Search

Reconstructing paleoenvironmental conditions using geochemical proxies from pedogenic carbonate must ensure that the pedogenic carbonate is not recrystallized. Calcareous root tubes (CRTs) formed by carbonate precipitation along the roots have been widely used for paleoenvironmental reconstruction in arid and semi-arid regions. However, whether further recrystallization occurs after CRT formation and its impact on the reliability of paleoenvironmental reconstruction remains uncertain. In this study, 52 Holocene age CRT samples obtained from 17 sites in the Tengger Desert of northwestern China were described using cathodoluminescence and optical microscopy to clarify this uncertainty. The CRT outer (detrital) layer is composed of detrital material and carbonate, while the inner (precipitated carbonate) layer is composed only of carbonate. The results of this study showed that recrystallized carbonates occurred in the detrital layers of 45 of the samples (~87%), but no recrystallization was observed in the precipitated carbonate layer in any of the CRT samples. CRT recrystallization is caused by the introduction of calcium-bearing meteoric waters after CRT formation. These CRT recrystallization characteristics not only occurred in the Tengger Desert, but also in other regions with seasonal soil moisture deficits. This study showed that carbonate from the CRT detrital layer is not a suitable material for 14C dating and δ13C and δ18O analyses; however, carbonate from the precipitated carbonate layer could be a suitable material for these analyses. Moreover, paleoenvironmental reconstruction results derived from changes in the Sr/Ca and Mg/Ca ratios of CRTs should not be affected by recrystallization.

In the hinterland of the desert, valuable archives of paleoenvironmental evolution are scarce. Calcareous root tubes (CRTs) have a strong potential for reconstructing paleoenvironmental conditions. It is still unclear, however, whether chemical elements in the CRTs can provide insights into paleoenvironmental conditions. In this study, the major- and trace-element composition of 32 CRT samples from the Alashan Desert were analyzed by X-ray fluorescence spectrometry. Results showed that the elemental composition and content change were controlled by the parent material and climatic conditions at the time of CRT formation. Ca, Mg, and Sr were significantly affected by climate, whereas the enrichment of P is likely related to the growth of plants. Higher (lower) Mg/Ca and Sr/Ca ratios corresponded to higher (lower) effective moisture and a higher (lower) Mg/Sr ratio indicated a higher (lower) temperature during the middle Holocene (8–5 cal ka BP). The reconstruction results for effective moisture were consistent with those in the Asian monsoon margin of northwestern China, which were caused by higher monsoon precipitation and lower evaporation. Therefore, chemical elements in the CRTs can reflect changes in paleo-effective moisture and paleotemperature at a millennial resolution in this area.

Using landform evolution and lake sediment records to reconstruct Quaternary environmental changes requires reliable chronology. However, there is an ongoing debate regarding the fossil shells of aquatic gastropods in carbonate rock area to be used for radiocarbon dating. The focus of this debate is whether living gastropods incorporate the dead carbon, which would affect the accuracy of the dating results. Living aquatic gastropods were selected from habitats on carbonate terrain in arid region. In this study, 64 shell samples from living gastropods, including Cipangopaludina chinensis, Gyraulus convexiusculus, and Radix auricularia, collected from the Alashan Plateau of northwestern China, were dated by accelerator mass spectrometry (AMS) 14C dating. The results revealed that only five samples (~8%) from the same site contained no dead carbon. The other 59 samples (~92%) contained dead carbon in various amounts: ~59% samples contained 0–10% dead carbon, and ~33% samples contained more than 10% dead carbon. Of the samples, 56 were Radix auricularia and their 14C ages varied from present to 3253 cal yr BP. Two of the samples were Gyraulus convexiusculus samples dated at 379 and 290 cal yr BP which are highly consistent with 14C ages of Radix auricularia samples from the same site. The other six Cipangopaludina chinensis samples were dated at 407–863 cal yr BP. Thus, most of living aquatic gastropods from habitats on carbonate terrain contained dead carbon. The amount of dead carbon in the gastropod shells was nonselective among the three species. Radiocarbon dating of aquatic gastropod shells may not be useful for studying processes that occurred over multi-millennial timescales at different localities in areas of carbonate rock. It is difficult to establish high-resolution chronologies using 14C ages of gastropod shells in arid regions with carbonate rocks unless the limestone effect has been corrected.

