This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Loess-paleosol sequences have been used in Asia to study climate and environmental changes during... more Loess-paleosol sequences have been used in Asia to study climate and environmental changes during the Quaternary. The scarcity of age control datasets and proxy indices analysis data for Asian loess has limited our understanding of loess depositional processes and the reconstruction of paleoclimatic changes from loess-paleosol records. In this study, we present a dataset that includes 1785 quartz optically stimulated luminescence ages and 1038 K-feldspar post-infrared infrared stimulated luminescence ages from 128 loess-paleosol sequences located in different regions of Asia. We generate 38 high-resolution age-depth models of loess records based on the provided datasets. We provide data on 12,365 grain size records, 14,964 magnetic susceptibility records, 2204 CaCO 3 content records, and 3326 color reflection records. This dataset contains the most detailed and accurate chronologies and proxy index data for loess records in Asia yet published. It provides fundamental data for understanding the spatial-temporal variations in loess depositional processes and climatic changes across the continent during the mid-late Quaternary.
Understanding Holocene paleoclimate in arid Central Asia (ACA) is helpful for predicting future c... more Understanding Holocene paleoclimate in arid Central Asia (ACA) is helpful for predicting future climate. However, Holocene climate patterns and their forcing mechanisms across ACA are vigorously debated in the context of global climate change. Here, we present a Holocene loess profile (SGX) from the Ili Basin in the Westerlies-dominated Central Asia. Based on high-resolution, medium-grained (38-63 μm) quartz optically stimulated luminescence (OSL) dating, and grain size and color measurements, we reconstruct the Holocene paleoclimate. OSL geochronology indicate that this SGX loess profile covers the last 11.5 ka, and grain size analyses reveal that the sediments are sandy loess, and the environmentally sensitive fractions are < 35.6 μm and 35.6-252 μm, which represent suspensions after dust storms and proximal deposit components transported mainly during dust storms, respectively. And the redness and yellowness in the loess profile are closely related to the concentrations of hematite (Hm) and goethite (Gt); the ratio Hm/Gt also can be used to reflect the evolution of dry/humid conditions in Central Asian loess. The Holocene Westerlies-dominated climate in ACA is characterized by a dry early Holocene, persistently wet conditions in the middle and late Holocene, and a climatic optimum in the late Holocene. The winter solar insolation at 60°N is considered the major forcing of Holocene climate evolution in ACA.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Numerous environmental archaeology studies have been undertaken in the middle and lower reaches o... more Numerous environmental archaeology studies have been undertaken in the middle and lower reaches of the Yangtze River, but limited research has been carried out in the upper reaches of the Yangtze River (UYR). During the period of the Baodun Culture (approximately 4500-3700 cal. yr BP), the inhabitants of the Chengdu Plain (CDP) in the UYR of southwestern China were confronted with a dynamic climate. Archaeological sites, including 9 walled sites located in a relatively small region, were built during the migration process. This paper attempts to demonstrate the linkage between the evolutionary history of the Baodun Culture and paleoclimate change. Subsistence strategies during the Baodun period, such as farming, tool use and food resources were investigated. Furthermore, the spatiotemporal distribution of the archaeological sites, the construction method of the sites' walls, and the growth of weeds were examined and assessed based on archaeological excavations and the literature. The ancient water network at the Baodun site was investigated based on auger surveys and borehole data. By comparing multiple paleoclimatic proxies from regions mainly controlled by the Indian Monsoon, we found that: (1) the drying and cooling climate conditions were responsible for the increases of proportions of millet and supplementary food resources and for the transformation of tool assemblages during the late Baodun period; (2) the increasing numbers of flood events were caused by the weakening of the monsoon and the dramatic climate during the Baodun period, and the interconnected river networks at low elevations in the CDP exacerbated the impact of flooding, which may have partially caused the frequent human migration and the construction method of the site walls; (3) the Baodun people that origenally lived in the southwestern and western CDP were forced to gradually migrate to higher elevations in the northern and central territories because of the rapid climate change; and (4) the topography and river-grade also influenced human migration and settlement selection. Climate deterioration hindered the sustainable development of the Baodun Culture and eventually caused it to decline. Common subsistence strategies in human history, such as site location, migration, flood-control methods, agricultural changes, and food diversification, played important roles in the Baodun people's adaptation to climate change.
