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Glacier-fed lakes on the Tibetan Plateau (TP) have undergone rapid expansions since the late 1990s, concurrent with the changing climate. However, the dominant cause(s) of lake area increases is still debated. To identify the drivers of lake expansion, we studied Aweng Co, a glacier-fed lake in the western TP, where surface area has increased (0.74 km2 year−1) since the late 1970s and most rapidly (0.998 km2 year−1) since the late 1990s. A water balance model was used to clarify the reasons for increased lake water volume, supported by stable isotope hydrology and the δ18O change recorded in recent sediments. Results showed that glacial meltwater probably had the biggest impact on changes in Aweng Co lake level in recent decades, but that precipitation was also an important contributor. Our study shows that δ18O of carbonate (δ18Ocarb) has great potential for indicating source changes of water supply in such lakes, but there is a need to be cautious when interpreting δ18Ocarb due to the influence of multiple hydrological factors, which can change in dominance over time. [ABSTRACT FROM AUTHOR]

Paleoenvironmental history in the monsoonal margin in the northeast Tibetan Plateau provides important clue to the regional climate. Previous researches have been limited by either poor chronology or low resolution. Here we present a high-resolution pollen record from a 40.92-m-long sediment core (DLH) taken from Dalianhai, a terminal lake situated in the Gonghe Basin, the northeast Tibetan Plateau for reconstructing the vegetation and climate history since the last deglacial on the basis of a chronology controlled by 10 AMS C dates on plant remains preserved in the core sediments. The pollen assemblages in DLH core can be partitioned into 6 pollen zones and each zone is mainly characterized by the growth and decline of tree or herb pollen percentage. During the periods of 14.8-12.9 ka and 9.4-3.9 ka, the subalpine arboreal and local herbaceous pollen increased, indicating the subalpine forest developed in the surrounding mountains and a desert steppe or typical steppe developed in Gonghe Basin under a relatively moister climate. During the periods of 15.8-14.8 ka, 12.9-9.4 ka and 3.9-1.4 ka, the forest shrank or disappeared according to different degrees of aridity, and the desert steppe degraded to a more arid steppe desert in the basin, indicating a dry climate. After 1.4 ka, vegetation type around Dalianhai was mainly dominated by steppe suggested by increased Artemisia. Our results suggested the climate history in this region was dry from 15.8-14.8 ka, humid from 14.8-12.9 ka and dry from 12.9-9.4 ka, after which the climate was humid during 9.4-3.9 ka, followed by dry conditions during 3.9-1.4 ka and humid conditions in the last 1.4 ka. The change of pollen percentage and the evolution of palaeovegetation in Dalianhai since the last deglacial were similar to those recorded in Qinghai Lake. The forest expanded in the mountains around Dalianhai during the Bølling-Allerød period, shrank during the Younger Dryas and the early Holocene, then it developed and reached its maximum in the mid-Holocene. During the late Holocene, the vegetation began to shrink till disappearance. However, the timing of forest expansion in the Holocene lagged behind that of Qinghai Lake, and this spatial heterogeneity was probably caused by the different forest species between these two places. The maximum of forest development in the mid-Holocene was inconsistent with the period of stronger summer monsoon in the early Holocene indicated by stalagmite records, the reason might be related to the complexity of vegetation response to a large-scale climatic change. [ABSTRACT FROM AUTHOR]