Rare earth elements (REEs) have been widely used to infer the provenance of sediments. However, sedimentary sorting and chemical weathering may produce REE compositions within sediments that vary with grain size, leading to complications and uncertainty when tracing possible source areas. In desert areas, the extent to which REE compositions within eolian sands are affected by sedimentary sorting along with which REE proxies can be used to indicate provenance requires further study. During our work, 73 samples were collected from the Badain Jaran Desert (BJD) and some nearby regions. These were analyzed for trace elements and REEs. Our results showed that the REE composition of these eolian sands varied considerably among the various grain-size fractions. We conclude that the REE composition of these eolian sands in the BJD is a function of sedimentary sorting and provenance rather than of chemical weathering. Among the REE proxies considered, variations in (La/Yb)N and Y/REE values seem mainly to have been affected by sedimentary sorting, whilst δCe, (La/Sm)N, (La/Gd)N, Y/Tb, Y/Er, and Ce/Nd ratios appeared primarily to have been governed by provenance. Therefore, we can infer that care is needed when using (La/Yb)N and Y/REE as proxies for determining eolian sand provenance; however, δCe, (La/Sm)N, (La/Gd)N, Y/Tb, Y/Er, and Ce/Nd ratios offer a more reliable perspective. Moreover, by using (La/Sm)N and (La/Gd)N as provenance proxies, we determined that hinterland lacustrine sediments are an important source of

Groundwater, rather than regional precipitation, is critical to the development and maintenance of lakes in arid regions. We selected a sedimentary section in the Badain Jaran Desert, northwestern China, where the lakes are mainly groundwater-recharged, to reconstruct past vegetation development and environmental evolution, and to address the driving mechanisms of lake evolution by applying lithological and pollen analyses. Our results show the following: aeolian deposits indicate an extremely dry environment before 11 ka; peat deposition from 11 to 10.2 ka indicates humidification after the Younger Dryas event; limnetic deposits and dry steppe landscape indicate increased humidity from 10.2 to 7.2 ka; lacustrine deposits and dry steppe landscape with few drought resistant plants indicate the highest humidity from 7.2 to 5.4 ka; lacustrine deposits and desert steppe landscape with increasing Ephedra and decreasing Artemisia indicate gradual aridification from 5.4 to 3.6 ka; and shallow lake deposits and abundant drought resistant plants indicate the driest conditions from 3.6 to 0.8 ka. Here, we comparatively analyzed modern hydrologic data from the Badain Jaran Desert and surrounding regional studies of environmental evolution. It was found that the effective moisture changes in the desert, which proved to be different from both the monsoonal area and the region under the influence of westerlies, were controlled by groundwater recharge from glacier meltwater and regional precipitation over the northeastern Tibetan Plateau.