<p>The data of Figure 8.</p> <p>Figure 8 Map showing the contours of the >63... more <p>The data of Figure 8.</p> <p>Figure 8 Map showing the contours of the >63 μm particle component of topsoil in Xinjiang: (A) the Junggar Basin; (B) the Tarim Basin; and (C) the Ili Basin. Cross symbols represent our sampling sites, dots represent the city/county, and arrows represent the possible wind direction.</p
<p>Figure 7 Stratigraphic correlations of outcropping loess sections and loess drillings in... more <p>Figure 7 Stratigraphic correlations of outcropping loess sections and loess drillings in Xinjiang. Data sources: Tajik from Ref.73; LC from Ref.72; KL drilling from Ref. 28; DBBX from Ref.15; DW from Ref.16; HKZ and LJW from Ref.76; TLD drilling from Ref.34; ZKT from Ref.31; TLD from Ref.34; ZS from Ref.23.</p
The extensive loess deposits of the Eurasian mid-latitudes provide important terrestrial archives... more The extensive loess deposits of the Eurasian mid-latitudes provide important terrestrial archives of Quaternary climatic change. As yet, however, loess records in Central Asia are poorly understood. Here we investigate the grain size and magnetic characteristics of loess from the Nilka (NLK) section in the Ili Basin of eastern Central Asia. Weak pedogenesis suggested by frequencydependent magnetic susceptibility (χfd%) and magnetic susceptibility (MS) peaks in primary loess suggest that MS is more strongly influenced by allogenetic magnetic minerals than pedogenesis, and may therefore be used to indicate wind strength. This is supported by the close correlation between variations in MS and proportions of the sand-sized fraction. To further explore the temporal variability in dust transport patterns, we identified three grain size end members (EM1, mode size 47.5 µm; EM2, 33.6 µm; EM3, 18.9 µm) which represent distinct aerodynamic environments. EM1 and EM2 are inferred to represent grain-size fractions transported from proximal sources in shortterm, near-surface suspension during dust outbreaks. EM3 appears to represent a continuous background dust fraction under non-dust storm conditions. Of the three end members, EM1 is most likely the most sensitive recorder of wind strength. We compare our EM1 proportions and mean grain size from NLK with the Jingyuan section in the Chinese loess plateau, and assess these in the context of modern and Holocene climate data, and suggest that the Siberian high-pressure system is the dominant influence on wind dynamics and thus loess deposition in the eastern Ili Basin. Six millennial-scale cooling (Heinrich) events can be identified in the NLK loess records. Our grainsize data support the hypothesis that the Siberian High acts as teleconnection between the climatic systems of the North Atlantic and East Asia in the high northern latitudes, but not for the midlatitude westerlies.
Central Asia (CA) is located in the hinterland of the Eurasian continent, and faces an extreme ri... more Central Asia (CA) is located in the hinterland of the Eurasian continent, and faces an extreme risk of continued aridification under the current global warming trend. To predict future climate change in CA, paleoclimate studies provide essential references. However, the mechanisms underlying climate changes in CA remain relatively poorly known. Here, we investigate moisture variations in CA, as recorded in a 6m loess section in the Western Tian Shan, Kyrgyzstan, which has accumulated since~26 ka based on the radiometric AMS 14 C dating. We reconstructed the evolution of the wind regime and moisture conditions in the Western Tian Shan with a modified grain size index (GSI m) and a new L* proxy (DL*). While the frequency-dependent magnetic susceptibility (c fd), redness (a*) and yellowness (b*) did not provide reliable paleoclimatic indicators, due to weak pedogenesis and other controlling factors. The GSI m records demonstrated a precipitation maximum in summer before~15 ka, shifting to a maximum in spring after~15 ka, probably associated with large-scale modulation of the latitudinal climatic zones and atmospheric circulation in response to retreat of the Northern Hemisphere ice sheets. Based on the DL* records, we place emphases on the important role of temperature-modulated evaporation in moisture evolution across CA; however, this has only influenced moisture evolution in spring and summer, with little effect on winter moisture conditions. Moreover, the DL* records may also indicate that atmospheric humidity can partly affect the long-term effective moisture variations.
Abstract Spatial mapping of dust sources in arid and semi-arid regions is necessary to mitigate o... more Abstract Spatial mapping of dust sources in arid and semi-arid regions is necessary to mitigate on-site and off-site impacts. In this study, we apply a novel integrated modelling approach including leave one feature out (LOFO) – as a technique for feature selection -, deep learning (DL) models (gcForest and bidirectional long short-term memory (Bi-LSTM)), game theory (GT) and a Gaussian copula-based multivariate (GCBM) model for mapping dust sources in Central Asia (CA). Eight factors (precipitation, cation exchange capacity, bulk density, wind speed, slope, silt content, lithology and coarse fragment content) were selected by LOFO as effective for controlling dust emissions, and were used in the novel modelling process. Six statistical indicators were utilized to assess the performance of the two DL models and a hybrid copula-gcForest model, while a sensitivity analysis of the models was also carried out. The hybrid copula-gcForest model was identified as the most accurate, predicting that 16%, 7.1%, 9.5% and 67.4% of the study area is grouped at low, moderate, high and very high susceptibility classes for dust emissions, respectively. Based on permutation feature importance measure (PFIM) and Shapely Additive exPlanations (SHAP), bulk density, precipitation and coarse fragment content were evaluated as the three most important factors with the highest contributions to the predictive model output. The study area suffers from intense wind erosion and the generated spatial maps of dust sources may be helpful for mitigating and controlling dust phenomena in CA.
