A 1000-year record of Mg/Li and Li/Ca ratios of ostracod shells in Lake Qinghai,NE Tibetan Plateau

1 Introduction Lake Qinghai,famous as the largest inland saline lake in China,located on the high-altitude northeastern Tibetan Plateau,and four junctional zones of the East Asian summer monsoon(EASM),Indian summer monsoon(ISM),East Asian winter monsoon and the westerly jet stream prevail,making it sensitive to global climate change

Hydro-Chemical Processes in Lake Qinghai throughout Climate Warming: In Situ Investigations of the Largest Lake in China

In the wake of climate warming, the water level of Lake Qinghai has been continuously and rapidly declining during the past decades, causing the regional government and citizens to worry about its future as a water resource. To understand the lake evolution process, the hydro-chemical characteristics of Lake Qinghai were investigated in August of 2008. The results show that Na+ and Cl- are the dominant cations and anions in the lake water, respectively, and hydrochemistry type is Cl-- Na+ with an obvious characteristic of a saline lake. The Gibbs plot illuminates that evaporation/crystallization is responsible for the chemical composition of the lake water. The variation in hydro-chemical regime might be attributed to the reduced lake levels between 1960s and 2000s. The lake level significantly correlated with the precipitation and evaporation in the Lake Qinghai catchment. In addition, changes of the lake level in the future are simulated according to climate warming scenarios from the IPCC report. The simulated results suggest that the lake level could rise again in the following decades due to the increased precipitation under the climate warming conditions, which is already a trend in the lake level observation data.

Geochronology of a surface core in the northern basin of Lake Qinghai: Evidence from ^(210)Pb and ^(137)Cs radionuclides

The radioactivities of 210Pb and 137Cs have been measured to estimate the dates of the sediments of a surface core （QH0407-C-2） in the northern basin of Lake Qinghai. The sedimentation rate derived from 210Pb radioactivity correlates well with that inferred from （137）Cs radioactivity. The dates calculated from depth sedimentation rate （cm/a） are similar to those derived from mass accumulation rate （g·cm-2·a-1） between 0-5 cm, but are significantly different below 5 cm, which has been ascribed to the compaction of surface sediments during early diagenesis. The dates derived from mass accumulation rate are consistent with those calculated from the AMS 14C dating model. The precipitation-controlled indices based on the chronology data derived from mass accumulation rate are similar in trends to the precipitation reconstructed from tree rings in adjacent region, which further verifies the reliability of the geochronology data.

Environmental changes during the past 13500 cal. a BP deduced from lacustrine sediment records of Lake Qinghai, China

A 475-cm long sediment core (QH-2005) from Lake Qinghai was used to carry out multi-proxy analysis of δ18O and body length of ostracod valves and redness and grain size of sediments, in order to reconstruct environ-mental changes during the past 13500 cal. a BP. The age model was based on 6 14C dates for bulk orgnic carbon (BOC) and 2 14C dates for lignin. The lignin 14C dates are apparently younger than the corresponding layers' BOC 14C dates, indicating that the reservoir age varied from 728 to 1222 a since the Late Glacial and from 2390 to 2490 a immediately before the pre-bomb era. Hence, the 14C age model for Core QH-2005 was corrected by the changing reservoir age. Ostracod δ18O values were primarily related to dilution and evaporative enrichment of the lake water. The reconstructed salinity based on ostracod body length coincides well with ostracod δ18O values. High redness and mean grain size (MZ) values indicate increased riverine supply to Lake Qinghai associated with increasing monsoon rainfall. Multi-proxy results show that climate during 13500-10900 cal. a BP was relatively cold and dry with fre-quent short-term fluctuations; a warm and wet climate began at about 10900 cal. a BP and culminated around 6500 cal. a BP as a result of monsoon strengthening; the climate became cold and dry afterwards and has remained rela-tively stable since 3400 cal. a BP. Our data also reveal short-term (millennial/centennial timescales) climatic fluctua-tions including: Younger Dryas events, ice-rafting events 8 and 1 (by ～11000 cal. a BP and ～1600 cal. a BP respec-tively), 8200 cal. a BP cold event, Little Ice Age and the Medieval Warm Period.