For lakes in desert hinterlands that are not recharged by river runoff, sediment input solely comes from wind transport. While the processes of sediment transport and deposition in these lakes differ significantly from those with river discharge, the spatial distribution of sediment grain size in these groundwater-recharged lakes remains largely unknown. Moreover, whether the grain size distribution in these lake sediments can be used as a proxy in the study of past climatic change and environmental evolution studies is unclear. In this study, five lakes with a range of surface areas that had no runoff recharge were selected from the hinterland of the Badain Jaran Desert of northwestern China, and a total of 108 samples of lake surface sediments were collected to examine the spatial distribution of grain size. Moreover, an end-member-modeling algorithm was used to calculate end members from all grain size measurements. Our results showed that both the median and mean grain sizes in the lake sediments decreased from the nearshore to the offshore, deep-water zone. However, the lowest median and mean grain sizes were not found in the center of the lakes, in contrast to lakes recharged by surface runoff. The median grain size of sediment in the lake center was negatively correlated with lake level, and thus could help reveal lake evolution at low resolutions. Moreover, EM1 and EM2 were interpreted as wind transported sediment, and sediment perturbed by lake waves after wind transport, respectively. The modal grain size of EM1 varied slightly between lakes, while changes in the modal grain size of EM2 were related to lake area. Given the positive relationship found between EM2 content and lake level, changes in the EM2 content (%) can serve as a rough indicator of lake level fluctuations at low temporal resolutions.

In the hinterland of deserts, it is difficult to reconstruct paleovegetation using fossil pollen because of the low pollen concentration. Therefore, an efficient method is needed to reconstruct the paleovegetation of desert regions. In this study, 34 Holocene calcareous root tube (CRT) samples were collected from the Alashan Desert in northwest China, and lipid molecular proxies from CRTs were selected to address this deficiency. The results show that n-alkanes mainly maximized at C27, C29, and C16, and that the carbon preference index is close to 1. Thus, the sources of n-alkanes from CRTs were the roots of higher plants and microorganisms, and thus changes in n-alkanes from CRTs could reveal variations in vegetation cover. The n-alkane Cmax of long-chain n-alkanes (C>25) in CRTs, maximizing at C27, indicated that vegetation in the Alashan Desert was characterized by shrub vegetation during the Holocene. Changes in the ratio of (C27+C29)/(C31+C33) indicated that the biomass of shrub vegetation increased during the period 7–2 cal ka BP. Moreover, the relative concentration of short-chain to long-chain n-alkanes decreased from 7 to 2 cal ka BP, suggesting that the effective moisture decreased during that period.

Chemical weathering is an important process that controls the evolution of the Earth’s surface. By accurately and reliably estimating the intensity of chemical weathering, we can improve our understanding of the processes occurring at the Earth’s surface as well as environmental changes. However, chemical weathering indices, which are influenced by source rocks and grain size, may not always accurately reflect the intensity of chemical weathering. Therefore, the use of chemical weathering indices to reliably reflect the changes in the intensity of chemical weathering in deserts remains uncertain. In this study, several chemical weathering indices, including the chemical index of alteration, Parker’s weathering index, chemical index of weathering, plagioclase index of alteration, chemical proxy of alteration, Rb/Sr, and αAlE indices, were calculated for 521 eolian sand samples collected from across twelve deserts in northern China. The results show that, for all the chemical weathering indices, eolian sands from the different deserts differed significantly. Rather than the climatic conditions in the studied deserts. factors such as source rocks and grain size had a larger impact on these indices. These indices cannot generally be used to reflect the intensity of chemical weathering. However, results showed that when the mean annual precipitation varies greatly between deserts, the changes in the WIP values of the fine fraction samples (