Hala Lake is located in the Qilian Mountains, Qinghai Province, China, at 4,078 m a.s.l. Its sediments contain an archive of climate and hydrologic changes during the Late Quaternary, as it is located close to the area influenced by the East-Asian summer monsoon and westerly-driven air masses. Sedimentation patterns and depositional conditions within the lake were investigated using eight sediment cores from different water depths, and this information was used to evaluate the feasibility of using a single core to reconstruct past climate and hydrological conditions. Long core H7, from the center of the lake (65 m water depth) and core H8 from a western, near-shore location (20 m water depth), were compared in detail using sediment composition and geochemical data (X-ray fluorescence, loss-on-ignition and CNS analysis). Age models were constructed using 17 AMS radiocarbon dates and indicate negligible reservoir error for sediments from the lake center and ~1,000 year errors for the near-shore sediment core. Cores H1-H5 and HHLS21-1 revealed a sediment succession from sand and silty clay to laminated clay on the southern side of the lake. Undisturbed, finely laminated sediments were found at water depths ≥15 m. Core H5 (2.5 m long), from 31 m water depth, yielded abundant green algal mats mixed with clayey lake deposits and was difficult to interpret. Algae occurred between 25 and 32 m water depth and influenced the dissolved oxygen content of the stratified lake. Comparison of cores H7 and H8 yielded prominent mismatches for different time periods, which may, in part, be attributed to internal lacustrine processes, independent of climate influence. We thus conclude that data from a single sediment core may lead to different climate inferences. Common shifts among proxy data, however, showed that major climate shifts, of regional to global significance, can be tracked and allow reconstruction of lake level changes over the last 24,000 years. Results indicate advance of glaciers into the lake basin during the LGM, at which time the lake experienced lowest levels, 25-50 m below present stage. Stepwise refilling began at ca. 16 kyr BP and reached the −25 m level during the Bølling/Allerød warm phase, ca. 13.5 kyr BP. A desiccation episode falls within the Younger Dryas, followed by a substantial lake level rise during the first millennium of the Holocene, a result of climate warming, which promoted glacier melt. By ca. 7.6 kyr BP, the lake reached a stable high stand similar to the present level, which persisted until ca. 6 kyr BP. Disturbed sediments in core H7 indicate a single mass flow that was most likely triggered by a major seismic event ~8.5 kyr BP. Subsequent lake development remains unclear as a consequence of data mismatches, but may indicate a general trend to deteriorating conditions and lake level lowstands at ca. 5.0-4.2, 2.0 and 0.5 kyr BP. [ABSTRACT FROM AUTHOR]

Grain-size distributions and detrital minerals were investigated for modern dust and for lacustrine sediment in Lake Barkol region, northwest China. Characteristics of the modern dust and lacustrine sediments, principle component analysis, and changes of quartz contents all suggest grain size 45-138 μm in the core sediment is the dust sensitive component. It indicates that high dust flux climate occurred at mid-Holocene (5.5-4.5 cal ka BP), corresponding to the high dust flux record in northwest Pacific and the drought interval of deserts in northwest China during the mid-Holocene. The strong dust activity is in contradiction with the climatic optimum recorded by the lacustrine evidence in Xinjiang. Different responses of the dust source region and watershed to the regional climate may have led to the inconsistency between dust and climate records during the mid-Holocene in arid central Asia. [ABSTRACT FROM AUTHOR]

Using -24‰ and -14‰ as the endpoints of stable carbon isotopic composition of total organic carbon (δ13 CTOC) of surface soil under pure C3 and C4 vegetation, and surface soil δ13 CTOC data from eastern China, Australia and the Great Plains of North America, we estimate the relative abundance of C3/C4 plants (i.e., the ratio of C3 or C4 biomass to local primary production) in modern vegetation for each region. The relative abundance of modern C3/C4 vegetation from each region is compared to the corresponding climatic parameters (mean annual temperature and precipitation) to explore the relationship between relative C4 abundance and climate. The results indicate that temperature controls the growth of C4 plants. However, even where temperature is high enough for the growth of C4 plants, they will only dominate the landscape when precipitation declines as temperatures increase. Our results are consistent with those of other investigations of the geographic distribution of modern C4 plant species. Therefore, our results provide an important reference for interpretation of past C3/C4 relative abundance records in these three regions. [ABSTRACT FROM AUTHOR]

A 1000-year high-resolution (~10 years) chironomid record from varved sediments of Sugan Lake, Qaidam Basin on the northern Tibetan Plateau, is presented. The chironomid assemblages are mainly composed of the relatively high-saline-water taxa Psectrocladius barbimanus-type and Orthocladius/ Cricotopus, and the relatively low-saline-water taxa Procladius and Psectrocladius sordidellus-type. Variations in the chironomid fauna and inferred salinities suggest that over the last millennium, the Sugan Lake catchment has alternated between contrasting climatic conditions, having a dry climate during the period 990-1550 AD, a relatively humid climate during the Little Ice Age (LIA) (1550-1840 AD), and a dry climate again from 1840 AD onwards. At the decadal to centennial scale, a wet event around 1200-1230 AD, interrupting the generally arid period (990-1550 AD), and a dry event around 1590-1700 AD, punctuating the generally humid period (1550-1840 AD), are clearly documented. Trends in the chironomid-based salinity time series indicate a highly unstable climate during the LIA when salinity fluctuations were of greater magnitude and higher frequency. The effective moisture evolution in the Sugan Lake catchment during the last millennium reconstructed by chironomid analysis is in broad agreement with previous palaeo-moisture data derived from other sites in arid Northwest China (ANC). The LIA, characterized by generally humid conditions over the westerly- dominated ANC was distinctly different from that in monsoonal China, implying an "out-of-phase" relationship between moisture evolution in these two regions during the past 1000 years. [ABSTRACT FROM AUTHOR]

