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The detailed evolution of valley-damming by glaciers on the southeastern Tibetan Plateau, including the large Gega paleolake, is reconstructed based on observed sediment sequences, and optically stimulated luminescence (OSL) dating. In total, six main lithofacies associations are inferred that represent three relevant sedimentary environments associated with the paleolakes, i.e. lacustrine, deltaic and fluvial. Since the local last glacial maximum (LGM), there have been at least three river-blocking episodes and consequent phases of lacustrine development in the Gega and Jiedexiu dammed lakes. They occurred at ca. 25–17 ka, 14–11 ka, and ∼4 ka. Sedimentological evidence shows that the glacier-dammed lakes were not stable; they experienced oscillations of lake level through short-time drainage events. The damming events and subsequent outburst floods were likely triggered by changes in the extent and thickness of glaciers, caused by rapid climatic changes. This seems to be consistent with proglacial lakes occurring elsewhere, although the dynamics of glacier-dammed lakes can be highly variable between catchments and through time due to the influence of climate-dependent factors on the proglacial lakes.

The variability and dynamics of the Asian monsoon (AM, hereafter indicates both of the summer and winter monsoons.) at orbital and millennial timescales has attracted wide interest. Chinese loess deposits, covering an area of ~500 × 103 km2 and with a thickness of several tens to more than three hundred meters, is an ideal continental archive to reconstruct AM variations during the Quaternary epoch. Over the past thirty years, since the earliest paper published in an international journal that linked the Asian monsoon and Chinese loess deposits, many studies have been undertaken focusing on this research topic. These results have greatly deepened our understanding of the variations of the AM climate and their driving mechanisms during the past ~2.6 Myr. In this paper, we emphasize recent progress on the AM variability and dynamics revealed by Chinese loess records; in particular, we discuss the reliability and precision of the timescale and the monsoon proxy indicators for the loess-paleosol sequences, which are two fundamental aspects for understanding AM behavior. We analyze what we know and discuss what we do not know about the AM. We refine the timescale for the typical loess-paleosol sequence in the central Chinese Loess Plateau (CLP), which can be used as a new timescale to study palaeoclimate and palaeoenvironmental changes in the monsoonal Asia. We conclude that low-latitude insolation changes induced by precession, and global ice volume, temperature at high-latitudes, as well as sea-level changes forced variations of the AM at orbital time scales. High-latitude cooling events and low-latitude hydroclimate process at millennial time scales, such as climate changes associated with Heinrich events and Dansgaard-Oeschger cycles in Northern Atlantic and Greenland, have also modulated AM variability. We suggest that high-latitude forcing of AM variations occurs through ocean and atmospheric circulation linkages, although the roles of atmospheric CO2, ocean and vegetation feedbacks need further investigation. In future study, high-resolution independent dating, novel proxy indices and transient numerical simulations are still basic tools to understand the loess deposition and AM variations that require considerably more work. Issues such as reliable spatial comparison and regional linkages of records (dependent on precise and accurate numerical chronologies), and quantitative reconstruction of the AM variations, should be given priority in the study the past climate change in Asia, and low-latitude hydroclimate process.

River aggradation or incision at different spatial-temporal scales are governed by tectonics, climate change, and surface processes which all adjust the ratio of sediment load to transport capacity of a channel. But how the river responds to differential tectonic and extreme climate events in a catchment is still poorly understood. Here, we address this issue by reconstructing the distribution, ages, and sedimentary process of fluvial terraces in a tectonically active area and monsoonal environment in the headwaters of the Yangtze River in the eastern Tibetan Plateau, China. Field observations, topographic analyses, and optically stimulated luminescence dating reveal a remarkable fluvial aggradation, followed by terrace formations at elevations of 55–62 m (T7), 42–46 m (T6), 38 m (T5), 22–36 m (T4), 18 m (T3), 12–16 m (T2), and 2–6 m (T1) above the present floodplain. Gravelly fluvial accumulation more than 62 m thick has been dated prior to 24–19 ka. It is regarded as a response to cold climate during the last glacial maximum. Subsequently, the strong monsoon precipitation contributed to cycles of rapid incision and lateral erosion, expressed as cut-in-fill terraces. The correlation of terraces suggests that specific tectonic activity controls the spatial scale and geomorphic characteristics of the terraces, while climate fluctuations determine the valley filling, river incision and terrace formation. Debris and colluvial sediments are frequently interbedded in fluvial sediment sequences, illustrating the episodic, short-timescale blocking of the channel ca. 20 ka. This indicates the potential impact of extreme events on geomorphic evolution in rugged terrain.

Variations of precipitation in tropical-subtropical regions are fundamentally important to human sustainable development. However, the dominant cyclicity and the mechanism of orbital-scale precipitation variations remain under extensive debate. Here, we used a newly drilled core from the Tianyang (TY) maar lake (South China) to reconstruct Asian monsoon precipitation variations over the past ~ 250,000 years, providing a new independent paleoprecipitation record for the core tropical monsoon region. The measured magnetic susceptibility and grain size records of TY maar lake reveal dominant precession and semiprecession cycles, evidencing the low-latitude insolation forcing on tropical monsoon precipitation variations. Feedbacks of Intertropical Convergence Zone shifts and orbital-scale El Nino/Southern Oscillation variations are suggested to play important roles in this forcing mechanism. Moreover, we detected correlation between the rainstorms and the tropical zonal sea surface temperature gradient during the moderate Marine Isotope Stage (MIS) 5a. This correspondence further confirms the effect of tropical internal feedbacks on orbital-scale precipitation variations. However, the glacial-interglacial cycle is weak in our record, indicating that the variability of Asian monsoon precipitation is likely modulated by certain other processes such as latitudinal effects and air-sea feedback.