Valuable archives of paleoenvironmental changes are scarce in the hinterlands of deserts. Calcareous root tubes (CRTs), a form of pedogenic carbonate, are widely distributed in the hinterland of the Tengger Desert, Northwest China. The investigations of δ13C and δ18O values within CRTs from the Tengger Desert have a great potential to provide new significant archives for paleoenvironmental reconstructions in this area. In this study, 30 CRT samples from the Tengger Desert were collected. All the samples were described using cathodoluminescence (CL), and their δ13C and δ18O values were measured. The results revealed that limited marine carbonate was incorporated in the CRTs in the Tengger Desert and δ13C and δ18O values of the inner belt of the CRTs were not affected by recrystallization. Therefore, δ13C and δ18O values of the CRTs could accurately record environmental conditions in the Tengger Desert. The carbon source of the CRTs was a mixture of soil CO2 derived from root respiration and atmospheric CO2. Furthermore, δ13C values of most samples were lower than − 3.0‰, indicating that C3 vegetation was the main vegetation in the Tengger Desert during the middle and late Holocene. Moreover, δ18O values of the CRTs were ultimately inherited from summer precipitation. Influenced by the 'amount effect' in summer and strong evaporation, the lower δ18O values of the CRTs revealed that relatively higher effective moisture occurred from 7 to 4 cal kyr BP while the higher δ18O values indicated that relatively lower effective moisture occurred from 4 to 2 cal kyr BP in the Tengger Desert. The Holocene millennial-scale moisture changes in the hinterland of the Tengger Desert suggest an arid early Holocene (11.7–7 cal kyr BP), a relatively humid mid-Holocene (7–4 cal kyr BP), and a humid to arid late Holocene (4–2 cal kyr BP). The discrepancy of effective moisture change reconstruction based on the CRTs in the Tengger Desert and adjacent lake sediments during the early Holocene demonstrated that the reliability of the reconstructed results from lake sediments during this period needs further investigation.

The Lenglongling Mountains (LLM) located in northeastern part of the Tibet Plateau, belong to a marginal area of the East Asian summer monsoon (EASM) and are sensitive to monsoon dynamics. Two tree-ring width chronologies developed from six sites of Picea crassifolia in the LLM were employed to study the regional drought variability. Correlation and temporal correlation analyses showed that relationships between the two chronologies and self-calibrated Palmer Drought Severity Index (sc_PDSI) were significant and stable across time, demonstrating the strength of sc_PDSI in modeling drought conditions in this region. Based on the relationships, the mean sc_PDSI was reconstructed for the period from 1786 to 2013. Dry conditions prevailed during 1817-1819, 1829-1831, 1928-1931 and 1999-2001. Relatively wet periods were identified for 1792-1795 and 1954-1956. Spatial correlations with other fourteen precipitation/drought reconstructed series in previous studies revealed that in arid regions of Northwest China, long-term variability of moisture conditions was synchronous before the 1950s at a decadal scale (1791-1954). In northwestern margin of the EASM, most of all selected reconstructions had better consistency in low-frequency variation, especially during dry periods, indicating similar regional moisture variations and analogous modes of climate forcing on tree growth in the region.

In the Asian monsoon margin of northwest China, millennial-scale precipitation and effective moisture changes during the Holocene differ from those observed in the primary monsoon area. Whether these differences were caused by a change in precipitation or other hydroclimate factors remains controversial. We selected Huahai Lake, located in the western portion of the Hexi Corridor, at the northwest margin of the Asian monsoon area, to address this question. Using paleoclimate proxies (mineralogical assemblages and immobile elements) and results from a previous study, we inferred hydroclimate changes in this area during the early and middle Holocene (10.5–5.5 cal ka BP). Heavy precipitation and abundant runoff occurred during the early Holocene (10.5–8.8 cal ka BP). Proxies (carbonate content, total organic carbon and C/N) for precipitation minus evaporation (P − E) in the same section, however, revealed low P − E during the early Holocene and highest P − E in the middle Holocene (8.8–5.5 cal ka BP). Therefore, on a millennial timescale, precipitation amount and effective moisture changes were asynchronous during the early and middle Holocene. The precipitation and effective moisture pattern in the study area during that time span was different from patterns in both the Asian monsoon and westerly wind-influenced areas, suggesting an interplay between the two climate features. High precipitation during the early Holocene corresponded to a strengthened Asian monsoon. Highest P − E in the study area occurred during the middle Holocene and may have been caused by low evaporation, rather than high precipitation.