Distributions and hydrogen isotopic compositions of plant leaf wax from Orinus kokonorica along a general aridity gradient around Lake Qinghai, China

To quantitatively analyze the response of distributions and hydrogen isotopic compositions(δD) of plant leaf wax to moisture, and to better understand their implications for paleoclimatic reconstruction, we measured average chain length(ACL) and δD values of n-alkanes and n-fatty acids(n-FAs) from Orinus kokonorica, a typical and representative plant in Lake Qinghai area, along a distance transect extending from lakeshore to wetland to dryland in the arid ecosystem. The results showed that the ACL values of n-alkanes and n-FAs were negatively correlated with soil water content(SWC) with R2=0.593 and R2=0.924, respectively. This is as a result of plant's response to water loss with more abundance in long-chain n-alkyl lipids under increasing aridity by analyzing relationships between the molecular ratios of long-chain n-alkyl lipids(n-alkanes and n-FAs) from O. kokonorica and SWC. The δD values of C29 n-alkane and C28 n-FA were also negatively correlated with SWC with R2=0.778 and R2=0.760, respectively, which may due to enhanced D-enrichment in leaf water by evapotranspiration(soil water evaporation and leaf water transpiration) with increasing aridity. Our results demonstrated that moisture exerts a significant control on the ACL and δD values from O. kokonorica in an arid ecosystem. This preliminary study on a modern single plant(O. kokonorica) sets a foundation for comprehending these values as quantitative proxies for paleo-humidity reconstruction.

Sedimentary environment change in northwestern of Lake Qinghai Based on the ^(137)Cs and ^(210)Pb

Lake Qinghai is located in the northeastern margin of qinghai-tibet plateau.It’s very sensitive to climate change.Through the research of modern sedimentary environmental change in Lake Qinghai,We expect to gain the information about its response to global environmental change.Our study collected three sedimentary columns of Lake Qinghai in the northwestern,Column samples’length

ERA5-Land青藏高原湖冰特征误差分析及FLake模式改进

青藏高原上湖泊众多,其中大多数被季节性湖冰覆盖。湖冰对气候变化响应敏感,其生消过程会显著改变湖-气交换通量。而现有的高原湖冰长时间观测数据较少,需要利用湖冰再分析资料进行研究。但目前对ERA5-Land湖冰资料在高原的适用性及改进方法还不甚清楚。因此,本文首先利用2010-2022年青海湖和鄂陵湖的湖冰观测数据,评估了ERA5-Land再分析资料对青藏高原典型湖泊湖冰特征的模拟能力。结果表明:ERA5-Land资料对青海湖和鄂陵湖的冰厚平均高估0.54~0.62 m,对封冻期天数高估约68 d·a^(-1)。其次对再分析湖冰数据误差来源进行分析,通过对比ERA5-Land和鄂陵湖观测资料及其各自驱动模式的模拟结果,得出误差主要来源于输出ERA5-Land湖冰数据的FLake一维湖泊模式。最后基于2010-2022年青海湖和鄂陵湖的MCD43A3地表反照率产品,利用其多年平均反照率和动态日均反照率改进了FLake模型,模拟冰厚平均偏差可分别减小85%和90%,封冻期天数的模拟偏差减小了约6d·a^(-1)和8d·a^(-1)。两种方法均可以改进FLake模型对湖冰的模拟效果,特别是对积雪覆盖时间较长的湖泊,动态反照率方法改进效果更明显。本研究揭示了ERA5-Land湖冰特征的主要误差来源为FLake模式中的湖冰反照率,并对该参数进行了改进,提高了模型对湖冰的模拟效果,可为提高ERA5-Land再分析湖冰数据在青藏高原典型湖泊的模拟精度提供参考。

