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It is generally believed that water vapour from the North Atlantic transported by the mid‐latitude westerlies dominates precipitation variations in arid Central Asia, where monsoonal water vapour source is beyond the reach. This study reexamines water vapour sources for arid Central Asia based on daily reanalysis data. The results reveal two water vapour sources for arid Central Asia: the westerly water vapour transport from the North Atlantic and the monsoonal water vapour transport from the tropical Indian Ocean and South China Sea. The monsoonal transport includes two pathways: lower tropospheric water vapour along the eastern and northern periphery of the Tibetan Plateau from the tropical Indian Ocean and South China Sea, and middle‐upper tropospheric water vapour via the Tibetan Plateau from the tropical Indian Ocean. Precipitation variability during the monsoonal transport events explains 81% of the total variance. The monsoonal transport is related to a weakened East Asian summer monsoon (EASM) that is accompanied by persistent westward shift of the western Pacific subtropical high and increasing frequency of Mongolian anticyclone activities. The EASM has experienced a persistent weakening trend since 1958, causing an increasing contribution of the monsoonal water vapour transport and thereby enhancing summer precipitation in arid Central Asia. In particular, the monsoonal easterly water vapour has become the dominant source for arid Central Asia in the lower troposphere during the last decade. This study highlights the important role of the EASM in the wetting trend of summers in arid Central Asia during the past six decades. [ABSTRACT FROM AUTHOR]

The Holocene moisture–temperature correlation on varying spatial–temporal scales in arid Central Asia (ACA) is still controversial. It has been widely reported that ACA experienced multi-centennial alternations between warm/dry and cold/wet climates over the past two millennia. However, less attention has focused on orbital-scale moisture–temperature relationship at a regional scale across ACA. Here, we contribute a framework including a set of quantitative algorithms to acquire reliable pollen-based climatic reconstructions. We apply this methodology to a new pollen record from a wetland in northern Xinjiang (southeastern ACA) for quantitative reconstructions of moisture availability (actual/potential evapotranspiration ratio, AET/PET) and summer temperature (mean temperature of the warmest month, MTWA) over circa the last 10,300 years. We select AET/PET and MTWA because they are evaluated to be most statistically independent and ecologically significant. The effect of differing spatial extents of calibration-sets on model performance is tested to determine the optimal extent. We critically assess the reliability of all reconstructions through calculations of statistical significance, analogue quality and goodness-of-fit statistics. Our final reconstructions are statistically significant with independent features of AET/PET and MTWA, showing an increasing (declining) trend of Holocene moisture (temperature). This anti-phase pattern is consistent with other records and model simulations across southeastern ACA. The data-model consistency postulates that (i) the glacier meltwater from Tien Shan ('Water Tower of Central Asia') is crucial to support major streamflow and watersheds over ACA, and (ii) the Holocene wetting trend may be determined by the interacting effects between decreased summer temperature and increased winter precipitation. [ABSTRACT FROM AUTHOR]

The term 'westerlies-dominated climatic regime' describes the pattern of precipitation/moisture variations between westerlies-dominated arid Central Asia (ACA) and mid-latitude monsoon-dominated Asia on decadal to multi-millennial time scales. However, no attempts have been made to define its core region and the possible physical mechanisms responsible during the period of instrumental observations. The present study investigates the spatiotemporal variations of summer and winter precipitation on interannual to decadal time scales over mid-latitudes of the Eurasian continent using Empirical Orthogonal Function (EOF) analysis. Our results suggest the existence of an opposing pattern of summer precipitation variations between ACA and mid-latitude monsoon-dominated Asia and Mediterranean on decadal time scales. Based on these results, the core region influenced by the westerlies is outlined, including arid central Asia and Xinjiang in China (36°-54°N, 50°-90°E). By using monthly NCEP-NCAR reanalysis, the relationship between the 'westerlies-dominated climatic regime' and atmospheric circulation were also analyzed. The combination of the zonal climatic teleconnection pattern and anomalous Indian summer monsoon precipitation (ISMP) causes the precipitation characteristics of the 'westerlies-dominated climatic regime' precipitation pattern. In addition, the Atlantic Multidecadal Oscillation (AMO) may also have an important effect on the 'westerlies-dominated climatic regime'. [ABSTRACT FROM AUTHOR]