The Alxa Desert in north-central China has a unique landscape that contains hundreds of lakes and the highest sand dunes in the world. To date, however, the explanation of the water source in this desert is still controversial. In this paper, continuous hydrometeorological observations, including precipitation, evaporation, water level and temperature, in the interior of the Alxa Desert are presented and the water balance of a typical desert lake is calculated. The moisture, Cl − concentration, δ 2 H and δ 18 O of several sand profiles, the hydrogeochemical characteristics of some lakes and groundwater, and the elemental composition of some travertine samples are analyzed to investigate the rainfall percolation and groundwater recharge. The results showed that local precipitation is not the major replenishment source of the lakes and groundwater in the Alxa Desert. It is supposed that the groundwater from deep strata in the adjacent fracture zone might recharge the desert lake group from the southeast along an altitudinal gradient.

Calcareous root tubes or rhizoliths have a strong potential for paleoenvironmental studies, especially in reconstructing paleoenvironmental conditions and paleovegetation. Previous studies suggested that the effectivity of the moisture level affects the formation of calcareous root tubes in the deserts of the Alashan Plateau, Northwest China. However, it remains unclear whether the temporal distribution of calcareous root tubes can be used to reconstruct paleo-effective moisture in this area. In this study, based on conventional 14C dating results of 34 Holocene calcareous root tube samples collected from the Badain Jaran Desert, the Tengger Desert and the Ulan Buh Desert in the Alashan Plateau of northwestern China, millennial-scale changes in paleo-effective moisture during the Holocene in this area were reconstructed. The frequency of the 14C dating results demonstrates that ~ 62% of the Holocene samples were dated to 7–5 cal kyr BP, and ~ 38% of the Holocene samples were dated to 4–2 cal kyr BP, indicating an arid period during the early Holocene (before 8.0 cal kyr BP), a humid period during the mid-Holocene (8.0–5.0 cal kyr BP) and a humid to arid period during the late Holocene (after 5.0 cal kyr BP). The reconstruction results were consistent with other previous reconstruction results from lake sediments and aeolian sand–lacustrine sequences, which indicated that temporal distribution of calcareous root tubes can reflect millennial-scale changes in paleo-effective moisture in this area. However, a single sample could indicate local environmental changes that may differ from the overall desert environmental changes. Hence, the relatively humid environmental record obtained from the presence of calcareous root tubes is a local signal or a regional signal that should be noted.

Accurate identification of the provenance of eolian sand in deserts is essential to study sedimentation processes in the earth system. Exposed bedrock surrounding the desert has been regarded as the main source of eolian sand in some deserts of the world. However, few studies have focused on whether paleolacustrine deposits and bedrock outcrops in desert hinterlands are the main sources of eolian sand. In this study, we selected the Ulan Buh Desert in northwestern China as the study area, and a total of 99 samples were collected throughout the desert and nearby regions to study the provenance of the current eolian sand based on their heavy mineral assemblages and contents. The results showed similar heavy mineral assemblages among the eolian sand, the bedrock to the northwest of the desert, and the paleolacustrine deposits and exposed bedrock in the desert hinterlands, suggesting multiple provenance for the eolian sand in the Ulan Buh Desert. The sources of the eolian sand in the Ulan Buh Desert include bedrock to the northwest, gobi to the west, and paleolacustrine deposits and exposed bedrock in the desert hinterlands. Helan Mountains bedrock and Yellow River fluvial deposits near the desert contribute little to the eolian sand. Moreover, the paleolacustrine deposits and exposed bedrock in the desert hinterlands should not be neglected as the potential provenance of eolian sand in other studies. This study enhances understanding the provenance of eolian sand in the deserts of northern China.