Mineralogy of the otoliths of naked carp Gymnocypris przewalskii (Kessler) from Lake Qinghai and its Sr/Ca potential implications for migratory pattern

Otoliths are biogenic carbonate minerals whose microstructure and microchemistry have been used for age determination, stock identification, life history and environmental tracing. Using X-ray diffraction （XRD） and Fourier transform infrared （FTIR） spectroscopy, we have determined the mineral types and crystalline characteristics of three pairs of otoliths from naked carp Gymnocypris przewalskii, the predominant fish in Lake Qinghai. The results indicate that the mineral of both lapillus and sagitta of the naked carp is aragonite, and that of asteriscus is vaterite. The aragonite of lapillus has prefect crystallization. Given the shape of lapillus and the sensitivity of its aragonite to water chemistry, lapillus was used to analyze temporal Sr/Ca ratios along the maximal growth axis by an electron probe microanalyzer （EPMA）. Consistent variations of Sr/Ca ratios with a range of 1.0x10-3-5.0~10-3 on the long and short radii indicate that Sr/Ca ratios of lapillus potentially respond to the chemical compositions of the host waters during the period of the naked carp＇s growth and migration. Discontinuous （dark） zones of lapillus were formed during fall and winter when the naked carp grows slowly in Lake Qinghai, resulting in similar low Sr/Ca ratios to lake water, whereas incremental zones with higher St/Ca ratios respond to its migratory river waters during spring and summer. Various Sr/Ca ratios of incremental zones suggest that the migratory pattern of the naked carp may be much more flexible, rather than in a single river. Therefore, high-resolution otolith microchemistry of the naked carp can be used to trace its migratory behavior, which is of significance for determining its migratory pattern and life history of this precious species inhabiting the Tibetan Plateau.

Clay mineral records of the Erlangjian drill core sediments from the Lake Qinghai Basin, China

Located at the northeastern margin of the Qinghai-Tibet Plateau(QTP) in the Asian interior, the Lake Qinghai is sensitive to environmental change and thus an outstanding site for studying paleoenvironmental changes. Thick deposits in the Lake Qinghai provide important geological archives for obtaining high-resolution records of continental environmental history. The longest drilling core obtained from the Lake Qinghai, named Erlangjian(ELJ), reached about 1109 m and was investigated to determine its clay mineral assemblage and grain size distributions. Clay mineralogical proxies, including type, composition, and their ratios, as well as the illite crystallinity(KI) and chemical index(CI), in combination with grain size data, were used for reconstructing the history of paleoenvironmental evolution since the late Miocene in the Lake Qinghai Basin. The clay mineral records indicate that the clay mainly comprise detritus originating from peripheral material and has experienced little or no diagenesis. The proportion of authigenic origin was minor. Illite was the most abundant clay mineral, followed by chlorite, kaolinite, and smectite. Variations of clay mineral indexes reflect the cooling and drying trends in the Lake Qinghai region, and the grain size distribution is coincided with the clay minerals indexes. The paleoclimatic evolution of the Lake Qinghai Basin since the late Miocene can be divided into five intervals. The climate was relatively warm and wet in the early of late Miocene, then long-term trends in climate change character display cooling and drying; later in the late Miocene until early Pliocene the climate was in a short relatively warm and humid period; since then the climate was relatively colder and drier. These results also suggest multiple tectonic uplift events in the northeastern QTP.