The cycle of precipitation change indicated by different proxy indicators are found to be inconsistent, which results in the “Chinese 100-kyr Problem”. The loess deposited in the past ~350 ka at the low latitude of East Asia is measured here. We find that the magnetic susceptibility varied at 100-kyr and 40-kyr cycles, can be interpreted as proxy for temperature. In contrast, the DCB-extractable iron varied at 50-kyr, 20-kyr and 10-kyr cycles, can be interpreted as proxy for precipitation. Our results indicate that the temperature and precipitation in the past ~350 ka at the low latitude of East Asia have varied at different cycles, and the change of East Asian summer monsoon indicated by the precipitation in this region is mainly forced by the insolation change due to a variation in the precession.

The Lanshanmiao (LSM) Palaeolithic site, which was excavated in the summer of 2017 by the Zhejiang Provincial Institute of Cultural Relics and Archaeology, is the only excavated palaeolithic site in central Zhejiang Province to date. Luminescence dating methods, including optical stimulated luminescence (OSL) and thermal transfer OSL (TT-OSL) for quartz and post-infrared (IR) stimulated luminescence (pIRIR290) for feldspar, were used to determine the age of the LSM site. The results showed that the LSM section developed before 145.5 ± 12.5 ka and ended after 17.1 ± 1.0 ka. The TT-OSL dating of samples NJU2576 and NJU2615 showed that palaeolithic artifact-bearing layer was between 150 and 100 ka in age. The age range of the palaeolithic layer mainly corresponded to the transition between Marine Isotope Stage (MIS) 6 and MIS5. Our study showed that hominins prominently occupied the LSM site during the glacial and interglacial stages, when it exhibited a floodplain environment.

Variability in East Asian summer monsoon precipitation during the Holocene remains of debate. In this study, we use a closed lake with well‐dated lake beach ridges located on the margin of the East ...

Although the development of Gobi Desert in central and eastern Asia has greatly affected the regional and even the global climate, its precise origin and evolution have yet to be determined. The three preconditions for the formation of Gobi Desert are: i) a dry climate, ii) basin landforms and iii) abundant sediment production. In this study, we present a synthesis of both new and published data on the formation and evolution of Gobi Desert in central and eastern Asia. We conclude that the combined effects of mountain building, the mid-latitude westerly circulation and changes in the Asian monsoon, accompanied by global cooling, were principally responsible for the formation of modern Gobi Desert landscapes in central and eastern Asia during the late Pliocene. The arid climate in central and parts of eastern Asia probably developed in the early Cenozoic, from ~50 Ma. Related events included the collision of the Indian and Asian plates, the closure and complete retreat of the Paratethys Ocean from central Asia, and the growth of the Himalayas and the Tibetan Plateau in the Eocene through late Miocene, which blocked the water vapor supply and intensified the aridification of the Asian interior. Superimposed on the topographic changes was the process of stepwise global cooling since the early Oligocene, and in particular since the late Miocene, which controlled the formation and evolution of the Gobi Desert landscape. Global cooling weakened the Asian monsoon circulation, strengthened the westerly circulation and enhanced physical weathering processes in mountain areas, which together promoted both the aridification of the Asian interior and sediment production. These processes finally resulted in the establishment of the modern Gobi Desert landscape in the late Pliocene. We estimate that the modern Gobi Desert landscape was formed at ~2.6 Ma and was the result of the stepwise evolution of Asian topography and climate during the Cenozoic, dominated by Asian tectonic deformation and uplift, and the evolution of Asian monsoon climate and the westerly circulation, forced by global temperature change.

We investigated climate niches of grasses at regional scales and quantitatively reconstruct Asian monsoon precipitation at the sand-loess transitional zone in northern China. Our results provide direct evidence that certain grass lineages have been specialized in specific habitats: Pooideae grasses stand out and occupy a much cooler environment than all other subfamilies; Pooideae, Aristidoideae, and Chloridoieae occupy dry environments. Pooideae grasses occupy the coldest and driest environments compared to all other subfamilies, with a mean annual temperature (MAT) and precipitation (MAP) of ~13.6 to ~15.3°C and 224 to ~1674 mm, respectively, at a regional scale. We built a database for grasses and their corresponding climate parameters. Based on this database, past climate parameters at the margin of the Asian summer monsoon since ~70 ka were quantitatively reconstructed by phytolith assemblages. They show that this area was dominated by cold- and dry-adapted grasses since ~70 ka with a MAT and MAP of ~3.3 to ~11.0 °C and ~442 to ~900 mm, respectively, generally consistent with the results of phytolith-based transfer function reconstructions and with the results of previous nearby pollen-based quantitative reconstructions. With the improvement of the species-climate and ecosystem dataset, our database-based method is a promising quantitative reconstruction approach to past climatic change in the monsoon region.