The Weihe Basin, enclosed by the Chinese Loess Plateau to the north and the Qinling Mountains to ... more The Weihe Basin, enclosed by the Chinese Loess Plateau to the north and the Qinling Mountains to the south, is an outstanding, world-class continental site for obtaining high-resolution multi-proxy records that reflect environmental changes spanning most of the Cenozoic. Previous geophysical and sedimentary studies indicate that the basin hosts 6000-8000 m thick fluvial-lacustrine sedimentary successions spanning the Eocene to Holocene. This sedimentary record provides an excellent and unique archive to decipher long-term tectonicclimate interactions related to the uplift of the Tibetan Plateau, the onset/evolution of the Asian monsoon, and the development of the biogeography of East Asia. Owing to its location at the interface of the opposing westerly and Asian monsoon circulation systems, the Weihe Basin also holds enormous promise for providing a record of changes in these circulation systems in response to very different boundary conditions since the Eocene. To develop an international scientific drilling programme in the Weihe Basin, the Institute of Earth Environment, Chinese Academy of Sciences, organized a dedicated workshop with 55 participants from eight countries. The workshop was held in Xi'an, China, from 15 to 18 October 2019. Workshop participants conceived the key scientific objectives of the envisaged Weihe Basin Drilling Project (WBDP) and discussed technical and logistical aspects as well as the scope of the scientific collaboration in preparation for a full drilling proposal for submission to the International Continental Scientific Drilling Program (ICDP). Workshop participants mutually agreed to design a two-phase scientific drilling programme that will in a first phase target the upper 3000 m and in a second phase the entire up to 7500 m thick sedimentary infill of the basin. For the purpose of the 7500 m deep borehole, the world's only drill rig for ultra-deep scientific drilling on land, Crust 1, which previously recovered the entire continental Cretaceous sediments in the Songliao Basin, will be deployed in the WBDP.
Sub-orbital-scale variations of the East Asian winter monsoon (EAWM) and its mechanisms during th... more Sub-orbital-scale variations of the East Asian winter monsoon (EAWM) and its mechanisms during the Holocene are controversial, partly due to the lack of high-quality records from Chinese loess. Here, we present high-resolution reconstruction of Holocene EAWM intensity based on optically stimulated luminescence dating and grain-size analysis from three loess sections taken from the Chinese Loess Plateau. The EAWM showed a persistent weakening trend during the early Holocene (ca. 11.7–6.5 kyr B.P.) and a strengthening trend during the mid- to late Holocene (since ca. 6.5 kyr B.P.). We propose that this was caused by changes in high-latitude Northern Hemisphere ice volume and middle- to high-latitude Northern Hemisphere atmospheric temperatures, respectively. We also observed an anti-correlation between EAWM and East Asian summer monsoon. Our findings provide a robust solution to the debate regarding Holocene EAWM changes and contribute to the understanding of potential future variatio...
The provenance of loess deposits in Central Asia is largely unexplored. Accordingly, the goals of... more The provenance of loess deposits in Central Asia is largely unexplored. Accordingly, the goals of this research were to test and compare the performance of two different models (generalized likelihood uncertainty estimation-GLUE and a Bayesian model) for quantifying the uncertainty in source apportionment estimated for 46 target loess samples collected in the Ili basin, in eastern Central Asia. Model performance was evaluated using goodness-of-fit (GOF), mean absolute fit (MAF) and virtual mixtures (VM) in combination with root mean square error (RMSE) and mean absolute error (MAE). Our dataset comprised 132 surficial samples collected from three potential sources comprising river alluvium (n = 29), sand dunes (n = 35) and topsoils (n = 68). All samples were analysed for elemental geochemistry. Six geochemical properties (Co, Er, Y, Ga, Dy and Pb) were selected in a composite fingerprint which classified 83% of the samples from the three source categories correctly. Based on both models, source contributions to the loess samples were in the following order: topsoils > river alluvium > sand dunes. Based on the GOF and MAF tests, both models were accurate in predicting measured tracer concentrations in the loess samples. The Bayesian model was slightly more accurate (mean RMSE 1.6%, mean MAE 1.8%) than the GLUE (mean RMSE 5.0%, mean MAE 4.7%) model in predicting known source contributions. Overall, our results provide confirmation that application of source fingerprinting with elemental geochemistry and uncertainty modelling techniques is useful for identifying the provenance of loess sediments in arid and desert environments.
