BP, open alpine meadow around Tiancai Lake indicates a relatively cold and dry climate, corresponding to the Younger Dryas cold event (YD). Between 11,510 and ∼10,000 cal. yr BP, the vegetation types around Tiancai Lake changed into Picea and Abies forest and alpine Rhododendron shrubland, reflecting increases in the temperature and humidity. From ∼10,000 to 6100 cal. yr BP, Tsuga forest expanded persistently toward Tiancai Lake, indicating further climate changed towards warmer and wetter conditions. Between 6100 and 3410 cal. yr BP, Tsuga forest was the dominant vegetation type nearest to Tiancai Lake, denoting warm and humid climatic conditions, corresponding to the Holocene climatic optimum in the northwestern Yunnan Province. Tsuga forest in mountains around Lugu Lake shrank quickly at 3410 cal. yr BP, reflecting significant decline of humidity. Since 2930 cal. yr BP, Tsuga forest around Tiancai Lake shrank gradually, indicating a fluctuating decrease of temperature. These climatic changes reflect changes of the southwest monsoon, namely, warm and humid climate indicating strong southwest monsoon, cold and dry climate denoting weak southwest monsoon. [Copyright &y& Elsevier]

Abstract: As one of the pioneering projects of the Chinese Environmental Scientific Drilling (CESD) Program, a 206.5m long sediment core (CE) was retrieved from Co Ngoin (Co = lake) Basin in the central Tibetan Plateau. Limnic records of the abundance of ostracod shells and their oxygen and carbon isotope measurements, together with the geochemical and the sedimentological investigations, were carried out on the interval between 143 and 52m core depths, corresponding to ca. 2.01–0.84Myr. Distinct oscillations of the abundance and the chemical compositions of ostracod shells have yielded the original information about variations in lakewater chemistry in association with the change in the Indian monsoon over the period of 2.01 to 0.84Myr. The climate conditions during the Early Pleistocene were characterized by frequent oscillations and the ostracod records had expressed its synchronous response to these oscillations. A major climate change occurred in the Co Ngoin area at about 0.93Myr. A pronounced fluctuation in ostracod δ 18O and δ 13C during the Mid-Pleistocene transition (MPT) is possibly associated with an increase in continental ice sheets. The compositional and the sedimentological characters of the immediately overlying sediments imply a shallow aquatic environment and also a harsh (salinity?) condition beyond the tolerance limits for ostracod survival, resulting in the disappearance of the Qinghaicypris crassa Huang 1979 around 0.84Myr. [Copyright &y& Elsevier]

Abstract: Element content, grain size, pollen and 210Pb dating analysis were performed on 80 cm sediment core from Taibai Lake, a shallow lake in the middle reach of Yangtze River in China, to reveal the response of catchment environment to climate changes and human activities during the past four centuries. The 210Pb dating suggests that 0–39.5 cm of the core represents the past 163 years and bottom of the core is at ca. 1590 AD. Major changes showed in the core are compared with the records from historical documents, including population, cultivation and climate etc. 1700–1810 AD was the period with intensive human activities in Taibai Lake catchment, behaving as deforestation and cereal cultivation expansion, signaled in the sediments by low percentage of pinus pollen and high percentage of Gramineae pollen, high content of <16 μm fraction. Another period with intensive human activities was since 1928 AD, behaving as deforestation, reservoir construction, land reclamation, soil loss. The high sedimentation flux epochs, such as 1900–1920 AD, 1931 AD, 1938–1939 AD and 1954 AD, were correlated with high precipitation; nevertheless, the high sedimentation flux epochs in 1958–1970 AD and 1983–1993 AD were correlated with the land reclamation around Taibai Lake and soil loss due to intensive cultivation development respectively. The two coldest stages during the “Little Ice Age” were in 1650–1700 AD and 1810–1900 AD, consistent with the historical records generally, characterized by weak weathering, high forest coverage and weak human activities in Taibai Lake catchment. [Copyright &y& Elsevier]