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Ancient cities are excellent spatiotemporal indicators for the study of historical human activities and environmental change. The ancient city of Sanchahe is located at the southern margin of the Mu Us Desert, China. It is an ideal location for studying the complex relationships between historical desertification and human activities. Field observations of the ancient city walls, a well, and a spring, as well as 14C dating, grain size, spatial analysis of archaeological sites, and analyses of historical seismicity, indicated that neotectonics may have contributed to crustal uplift and accelerated fluvial incision of the Wuding River. This rapid incision caused a decline in groundwater levels, which is an important reason for the irreversible environmental degradation around Sanchahe city over the past 800 yr. This study provides new evidence for such environmental degradation and may contribute to a better understanding of historical desertification in the Mu Us Desert. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Three ostracod species were identified and related ecological information are reported in the Badain Jaran Desert. • The node formation of Limnocythere inopinata is affected by a combination of the salinity and Ca2+ content of lake water. • The relationship between the percentage of noded individuals and salinity of lake water is complex. Limnocythere inopinata (Baird, 1843) is a widely distributed ostracod in modern non-marine waters and Quaternary sediments. Based on its morphological variation (the number and position of its nodes), different phenotypes have been identified. However, the factors controlling its morphological variation are currently open to debate, which hinders palaeoecological reconstructions based on this species. In this study, ostracod distribution and hydrochemical analyses of the ambient environment of 21 lakes in the Badain Jaran Desert were carried out. Three ostracod species belonging to two genera are identified as Limnocyhtere inopinata , Cypris cf. granulate and Cypris sp. with the dominant species L. inopinata represented by six phenotypes. The distribution features of these ostracods in the lakes and related ecological information are reported. In addition, the factors controlling the morphological variations of L. inopinata were analysed. Our data indicate that the noded individuals of L. inopinata prefer water with appropriate Ca2+ content (30–40 mg L−1) and low salinities (below 4.60 g L−1). The percentage of noded individuals of L. inopinata increases with increasing salinity only within a certain salinity range. Hence, caution should be exercised in reconstructions of palaeosalinity based on the morphological variability of L. inopinata. [ABSTRACT FROM AUTHOR]

Mega-dunes in the lake group area of the Badain Jaran Sand Sea, China, are generally taller than dunes in the non-lake group area. This spatial distribution of dune heights may provide a new perspective on the controversy regarding the dunes' formation mechanism. In this study, we calculated the relative heights and slopes of individual dunes based on a digital elevation model, and we confirmed the height distribution of abnormally tall dunes in the lake group area of the sand sea. It was also found that slopes of more than 10° in the lake group area are more common than those in the non-lake group area. Based on meteorological observations, coupled with the measurement of water content in the sand layers, we propose a conceptual model demonstrating that moisture exchange between the lakes and soil via non-rainfall water will humidify dune slopes and form a more favorable accumulation environment for aeolian sand, thus increasing dune heights. Although long-term observations are yet to be carried out, the present study can be used as evidence for understanding the basis of dune formation in the lake group area and assessing groundwater utilization in deserts. [ABSTRACT FROM AUTHOR]

Abstract: 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 14C 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

The relationship between the variation of CO 2 flux and the pH of inorganic factors. [Display omitted] • The difference of CO 2 absorption and release is obvious during the day and night. • Yindeer Lake was a net sink of CO 2 during the study period. • The lakes can absorb large amounts of CO 2 every year to slow down global warming. • Meteorological factors controlling CO 2 fluxes differed by time scale. • pH is the main influencing factor controlling CO 2 absorption and release. Carbon sequestration levels in lakes are often underestimated despite being vital for the comprehensive analysis of CO 2 budget and significantly influencing inland lakes in arid areas. In this study, the eddy covariance (EC) technique was used to measure CO 2 flux for six consecutive years during 2012–2017 in a small salt-lake (Yindeer Lake) replenished by groundwater in southeastern Badain Jaran Desert, China. The results indicate that: (1) Yindeer Lake was a net sink of CO 2 , which led to the estimate that the lakes in the Badain Jaran Desert can absorb approximately 1.91 × 103 t of CO 2 per year and help slow down the rate of global warming. (2) The effects of meteorological factors on the CO 2 flux of the lake vary with timescales. (3) Inorganic processes, in which pH is the main influence mechanism, control CO 2 absorption and releases in Yindeer Lake. Thus, the study results provide a new guide for solving the "missing sink" problem. [ABSTRACT FROM AUTHOR]

