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The palaeolake evolution across the Tibetan Plateau and adjacent areas has been extensively studied, but the timing of late Pleistocene lake highstands remains controversial. Robust dating of lacustrine deposits is of importance in resolving this issue. This paper presents C or optically stimulated luminescence (OSL) age estimates from two sets of late Quaternary lacustrine sequences in the Qaidam Basin and Tengger Desert (northeastern Tibetan Plateau). The updated dating results show: (1) the radiocarbon dating technique apparently underestimated the age of the strata of >30 ka BP in Qaidam Basin; (2) although OSL and C dating agreed with each other for Holocene age samples in the Tengger Desert area, there was a significant offset in dating results of sediments older than ∼30 ka BP, largely resulting from radiocarbon dating underestimation; (3) both cases imply that most of the published radiocarbon ages (e.g., older than ∼30 ka BP) should be treated with caution and perhaps its geological implication should be revaluated; and (4) the high lake events on the Tibetan Plateau and adjacent areas, traditionally assigned to MIS 3a based on C dating, are likely older than ∼80 ka based on OSL chronology. [ABSTRACT FROM AUTHOR]

Abstract: Radiocarbon dating of lake sediments is often hampered by the presence of a lake reservoir effect (LRE, also ‘dead carbon’ or ‘old carbon’ effect) especially in dry and cold regions with a sparse plant cover in the catchment. The Tibetan Plateau became a hotspot of the palaeoenvironmental and climate research community in recent years and the assessment of present-day LREs is a crucial prerequisite for the establishment of reliable radiocarbon age–depth relationships for lake sediment cores. This paper examines the spatial variability of LREs within individual lakes, through a discussion of new data for Lake Donggi Cona and a compilation of previously published data for five additional lakes where LRE data are available for different sites. Lake reservoir effects for Lake Donggi Cona on the northeastern Tibetan Plateau were determined for shells of aquatic snails collected alive close to the lake's shore. The largest determined LRE of 20,000 14C years is significantly larger than previously reported LREs from the central part of the lake, and larger than any previously published LRE for the Tibetan Plateau. Relatively low LREs in the central regions of lakes, higher LREs towards the margins, and high LREs in tributaries and spring waters are apparently a common pattern of Tibetan Plateau lakes. The differences in LREs within individual lakes or catchment areas are attributed to the more prolonged exchange of the lake water's dissolved inorganic carbon with the atmospheric CO2 in central lake regions on the one hand and the increasing influence of 14C free or poor stream and groundwater due to the dissolution of carbonaceous basement rocks towards its margins. Generally higher LREs were recorded in the three tectonically active lake regions of the six examined catchments, and it is speculated that rising crustal CO2 further contributes to the LREs in these catchments. In addition to these observations and inferences, elevated 14C levels of the atmosphere as a result of nuclear bomb testing are often ignored if LREs for modern materials are reported by convention relative to the atmospheric 14C activity of the year 1950. LRE data reported in this way represent unrealistic minimum estimates. [Copyright &y& Elsevier]

Abstract: This paper presents three parallel datasets of total organic carbon (TOC) and total inorganic carbon (TIC) as well as carbonate content (CaCO3) of lake sediment from two lakes on the Tibetan Plateau in order to compare different methods and different machines. The results indicate that two carbon analyzers (a Shimadzu TOC-VCPH with solid sample module SSM-5000A and an Elementar Vario EL II) provide very similar TOC and TIC content despite slightly different performance procedures and temperature controls. A TOC record determined by a wet oxidation method and a carbon analyzer shows consistent down core variation although it seems that the wet oxidation method may overestimate TOC content due to the existence of some reduced compounds or minerals in the sediment. TIC content measured by a carbon analyzer and carbonate content determined by a chemical method exhibit similar fluctuation trends in both cores. This suggests that TIC content may be used as an environmental proxy roughly taking the place of carbonate content, especially in sediment with simple carbonate compositions. [Copyright &y& Elsevier]