Recognizing the sedimentary environments of sand layers in desert areas aids in evaluating the reliability of using these materials to assess paleoenvironmental changes. Nevertheless, determining whether eolian sand has ever been in a subaqueous sedimentary environment remains difficult. The work presented here tests microtextures on quartz grains from a predominantly eolian environment and tries to differentiate grains shaped purely by eolian processes from those also subjected to subaqueous action. In this study, 124 samples including lake sediments, river sediments, and eolian sediments were collected from the Badain Jaran Desert hinterland and adjacent areas. Microtextural assemblages on the quartz grains were analyzed by scanning electron microscopy. The results reveal that the microtextural features have variable frequencies among different sand samples, including lake sediments, eolian sand, and river sand. Eolian sand deposited in a subaqueous sedimentary environment not only has the specific microtextures of subaqueous sedimentary environments such as V-shaped percussion cracks, straight or curved grooves and scratches, oriented etch pits, solution crevasses, and scaling but also retains the unique microstructures of eolian sedimentary environments such as crescentic percussion marks. Therefore, the above microtextural features can distinguish whether eolian sand has ever been in a subaqueous sedimentary environment. This study provides a new method for discriminating the sedimentary environments of eolian sands in desert hinterlands.

Calcareous root tubes are widely distributed across the Badain Jaran Desert and the Tengger Desert of the Alashan Plateau in northwest China. However, the reliability of their 14 C dating results and their environmental significance remain unclear. In this study, the conventional 14 C ages of 31 calcareous root tube samples and one aquatic mollusc shell sample, which were all collected from the Badain Jaran Desert and the Tengger Desert, were measured. The results reveal that nine of the 14 calcareous root tube samples from the Badain Jaran Desert were from Marine Isotope Stage (MIS) 3, while two samples were from MIS 2. The other three samples were dated to the mid-Holocene, one of which is consistent with the aquatic mollusc shell sample collected from the shoreline of Zhunzhahanjilin Lake in the Badain Jaran Desert. Moreover, the 17 calcareous root tube samples from the Tengger Desert were all dated to the mid- and late-Holocene, most of which were from the mid-Holocene. The results demonstrate that calcareous root tubes can be used as

The pattern of Holocene environmental changes in the Asian monsoon margin on a millennial timescale remains controversial. Based on lithological characteristics and sedimentological proxies, we reconstructed Holocene-effective humidity changes and the lake evolution of Huahai Lake in the marginal area of the Asian monsoon in the Hexi Corridor of NW China. Our results show that alluvial and aeolian deposition before 10.4 cal ka BP indicate an arid environment, that lacustrine deposition from 10.4 to 8.8 cal ka BP indicates a transition from an arid to a humid environment, and that lacustrine deposition from 8.8 to 5.5 cal ka BP occurred during the most humid conditions, indicated by proxy records (grain size, carbonate, TOC, and C/N). After 5.5 cal ka BP, a depositional hiatus implicates an arid environment in the late Holocene. Holocene environmental changes on millennial timescales in Huahai Lake imply that climate was arid to humid in the early Holocene, most humid in the mid-Holocene and arid in the late Holocene. These moisture changes were influenced by the Asian monsoon, particularly the transportation of water vapor by the Indian monsoon. In addition, these moisture changes could have been affected by westerly winds that could have contributed to the water vapor supply to this region during the mid-Holocene. The most humid conditions that occurred in the study area during the mid-Holocene may have been caused by strong westerlies and low levels of evaporation.

In the regions surrounding the Qinghai Tibet Plateau, changes in erosion rates have been linked to the tectonics, climate and topography over different time scales. To understand the mechanisms governing the changes of erosion rates, it is important to study erosion rates by different methods and for different time scales. In inland drainage basins, deposition rates of terminal lake sediments can indicate basin-wide erosion rates at the millennial-scale. This paper presents three lake records of the Last Deglaciation and Holocene (Huahai Lake, Zhuye Lake and Yanchi Lake) from the Hexi Corridor, north of the Qilian Mountains, in arid China. Organic matter, terrestrial pollen concentrates, seeds, grasses and plant debris are used for conventional and AMS 14 C dating. On the basis of 66 radiocarbon dates, lithology and grain-size, we infer relatively high basin-wide erosion rates during the Last Deglaciation and early Holocene in the three drainage basins, when the three lake sediments were seriously affected by reworking. The deposition rates were an order of magnitude or greater in these lakes during the Last Deglaciation and early Holocene than during the mid-to-late Holocene. During the transition period of the last glacial–interglacial cycle, significant climatic changes occurred in East and Central Asia, corresponding to the strengthening of the Asian summer monsoon and to increasing effective moisture in arid Central Asia, which can have strong impacts on basin-wide erosion rates north of the Qinghai Tibet Plateau. Moreover, melting glaciers in the Qilian Mountains probably also contributed to the high basin-wide erosion rates. At the same time, tectonic activity was not recognizable in the study area during that period. In the arid and semiarid regions surrounding the Qinghai Tibet Plateau, dramatic changes in erosion rates appear during the transition periods of the glacial–interglacial cycles, which illustrate the climatic controls on erosion rates at this time scale.

