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The mid-latitude Westerlies (MLW) are one of the most important atmospheric circulation systems in the Northern Hemisphere, exerting a huge influence on the climate of the region downwind, and thus on vegetation, water resources, and human wellbeing. However, the seasonal variation of the MLW during the Holocene is not yet been fully understood, especially when its contribution is the most important. Here, we used end-member (EM) modeling analysis of the grain-size distributions of a high-altitude aeolian sedimentary sequence (4452 m a.s.l.) from the Yarlung Zangbo River valley in the southern Tibetan Plateau to reveal variations in the winter MLW during the Holocene. Analysis of seasonal differences in modern atmospheric circulation suggests that the southern Tibetan Plateau was heavily influenced by the mid-latitude Westerlies at the 400, 500, and 600 hPa levels in winter, while it was seldom influenced at these levels in summer. Four grain-size end-members are identified, representing distinct aerodynamic environments, of which EM1 (modal grain size 8.1 μm) can be used as a proxy of the winter MLW. A reconstruction of the variation of the winter MLW during the Holocene based on EM1 revealed that a weaker winter MLW occurred during the Early to Middle Holocene, and a stronger winter MLW during the Middle to Late Holocene. Overall, we suggest that this change in the winter MLW was closely related to the insolation/temperature/pressure gradient between low and high latitudes in the Northern Hemisphere.

Aeolian processes have been studied extensively at low elevations, but have been relatively little studied at high elevations. Aeolian sediments are widely distributed in the Yarlung Zangbo River basin, southern Tibetan Plateau, which is characterized by low pressure and low temperature. Here, we comprehensively analyzed the wind regime using data since 1980 from 11 meteorological stations in the study area, and examined the interaction between the near-surface wind and aeolian environment. The wind environment exhibited significant spatial and temporal variation, and mean wind speed has generally decreased on both annual and seasonal bases since 1980, at an average of 0.181 m/(s·10a). This decrease resulted from the reduced contribution of maximum wind speed, and depended strongly on variations of the frequency of sand-driving winds. The drift potential and related parameters also showed obvious spatial and temporal variation, with similar driving forces for the wind environment. The strength of the wind regime affected the formation and development of the aeolian geomorphological pattern, but with variation caused by local topography and sediment sources. The drift potential and resultant drift direction were two key parameters, as they quantify the dynamic conditions and depositional orientation of the aeolian sediments. Wind affected the spatial variation in sediment grain size, but the source material and complex topographic effects on the near-surface wind were the underlying causes for the grain size distribution of aeolian sands. These results will support efforts to control aeolian desertification in the basin and improve our understanding of aeolian processes in high-elevation environments.

The Holocene Climate Optimum (HCO) was an important interval in the development of human civilization and has been the focus of many paleoclimatic studies. However, there are significant regional differences in the timing of the HCO due to the complex response of regional climates to insolation changes, associated with internal feedbacks within the climate system. Here, we present the results of a study of magnetic and geochemical properties of loess-paleosol sequences from across mid-latitude Asia, with the aim of assessing differences in the timing of the HCO. The HCO generally occurred after ~5 ka in Tajikistan and Xinjiang; during 5–2.5 ka in the western Chinese Loess Plateau (CLP); and during ~8–2.5 ka in the central CLP. This asynchroneity reflects differences in the response of regional climates to global climate change. Specifically, the difference in timing between the central and western CLP may have been related to shifts in the position of the East Asian summer monsoon rain belt, due to the changing longitudinal position of the Western Pacific Subtropical High, together with changes in the east-west thermal gradient in the equatorial Pacific (i.e. shifts between La Nina and El Nino conditions).

K-feldspar pIRIR dating was used to establish a chronological framework for the KS15-05 loess section in the Yili Basin, northern Xinjiang Province, China, in arid central Asia. The reliability of the dating results was verified from the luminescence characteristics and internal checks. The chronology was used to calculate mass accumulation rates (MARs) for the section and the paleoclimatic proxies of grain size and magnetic susceptibility were also analyzed. The high dust accumulation patterns during the last glacial maximum in Yili Basin are consistent with those of the Chinese Loess Plateau (CLP). On a millennial-scale, the Bolling-Allerod (B/A) interstadial is clearly reflected in the KS15-05 section by the variation of the 2–10 μm grain-size fraction, suggesting the influence of the Westerlies which dominate the modern atmospheric circulation of the region. However, the B/A interstadial is poorly recorded in grain-size records of the CLP and this disparity may provide additional information about the nature of the transmission of climate signals from the North Atlantic region to Asia. Specifically, the zonal transmission of the B/A warm signal to the CLP may have been obscured by the cooling effect of High-latitude cold air to the north of the CLP.

