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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]

Formation and evolution of the Asian landform was determined by growth of the Himalaya-Tibetan Plateau and evolution of the Asian monsoon climate during the Cenozoic period. In this process, mountain building and degradation, and river drainage reorganization are the most obvious results. On the other hand, developments of large scale drainages preserved in related basin sediments are direct records of evolution of Asian landforms. In this study, we use thick fluvial-lacustrine sediments in the Weihe Basin near the northeastern Tibetan Plateau, and Ocean Drilling Program (ODP) sediment cores from Arabian Sea adjacent to the southwest Himalaya-Tibetan Plateau, to reconstruct erosion processes of the Himalaya-Karakorum and Qinling Mountains and infilling history of the Weihe Basin and northern Arabian Sea during the Cenozoic. Based on independent stratigraphic chronology and source-to-sink analyses, our results show that the large drainages of the Wei River and the Indus River were established at an upper limit of time by middle Eocene. Since the formation of these large drainages is mainly determined by topography and precipitation/runoff, we deduce that key parts of Asian landform such as southwestern/western Tibetan Plateau and Qinling Mountains had grown to a significant elevation to form the proto-Indus and proto-Wei rivers catchment. The modern-analogue Asian topography was established at least by the middle Eocene. Our new results support an early origin of the Asian landforms as responses to the collision of Indian and Eurasian plates and erosion by the Asian hydrology processes. • The large drainage of the proto- Weihe and Indus Rivers was established by ∼46 Ma. • A modern-like Asian topography and climate was preliminary built by middle Eocene. • Global temperature and tectonic deformations have determined the Asian landscape. [ABSTRACT FROM AUTHOR]

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: A series of 14C ages were made in two lake sediment cores from Co Ngoin and Zigê Tangco, central Tibetan Plateau, China, using bulk organic carbon, plant remains, chitin of cladocera, and carbonates. The old 14C ages of the surface sediments in both cores suggests that there is a significant reservoir effect in these lakes. The magnitude of the reservoir age of different material is variable. Authigenic carbonate has the largest reservoir age, while plant remains and chitin show smaller deviations. Due to a lack of terrestrial macrofossils at most depths, a regression approach was used to obtain the approximate 14C reservoir correction for bulk organic matter, which is 3260 14CBP and 2010 14CBP for Co Ngoin and Zigê Tangco respectively. [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]