Abstract: Deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes. One approach going beyond classical methods is the unmixing of grain-size distributions. This paper presents a flexible end-member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties. It has been applied to the detrital grain-size components of lacustrine surface sediment samples of Lake Donggi Cona, Qinghai Province, China. It allows up to five grain-size end-members to be characterised and quantified in an optimal model. An end-member with a major mode in the clay domain accounts for 34% of variance within the grain-size data set. It may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer. Three end-members in the fine sand to medium silt domains make up 60% of lacustrine sedimentation. They may represent local to remote aeolian processes that peak in wintertime. A multimodal end-member explaining the remaining 6% of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors. Several model runs of different scaling and numbers of end-members provided a suitable way to determine uncertainties inherent to the model. A comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end-members. The clay and medium silt end-members are robust features of detrital sedimentation within Lake Donggi Cona. They alone explain 54.4% of total variance in the data. However, no spatial pattern or relation to water depth is found for any of the grain-size end-members. Thus, when past detrital sedimentation at Lake Donggi Cona is reconstructed, a special focus should be on the robust features attributed to aeolian and suspension-related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes. Further applications of the end-member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability. [Copyright &y& Elsevier]

Abstract: This paper aims to highlight the potential of using elemental and stable isotope analyses of aquatic macrophytes in palaeolimnological studies. Potamogeton pectinatus material was collected from modern plants (n =68) and from late glacial and Holocene-aged sediments from Koucha Lake (northeastern Tibetan Plateau; 34.0°N; 97.2°E; 4540m a.s.l.). It was analyzed for δ13C Potamogeton (modern: −23 to 0‰, fossil: −19 to −4‰) and δ15N Potamogeton (modern: −11.0 to +13.8‰, fossil: −9.5 to +6.7‰) in addition to elemental carbon and nitrogen (modern C/N Potamogeton : 7 to 29; fossil: 13 to 68) and sulfur (fossil: 188–899μmol/g dry weight). Fossil data were interpreted in terms of palaeo-nutrient availability and palaeo-productivity based on the modern relationships between various proxies and certain environmental data. Productivity of Potamogeton pectinatus mats at Koucha Lake as indicated by palaeo-ɛ Potamogeton -TIC (i.e. the enrichment of δ13C Potamogeton relative to the δ13CTIC) was reduced during periods of high conductivity, especially between 10.3 and 7.4cal kyr BP. Potamogeton pectinatus material from these periods was also characterized by high S Potamogeton indicating high sulfide concentrations and anoxic conditions within the sediments. However, C/N Potamogeton ratios and δ15N Potamogeton from the lower core section were found to have been altered by decompositional processes. A pronounced shift in the aquatic productivity of Lake Koucha occurred at ∼7.4cal kyr BP when the hydrological conditions shifted towards an open lake system and water depth increased. At this time a strong increase in productivity led to a strong decrease in the water HCO3 – concentration as inferred from the application of a ɛ Potamogeton -TIC-lnHCO3 − transfer function. A comparison of reconstructed productivity changes from Koucha Lake with further environmental proxies suggests that primary productivity changes are probably a function of internal lake dynamics and were only indirectly triggered by climate change. [Copyright &y& Elsevier]

Abstract: Water level and chemistry of Lake Qinghai are sensitive to climate changes and are important for paleoclimatic implications. An accurate understanding of hydrological and chemical budgets is crucial for quantifying geochemical proxies and carbon cycle. Published results of water budget are firstly reviewed in this paper. Chemical budget and residence time of major dissolved constituents in the lake are estimated using reliable water budget and newly obtained data for seasonal water chemistry. The results indicate that carbonate weathering is the most important riverine process, resulting in dominance of Ca2+ and DIC for river waters and groundwater. Groundwater contribution to major dissolved constituents is relatively small (4.2 ± 0.5%). Wet atmospheric deposition contributes annually 7.4–44.0% soluble flux to the lake, resulting from eolian dust throughout the seasons. Estimates of chemical budget further suggest that (1) the Buha-type water dominates the chemical components of the lake water, (2) Na+, Cl−, Mg2+, and K+ in lake water are enriched owing to their conservative behaviors, and (3) precipitation of authigenic carbonates (low-Mg calcite, aragonite, and dolomite) transits quickly dissolved Ca2+ into the bottom sediments of the lake, resulting in very low Ca2+ in the lake water. Therefore, authigenic carbonates in the sediments hold potential information on the relative contribution of different solute inputs to the lake and the lake chemistry in the past. [Copyright &y& Elsevier]