This study analyzed the spatial differences of the precipitation variations in the mid-latitude Asia and their possible physical mechanisms during 1960–2009. The annual precipitation showed an opposite variations between the westerlies-dominated arid Central Asia (ACA) and monsoon-dominated North China (NC) during the study period. Given the different contributions of seasonal precipitation to annual total precipitation in ACA and NC, the atmospheric circulation anomalies during the major precipitation seasons (winter in ACA/summer in NC) were analyzed. In winter, negative North Atlantic Oscillation may cause negative height anomalies over the north side and positive anomalies over the south side of the ACA. Together, the enhanced pressure gradient and anomalous westerly wind brings more water vapor to ACA, and leaves less precipitation in NC. In summer, the low-pressure anomalies in Northeast China, along with a weaker summer monsoon and negative height anomalies in Eastern Europe together contribute to reduced (excessive) summer precipitation in NC (ACA). The interactions between ENSO and NAO may result in the opposite precipitation variations between ACA and NC. A significant 2–3-year cycle is identified in ACA, which is linked to the variations of westerly circulation in the middle troposphere. [ABSTRACT FROM AUTHOR]

• Single grain K-feldspar pIR 50 IR 170 dating effectively dates samples over past 1 kyr. • Highest lake levels in Qaidam Basin over past 1 kyr during Little Ice Age. • Out-of-phase Central and East Asian precipitation drive asynchronous lake change. • EASM did not penetrate as far inland as Qaidam Basin during past 1 kyr. The moisture and precipitation evolution of mid-latitude Asia are dominated by the East Asian summer monsoon (EASM) and mid-latitude Westerlies atmospheric systems. How these two systems interacted along their transition zone in the northern Tibetan Plateau remains unclear, especially over centennially to millennial timescales. This study investigates moisture evolution along the EASM-Westerlies transition zone using 10 Late Holocene paleolake shorelines from Toson Lake in the northern Tibetan Plateau. Shorelines are dated using a newly developed single-grain post infrared-infrared stimulated luminescence (pIR 50 IR 170) dating protocol for 14,500 K-feldspar grains and used to reconstruct the evolution of Toson Lake over the past millennium. Results show that Toson Lake was stable during the Medieval Warm Period (MWP), expanded during the Little Ice Age (LIA) with a distinct highstand from AD1600–1700 punctuated by short-duration low period at ∼ CE 1650. After which, Toson Lake dramatically contracted into the Current Warm period (CWP). Lake level changes are consistent with Westerlies precipitation variability across Central Asia, in contrast to records from the EASM dominated northeastern Tibetan Plateau and northern China documenting an arid LIA and wet MWP. Reanalysis of modern climatic data are combined with our lake chronology to reveal that although EASM strength influences precipitation variability across northeastern Tibetan Plateau (NETP) and northern China, EASM precipitation has not directly penetrated deep inland over the past millennium. Instead, Westerlies moisture, modulated by the see-saw of the North Atlantic Oscillation, together with the moisture controlled by the anticyclonic circulation over Mongolia and negatively related to the EASM strength, dominated water vapour transport to the mid-latitudes of Central Asia. Out-of-phase moisture transport and interaction between the Westerlies and EASM drives asynchronous lake evolution between Central and East Asia over centennial-millennial timescales. [ABSTRACT FROM AUTHOR]