This paper presents new field observations that assist in further defining the extent of Last Permafrost Maximum (LPM) permafrost and frozen ground in north China. In that respect, this region is specific by its arid environment and continental position. Bedrock exposures and sand and gravel pits were examined along a south-north transect from southern Ordos as far as the vicinity of Dongsheng District, Ordos City on the Ordos Plateau (North China). Attention focussed upon the recognition of sand-wedge remains and possible cryoturbations. Two types of wedge structures were recognized: type A wedges extend to depths in excess of 3.0 m and are thought to have formed under conditions of continuous permafrost. Type B wedges are restricted to the upper 1.5 m and are thought to reflect discontinuous permafrost and/or deep seasonal frost. OSL dating of wedge infills indicates that type A wedges formed between 23–19 ka and younger type B wedges formed until the early Holocene. It is now possible to delineate a more exact position of the boundary between continuous permafrost and discontinuous permafrost and/or deep seasonal frost on the Ordos Plateau during the LPM. This boundaries occur between Dongsheng and Jinbian at 37°-39°N.

Sand-loess sequences in the desert-loess transition zone are sensitive terrestrial archives for recording past climatic changes and atmospheric dust activities. However, a high-resolution chronology for relative long-term sand-loess sequences is still rare. In this study, we used quartz SAR OSL and K-feldspar pIRIR (pIRIR290) methods to date a 16.8 m sand-loess sequence at Zhenbeitai in Yulin (North-Central China). The quartz is sensitive, fast component dominated but saturates at ∼150 Gy. The measured K-feldspar pIRIR290 De showed no dependency on the first IR stimulation temperature between 50 °C and 260 °C. Dose recovery results were consistent with unity up to ∼800 Gy for a test dose of approximately 30% of the equivalent dose to be measured. The resulting pIRIR290 ages are consistent with the stratigraphy up to ∼121 ka. Thus, a high-resolution chronology up to the last interglacial could be established for the Zhenbeitai sand-loess section. Derived mass accumulation rates show sedimentation rates of ∼10–80 cm/ka for the upper loess (

River aggradation or incision at different spatial-temporal scales are governed by tectonics, climate change and surface processes which all adjust the ratio of sediment load to transport capacity ...

Like other complex systems, sand dunes alternate between stable states, which have coexisted for 12,000 years in northern China., Dune systems can have alternative stable states that coexist under certain environmental conditions: a vegetated, stabilized state and a bare active state. This behavior implies the possibility of abrupt transitions from one state to another in response to gradual environmental change. Here, we synthesize stratigraphic records covering 12,000 years of dynamics of this system at 144 localities across three dune fields in northern China. We find side-by-side coexistence of active and stabilized states, and occasional sharp shifts in time between those contrasting states. Those shifts occur asynchronously despite the fact that the entire landscape has been subject to the same gradual changes in monsoon rainfall and other conditions. At larger scale, the spatial heterogeneity in dune dynamics averages out to produce relatively smooth change. However, our results do show different paths of recovery and collapse of vegetation at system-wide scales, implying that hysteretic behavior occurs in spatially extended systems.

As a significant component of the global climate system, the East Asian monsoon (EAM) is crucial in understanding general climate change. The response of sensitivity and extent of the EAM to orbital-timescale climate change remains controversial. The composition of oxygen isotopes of authigenic (pedogenic) carbonate in loess deposits from the Northeastern Tibetan Plateau was measured, which is at the modern northwestern boundary of the present-day EAM, and compared with equivalent data from northeastern China under the influence of the EAM and two selected sites in the zone under the influence of the westerlies (Bayanbulak (Xinjiang) and Kesselt (Belgium)). The data enable discussion of the paleoclimatic implication of δ18O of carbonate in loess deposits and extension (changes) of the EAM-affected area during the Last Glacial Maximum and early Holocene. The δ18O values of authigenic carbonate at the Northeastern Tibetan Plateau were close to those from the westerly climate zone, but higher than those from regions affected by the Asian monsoon during the Last Glacial Maximum and early Holocene. This indicates that precipitation moisture sources at the Northeastern Tibetan Plateau were likely not directly derived from the EAM during Last Glacial Maximum and early Holocene. In contrast, the westerlies and locally recycled or evaporated moisture were possibly the dominant influencing factors of the relatively δ18O-enriched soil water and the authigenic carbonate in Northeastern Tibetan Plateau. Further study of loess carbonate records from the Northeastern Tibetan Plateau will reveal the past climate changes in the plateau region and provide valuable clues for the interaction between the Asian monsoon and westerly climate systems.