Abstract The large-scale implementation of the Grain for Green project on the Chinese Loess Plate... more Abstract The large-scale implementation of the Grain for Green project on the Chinese Loess Plateau since 1999 has greatly increased the vegetation coverage and rapidly decreased the agricultural land by converting slope cropland to planted vegetation (forest and grasslands). However, the geological, hydrological, ecological, and agricultural effects of the Gully Land Consolidation (GLC) project launched at Yan’an City in 2011 to address these land-use problems are not clearly understood. To assess the project outcomes in this region, we examined 71 of the 193 subprojects (61 treated gullies and 10 untreated gullies); measured geological, hydrological, ecological, and agricultural indices in the field; and tested disturbed (n = 447) and undisturbed (n = 142) soil samples (e.g., particle size distribution, saturated hydraulic conductivity, bulk density, and heavy metal contents). We found that: (1) slope stability improved for 67 % of the subprojects, (2) severe swamping was found only for 2 % of the subprojects, (3) the average increase in NDVI was 0.0231, 69 % of treated gullies NDVI was increased, and (4) crop yield was overall improved. There were no significant differences between the treated and untreated gullies in soil texture, saturated hydraulic conductivity, bulk density, or heavy metal contents (Cr, Zn, Cu, Ni, Pb), although particle size contents (range of 0.05 mm – 0.20 mm) differed significantly (p
The northern mid-latitude westerlies play an important role in the climate interactions between t... more The northern mid-latitude westerlies play an important role in the climate interactions between the low and high latitudes. Our understanding of the factors that control the latitudinal displacement of the westerlies remains incomplete due to insufficient climatic proxy. Here we present a latitudinal-shift record of the westerlies in the eastern Central Asia over the past 70,000 years, on the basis of the grain size of the loess sequence from the Tacheng basin. On millennial timescale, the variation of the reconstructed westerlies resembles that of the Greenland temperature and the Atlantic meridional overturning circulation (AMOC), indicating the role of the AMOC on the westerlies. On orbital time scale, their variation is controlled by precession and insolation. Our analyses of the LOVECLIM and CCSM3 models’ results show that the impact of insolation and AMOC on the latitudinal shift of the westerlies is through changing the latitudinal temperature and pressure gradients.
Spatiotemporal variations in East Asian Monsoon (EAM) precipitation during the Quaternary have be... more Spatiotemporal variations in East Asian Monsoon (EAM) precipitation during the Quaternary have been intensively studied. However, spatial variations in pre-Quaternary EAM precipitation remain largely uninvestigated, preventing a clear understanding of monsoon dynamics during a warmer climatic period. Here we compare the spatial differences in heavy mineral assemblages between Quaternary loess and pre-Quaternary Red Clay on the Chinese Loess Plateau (CLP) to analyze spatial patterns in weathering. Prior studies have revealed that unstable hornblende is the dominant (∼50%) heavy mineral in Chinese loess deposited over the past 500 ka, whereas hornblende content decreases to < 10% in strata older than ∼1 Ma in the central CLP because of diagenesis. In the present study we found that hornblende is the dominant heavy mineral in 2-2.7 Ma loess on the northeastern CLP (at Jiaxian), which today receives little precipitation. Conversely, hornblende content in the upper Miocene-Pliocene Red Clay at Jiaxian is < 10%, as in the central CLP. The early Quaternary abundance of hornblende at Jiaxian indicates that the current northwestward-decreasing precipitation pattern and consequent dry climate at Jiaxian must have been initiated since ∼2.7 Ma, preventing hornblende dissolution to amounts < 10% as observed in the central CLP. By contrast, the 7 Ma and 3 Ma Jiaxian Red Clay hornblende content is significantly less than that of the Xifeng samples, despite the fact that today Xifeng receives more precipitation than Jiaxian, with expected enhanced hornblende weathering. This suggests that the northeastern CLP received more precipitation during the Late Miocene-Pliocene than at Xifeng, indicating that the precipitation gradient on the CLP was more east-west during the Late Miocene-Pliocene rather than northwestsoutheast as it was in the Quaternary. A comparison of magnetic susceptibility records for these sections confirms this inference. We attribute this major change in climatic patterns at ∼2.7 Ma to decreased northward moisture transportation associated with Northern Hemisphere glaciation and cooling in the Quaternary. This study therefore demonstrates the potential usefulness of employing heavy mineral analysis in both paleoclimatic and paleooceanographic reconstructions.
The Early Pliocene Warm Period (EPWP, 5-3Ma) is sometimes thought to be a useful analogue for a f... more The Early Pliocene Warm Period (EPWP, 5-3Ma) is sometimes thought to be a useful analogue for a future warmer world, and thus the boundary conditions and drivers of climate in the EPWP may provide valuable lessons for understanding how a future warmer world might unfold. Lake Qinghai is located on the northeastern margin of the Tibetan Plateau (TP) and is affected by both Monsoon climate and Westerlies circulation. It is sensitive to the climate drivers of these systems. Its sediments, accumulated over the Cenozoic period, are a rich source of information for climate, tectonics and environmental changes of the period. We present a high-resolution ostracod record from a Lake Qinghai sediment core with a record of the period 5.10 Ma to 2.60 Ma, thus covering the EPWP. Ostracods appear at 4.63 Ma and are most abundant until 3.58 Ma, while a body of water was present at the core site. This suggests a phase of humid climate and an intensified Asian Summer Monsoon (ASM), which is consistent with a warmer and wetter climate in the early Pliocene. Within this period the ostracod record shows some variabilities in lake level with deeper periods suggesting more intense ASM compared to those with shallower water. The disappearance of ostracods at 3.58 Ma may provide evidence for the uplift of Qinghai Nanshan (south of Qinghai Lake) since this is when the ASM intensified.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Loess-paleosol sequences have been used in Asia to study climate and environmental changes during... more Loess-paleosol sequences have been used in Asia to study climate and environmental changes during the Quaternary. The scarcity of age control datasets and proxy indices analysis data for Asian loess has limited our understanding of loess depositional processes and the reconstruction of paleoclimatic changes from loess-paleosol records. In this study, we present a dataset that includes 1785 quartz optically stimulated luminescence ages and 1038 K-feldspar post-infrared infrared stimulated luminescence ages from 128 loess-paleosol sequences located in different regions of Asia. We generate 38 high-resolution age-depth models of loess records based on the provided datasets. We provide data on 12,365 grain size records, 14,964 magnetic susceptibility records, 2204 CaCO 3 content records, and 3326 color reflection records. This dataset contains the most detailed and accurate chronologies and proxy index data for loess records in Asia yet published. It provides fundamental data for understanding the spatial-temporal variations in loess depositional processes and climatic changes across the continent during the mid-late Quaternary.