Based on the data of the Alxa desert region and 27 meteorological stations recorded by 1960–2013, T ≥ 0 and T ≥ 10 °C accumulated temperatures were analyzed by using sliding average, linear regression, Mann–Kendall abrupt change test, and kriging interpolation methods. The results show that the T ≥ 0 °C accumulated temperature increased significantly by 9.94 °C/a and that of the T ≥ 10 °C increased by 8.88 °C/a during 1960–2013. The increases in the eastern study area were the most obvious, followed by those in the western and central regions. Additionally, the trends of these regions were highly consistent with that of the entire study area. The accumulated temperatures in the study area increased modestly prior to the 1980s, after which time a fairly steady climb began during the late 1980s. The two abrupt change points of T ≥ 0 and T ≥ 10 °C were in 1996 and 1998, respectively. Additionally, the accumulated temperatures increased significantly around 2000. The analysis shows that higher accumulated temperature occurred in the Alxa desert region than in the surrounding area. The distribution of increases in T ≥ 0 and T ≥ 10 °C accumulated temperatures around the study area presented varying spatial differentiation. For T ≥ 0 °C accumulated temperature, an increase at the edge of the Tengger desert was the most obvious. T ≥ 10 °C accumulated temperature exhibited a smaller increase than that of T ≥ 0 °C. In addition, the smallest amplitude of temperature increase was measured in the central Alxa desert region and in the surrounding area.

Free water surface evaporation is an important process in the hydrologic and energy cycle. Accurate calculation of free water evaporation helps in evaluating the reliability of data on the distribution and quantity of water resources. However, the applicability of evaporation models to the calculation of free water surface evaporation in hyper-arid regions is still uncertain. Moreover, the accuracy of previously used evaporation models should be evaluated for hyper-arid regions. In this study, the Ejina basin in the hyper-arid region of northwest China was selected to address this issue. Measured meteorological data (1993–2008) were used to calculate free water surface evaporation using the Dalton model, Penman formula, and energy balance equations. Results from two different Dalton models were higher and lower than the results from E601 pan evaporation, respectively. Results from the Penman formula were lower than results from E601 pan, whereas results from the energy balance equations are higher than the results from E601 pan. The results indicate that previous evaporation models are not suited for calculating free water surface evaporation in hyper-arid regions if not modified. Using meteorological data and radiation data (1993–2000), the Dalton model, energy balance equations, and Penman formula were modified to calculate free water surface evaporation for 2001–2008. The average annual evaporation from the three modified models was slightly lower than the evaporation from E601 pan during 2001–2008. However, the errors in the values were only 11–14 mm, which were much lower than in previous models. The modified Dalton model and Penman formula yielded a higher accuracy of the calculation, whereas the modified energy balance equations had the lowest accuracy.