Alluvial-fan successions record changes in hydrological processes and environments that may reflect tectonic activity, climate conditions and changes, intrinsic geomorphic changes, or combinations of these factors. Here, we focus on the evolution of a stream-dominated fan in a tectonic depression of the Xining basin of China, laid down under a semi-arid climate in the northeastern Tibetan Plateau (NETP). The fan succession is composed of three facies associations, from bottom to top: (1) matrix to clast-supported, poorly sorted, planar cross-stratified to crudely stratified sheets of coarse-grained sediments, (2) horizontal laminated sand, laminated layers of reddish fine silt and yellow coarse silt with stacked mounds of sand, and (3) clay-rich deposits with incipient paleosols. The succession shows rapid sediment aggradation from high-energy to low-energy alluvial fans and finally to a floodplain. The dating results using optically stimulated luminescence (OSL) method show that a gravelly, high-energy fan was deposited during MIS 6, after which a low-energy fan, mainly composed of sand and silt, was deposited and finally covered by flood loam during the MIS 6&ndash, 5 transition and the warmer last interglacial. Stacked sand mounds are interpreted from their sediment structure and grain-size distribution as shrub-coppice dunes in low-energy fan deposits. They may be considered as a response to the interaction of alluvial and aeolian processes in a semi-arid environment.

The Hulunbuir dune field is located at the northern margin of the temperate monsoon zone in East Asia, and changes in dune activity and pedogenesis in the dune field are highly sensitive to the advance and retreat of the East Asian summer monsoon (EASM) and to human activity. Thus, the stratigraphic sequences of paleosol and aeolian sand of the dune field have great potential for reconstructing the history of dune activity and pedogenesis and their response to past fluctuations in monsoon precipitation and the intensity of human activity. However, our knowledge of the evolution of the landscape and paleoclimate of the dune field is limited. Here, we present the results of analyses of quartz optically stimulated luminescence (OSL), grain size and magnetic susceptibility (MS) from 13 representative sections in the Hulunbuir dune field. The grain-size analysis indicates that the sand layers are composed of typical aeolian sand, and the MS variations of the aeolian sand and sandy paleosol sequences mainly reflect changes in the intensity of pedogenesis. We combine our new OSL dating results with previously published OSL ages to refine the chronology of sand dune development. An OSL age hiatus in both aeolian sand and paleosol during the 5–7 ka indicates that aeolian deposition in Hulunbuir ceased almost completely during this period, which corresponds to the peak in EASM strength. Thus, our study provides new evidence for a delayed response of the EASM maximum to peak insolation forcing (11–10 ka) in the mid-latitude monsoon margin. In addition, we speculate that peaks in probability density (PD) from 1.2–0.7 ka and from 0.25–0 ka of aeolian sand accumulation correspond to population increases and the development of cultivation and animal husbandry in the Hulunbuir dune field.

The Hunshandake Sandy Land, which is highly sensitive to climate change, is located in North China along the margins of the area influenced by the East Asian monsoon. The upper reach of the Xilamulun River, which drains the Hunshandake Sandy Land, provides an opportunity to test the response of a river landform within a sandy region to climate change. We investigated terraces at 4 sites along a 38-km-long stretch and performed OSL dating on 26 terraces. The dating results revealed 23 terraces with unsaturated ages ranging from 0.3 ka to 36.2 ka. The observed relationship between the terrace heights and ages is abnormal, i.e., the terrace age does not increase with the terrace height. In this case, aeolian and fluvial interactions were analyzed, and a precipitation-dominated terrace formation model was developed. Higher terraces formed when the riverbed aggraded due to decreased sediment discharge and increased aeolian sand input during a period of reduced precipitation. In contrast, lower terraces developed when the riverbed eroded during a period of enhanced precipitation. We conclude that the terraces along this Hunshandake Sandy Land river respond to precipitation changes, even in the absence of background uplift.

Recent chronological studies have revealed significant site-specific variations in loess sedimentation, which challenge the use of loess deposits as continuous, easily analyzable paleoclimate and dust records. However, the regional comparability of loess sedimentation at subglacial-interglacial time scales has not yet been systematically tested. This study focused on the spatial and temporal variability of loess sedimentation on the Chinese Loess Plateau (CLP) during the last 20 thousand years and found a clear seesaw pattern across the CLP, indicated by rapid dust accumulation at the desert margin and reduced accumulation/less preservation on the main part of the CLP after ca. 15 ka. This spatial inhomogeneity of loess sedimentation at millennial time scales is controlled by various dust transportation, trapping, and postdepositional processes in different geographic settings, which are ultimately attributed to a combined effect of a weakened winter monsoon and enhanced summer monsoon after the termination of Heinrich event 1.

Loess deposits in Xiashu are representative of such deposits in Southeastern China that are mainly distributed in the middle and lower reaches of the Yangtze River valley. These loess-paleosol sequences provide a key archive of past climate change in humid, subtropical regions. However, the ages of the sequences are not well constrained. In this study, the standard quartz single-aliquot regenerative (SAR) dose optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (post-IR IRSL; pIRIR290) methods are used to date two loess sequences in Nanjing region. Our results show that quartz SAR OSL and K-feldspar pIRIR290 ages are more or less indistinguishable from one another up to ∼50 ka. Beyond this age, the K-feldspar pIRIR ages increased systematically with deposition depth, agreeing well with the expected ages as far as ∼200 ka. On the basis of a fully independently-dated timescale, we are therefore able to propose, for the first time, a new age model for the Xiashu Loess deposits accumulated since the penultimate interglacial period. Using our newly obtained luminescence dating ages, we observe a marked difference between the loess accumulation rates in the two sequences, potentially forced by regional depositional processes and loess preservation.