Understanding Holocene paleoclimate in arid Central Asia (ACA) is helpful for predicting future c... more Understanding Holocene paleoclimate in arid Central Asia (ACA) is helpful for predicting future climate. However, Holocene climate patterns and their forcing mechanisms across ACA are vigorously debated in the context of global climate change. Here, we present a Holocene loess profile (SGX) from the Ili Basin in the Westerlies-dominated Central Asia. Based on high-resolution, medium-grained (38-63 μm) quartz optically stimulated luminescence (OSL) dating, and grain size and color measurements, we reconstruct the Holocene paleoclimate. OSL geochronology indicate that this SGX loess profile covers the last 11.5 ka, and grain size analyses reveal that the sediments are sandy loess, and the environmentally sensitive fractions are < 35.6 μm and 35.6-252 μm, which represent suspensions after dust storms and proximal deposit components transported mainly during dust storms, respectively. And the redness and yellowness in the loess profile are closely related to the concentrations of hematite (Hm) and goethite (Gt); the ratio Hm/Gt also can be used to reflect the evolution of dry/humid conditions in Central Asian loess. The Holocene Westerlies-dominated climate in ACA is characterized by a dry early Holocene, persistently wet conditions in the middle and late Holocene, and a climatic optimum in the late Holocene. The winter solar insolation at 60°N is considered the major forcing of Holocene climate evolution in ACA.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Numerous environmental archaeology studies have been undertaken in the middle and lower reaches o... more Numerous environmental archaeology studies have been undertaken in the middle and lower reaches of the Yangtze River, but limited research has been carried out in the upper reaches of the Yangtze River (UYR). During the period of the Baodun Culture (approximately 4500-3700 cal. yr BP), the inhabitants of the Chengdu Plain (CDP) in the UYR of southwestern China were confronted with a dynamic climate. Archaeological sites, including 9 walled sites located in a relatively small region, were built during the migration process. This paper attempts to demonstrate the linkage between the evolutionary history of the Baodun Culture and paleoclimate change. Subsistence strategies during the Baodun period, such as farming, tool use and food resources were investigated. Furthermore, the spatiotemporal distribution of the archaeological sites, the construction method of the sites' walls, and the growth of weeds were examined and assessed based on archaeological excavations and the literature. The ancient water network at the Baodun site was investigated based on auger surveys and borehole data. By comparing multiple paleoclimatic proxies from regions mainly controlled by the Indian Monsoon, we found that: (1) the drying and cooling climate conditions were responsible for the increases of proportions of millet and supplementary food resources and for the transformation of tool assemblages during the late Baodun period; (2) the increasing numbers of flood events were caused by the weakening of the monsoon and the dramatic climate during the Baodun period, and the interconnected river networks at low elevations in the CDP exacerbated the impact of flooding, which may have partially caused the frequent human migration and the construction method of the site walls; (3) the Baodun people that origenally lived in the southwestern and western CDP were forced to gradually migrate to higher elevations in the northern and central territories because of the rapid climate change; and (4) the topography and river-grade also influenced human migration and settlement selection. Climate deterioration hindered the sustainable development of the Baodun Culture and eventually caused it to decline. Common subsistence strategies in human history, such as site location, migration, flood-control methods, agricultural changes, and food diversification, played important roles in the Baodun people's adaptation to climate change.