Abstract: This paper discusses the range of lake level changes, using hydro-acoustic techniques and sediment core data for Lake Nam Co in Central Tibet (China). This second largest Tibetan lake is situated at an elevation of 4718 m a.s.l. Lake level changes with different high stands documented by beach remnants are widespread on the Tibetan Plateau and also in Lake Nam Co. They indicate significant changes in the hydrological system triggered by the monsoonal circulation. Using hydro-acoustic techniques submerged beach remains at approximately 10/15 m, 30 m, 45 m, 70 m and 95 m below present day lake level were detected, indicating a more negative water balance than today. The −10/−15 m lake level is dated to an age equal to the Little Ice Age. All deeper lake levels are assumed to have been formed prior to ∼10000 cal BP. Folded older sediments, detected in the hydro-acoustic profiles indicate a possible larger extent of the glaciers during or prior to the Last Glacial Maximum (LGM). This is followed by a low stand or even by possible desiccation of the entire lake basin during or after the LGM. [Copyright &y& Elsevier]

Heavy metal contamination has affected many regions in the world, particularly the developing countries of Asia. We investigated 8 heavy metals (Cu, Zn, Cd, Pb, Cr, Co, Ni, and As) in the surface sediments of 18 lakes on the Tibetan Plateau. It was found that the distributions of the heavy metals showed no clear spatial pattern on the plateau. The results indicated that the mean concentrations of these metals in the sediment samples diminished as follows: Cr > As > Zn > Ni > Pb > Cu > Co > Cd. The results of geoaccumulation index (Igeo) and potential ecological risk factor (Eir) assessments showed that the sediments were moderately polluted by Cd and As, which posed much higher risks than the other metals. The values of the potential ecological risk index (RI) showed that lake Bieruoze Co has been severely polluted by heavy metals. Principal component analysis, hierarchical cluster analysis, and Pearson correlation analysis results indicated that the 8 heavy metals in the lake surface sediments of the Tibetan Plateau could be classified into four groups. Group 1 included Cu, Zn, Pb, Co, and Ni which were mainly derived from both natural and traffic sources. Group 2 included Cd which mainly originated from anthropogenic sources like alloying, electroplating, and dyeing industries and was transported to the Tibetan Plateau by atmospheric circulation. Group 3 included Cr and it might mainly generate from parent rocks of watersheds. The last Group (As) was mainly from manufacturing, living, and the striking deterioration of atmospheric environment of the West, Central Asia, and South Asia. [ABSTRACT FROM AUTHOR]

Massive carbonate banks representing ancient lacustrine deposits are exposed in the catchment of the lake Tangra Yumco (southern-central Tibetan Plateau) and nearby lake Xuru Co. Nine sediment samples were taken below and above these lacustrine deposits to determine periods of changing lake level using optically stimulated luminescence (OSL) applying a multiple-aliquot regeneration (MAR) protocol. According to facies and stratigraphy, samples below the carbonate banks indicate a rising and samples from above a falling lake level. The results indicate that the rising lake level of Tangra Yumco passed the sampling location at 10.5 and 2.1 ka while a falling lake level passed the sampling location at 0.9 ka. The rising lake level of Xuru Co passed the sampling location at 7.9 and 1.7 ka and a falling lake level at 0.5 ka showing a similar trend as at Tangra Yumco. Combining these results with recalculated cosmogenic nuclide ages and previously published feldspar luminescence data allows the establishment of a Holocene lake level reconstruction for Tangra Yumco, which is unique for the southern-central Tibetan Plateau. The lake level of Tangra Yumco crested a lake level highstand of 181–183 m above the recent lake level prior to 8.5 ka and has generally fallen after 8.5 ka, with a minor lake level rise at 2.1 ka. Lake level variations at Tangra Yumco occur simultaneously with other lakes on the Tibetan Plateau indicating that variations were controlled by monsoonal dynamics with a moist early Holocene and a successive reduction of available moisture thereafter. The average rate of the lake level rise between 10.5 and 8.5 ka is at least 0.05 m a−1 (compared with a modern value of 0.38 m a−1), providing valuable insights in the monsoonal impact on lake level change on the southern-central Tibetan Plateau. [ABSTRACT FROM AUTHOR]