The stable carbon isotopic composition of organic matter of aeolian silt deposits is regarded as an appropriate proxy index of paleovegetation, especially in the Chinese Loess Plateau in central China. In this study, a loess–paleosol sequence in the southeastern Inner Mongolia Autonomous Region in northeastern (NE) China, which is located outside the Chinese Loess Plateau, is chosen to reconstruct the vegetation history since ∼1.08 Ma. Temperature exhibits a threshold value, which determines the growth of C4 plants in this study area. The organic matter of the samples is derived from two different vegetation types, namely, the mixed C3 and C4 plants and the pure C3 plants. The δ13C of the organic matter shows negative values in loess units and higher values in paleosol units. This finding reflects the influence of temperature and summer monsoon intensity on the vegetation dynamics over glacial–interglacial cycles. On a longer time scale, the δ13C values are higher between ∼1.1 and ∼0.9 Ma and after ∼0.35 Ma, and lower between ∼0.9 and ∼0.35 Ma, which may be attributed to a long-term temperature variation. Our analysis shows that regional temperature is the most important limiting factor that forces vegetation changes at the glacial–interglacial time scale in NE China.

Dating ice cores drilled in the high mountain glaciers is difficult because seasonal variations cannot be traced at depth due to rapid thinning of the ice layers. Here we provide the first luminescence dating of the basal sediment of the Chongce ice cap in the north-western Tibetan Plateau. Assuming the sediment is of similar (or older) age as the surrounding ice, the luminescence dating of 42 ± 4 ka provides an upper constraint for the age of the bottom ice at the drilling site. This result is more than 1 order of magnitude younger than the previously suggested age of the basal ice of the nearby Guliya ice cap (∼ 40 km in distance).

Geomorphologically, alluvial deposits in river systems are expected to be older on higher terraces than on the lower terraces. However, loess deposits of aeolian origin may also occur on the surface of terrace systems and as seen in the Chinese Loess Plateau (CLP). Such loess is continuously, rather than episodically deposited. This study presents numerous dating results of loess cover on the Hanjiang River terrace system in the southern Qinling Mountains, an atypical loess deposit belt outside of the CLP. We name this “Hanjiang Loess”. Results indicate that the Hanjiang Loess deposited on the high, middle, and low terraces are also the oldest, old, and most recent, respectively, apparently analogous with alluvial expectations. We thus propose a modified depositional hypothesis, whereby terrace loess reflects the deposition of aeolian loess and other material, subsequent fluvial reworking. This depositional hypothesis should also be applicable to loess deposits on the river terraces in the Xiashu Loess, Quaternary Reticulate Red Clay, and Quaternary Red Clay in southern China, and other atypical loess areas outside of the CLP.

Showing features associated with archaic Homo sapiens and evolved Homo erectus , the Dali skull is a key fossil for understanding human evolution in China. Various dating methods such as U-series, IRSL, TL, ESR, ESR/U-series, and stratigraphical correlation with central Loess Plateau sequence were used to estimate the antiquity the Dali Man site with varying results. In this study, a total of 12 samples were taken in the sequence in the Dali Man site, from the aeolian loess-palaeosol sequence and underlying fluvial deposit layers including the palaeoanthropological level and dated by several optically stimulated luminescence (OSL) methods: coarse-grained quartz SAR OSL, thermally transferred OSL (TT-OSL), and K-feldspar post-IR infrared (IR) stimulated luminescence (post-IR IRSL; pIRIR 290 ) methods. Results show that the TT-OSL and pIRIR 290 ages were consistent up to ∼100 ka. For older samples, the feldspar ages were significantly older. These pIRIR 290 ages increased with the stratigraphy up to 310 ka. The best age estimation of the Dali Man layer providing by the feldspar pIRIR 290 suggested that the Dali Man lived in late period of L3 (MIS 8) stage. Furthermore, correlating the pIRIR 290 ages between 267.7 ± 13.9 ka and 258.3 ± 14.2 ka and new pollen analysis, we proposed a new viewpoint that the Dali Man was likely to live during a transitional period from glacial to interglacial climate in the S2/L3 (MIS 7/8) stage.

Interactions of fluvial and eolian processes are prominent in dryland environments and can significantly change Earth surface morphology. Here, we report on sediment records of eolian and fluvial interactions since the last glacial period, in the semiarid area of northwest China, at the limit of the Southeast Asian monsoon. Sediment sequences of last glacial and Holocene terraces of the Yellow River are composed of channel gravels, overlain by flood sands, eolian dunes, and flood loams. These sequences, dated by optically stimulated luminescence, record interlinks between fluvial and eolian processes and their response to climate change. Sedimentologic structures and grain-size analysis show flood loams, consisting of windblown sediment, deposited from floodwater suspended sediment. The gravel and sand were deposited during cold periods. During transitions from cold to warm phases, the river incised, and dunes were formed by deflation of channel and floodplain deposits (>70 and 21–16 ka). Dunes also formed at ~0.8 ka, probably after human intervention. After dune formation, flood loam covered dunes without erosion during peak discharges at the beginning of the subsequent warm period. The fluctuations of the Southeast Asian monsoon as a moisture-transporting agent have perhaps been the driving force for interactions between fluvial and eolian processes in this semiarid environment.