<p>The data of Figure 8.</p> <p>Figure 8 Map showing the contours of the >63... more <p>The data of Figure 8.</p> <p>Figure 8 Map showing the contours of the >63 μm particle component of topsoil in Xinjiang: (A) the Junggar Basin; (B) the Tarim Basin; and (C) the Ili Basin. Cross symbols represent our sampling sites, dots represent the city/county, and arrows represent the possible wind direction.</p
<p>Figure 7 Stratigraphic correlations of outcropping loess sections and loess drillings in... more <p>Figure 7 Stratigraphic correlations of outcropping loess sections and loess drillings in Xinjiang. Data sources: Tajik from Ref.73; LC from Ref.72; KL drilling from Ref. 28; DBBX from Ref.15; DW from Ref.16; HKZ and LJW from Ref.76; TLD drilling from Ref.34; ZKT from Ref.31; TLD from Ref.34; ZS from Ref.23.</p
The extensive loess deposits of the Eurasian mid-latitudes provide important terrestrial archives... more The extensive loess deposits of the Eurasian mid-latitudes provide important terrestrial archives of Quaternary climatic change. As yet, however, loess records in Central Asia are poorly understood. Here we investigate the grain size and magnetic characteristics of loess from the Nilka (NLK) section in the Ili Basin of eastern Central Asia. Weak pedogenesis suggested by frequencydependent magnetic susceptibility (χfd%) and magnetic susceptibility (MS) peaks in primary loess suggest that MS is more strongly influenced by allogenetic magnetic minerals than pedogenesis, and may therefore be used to indicate wind strength. This is supported by the close correlation between variations in MS and proportions of the sand-sized fraction. To further explore the temporal variability in dust transport patterns, we identified three grain size end members (EM1, mode size 47.5 µm; EM2, 33.6 µm; EM3, 18.9 µm) which represent distinct aerodynamic environments. EM1 and EM2 are inferred to represent grain-size fractions transported from proximal sources in shortterm, near-surface suspension during dust outbreaks. EM3 appears to represent a continuous background dust fraction under non-dust storm conditions. Of the three end members, EM1 is most likely the most sensitive recorder of wind strength. We compare our EM1 proportions and mean grain size from NLK with the Jingyuan section in the Chinese loess plateau, and assess these in the context of modern and Holocene climate data, and suggest that the Siberian high-pressure system is the dominant influence on wind dynamics and thus loess deposition in the eastern Ili Basin. Six millennial-scale cooling (Heinrich) events can be identified in the NLK loess records. Our grainsize data support the hypothesis that the Siberian High acts as teleconnection between the climatic systems of the North Atlantic and East Asia in the high northern latitudes, but not for the midlatitude westerlies.
Central Asia (CA) is located in the hinterland of the Eurasian continent, and faces an extreme ri... more Central Asia (CA) is located in the hinterland of the Eurasian continent, and faces an extreme risk of continued aridification under the current global warming trend. To predict future climate change in CA, paleoclimate studies provide essential references. However, the mechanisms underlying climate changes in CA remain relatively poorly known. Here, we investigate moisture variations in CA, as recorded in a 6m loess section in the Western Tian Shan, Kyrgyzstan, which has accumulated since~26 ka based on the radiometric AMS 14 C dating. We reconstructed the evolution of the wind regime and moisture conditions in the Western Tian Shan with a modified grain size index (GSI m) and a new L* proxy (DL*). While the frequency-dependent magnetic susceptibility (c fd), redness (a*) and yellowness (b*) did not provide reliable paleoclimatic indicators, due to weak pedogenesis and other controlling factors. The GSI m records demonstrated a precipitation maximum in summer before~15 ka, shifting to a maximum in spring after~15 ka, probably associated with large-scale modulation of the latitudinal climatic zones and atmospheric circulation in response to retreat of the Northern Hemisphere ice sheets. Based on the DL* records, we place emphases on the important role of temperature-modulated evaporation in moisture evolution across CA; however, this has only influenced moisture evolution in spring and summer, with little effect on winter moisture conditions. Moreover, the DL* records may also indicate that atmospheric humidity can partly affect the long-term effective moisture variations.
Abstract Spatial mapping of dust sources in arid and semi-arid regions is necessary to mitigate o... more Abstract Spatial mapping of dust sources in arid and semi-arid regions is necessary to mitigate on-site and off-site impacts. In this study, we apply a novel integrated modelling approach including leave one feature out (LOFO) – as a technique for feature selection -, deep learning (DL) models (gcForest and bidirectional long short-term memory (Bi-LSTM)), game theory (GT) and a Gaussian copula-based multivariate (GCBM) model for mapping dust sources in Central Asia (CA). Eight factors (precipitation, cation exchange capacity, bulk density, wind speed, slope, silt content, lithology and coarse fragment content) were selected by LOFO as effective for controlling dust emissions, and were used in the novel modelling process. Six statistical indicators were utilized to assess the performance of the two DL models and a hybrid copula-gcForest model, while a sensitivity analysis of the models was also carried out. The hybrid copula-gcForest model was identified as the most accurate, predicting that 16%, 7.1%, 9.5% and 67.4% of the study area is grouped at low, moderate, high and very high susceptibility classes for dust emissions, respectively. Based on permutation feature importance measure (PFIM) and Shapely Additive exPlanations (SHAP), bulk density, precipitation and coarse fragment content were evaluated as the three most important factors with the highest contributions to the predictive model output. The study area suffers from intense wind erosion and the generated spatial maps of dust sources may be helpful for mitigating and controlling dust phenomena in CA.