Biogenic silica contents of Lake Qinghai sediments and its environmental significance

Changes in the levels ofbiogenic silica （BSi%） in lake sediments have been widely used in order to study lake productivity and palaeoclimatic changes. However, the provenance of biogenic silica （BSi） needs to be investigated for each lake, especially for large lakes, as does the relationship between levels of BSi and relevant environmental factors. In this study, we measured the percentage of BSi contained in lake sediments, river sediments, and surface soils within the Lake Qinghai catchment, and compared the quantities and shapes of diatoms and phytoliths before and after the extraction processes. The results suggest that BSi in lake sediments is primarily derived from endogenous diatoms; therefore, BSi levels can be used to reflect the changes in primary productivity within the lake. Further comparisons showed that on long-term timescales, the variations in BSi% are generally consistent with those in total organic carbon （TOC） and grain size, reflecting the dominant impacts of precipitation on primary productivity in Lake Qinghai. On short-term timescales, however, the relationship between BSi% and TOC and that between BSi% and grain size are not clear or stable. For example, BSi% sometimes covaried with grain size, but it was sometimes out of phase with or even inversely related to grain size. We speculate that both climate and environmental processes, such as the dilution effect, influence short-term BSi% and its related environmental significance. As a result, BSi% should be used selectively as an indicator of climatic changes on different time scales.

Analysis to the Driving Force Model and Drives Factor on the Utilized Changes of Cultivated Land in Qinghai Lake Area

Using path analysis, correlation analysis, partial correlation analysis and system dynamics method to study the driving force of cultivated land in Qinghai Lake Area, and using gradually regression analysis to establish the driving force model of utilized change of cultivated land. Driving factors, action mechanism and process of utilized change of cultivated land were analyzed, and the differences during all factors were compared. The study provides some decision basis for sustainable utilization and management of land resources in Qinghai Lake Area.

Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii(Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China

Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chem- ical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modem otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-lnC ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-14C dating resuits of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction （XRD） patterns demonstrate that the ancient lapillus is composed of pure aragonite, iden- tical to modem one, indicating that the mineral of lapillus didn＇t change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca （（70.12±18.50）× 10-2） and δ18O （（1.76±1.03）‰） of ancient lapilli are significantly higher than those of modem lapilli （average Mg/Ca=（3.1 1±0.41）× 10-5 and δ18O =（-4.82±0.96）‰）. This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and δ18O ratios than modem Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today＇s Lake Gahai. Based upon the stratigraphy and altitude of naked carp re- mains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km2 during the Ming Dynasty, approximately ~5% larger than it is today.

Calibration of the U37K index of long-chain alkenones with the in-situ water temperature in Lake Qinghai in the Tibetan Plateau

Long-chain alkenones (LCAs) can potentially be used as indicators to understand past variations in lacustrine environments.Previous research has suggested that the relationship between the temperature and the unsaturation index of LCAs should be calibrated individually,because of the possible variations in the alkenone-producing algal species in the lacustrine environment.In this work,we have calibrated U37K' of water filter samples against the in-situ water temperature in Lake Qinghai,Tibetan Plateau.There are significant relationships between U37K' and the water temperature,a non-linear relationship was derived.Because the U37K' values did not respond sensitively at lower temperatures,we suggested that a quadratic regression (U37K' =0.0011×T2-0.0201×T+0.1959,n=15,r2=0.74) was appropriate than linear regression to represent the relationship between the in-situ temperatures and U37K'.Meanwhile,the U37K correlation relationship was not more significant than U37K' index in our study.Because of the C37:4 effects by salinity change,we suggest U37K is not as robust as the U37K' index as a temperature proxy,at least for the salt lake in the Tibetan Plateau.The calibration of the U37K' index in this work has provided a new understanding of historic climatic changes in the Tibetan Plateau.