Based on a study of the boron (B) isotope geochemistry of the loess-paleosol sequence of the Niuyangzigou section (NYZG) in Northeast (NE) China, the boron isotopic composition of paleo-rainwater ( δ 11 Bpr) is used for the first time as a potential proxy for tracing changes in the East Asian summer monsoon (EASM) since the mid-Pleistocene. The acid-soluble phase of loess in NE China, which is characteristically a sandy loess, has lower boron concentrations (0.26 to 0.89 μg/g) and more positive δ 11 B values, from −12.1‰ to +9.4‰, compared to the loess of the Chinese Loess Plateau (CLP). According to the mass balance of boron accumulation from three distinct sources, a mathematical inversion calculation is used to quantify the proportion of boron from each source and to capture the original δ 11 Bpr signature. The resulting δ 11 Bpr values range from +6.8 ± 0.95‰ in loess layers to +17.3 ± 3.32‰ in paleosol layers, and the boron accumulated in loess-paleosol layers is shown to be mainly from atmospheric precipitation and silicate weathering. Synchronous variations of reconstructed δ 11 Bpr and other loess-based proxies, both in NE China and in the CLP, are observed over a large spatial range and on several temporal scales. The linkage of δ 11 Bpr to the intensity of the EASM is attributed to the kinetic boron isotope fractionation associated with vapor-precipitate phase separation along the transport path of moisture-bearing air masses. A Rayleigh fractionation model is proposed to interpret δ 11 Bpr in terms of the proportion of water vapor loss after multi-step fractionation processes, which is independent of temperature. The monsoon record based on δ 11 Bpr shows a significant shift at ∼430 ka, implying an abrupt weakening of the EASM after the Mid-Brunhes Event (MBE), which provides evidence for regional disparities in monsoon evolution in response to the MBE. The ice volume in Northern Hemisphere is a possible factor controlling changes in the EASM in NE China over the past 800 kyr.

Climate factors, including precipitation and related vegetation cover, which are vital features of monsoon climates, differ across global/regional areas and are highly variable on a catchment scale. The correlation between fluvial processes and the phases of monsoon climate change are poorly understood in the north-eastern Tibetan Plateau (NETP), partially because direct monsoon climatic proxies from fluvial sediment are lacking. In this study, we compared the fluvial activity with monsoon climate changes reconstructed from pollen analysis, optically stimulated luminescence (OSL) dating, and sedimentary features of terrace sediments in the Datong catchment. The results show that pollen from upstream, for example, 20–30 km from the sample site and transported by water flow, makes the greatest contribution to the pollen assemblages of overbank sediments, which provides reliable regional climatic information. The overbank sediments of the fourth terrace (T4) are dated to around 57.1 ka; beneath these, the lower braided-river gravel was likely deposited during the early part of the Marine Isotope Stage (MIS) 4. The pollen-inferred vegetation is forest-steppe, reflecting a strong monsoon under warm and wet climate conditions during the deposition in the middle sediment unit, possibly during MIS 3. Afterwards, alluvium aggradation ended, and pronounced incision and abandonment was observed in the terrace surface followed by loess deposition which likely occurred during MIS 3–2, at the initiation of the decline of the monsoon. The basal sediment unit of the second terrace (T2) was dated to approximately 6.5–5.0 ka, indicating the start of alluvial aggradation during the Holocene Optimum. Relatively high arboreal pollen from the basal sediment unit of T2 shows a relatively strong monsoon with a warm and wet climate. This was followed by the deposition of the middle sediment unit when the climate was relatively drier with a weak monsoon, recorded by herbaceous vegetation dominated by Artemisia and Chenopodiaceae. It was deduced that during the following cold–warm transition, the river could incise deeply, and this terrace was formed under increasing monsoon conditions. The deep incision and formation of the two studied terraces correlate with different phases of climate change: a warm-to-cold climate transition (decreasing monsoon) for T4 and a cold-to-warm climate transition (increasing monsoon) for T2. We argue that the extreme climatic events at millennial–centennial scales during the Holocene, in addition to orbital-scale changes of monsoon variation, might have led to fluvial thresholds being crossed, causing intense incision and terrace formation. However, the correlation of fluvial processes in the NETP as a response to the East Asian monsoon at different temporal scales could be highly variable.

Cultural studies of Neolithic China have focused on the social aspects and the human–environment interactions associated with those cultures. However, the uneven spatial distribution of Neolithic sites in Northeastern China has not yet been explored. This study traces the relationship between human settlement patterns and the agro-ecological environment during the Holocene Optimum, based on the spatial distribution of 4184 Neolithic sites, together with optically stimulated luminescence (OSL) dating and pollen analysis of five profiles and 22 plant flotation samples from 10 of the archaeological sites in the West Liao River Basin, the hub of Neolithic Cultures in Northeastern China. The overwhelming majority (∼96.7%) of the Neolithic sites are located south of 43o30′N latitude in the West Liao River Basin on the southern fringe of the Horqin Dunefield. The dunefield, which has been commonly hypothesized as vegetated during the Holocene Optimum, was a typical steppe at that time and not suitable for growing millet, the primary staple crop of Neolithic Cultures. Our results and other archaeological site records reveal that the 43°30′N latitude was a remarkable barrier for the dispersal of human settlements in Northeastern China during the Neolithic Age. The barrier was probably formed by the low frost tolerance of millet and the temperature gradient associated with the latitude, making large-scale agricultural production impossible in the regions north of this latitude at the time. Our findings provide evidence for the natural northern limit of Neolithic Cultures in Northeastern China during the Holocene Optimum.