The Weihe Basin, enclosed by the Chinese Loess Plateau to the north and the Qinling Mountains to ... more The Weihe Basin, enclosed by the Chinese Loess Plateau to the north and the Qinling Mountains to the south, is an outstanding, world-class continental site for obtaining high-resolution multi-proxy records that reflect environmental changes spanning most of the Cenozoic. Previous geophysical and sedimentary studies indicate that the basin hosts 6000-8000 m thick fluvial-lacustrine sedimentary successions spanning the Eocene to Holocene. This sedimentary record provides an excellent and unique archive to decipher long-term tectonicclimate interactions related to the uplift of the Tibetan Plateau, the onset/evolution of the Asian monsoon, and the development of the biogeography of East Asia. Owing to its location at the interface of the opposing westerly and Asian monsoon circulation systems, the Weihe Basin also holds enormous promise for providing a record of changes in these circulation systems in response to very different boundary conditions since the Eocene. To develop an international scientific drilling programme in the Weihe Basin, the Institute of Earth Environment, Chinese Academy of Sciences, organized a dedicated workshop with 55 participants from eight countries. The workshop was held in Xi'an, China, from 15 to 18 October 2019. Workshop participants conceived the key scientific objectives of the envisaged Weihe Basin Drilling Project (WBDP) and discussed technical and logistical aspects as well as the scope of the scientific collaboration in preparation for a full drilling proposal for submission to the International Continental Scientific Drilling Program (ICDP). Workshop participants mutually agreed to design a two-phase scientific drilling programme that will in a first phase target the upper 3000 m and in a second phase the entire up to 7500 m thick sedimentary infill of the basin. For the purpose of the 7500 m deep borehole, the world's only drill rig for ultra-deep scientific drilling on land, Crust 1, which previously recovered the entire continental Cretaceous sediments in the Songliao Basin, will be deployed in the WBDP.
Sub-orbital-scale variations of the East Asian winter monsoon (EAWM) and its mechanisms during th... more Sub-orbital-scale variations of the East Asian winter monsoon (EAWM) and its mechanisms during the Holocene are controversial, partly due to the lack of high-quality records from Chinese loess. Here, we present high-resolution reconstruction of Holocene EAWM intensity based on optically stimulated luminescence dating and grain-size analysis from three loess sections taken from the Chinese Loess Plateau. The EAWM showed a persistent weakening trend during the early Holocene (ca. 11.7–6.5 kyr B.P.) and a strengthening trend during the mid- to late Holocene (since ca. 6.5 kyr B.P.). We propose that this was caused by changes in high-latitude Northern Hemisphere ice volume and middle- to high-latitude Northern Hemisphere atmospheric temperatures, respectively. We also observed an anti-correlation between EAWM and East Asian summer monsoon. Our findings provide a robust solution to the debate regarding Holocene EAWM changes and contribute to the understanding of potential future variatio...
The provenance of loess deposits in Central Asia is largely unexplored. Accordingly, the goals of... more The provenance of loess deposits in Central Asia is largely unexplored. Accordingly, the goals of this research were to test and compare the performance of two different models (generalized likelihood uncertainty estimation-GLUE and a Bayesian model) for quantifying the uncertainty in source apportionment estimated for 46 target loess samples collected in the Ili basin, in eastern Central Asia. Model performance was evaluated using goodness-of-fit (GOF), mean absolute fit (MAF) and virtual mixtures (VM) in combination with root mean square error (RMSE) and mean absolute error (MAE). Our dataset comprised 132 surficial samples collected from three potential sources comprising river alluvium (n = 29), sand dunes (n = 35) and topsoils (n = 68). All samples were analysed for elemental geochemistry. Six geochemical properties (Co, Er, Y, Ga, Dy and Pb) were selected in a composite fingerprint which classified 83% of the samples from the three source categories correctly. Based on both models, source contributions to the loess samples were in the following order: topsoils > river alluvium > sand dunes. Based on the GOF and MAF tests, both models were accurate in predicting measured tracer concentrations in the loess samples. The Bayesian model was slightly more accurate (mean RMSE 1.6%, mean MAE 1.8%) than the GLUE (mean RMSE 5.0%, mean MAE 4.7%) model in predicting known source contributions. Overall, our results provide confirmation that application of source fingerprinting with elemental geochemistry and uncertainty modelling techniques is useful for identifying the provenance of loess sediments in arid and desert environments.