Central Asia comprises a vast area of arid terrain which has an important impact on the global climate system. Although still debated, the pattern of climatic variations in central Asia is regionally distinctive and does not appear to be strongly related to changes in insolation. To understand the climatic evolution of central Asia, as well as its forcing mechanisms, it is necessary to characterize variations in the Westerlies, which have had a major influence on climate change in the region. Past variations in the Westerlies are commonly reconstructed from records of the composition, grain-size and mass accumulation rate (MAR) of loess and the eolian component of lacustrine sediments which are commonly mixed by the signal of surface atmospheric circulation. Here we present the results of grain-size analysis of a section of last glacial and Holocene loess deposits in the Tien Shan Mountains. The results indicate that the strength of the Westerlies was weakest during the last deglacial and early Holocene (16–6 ka), strongest during the mid-Holocene (6–3.1 ka), and moderate during the late Holocene (3.1–0 ka). By comparison with an independent record of humidity, we propose that the Westerlies were an important driver of moisture variations in central Asia, with strong Westerlies circulation resulting in high precipitation and vice versa during the past 16 kyr.

The pattern of changes in Holocene moisture conditions in the southern Tibetan Plateau (TP) and the associated driving mechanism are still controversial. Here, we present the results of an analysis of an aeolian sedimentary sequence from the Yarlung Zangbo River valley in the southern TP, which potentially provides a record of changes in moisture conditions during the Holocene, and hence changes in the atmospheric circulation process. Optically stimulated luminescence dating with the single-aliquot regeneration protocol was used to establish the chronology for the sequence, and geochemical and granulometric measurements were used to reconstruct the Holocene moisture history. The results indicate that moisture conditions were strongly influenced by the early Holocene maximum in summer insolation (30°N) and hence by the Indian summer monsoon (ISM), under which the weathering intensity was relatively high. However, at ∼7.6 ka the climate abruptly became drier, probably due to the weakening of the ISM. Subsequently, with the further decrease in summer insolation and increase in winter insolation, the variations in ISM-related moisture delivery to the southern TP were regulated by the enhanced winter mid-latitude Westerlies (MLW), resulting in increasing weathering intensity. Thus, the Holocene evolution of moisture conditions in the southern TP was mainly controlled by changes in the relative intensities of the ISM and the winter MLW, which depended on the variations of summer and winter insolation at 30°N. Overall, our results provide an improved understanding of the driving mechanism of climate change in the southern TP during the Holocene.

The expansion of poisonous plants can change vegetation community structures and affect grassland ecosystem service values. Stellera chamaejasme is one of the most important poisonous plants and has rapidly expanded in the arid areas of Northwest China in recent decades. The objective of this study was to elucidate the expansion process and model of an S. chamaejasme population. Therefore, we classified the S. chamaejasme population into five classes based on coverage: 31–40%, 41–50%, 51–60%, 61–70% and 71–80%. We investigated the spatial distribution patterns and the size compositions of S. chamaejasme under different coverages. The results show that the spatial distribution pattern of S. chamaejasme under low coverage (31–40%) at all study scales (0–100 cm) was random; the spatial distribution pattern translated to a clumped distribution from a random distribution at some scales, and the clumped distributions gradually became obvious, with coverage increasing from 41–50% to 61–70%; the spatial distribution tended to be random at all study scales when coverage was increased further (71–80%). However, the spatial distribution patterns were closely related to the size composition of the S. chamaejasme population. In particular, the quantity of older individuals had a significant impact on the variation of the spatial distribution patterns of S. chamaejasme. The spatial distribution pattern varied from a random distribution to a clumped distribution and then returned to a random distribution with increasing coverage (from 31–40% to 71–80%), and this may indicate that the S. chamaejasme patches experienced patch formation and extension and merged with each other.