Search

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]

Based on the analysis of carbonate content and loss on ignition for a long sediment core (737 m in length) drilled in Heqing, the orbital scale evolution of the Southwest Monsoon is revealed, by using overlapped spectral analysis and filter methods. It is shown that the obliquity cycle and precession cycle are the key factors for the Southwest Monsoon evolution and that the change of the global ice volume and the uplift of the Qinghai-Tibetan Plateau also impose great influences on it. [ABSTRACT FROM AUTHOR]

The δ18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake can be used as a better proxy to reflect monsoon changes, Low monsoon precipitation between 17.5 and 11 cal. ka BP is indicated by positive #180 values averaging 2.37‰. A fast shift in #180 from positive at 11 cal, ka BP to negative at 10 cal. ka BP indicates sharp increase of monsoon precipitation. An interval of generally high monsoon precipitation is observed between 10 and 6 cal. ka BP with δ18O values averaging -2,15‰. Decrease of monsoon precipitation between 6 and 2.5 cal. ka BP is indicated by positive δ18O values. δ18O keeps positive values averaging 3.0‰ between 2,5 and 0 cal, ka BP suggesting low high monsoon precipitation. The climatic changes indicated by δ18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake and our broader regional comparison show that the climate in Qinghai Lake since the late Glacial is probably controlled by southwest monsoon other than southeast monsoon. [ABSTRACT FROM AUTHOR]

Presents information on the environmental evolution and southwest monsoon changes recorded by lake sediments from Erhai Lake, Yunnan Province, China. Methodology; Environmental condition in Erhai Lake; Characteristics of lakes in Qinghai-Tibetan Plateau.

Climatic and environmental changes in the northeastern Tibetan Plateau are controlled by the Asian summer monsoon (ASM) and the westerlies, two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern Asia. During the past few decades, a series of Holocene palaeoclimatic records have been obtained from sediment cores from Lake Qinghai and from various other geological archives in the surrounding area of the northeastern Tibetan Plateau. However, because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used, the nature of Holocene climatic changes in the region remains unclear and even controversial. Here we review all major classes of the published data from drilled cores from Lake Qinghai, as well as other evidence from lakes and aeolian deposits from surrounding areas, in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the Holocene. Combining the results of moisture and precipitation proxies such as vegetation history, pollen-based precipitation reconstruction, aeolian activity, lake water depth/lake level changes, salinity and sediment redness, we conclude that moisture and precipitation began to increase in the early Holocene, reached their maximum during the middle Holocene, and decreased during the late Holocene - similar to the pattern of the East Asian summer monsoon (EASM) in northern China. It is clear that the region experienced a relatively dry climate and weak EASM during the early Holocene, as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations; generally low lake levels of Lake Qinghai and the adjacent Lake Hurleg and Lake Toson in the Qaidam Basin; and widely distributed aeolian sand deposition in the Lake Qinghai Basin and the nearby Gonghe Basin to the south, and in the eastern Qaidam Basin to the west. We argue that the ostracod δ 18 O record, which is widely used as a proxy of effective moisture and summer monsoon intensity in lake sediments, at least in Lake Qinghai, and which exhibits light values in the early Holocene and heavier values thereafter, cannot be used to reflect the strength of the EASM or the intensity of monsoon precipitation - as is also the case for leaf wax δ 2 H records. Rather, we argue that as is the case of the Chinese speleothem δ 18 O record, which also is often interpreted as an EASM proxy, it reflects variation in the δ 18 O of precipitation. Overall, we suggest that the EASM significantly affected precipitation in the northeastern Tibetan Plateau during the Holocene; and that it increased in strength during the early Holocene, reached a maximum during the middle Holocene and decreased during the late Holocene. [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]