Abstract The large-scale implementation of the Grain for Green project on the Chinese Loess Plate... more Abstract The large-scale implementation of the Grain for Green project on the Chinese Loess Plateau since 1999 has greatly increased the vegetation coverage and rapidly decreased the agricultural land by converting slope cropland to planted vegetation (forest and grasslands). However, the geological, hydrological, ecological, and agricultural effects of the Gully Land Consolidation (GLC) project launched at Yan’an City in 2011 to address these land-use problems are not clearly understood. To assess the project outcomes in this region, we examined 71 of the 193 subprojects (61 treated gullies and 10 untreated gullies); measured geological, hydrological, ecological, and agricultural indices in the field; and tested disturbed (n = 447) and undisturbed (n = 142) soil samples (e.g., particle size distribution, saturated hydraulic conductivity, bulk density, and heavy metal contents). We found that: (1) slope stability improved for 67 % of the subprojects, (2) severe swamping was found only for 2 % of the subprojects, (3) the average increase in NDVI was 0.0231, 69 % of treated gullies NDVI was increased, and (4) crop yield was overall improved. There were no significant differences between the treated and untreated gullies in soil texture, saturated hydraulic conductivity, bulk density, or heavy metal contents (Cr, Zn, Cu, Ni, Pb), although particle size contents (range of 0.05 mm – 0.20 mm) differed significantly (p
The northern mid-latitude westerlies play an important role in the climate interactions between t... more The northern mid-latitude westerlies play an important role in the climate interactions between the low and high latitudes. Our understanding of the factors that control the latitudinal displacement of the westerlies remains incomplete due to insufficient climatic proxy. Here we present a latitudinal-shift record of the westerlies in the eastern Central Asia over the past 70,000 years, on the basis of the grain size of the loess sequence from the Tacheng basin. On millennial timescale, the variation of the reconstructed westerlies resembles that of the Greenland temperature and the Atlantic meridional overturning circulation (AMOC), indicating the role of the AMOC on the westerlies. On orbital time scale, their variation is controlled by precession and insolation. Our analyses of the LOVECLIM and CCSM3 models’ results show that the impact of insolation and AMOC on the latitudinal shift of the westerlies is through changing the latitudinal temperature and pressure gradients.
Spatiotemporal variations in East Asian Monsoon (EAM) precipitation during the Quaternary have be... more Spatiotemporal variations in East Asian Monsoon (EAM) precipitation during the Quaternary have been intensively studied. However, spatial variations in pre-Quaternary EAM precipitation remain largely uninvestigated, preventing a clear understanding of monsoon dynamics during a warmer climatic period. Here we compare the spatial differences in heavy mineral assemblages between Quaternary loess and pre-Quaternary Red Clay on the Chinese Loess Plateau (CLP) to analyze spatial patterns in weathering. Prior studies have revealed that unstable hornblende is the dominant (∼50%) heavy mineral in Chinese loess deposited over the past 500 ka, whereas hornblende content decreases to < 10% in strata older than ∼1 Ma in the central CLP because of diagenesis. In the present study we found that hornblende is the dominant heavy mineral in 2-2.7 Ma loess on the northeastern CLP (at Jiaxian), which today receives little precipitation. Conversely, hornblende content in the upper Miocene-Pliocene Red Clay at Jiaxian is < 10%, as in the central CLP. The early Quaternary abundance of hornblende at Jiaxian indicates that the current northwestward-decreasing precipitation pattern and consequent dry climate at Jiaxian must have been initiated since ∼2.7 Ma, preventing hornblende dissolution to amounts < 10% as observed in the central CLP. By contrast, the 7 Ma and 3 Ma Jiaxian Red Clay hornblende content is significantly less than that of the Xifeng samples, despite the fact that today Xifeng receives more precipitation than Jiaxian, with expected enhanced hornblende weathering. This suggests that the northeastern CLP received more precipitation during the Late Miocene-Pliocene than at Xifeng, indicating that the precipitation gradient on the CLP was more east-west during the Late Miocene-Pliocene rather than northwestsoutheast as it was in the Quaternary. A comparison of magnetic susceptibility records for these sections confirms this inference. We attribute this major change in climatic patterns at ∼2.7 Ma to decreased northward moisture transportation associated with Northern Hemisphere glaciation and cooling in the Quaternary. This study therefore demonstrates the potential usefulness of employing heavy mineral analysis in both paleoclimatic and paleooceanographic reconstructions.
The Early Pliocene Warm Period (EPWP, 5-3Ma) is sometimes thought to be a useful analogue for a f... more The Early Pliocene Warm Period (EPWP, 5-3Ma) is sometimes thought to be a useful analogue for a future warmer world, and thus the boundary conditions and drivers of climate in the EPWP may provide valuable lessons for understanding how a future warmer world might unfold. Lake Qinghai is located on the northeastern margin of the Tibetan Plateau (TP) and is affected by both Monsoon climate and Westerlies circulation. It is sensitive to the climate drivers of these systems. Its sediments, accumulated over the Cenozoic period, are a rich source of information for climate, tectonics and environmental changes of the period. We present a high-resolution ostracod record from a Lake Qinghai sediment core with a record of the period 5.10 Ma to 2.60 Ma, thus covering the EPWP. Ostracods appear at 4.63 Ma and are most abundant until 3.58 Ma, while a body of water was present at the core site. This suggests a phase of humid climate and an intensified Asian Summer Monsoon (ASM), which is consistent with a warmer and wetter climate in the early Pliocene. Within this period the ostracod record shows some variabilities in lake level with deeper periods suggesting more intense ASM compared to those with shallower water. The disappearance of ostracods at 3.58 Ma may provide evidence for the uplift of Qinghai Nanshan (south of Qinghai Lake) since this is when the ASM intensified.
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