Methods for reconstruction of river runoff have been an important component of paleo-climatology and paleo-hydrology. The lower Heihe River was studied from 2002 to 2008 to reconstruct the annual average runoff at the Zhengyi Gorges hydrological station using measured data and improved water and energy balance equations. The results indicate that the reconstructed annual runoff and the measured runoff values are not equivalent. However, the difference between reconstructed and measured runoff values is within 10 %, which suggests that water and energy balance models can successfully reconstruct runoff from rivers in arid regions. Regional differences imply that parameters must be corrected when applying water and energy balance equations to prevent large errors. In addition, the latent heat of evaporation in arid lakes is greater than their net radiation, according to latent and sensible heat calculations, which demonstrates the existence of the "cold island effect".

The Asian summer monsoon and the westerly winds interact in the mid-latitude regions of East Asia, so that climate change there is influenced by the combined effect of the two climate systems. The Holocene millennial-scale Asian summer monsoon change shows the out-of-phase relationship with the moisture evolution in arid Central Asia. Although much research has been devoted to the long-term climate change, little work has been done on the mechanism. Summer precipitation, in the marginal regions of the Asian monsoon, is strongly affected by the monsoon and the westerly winds. The purpose of this paper is to examine the mechanism of the millennial-scale out-of-phase relationship by modern summer precipitation analysis in the northwest margin of the Asian monsoon (95–110°E, 35–45°N). First, the method of Empirical Orthogonal Function (EOF) analysis was carried out to the 1960–2008 summer rainfall data from 64 stations in that region; then the water vapor transportation and geopotential height field data were studied, in order to explain and understand the factors that influence the summer precipitation; lastly, the East Asian Summer Monsoon Index (EASMI), South Asian Summer Monsoon Index (SASMI), Summer Westerly Winds Index (SWI) were compared with the EOF time series. The results indicate the complicated interannual-scale interaction between the Asian summer monsoon and the westerly winds, which can result in the modern out-of-phase relationship in the study area. This study demonstrates that the interaction between the two climate systems can be considered as a factor for the millennial-scale out-of-phase relationship.

Deposits from the Huahai ancient lake in the Hexi Corridor were dated using conventional and AMS 14C. A 2500a “carbon storage effect” was defined at 9.25 m depth according to the 14C age difference between a plant macrofragment and detrital organic matter from the same layer. The chronology of this strata indicated that the mirabilite layer at the depth of 8.05 m–9.15 m had formed during the Younger Dryas (YD) event. The formation of the mirabilite layer indicated that the mean annual temperature in the Hexi Corridor dropped by 11 C° during the YD event compared with today. The lowest cold event occurred early in the YD, which is consistent with what has been revealed by other high-resolution records, such as those of Arctic ice cores and stalagmites in mid-latitude regions.

In arid regions, because of spatial variability, using single climate records is difficult to reconstruct the past climate change for the drainage basins. Holocene environmental records were collected from the upper, middle and lower regions of the Shiyang River drainage basin in the marginal area of the Asian monsoon (northwest China). The main objective of this paper was to compare the records from the terminal lake and the middle and upper reaches of the basin to study the basin-wide environmental changes. During the early Holocene the vegetation was sparse, and the effective moisture was relatively low in the basin. The Holocene Climatic Optimum started between 7.0 and 8.0 cal ka BP, during which the lake level reached the highest level in the terminal lake; the vegetation density and the effective moisture reached the highest level during the Holocene in the drainage basin. From 4.7 cal ka BP the terminal lake began to shrink, while the vegetation density decreased dramatically. In the middle and upper regions of the drainage, the effective moisture began to decrease since 3.5 cal ka BP, and the arid tendency was earlier in the terminal lake than it was in the middle and upper regions of the drainage basin. During the early Holocene the relatively arid environment was affected by the gradually intensifying East Asian monsoon and the dry westerly winds. The mid-Holocene Optimum benefited from the intensive East Asian monsoon and the humid westerly winds. Then, the East Asian monsoon retreated since the late-Holocene. In the basin the arid tendency may be related to the retracting of the East Asian monsoon. However, the intensifying acidification after 1.5 cal ka BP may be correlated to the increasing dryness of the westerly winds.