Influence of aquatic plants on the hydrogen isotope composition of sedimentary long-chain n-alkanes in the Lake Qinghai region, Qinghai-Tibet Plateau

The hydrogen isotopic composition(δD) of leaf wax long-chain n-alkanes(C27, C29, and C31) from lacustrine sediments has been widely applied to reconstruct terrestrial paleoclimatic and paleohydrological changes. However, few studies have addressed whether the aquatic-derived n-alkanes can affect the δD values of lake sedimentary long-chain n-alkanes, which are usually regarded as a recorder of the terrestrial hydrological signals. Here we systematically investigated δD values of long-chain n-alkanes from modern aquatic plants, both near-shore and off-shore surface sediments, surrounding terrestrial plant litters, as well as river water and lake water in Lake Qinghai and its satellite lakes on the northeastern Qinghai-Tibet Plateau. Our data showed that(i) δD values of long-chain n-alkanes from aquatic plants varied from-184‰ to-132‰ for n-C27, from-183‰ to-138‰ for n-C29, and from-189‰ to-130‰ for n-C31, respectively, with no significant differences among the three n-alkanes homologues;(ii) δD values of long-chain n-alkanes from aquatic plants were generally more positive than those from surrounding terrestrial plants, possibly because that they recorded the D-enrichment of lake water in this semi-arid region;(iii) δD values of long-chain n-alkanes from surface sediments showed significant differences among the three n-alkanes homologues, due to the larger aquatic input of n-C27 to the sedimentary lipid pool than that of n-C31, and(iv) n-C27 δD values of near-shore aquatic plants and near-shore sediments are more negative than those from off-shore as a result of lower δD values of near-shore lake water. Our findings indicate that in this region(i) the offset between sedimentary n-C27 and n-C31 δD values(ΔδDC27-C31) could potentially be used to evaluate if sedimentary long-chain n-alkanes are derived from a single source;(ii) while δD values of n-C27 may be influenced by lake water hydrological changes, sedimentary n-C31 is derived predominantly from terrestrial plants and thus its δD can serve as a relatively reliable indicator for terrestrial paleoclimatic and paleohydrological reconstructions.

A 12-kyr record of microbial branched and isoprenoid tetraether index in Lake Qinghai,northeastern Qinghai-Tibet Plateau:Implications for paleoclimate reconstruction

Branched and Isoprenoid Tetraether(BIT) index was considered as a proxy for terrestrial organic matter input in lake sediments, based on the assumption that branched glycerol dialkyl glycerol tetraethers(b GDGTs) are mainly derived from terrestrial soils. However, mounting evidences have showed that the in situ production of b GDGTs is widespread in lakes, challenging BIT as a reliable terrestrial input proxy. Recently, BIT has been proven to be a reliable proxy for paleohydrology in a small crater lake(Lake Challa) in accordance with a different mechanism. However, the response of BIT to paleohydrology variation may differ for different lakes. In this study, we investigate the variations in the BIT index and the concentrations of its related GDGTs in a 12-ka sediment core from Lake Qinghai, in combination with our previous results for surface sediments. We find that variations in BIT strongly depend on the concentration of crenarchaeol in both surface and ancient sediments of this lake, whereas b GDGT concentration varies much less remarkably. Considering that crenarchaeol production is positively correlated with water depth in Lake Qinghai, water depth may exert negative control on the BIT index in this lake. This case is inconsistent with the positive relationship between BIT and lake levels or rainfall intensity reported for Lake Challa, suggesting that the response of BIT to local paleohydrology is site specific in lacustrine systems. Hence, the application of sedimentary BIT as a paleohydrological proxy in a specific lake requires caution before confirming the environmental controls on BIT in that lake.

Hydrochemical Dynamic Characteristics and Evolution of Underground Brine in the Mahai Salt Lake of the Qaidam Basin Qinghai-Tibet Plateau

The mineral rock salts present in the Mahai Salt Lake of the Qaidam basin exhibit high solubilities in water. In addition, the multicomponent underground brine exhibits a high salinity and is easily precipitated. In the natural state, brine transport in the brine layer is extremely slow, and the brine is in a relatively stable chemical equilibrium state with the rock salt media. However, during mining, both the seepage and the chemical fields fluctuate significantly, thereby disrupting the equilibrium and leading to variations in the chemical composition and dynamic characteristics of the brine. Therefore, we selected underground brine from the Mahai Salt Lake, collecting a total of 183 brine samples over three stages of mining（i.e., the early stage of underground brine extraction, the initial stage of mining, and the later stage of mining）. Using a range of analytical techniques, the chemical dynamics of the underground brine water and its evolution were systematically studied. We found that evaporation and enrichment were the main mechanisms of underground brine evolution in the Mahai Salt Lake, with cation exchange and mineral dissolution/precipitation being key factors in determining the dynamic characteristics and evolution of the brine.