The variability and interaction of the East Asian summer monsoon (EASM), East Asian winter monsoon (EAWM) and Westerlies dominate mid-latitude Asian hydroclimate and influence over a billion lives in Asia. However, how variation in the EASM, EAWM and Westerlies influences climate change in their transition zones in NW China remain unclear. Specifically, how these atmospheric systems interact during strong-weak phases variation over different timescales is still hotly debated. This study investigates four loess-paleosol sequences in the transition zone between EASM and Westerlies-influenced areas along the central Hexi Corridor of NW China, and presents 63 quartz optically stimulated luminescence (OSL) ages to generate the most detailed chronology for any loess record within the Hexi Corridor. In combination with sedimentology, proxy indexes of magnetic parameters (χ lf , χ fd , χ ARM /SIRM) and grain size of these loess-paleosol sequences, and TraCE-21 ka climatic modelling, the loess deposition and climatic changes at central Hexi Corridor regions over the past 25 ka are reconstructed. Our results indicate that: (1) loess deposition initiated by at least 25 ka at Hexi Corridor. Loess depositional rates decrease from late last glacial into the Holocene, with maximum accumulation rates (140–180 g/cm3/ka) occurring during the Last Glacial Maximum. Depositional hiatuses up to 8 ka are recognized in late Quaternary Hexi Corridor loess, which suggests that high-resolution chronologies are necessary for robust paleoclimatic reconstructions from loess records in the region. (2) Over glacial-interglacial cycles, climate in the Hexi Corridor demonstrates a cold-dry glacial and a warm-moist interglacial, consistent with moisture changes observed in the monsoonal Chinese Central Loess Plateau and Westerlies-dominated Central Asia. However, moisture in central Hexi Corridor increased from the early Holocene to mid-Holocene, with a wettest period at 8–7 ka, and followed by a relatively wet late Holocene. These changes are most consistent with the EASM-dominated Chinese Central Loess Plateau and suggests that Westerlies influence in the central Hexi Corridor is minor over at least the past 25 kyr. (3) EAWM intensities demonstrate an anti-phase relationship to EASM intensities over the past 25 kyr in the Hexi Corridor, with decreasing EAWM intensity into the early-mid Holocene and an increase into the late Holocene. (4). EASM precipitation variability in the Hexi Corridor appears to not to be a direct nor singular response to changes in 30°N summer insolation. EASM lags insolation by 3 kyr during the Holocene, supporting the idea that high-latitude forcing through changes in ice volume, greenhouse gases, and/or meltwater input to North Atlantic and Southern oceans can effectively modulate EASM intensity and critically influence Hexi Corridor paleoclimatic conditions. • Loess depositional hiatuses up to 8 kyr occur in the Hexi Corridor. • Over the past 25 kyr, the wettest period occurs at 8–7 ka in the Hexi Corridor. • East Asian Summer Monsoon controls central Hexi Corridor precipitation since 25 ka. • East Asian Winter Monsoon is anti-phase to East Asian Summer Monsoon since 25 ka. • High-latitude forcing modulates EASM intensity and Hexi Corridor climatic changes. [ABSTRACT FROM AUTHOR]

Paleoclimatic changes in arid central Asia (ACA), one of the largest arid regions in the world, are complex and the nature of these changes on orbital cycles remains unclear. Widely distributed loess records in ACA potentially provide records of paleoclimatic variation, but these records are difficult to interpret due to a lack of robust high resolution chronologies. K-feldspar pIRIR dating was employed to date 37 samples from a 13 m loess-paleosol sequence (section KS15) in an intermontane basin of the Tianshan Mountains, central ACA, NW China. The reliability of the pIRIR ages was determined by using internal checks of luminescence characteristics of the pIR 50 IR 290 and pIR 200 IR 290 signals, and by comparing pIR 50 IR 290 and pIR 200 IR 290 ages. A high resolution chronology for the loess-paleosol sequence, spanning 130–45 ka, was established using Bacon age/depth modeling. In combination with climate proxy indexes of magnetic susceptibility, total organic material, and δ 13 C of organic remains from the sequence, our results suggest: (1) the pIRIR ages utilizing pIR 50 IR 290 and pIR 200 IR 290 signals are consistent for loess samples <150 ka; (2) eolian loess was deposited in intermontane basins of the Tianshan Mountains by at least ∼150 ka, with a steadily increasing rate of loess deposition from the last interglacial to the last glacial period; (3) ACA had a moist climate, characterized by paleosol development, during periods at 117–109, 97–85, 77–70 and 58–50 ka, corresponding to MIS 5d, MIS 5b, MIS 5–4 and MIS 3c; (4) ACA had dry climates, characterized by loess deposition, at 131–117, 109–97, 85–76, 70–58 and 50–46 ka, corresponding to MIS 5e, MIS 5c, MIS a and MIS 3b; and (5) during sub-stages of MIS 5 the ACA climate was characterized by cold-moist to warm-dry shifts which appear to be related to ∼21 ka precession cycles, but inversely related to Northern Hemisphere summer insolation patterns. Moisture variation in ACA thus has an anti-phase relationship to that in monsoonal East Asia. Orbital forcing may be responsible for this moisture variation in ACA. [ABSTRACT FROM AUTHOR]