The Homo erectus cranium, mandible and hundreds of associated lithic artifacts found in Lantian (central China) in the 1960s demonstrate that the area was important for hominin habitation during the early to middle Pleistocene. However, the region, which was not adequately researched until the early 2000s, still poses several questions regarding hominin behavior and lithic technology development. In this study, three loess-paleosol sequences (the Jijiawan, Ganyu and Diaozhai sites), from which in situ stone artifacts were recovered, are investigated and dated by optically stimulated luminescence (OSL), magnetostratigraphy and stratigraphic correlation. The results demonstrate that the artifacts are located within paleosol layers S4 (correlative with marine oxygen isotope stage (MIS) 11), S3 (MIS 9), S2 (MIS 7), and S1 (MIS 5); and within loess layer L1 (MIS 2-4). The main stone-knapping technique used was direct hard hammer percussion. In addition, the technological features of the stone tools found at these sites exhibit little variation, indicating the presence of a long-established, stable technology in the Lantian area. Our observations show that the ancient humans lived episodically on the terraces of the Bahe River from the early Pleistocene, indicating a long history of hominin occupation of the region.

Since 2010, we have found stone artifacts at the Houfang and Dishuiyan loess sections on the second terrace of the Hanjiang River and the Wolonggang thick natural loess section on the fifth terrace of the same river near the Xuetangliangzi site. We dated Dishuiyan and Houfang loess sections by optically stimulated luminescence (OSL) and thermally transferred OSL (TT-OSL) methods respectively. Dating results showed that the loess–paleosol deposited on the second Hanjiang River terrace as L1, S1, L2, and S2 in sequence. We dated the Wolonggang loess section by high-resolution paleomagnetostratigraphic analyses. The Jaramillo subchron was found at this section. Correlating with the central Loess Plateau, we recognized the continuous loess–paleosol sequence from L9 to L15. Investigations showed that loess was continuously deposited on the terraces of the Hanjiang River at Yunxian Basin since at least 1200 ka.

Luminescence dating of loess accumulation in China has raised questions over disturbance and gaps in the record, the magnitude of mass accumulation rates (MARs), and monsoon forcing mechanisms. Here we present a detailed quartz optically stimulated luminescence (OSL) chronology from the Xifeng Chinese Loess Plateau site. We reconstruct MARs and construct an age model for monsoon proxies at the site. The luminescence ages show significant pedogenic and anthropogenic disturbance in material deposited after ca. 20–22 ka. Analysis of other published data suggests that this disturbance may be more common than previously realized. MARs from undisturbed portions of Xifeng vary dramatically, with peaks potentially matching the timing of Heinrich events. The last glacial maximum peak MAR (22–27 ka) matches the Pacific and Greenland dust flux records, although appears earlier than peak MARs seen in many other OSL-dated Loess Plateau sites. East Asian monsoon grain-size and magnetic susceptibility records also show several differences between independently dated loess sites. This complicates our understanding of any lag between insolation forcing and monsoon response. Nevertheless, the Xifeng climate proxy changes show apparent broad agreement with the timing of Heinrich events in the North Atlantic, supporting assertions of a climatic teleconnection between the two areas.

There has been a significant debate about the nature and causes of the Pleistocene evolution of the Nihewan Basin, North China. We studied the eastern Nihewan Basin sedimentary facies at two main sites, Hutouliang and Donggou. A combination of field observations and measurements of sediment grain-size distribution was used to reconstruct the sequence of sedimentary environments since the middle Pleistocene, and optically-stimulated luminescence measurements were used to date the sediments. Our results indicate that a shallow lake occupied the basin center along the Sanggan River, probably lasting until ~440 kyr ago before disappearing completely ~340 kyr ago. It was succeeded by a phase of fluvial-dominated sediment accumulation which ended ~30 kyr ago. We suggest that the formation of the gorge resulted from the relative uplift of the Niuxin Mountain along the Liulengshan fault ~140 kyr ago. However, since ~30 kyr ago the fault may have become inactive and the river downcutting near Shixia was no longer offset by the relative uplift, which caused a shift from deposition to denudation in the Nihewan Basin from then on. The disappearance of the paleolake ~340 kyr ago may have been the culmination of the ongoing process of basin infilling.