Surface soil samples collected over a high spatial resolution in eastern China were analyzed for carbon Isotope composition (δ13C) of total organic carbon (TOC) and higher plant-derived long-chain n-alkanes, with the latter reported as weighted mean values. The two sets of δ13C values are significantly correlated and show similar trends in spatial variation. The spatial distribution of δ13C shows less negative values in the mid-latitudes between 31°N and 40°N and more negative ones at higher and lower latitudes. This is consistent with previously reported carbon isotope data from surface soil phytoliths in the same region and suggests that the mid-latitude area provides relatively favorable growing conditions for C4 plants. Furthermore, δ13C values of both TOC and long-chain n-alkanes from 12 surface soil samples collected from a small grassland in north China displayed similar carbon isotope values and the difference between paired δ13C of a soil samples remains relatively constant. Our data demonstrate that in eastern China, soil δ13C composition of both TOC and long-chain n-alkanes is effective indicators of C3/C4 ratios of the prevailing vegetation. This work suggests that -22% and -32% are good estimated end members for the weighted mean δ13C values of long-chain n-alkanes (C27, C29 and C31 n-alkanes) from soils under dominant C4 or C3 vegetation, allowing us to reconstruct paleovegetation trends. [ABSTRACT FROM AUTHOR]

Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceeds 3 m. Seasonal surface sediments trapped at the bottom of the lake suggest that sediments deposited during summer and autumn are mainly light colored monohydrocalcites, while those deposited in winter are dark organic matter, indicating that varve layers form under modern limnological conditions. Continuous varve sediments comprising four types have accumulated in the upper 5.5 m of Core SG03I from the center of the lake. All types exhibit clear seasonality indicative of annual deposition. Varve counts correspondence with 210Pb dates on recent sediments in the upper core suggest the continuous varves of the upper 5.5 m of the core formed in the late Holocene (2670 a BP). The Sugan Lake varve sequence is the first demonstration of annually laminated sediments reported in arid western China. [ABSTRACT FROM AUTHOR]

Samples of surface deposits in the Lake Sugan catchment, as well as surface lake sediments, eolian materials occulted in the lake ice cover, and airborne dust were collected for grain-size analysis. The results show that the coarse fraction of the lake sediments could be transported by ambient winds and to a lesser extent by river flow in the study area. Sediment cores were retrieved from Lake Sugan in December 2000, and 210Pb and 137Cs dating and grain-size analyses were performed on these samples. 210Pb ages and the volume percentage of the fraction of lake sediments >63 μm were used to reconstruct the dust storm history from 1957 to 2000. Observational data for dust storm events collected at a local meteorological station largely agrees with the reconstructed trend for the past 44 years, suggesting that lake sediments can be employed to trace the dust storm history of the northern Qinghai–Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Paleoecological records of soil δ13Corg from three regions in the middle latitudes of the Northern Hemisphere, including the Chinese Loess Plateau (CLP), the Great Plains and adjacent areas of North America and northwestern Europe, showed different variations since the Last Glacial period. An attempt was made to evaluate the causes for the difference in δ13Corg on the basis of the modern climatic data collected in these regions and of the modern C3 and C4 plant distributions. The analysis indicates that temperature, especially the growing season temperature, has a dominant control on the growth of C4 plants. When the mean annual or growing season temperatures are below the ‘threshold value’, the growth of C4 plants is limited. When the temperature is above the ‘threshold value’, C4 plants can grow under a wide range of precipitation. However, when the precipitation is high enough to favor the growth of trees, the proportions of C4 plants in local biomass will decline. The implicit control factor recovered by sedimentary records is consistent with the control factor on modern C3/C4 distribution. Pure C3 plants have been dominating the local biomass since the Last Glacial period in European loess region, mainly owing to the low local temperature. The increases in C4 plants from the late Pleistocene to the Hobocene in the Chinese Loess Plateau, the Great Plains and adjacent areas, mainly reflect the influence of increasing temperature. [ABSTRACT FROM AUTHOR]

Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating results. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000–1500 AD, a humid climate during the Little Ice Age (LIA) ( c. 1500–1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indicate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concentrations, decreased carbonate content and increased grain size. The humid period during the LIA recorded by the Bosten Lake sediments is representative of arid central Asia and is supported by numerous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipitation increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA. [ABSTRACT FROM AUTHOR]