There are significant differences in the interpretation of the moisture (precipitation) history of arid central Asia (ACA) during the Holocene, as inferred on one hand from speleothem oxygen isotope records, and on the other from lake sediments. Here we present the results of measurements of climatically-sensitive magnetic properties and soil color from four well-dated loess-paleosol sequences from the northern slopes of the Tienshan Mountains and the Yili River valley, Xinjiang, China, in the core area of ACA. Our results demonstrate that the characteristic Holocene paleosol, indicating relatively moist conditions, generally formed after ∼6 ka (1 ka = 1000 cal yr BP) in the study region, and that the accumulation of unweathered loess prevailed during the early Holocene, indicating a dry climate at that time. The magnetic proxies further reveal a trend of generally increasing moisture since the Last Glacial Maximum, with the wettest climate occurring during the late Holocene. This trend of increasing moisture during the Holocene is representative of the Xinjiang region and possibly of the whole of the core area of ACA, and is in marked contrast both to the mid-Holocene moisture maximum observed in the East Asian summer monsoon region and to the general decrease in the strength of the Indian summer monsoon since the early Holocene. Our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the Holocene in the core area of ACA, caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO). [ABSTRACT FROM AUTHOR]

The variability and interaction of the East Asian summer monsoon (EASM) and mid-latitude Westerlies have dominated Eurasian hydroclimates over orbital timescales and currently influence over a billion lives in Asia. Despite this, the mechanisms influencing EASM-Westerlies variability are still a matter of considerable debate. This study presents three loess-paleosol sequences in the NE Tibetan Plateau (NETP) dated at high-resolution by 50 K-feldspar pIRIR and 37 quartz OSL ages to produce the most detailed chronology for any loess record within the plateau. Combined with this chronology are sedimentology, magnetic susceptibility and grain size analyses with TraCE-21ka climatic modelling to constrain atmospheric controls on climatic changes over the NETP during the past 130 kyr. Our results indicate that deposition initiated by ∼130 ka with especially rapid rates during glacial periods, with maximum rates (140–180 g/cm2/ka) in early MIS 2. Over interglacial-glacial cycles, NETP climatic changes are consistent with warm-moist interglacial and cold-dry glacial conditions recorded in the monsoonal Chinese Loess Plateau and Westerlies-dominated Central Asia but anti-phase to Central Asia during interglacial and the Holocene substages. These results highlight how variation in EASM intensity strongly controls NETP moisture changes but that Holocene and last interglacial changes recorded in the NETP consistently lag 30°N summer insolation by 2–6 kyr. This study suggests high-latitude forcing effectively modulates EASM intensity and that factors such as ice volume, greenhouse gases, and freshwater input to northern Atlantic and Southern oceans critically influence NETP paleoclimatic conditions. • K-feldspar pIRIR dating can be used to date loess to at least 130 ka in the Tibetan Plateau. • A moist interglacial-dry glacial climate pattern occurred across Eurasia. • EASM dominated paleoclimatic changes during past 130 ka in the NE Tibetan Plateau. • EASM precipitation is consistently lagged 2–6 ka to July 30°N insolation. • High-latitude forcing induced lags in EASM precipitation to insolation. [ABSTRACT FROM AUTHOR]