Carrying Capacity of Grassland and Sustainable Development of Animal Husbandry in Qinghai Lake Area

Based on the estimation of carrying capacity of grassland and status analysis of animal husbandry in Qinghai Lake area, the paper explores the strategic measure of sustainable development of animal husbandry in Qinghai Lake area under the actual conditions.

Study on Changes of Grassland Landscape Pattern in Qinghai Lake Watershed

The changes of grassland landscape pattern in Qinghai Lake watershed from 1977 to 2000 were studied by adopting 3S technologies and landscape pattern analysis.The results showed that the amount of grassland landscape patch reduced,landscape fragmentation and resolution decreased,but average patch area and fractal dimension increased;through analyzing the landscape change of counties in Qinghai Lake watershed,the grassland landscape structure of Tianjun,Gangcha and Haiyan counties showed a similar change trend;but in Gonghe County grassland patch amount,landscape fragmentation and resolution increased,average patch area decreased,that is,the grassland landscape structure in this county showed a different trend.

Modern pollen rain in the Lake Qinghai basin, China

Lake Qinghai is the largest inland brackish lake in China and lies within the NE Tibetan Plateau. Our study shows that pollen assemblages in each vegetation belt are significantly correlated with the vegetation types of this area. Among the herbaceous and shrubby pollen assemblages, Artemisia is over-represented, while Poaceae, Cyperaceae and Polygonaceae are under-represented. Artemisia/ Chenopodiaceae (A/C) ratios with the regional vegetation characteristic can be used as a proper index to reconstruct the history of vegetation and climate in Lake Qinghai basin. Modern pollen in the lake mainly comes from the nearby vegetation, controlled by the directions and velocity of the wind. The distribution of modern pollen in Lake Qinghai tends to be similar in most part of the lake. The difference of pollen sedimentation process in the lake can be potentially influenced by the focusing function of the lake, river streams, and lake current.

Evaluation of spatial-temporal dynamics in surface water temperature of Qinghai Lake from 2001 to 2010 by using MODIS data

Lake surface water temperature （SWT） is an important indicator of lake state relative to its water chemistry and aquatic ecosystem,in addition to being an important regional climate indicator.However,few literatures involving spatial-temporal changes of lake SWT in the Qinghai-Tibet Plateau,including Qinghai Lake,are available.Our objective is to study the spatial-temporal changes in SWT of Qinghai Lake from 2001 to 2010,using Moderate-resolution Imaging Spectroradiometer （MODIS） data.Based on each pixel,we calculated the temporal SWT variations and long-term trends,compared the spatial patterns of annual average SWT in different years,and mapped and analyzed the seasonal cycles of the spatial patterns of SWT.The results revealed that the differences between the average daily SWT and air temperature during the temperature decreasing phase were relatively larger than those during the temperature increasing phase.The increasing rate of the annual average SWT during the study period was about 0.01℃/a,followed by an increasing rate of about 0.05℃/a in annual average air temperature.The annual average SWT from 2001 to 2010 showed similar spatial patterns,while the SWT spatial changes from January to December demonstrated an interesting seasonal reversion pattern.The high-temperature area transformed stepwise from the south to the north regions and then back to the south region from January to December,whereas the low-temperature area demonstrated a reversed annual cyclical trace.The spatial-temporal patterns of SWTs were shaped by the topography of the lake basin and the distribution of drainages.