A high-resolution loess section in the western Chinese Loess Plateau, Yuanbao Section, was sampled for organic carbon isotopic analyses. The soil organic carbon isotope (δ Corg) varied between -22.6‰ and -27.5‰ during the last glacial at the section. During the last interstadial, the δ Corg values were more negative than those in both early and late periods of the last glacial by 4‰. The isotopic composition indicates a coupled response of the pure C3 plants to the temperature, precipitation and the concentration of atmospheric CO2. Decrease in temperature and the atmospheric CO2 concentration from the last interstadial to Last Glaicial Maximum (LGM) caused the organic carbon isotopes to become positive by 1.5‰ 2.0‰. The amplitude of 4‰ in the δ Corg variation during the last glacial should be mainly caused by the precipitation change. Therefore, the δ Corg variations of the Yuanbao Section during the last glacial period documented the large-amplitude fluctuation of the monsoon precipitation, which is estimated to be 250-310 mm more during the last interstadial than that in the LGM, and 100 mm more than that during early last glacial. The rapid changes of the monsoon precipitation on millennial scale during the last glacial have also been recorded in the isotopic variations in Yuanbao loess section. As the isotopic composition varies complicatedly as shown in the loess-paleosol sequence, it cannot be simply attributed to the abundances of C3 and C4 plants or be used as an indicator of the summer monsoon variations. [ABSTRACT FROM AUTHOR]

Lake Sugan at the northern edge of the Qaidam Basin was selected as the research object. The temporal sequence of sedimentary cores retrieved from Lake Sugan since 2 kaBP was reconstructed using the 210Pb, AMS 14C and conventional 14C dating methods. Carbon and oxygen isotopes of carbonate in the fine-grained lake sediments were analysed. Combined with the changes of δ18O values of surface water and air temperature observation data in the study area, it might be thought that the δ18O value of the carbonate indicates effective moisture, and the changes in δ13C values are related to annual freeze-up duration of the lake and indirectly indicate air temperature changes in winter half year. From the above, the sequence of climatic changes in the region since 2 kaBP was established. The climatic changes experienced five stages: Warm-dry climate during 0-190 AD; cold-dry climate during 190-580 AD; warm-dry climate during 580-1200 AD (MWP); cold-wet climate during 1200-1880 AD (LIA); cold-dry climate during 1880-1950 AD; and climate warming since 1950s. The air temperature changes in winter half year reflected by carbon isotope since 2 kaBP are in good agreement with the historical literature records and other geologic records, which shows that the climate changes recorded by the stable isotopes from Lake Sugan since 2 kaBP are of universal significance. [ABSTRACT FROM AUTHOR]

Studies high-resolution precipitation variations in the northeast Tibetan Plateau in China over the last 800 years until 2003, documented by Qinghai Lake sediment cores. Climatic history of the plateau; Area with the highest sedimentary rate; Dry periods in the area.

Considers pollen transport in the Shiyang River drainage in China. Contribution of the pollen transported by wind and fluvial flows to the pollen spectra in the river's drainage; Dissimilar effects of dispersal agents on transport of pollen and the structure of pollen spectra.

Estimates the history of groundwater recharge and climatic changes during the last 1000 years until 2003 in Badain Jaram Desert, China. Wet phases and dry episodes within the period; Occurrence of large-scale climate difference between mountain regions and the desert basin during the 20th century.

Examines temperature variations in the Tibetan Plateau (TP) in China over the last two millennia until 2003. Regional features of climatic change on the plateau during the last 2000 years; Main climatic episodes during the period; Most prominent similarities between the temperature variations of the TP and eastern China.

Presents a study on two loess sections, one located at Wuwei near the Tengger Desert in northwestern China, another located near Ganzi at the southeast margin of the Tibetan Plateau in southwest China. How the study reveals a coeval drying step occurred at ∼250 kaBP, expressed by the increase in eolian grain-size at Wuwei, and by a drastic extension of C4 plants and a decrease of loess chemical weathering intensity at Ganzi; Examination of the available eolian data, which indicates that the event has also been clearly documented in the loess sections near the deserts in northern China, and in the eolian records from the North Pacific; Effect of the southwest Asian monsoon on the Ganzi climate; Interpretation of this drying step as a result of decreased influence of the southwest summer monsoon; Cause of the decrease in monsoon moisture due to the uplift of the Hengduan Mountains, the southeast margin of the Tibetan Plateau at ∼250 ka ago.

The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka = thousands of years before present, where the 'present' is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7-7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8-5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5-8.5 ka, and by two centennial-scale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change. [ABSTRACT FROM AUTHOR]