We present radiometric data from nine lakes across the Tibetan Plateau, and compare their reliability in relation to recent research. Unsupported Pb profiles show, except for one particular lake, non-exponential decline of Pb activity with sediment depth. Stratigraphic dates based on global atmospheric nuclear weapons maximum fallout of Cs (1963) support the use of the constant rate of Pb supply (CRS) model in four of the dated cores. The discrepancy in the others is likely due to recent increased input of catchment-derived Pb. Pb dates in this study suggest that post depositional diffusion of Cs activity has been significant. The practice of assigning early 1950s dates (start of global atmospheric thermonuclear testing) to lake sediment sequences on the Tibetan Plateau should be used with caution. Cs profiles from Tibetan lake sediment cores and their geographical distribution suggest that Cs derived from the 1986 Chernobyl accident or atmospheric testing in China was not sufficient to form a significant peak effective for dating. [ABSTRACT FROM AUTHOR]

The Western Qinling orogenic belt marks the northeastern margin of the Tibetan Plateau. Its late Cenozoic orogenic history is recorded in an excellent sedimentary sequence exposed in the Tianshui sub-basin of the Longzhong basin. According to the magnetostratigraphic analysis from the Yaodian and Lamashan sections, we speculate that the late Cenozoic Tianshui basin accumulated lacustrine/floodplain deposits from ~14.8 to ~2.6 Ma. In addition, detrital apatite fission-track thermochronologic and paleocurrent data reveal that the detritus of the Tianshui basin mostly derived from the Western Qinling and that the youngest population age represents a ~14 Ma volcanic intrusion, which can be related to the lithospheric deformation and uplift of the Tibetan Plateau. Furthermore, two stages of variations in depositional facies and average accumulation rates were attributed to the pulse uplift and deformation of the Western Qinling at 9.2-7.4 and ~3.6 Ma. [ABSTRACT FROM AUTHOR]

Information on changes in land-surface features on the Tibetan Plateau (TP) during the Holocene may help our understanding of the forcing of monsoonal circulation. We analyse vegetation changes during the last 9000 years from pollen records of four lakes (Hurleg Lake in the Qaidam Basin; Qinghai Lake on the northeastern TP; Zigetang Lake on the central TP and Koucha Lake on the eastern TP) which represent different regions and vegetation types on the Plateau today. A set of modern pollen assemblages from 111 lake sediment samples originating from different vegetation types is used for the interpretation of the Holocene pollen records. Four types of numerical analyses are used to infer different aspects of pollen-stratigraphical and inferred vegetation changes: biome reconstruction; ordination (to infer palynological compositional turnover); rate-ofassemblage- change analysis, and a pollen-LAI (leaf area index) transfer function. Our results show strong regional differences in inferred vegetation change in terms of timing, strength and the nature of change. The greatest changes in compositional turnover and LAI are found in the Qinghai Lake record, indicating that forests were replaced by steppe vegetation in a step-wise fashion since the mid Holocene. Alpine steppe vegetation on the central and eastern TP was relatively stable throughout the Holocene, only showing a gradual replacement of temperate steppe by high-alpine meadows. The Qaidam Basin was dominated by temperate desert throughout the Holocene. The documented palynological and inferred vegetation changes can be most parsimoniously explained by climate change, although human impacts cannot be excluded as a contributing factor. Comparison of our findings with sensitivity analyses of numerical climate simulations suggests that longterm vegetation change may have had only a weak influence on regional climate change on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]