The distinct effects of the lakes on the maximum and minimum temperatures cause a large discrepancy in diurnal temperature differences between the dry basin and lake basins. Discussion The above findings demonstrate that daily average temperature and the monthly minimum temperature inside the lake basins are warmer than those in the dry basin, particularly during the cold season. This suggests that, once the lake area reaches 1.91km SP 2 sp , the temperature difference between the lake basin and the dry basin (warm island intensity) becomes significant, but only in winter. Figure 4(a) shows that, the daily maximum temperature is lower in the lake basins than in the dry basin but differences between lake basins and the dry basin are not significant. [Extracted from the article]

The spatio-temporal characteristics and driving mechanisms of the Asian summer monsoon (ASM) during the early and middle Holocene remain unclear. Moreover, the timing of maximum monsoon precipitation in the Asian monsoon margin of northwest China during this period is also a subject of considerable debate. Herein, we analyzed phytolith assemblages within 55 calcareous root tube (CRT) samples from the hinterland of the Tengger Desert to quantitatively reconstruct Holocene millennial-scale precipitation changes and discuss the potential forcing mechanisms. Our results revealed that the mean annual precipitation (MAP) was 138 ± 53 to 149 ± 18 mm during 10.0–7.0 cal kyr BP, 179 ± 26 to 192 ± 26 mm during 7.0–5.0 cal kyr BP, and 129 ± 20 to 161 ± 13 mm during 5.0–1.0 cal kyr BP. The quantitative reconstruction results suggested that precipitation in this area was low in the early Holocene, then increased to a maximum in the middle Holocene (30% higher precipitation than present), and gradually decreased in the late Holocene. Maximum monsoon precipitation did not occur until the middle Holocene in this area because the northernmost margin of the ASM reached its northernmost latitude lagging behind its maximum monsoon intensity suppressed by high-northern latitude ice volume forcing during the early Holocene despite high summer insolation. In addition to quantifying the Holocene millennial-scale precipitation changes in the northwestern margin of the ASM, this study also provides new evidence for spatial and temporal variations of the ASM during the Holocene. [ABSTRACT FROM AUTHOR]

• New methods to quantitatively reconstruct consecutive lake level changes in desert. • The highest lake levels occurred at the early Holocene in BJD hinterland. • Increase in meltwater resulted in high lake levels during the early Holocene. Quantitative reconstruction of consecutive paleolake-level fluctuations may help reconstruct lake evolution during the Holocene. However, the reconstruction of a groundwater recharged lake in a desert hinterland is challenging. In this study, 23 samples of lake bottom sediments were obtained from eight groundwater recharged lakes in the hinterland of the Badian Jaran Desert in northwest China to establish models between the grain size component and lake level. Our results showed that the four grain size components of the sediments could be separated using the Weibull function. The first two fine grain components (W1 and W2) were deposited in the atmospheric dust. The two coarser components (W3 and W4) could be interpreted as sediments transported by wind from the surrounding sand dunes, while W3 was subsequently redistributed by lake waves. Changes in the lake water depth could be expressed by the W1 and W2 component contents, as well as the modal size of W3. Using the above models, unmixing grain size components of the lake sediment obtained from the ZZH section located in a seasonal lake (Zhunzhahan Jaran Lake) in the desert hinterland were used to quantitatively reconstruct the lake-level fluctuations during the Holocene. The lake level frequently fluctuated between 3.82 and 9.21 m during 10.6–8.6 cal kyr BP, slightly fluctuated between 3.41 and 5.26 m during 8.6–4.7 cal kyr BP, and markedly declined from 6.09 m to 4.46 m during 4.7–3.5 cal kyr BP. Lake-level changes in the hinterland of the Badian Jaran Desert did not correspond to the effective moisture changes during the early Holocene. Instead, the rise in lake level during the early Holocene would have resulted from the input of groundwater from the meltwater in the mountains of the recharge area. The data reveal new methods for quantitatively reconstructing consecutive paleolake-level fluctuations by groundwater recharged lakes in the desert hinterland. [ABSTRACT FROM AUTHOR]