Geochemical characteristics have been intensively used to assign sediment properties to paleoclimate and provenance. Nonetheless, in particular concerning the arid context, bulk geochemistry of different sediment archives and corresponding process interpretations are hitherto elusive. The Ejina Basin, with its suite of different sediment archives, is known as one of the main sources for the loess accumulation on the Chinese Loess Plateau. In order to understand mechanisms along this supra-regional sediment cascade, it is crucial to decipher the archive characteristics and formation processes. To address these issues, five profiles in different geomorphological contexts were selected. Analyses of X-ray fluorescence and diffraction, grain size, optically stimulated luminescence and radiocarbon dating were performed. Robust factor analysis was applied to reduce the attribute space to the process space of sedimentation history. Five sediment archives from three lithologic units exhibit geochemical characteristics as follows: (i) aeolian sands have high contents of Zr and Hf, whereas only Hf can be regarded as a valuable indicator to discriminate the coarse sand proportion; (ii) sandy loess has high Ca and Sr contents which both exhibit broad correlations with the medium to coarse silt proportions; (iii) lacustrine clays have high contents of felsic, ferromagnesian and mica source elements e.g., K, Fe, Ti, V, and Ni; (iv) fluvial sands have high contents of Mg, Cl and Na which may be enriched in evaporite minerals; (v) alluvial gravels have high contents of Cr which may originate from nearby Cr-rich bedrock. Temporal variations can be illustrated by four robust factors: weathering intensity, silicate-bearing mineral abundance, saline/alkaline magnitude and quasi-constant aeolian input. In summary, the bulk-composition of the late Quaternary sediments in this arid context is governed by the nature of the source terrain, weak chemical weathering, authigenic minerals, aeolian sand input, whereas pedogenesis and diagenesis exert only limited influences. Hence, this study demonstrates a practical geochemical strategy supplemented by grain size and mineralogical data, to discriminate sediment archives and thereafter enhance our ability to offer more intriguing information about the sedimentary processes in the arid central Asia.

Little is known about the long-term climatic evolution of north-eastern (NE) China, because well-preserved terrestrial paleoenvironmental archives are scarce in this vast region. The extensive loess deposits in the Chifeng region are the thickest and most complete loess–paleosol sequence in NE China, and have significant potential for reconstructing the paleoclimate of the region. Here, we present new high-resolution magnetostratigraphic results from two loess–paleosol sections in the Chifeng region: the Sanbahuo (SBH) and Toudaojingzi (TDJZ) sections. The results demonstrate that both sections record the Brunhes normal polarity chron and the upper portion of the Matuyama reversed polarity chron. Based on these new results, the base of the TDJZ loess sequence is dated at ca. 1.22 Ma, representing the oldest known loess deposits in NE China. The initiation of loess accumulation in NE China was roughly synchronous with the large expansion of the Eurasian loess belt during the late Early Pleistocene (1.2–0.7 Ma), probably reflecting a widespread intensification of aridity in northern mid-latitudes. We suggest that global cooling during the Mid-Pleistocene climatic transition led to increased aridity and more favorable conditions for promoting the availability of silt for entrainment, transport and deposition.

This paper examines the relationship between the extent of permafrost during the Last Permafrost Maximum (LPM, largely between 22 and 17 ka BP) and the altitudinal and latitudinal temperature gradients that controlled its extent. The region chosen, namely, the Qinghai-Tibet Plateau and the transition to the northern adjacent plains in the North China Plain, is of relatively limited extent in order to avoid regional effects. This area extends over 15 degrees of latitude while altitudes vary from 1000 to 1500 m above sealevel (asl) in the northern plains to more than 4000 m asl in the central-to-south part of the Qinghai-Tibet Plateau. The respective lowest southernmost permafrost occurrences at a northern and a southern position are used for reconstruction of the latitudinal and altitudinal gradients. As a first approximation, we conclude that the elevation compensation during the LPM for a 1° latitude change was between 309 m and 385 m. This is considerably higher than the value calculated for existing permafrost in the region that uses thermal data at a depth of zero amplitude change (139–198 m altitudinal compensation for 1° latitude).

The Quaternary wind-blown Chinese loess-paleosol sequence, which developed as a product of the intensification of Northern Hemisphere glacial-interglacial cycles, is a major source of information on aridification of the Asian interior. In northeastern (NE) China, extensive loess deposits occur that have great potential for reconstructing the long-term paleoclimatic evolution of the region. Despite existing geochemical data indicate that the probable major source areas for these loess deposits were the nearby Horqin and Otindag deserts, it is still unclear that whether there was a long-term change in the detrital source of these loess deposits. In addition, the aridity history and long-term desert evolution of NE China are currently poorly understood. In the present study, we measured the silicate Nd and Sr isotopic composition of the 28–45 μm grain-size fraction from multiple loess sections (NYZG, SBH, and TDJZ). The results show that the loess deposits of the three sites were dominantly sourced from the Otindag sandy desert and that this source remained constant for the past 1.2 Ma. Notably, the 87Sr/86Sr ratios are influenced mainly by variations in the content of clay-sized material present in the form of aggregates or adhering to the surface of coarser particles. Therefore, caution is needed in the use of 87Sr/86Sr ratios of the 28–45 μm fraction as a tracer of eolian dust, when the clay minerals are not completely removed during the pretreatment process. The grain-size variability of the three sections indicates that stepwise enhancement of aridification in the Otindag sandy desert occurred at 1.2 Ma, 0.9 Ma, and 0.7 Ma, which coincided respectively with the beginning of the Mid-Pleistocene transition (MPT), an extremely cold event at ~0.9 Ma within the MPT, and the establishment of a full glacial climate at the termination of the MPT. This finding supports the hypothesis that the growth of high-latitude ice sheets was the major driver of the long-term aridification of Asian dust source areas.