Grain Size Component Research Articles

Quantitative contributions of different atmospheric circulation systems to Holocene aeolian activity in northwestern China: Evidence from a closed interdune lake in the Tengger Desert hinterland

The aeolian deserts of northwestern China are major landscape types in the arid regions of the Northern Hemisphere, and collectively they are one of the largest dust source regions on Earth. However, owing to occurrence of sedimentary hiatuses within aeolian deposits in the deserts, we lack clear knowledge of the history of Holocene aeolian activity and the interaction between aeolian processes and their potential drivers. In this study, we extracted an environmentally sensitive grain-size component from the sediments of a closed interdune lake in the hinterland of the Tengger Desert. Our methodology included the application of End Member Analysis (EMA) of different modern sediment types from catchment to regional scales. We reconstructed aeolian activity over the past 13 cal ka BP and quantified the contributions of environmental factors. The results indicated that the EM 2 fraction of the interdune lake sediments is mainly transported by local winds and reflects changes in the intensity of aeolian activity. Based on EM 2 the strongest aeolian activity occurred during 13.0–7.0 cal ka BP, especially during 8.0–7.0 cal ka BP, and the weakest activity occurred during 7.0–3.5 cal ka BP. Aeolian activity increased after 3.5 cal ka BP, but with a gradually weakening trend. The occurrence of the weakest aeolian activity in the Tengger Desert during the Middle Holocene differs from that on the Asian Summer Monsoonal Boundary and in the area influenced by the Westerlies-dominated climate regime. Thus, there was a clearly defined spatio-temporal differentiation of Holocene aeolian activity across the deserts and dune fields of northern China. Quantitative analysis of the contributions of the potential drivers indicated that wind activity forced by different atmospheric circulation systems, rather than changes in vegetation cover, were the most important driver of regional aeolian activity, although their relative effects varied during the Holocene.

Assessment of two grainsize methods for peat sediments and their paleoenvironmental significance: the Yueliangwan Peatland in northeast Asia

Grainsize is an important indicator in paleoenvironmental research. Over the past few decades, different pretreatment methods have been proposed for grainsize determination of peat sediments. Assessing the reliability of the grainsize measurements is critical to ensure the paleoenvironmental significance represented by different grainsize components. In this study, using peat sediments from the Yueliangwan peatland in northeast Asia, the effects of two pretreatment methods on grainsize measurement were compared. It was found that these two pretreatment methods on peat sediments produced grainsize features with totally different parameters and distribution characteristics. Grainsize method 1, which used a hydrogen peroxide water bath treatment, did not reflect accurate results for grainsize in peat sediments. Grainsize method 2, which used muffle furnace combustion, does reflect the true results because the organic matter, such as plant residues, spores and pollen, is totally removed. The presence of this stubborn organic matter in peat samples greatly disturbs the accuracy of grainsize measurements, and the reliability of grainsize measurements can be affected by the presence of stubborn organic matter. Based on the grainsize grade-standard deviation analysis using method 2, the East Asian Winter Monsoon evolutionary history in northeast Asia during the Little Ice Age (1300–1750 CE) was reconstructed and divided into three stages: the strengthening stage (1346–1425 CE), the strongest stage (1425–1525 CE) and the weakening stage (1525–1725 CE).

Sensitive Grain-Size Components of Last Glacial Loess on Chinese Loess Plateau and Their Response to East Asian Winter Monsoon

Chinese loess provides the most detailed terrestrial records of paleoclimate changes. We employed the grain-size components of aeolian sediments to reconstruct the history of the East Asian winter monsoon (EAWM) on the Chinese Loess Plateau (CLP). Here, using the grain-size class vs. standard deviation method, we extracted the environmentally sensitive grain-size components of nine last glacial loess sections. The grain-size class vs. standard deviation diagrams showed two major grain-size components (fine and coarse), which varied from section to section. Material resource distances and post-depositional pedogenesis were the main factors affecting environmentally sensitive grain-size components. The coarse grain-size components of the Yulin, Baicaoyuan, Xifeng, and Luochuan sections were influenced by the transportation distance, while we attributed the fine grain-size components of the Weinan, Shaoling, Duanjiapo, and Chaona sections to pedogenesis. At the same time, the Mianchi section’s sensitive grain-size component was also coarse, and was affected by the local circulation from the nearby Yellow River terrace. Our comparison of sensitive grain-size components and EAWM revealed that the coarse grain-size components were progressively finer along with the EAWM from the northwest to the southeast on the CLP, and they can be regarded as the most suitable proxy indicator of the EAWM on the CLP.

Westerly Variations in the Eastern Tibetan Plateau since the Last Interglacial Revealed by the Grain-Size Records of the Ganzi Loess

The westerlies play an important role in driving climate change in the Tibetan Plateau (TP). However, little is known about the history of the westerlies in the TP owing to limited observations and a lack of robust reconstructions. The widely distributed eolian loess in the eastern TP is one of the ideal materials to retrieve the intensity history for the westerlies. A detailed grain-size and endmember model analysis (EMMA) on the Ganzi loess sequence located in the eastern TP revealed that the EMMA decomposed the loess grain-size components into four endmembers: EM1 (modal size 1.42 μm) is related to pedogenesis, and EM2 (modal size 7.10 μm) is transported by the westerlies. Silt modes (EM3 and EM4) are transported by the TP winter monsoon or near-surface airflows. The mass accumulation rate (MAR) of EM2 indicated the westerly variations. Combined with the MAR, we reconstructed the history of westerly intensity since the last interglacial period from the Ganzi loess sequence. We found that the intensity of the westerlies showed typical glacial/interglacial variations since the last interglacial period in the eastern TP. The westerly intensity was strong with large fluctuations during the glacial period, whereas it was weak and stable during the Holocene and the last interglacial. The temperature gradient between high and low latitudes caused by changes in insolation and ice volume in the northern hemisphere were the dominant forcing mechanisms for the westerly intensity variations.

Middle to Late Quaternary changes in ice rafting and deep current transport on the Alpha Ridge, central Arctic Ocean and their responses to climatic cyclicities

To address the Arctic Ocean response to the Quaternary climate change, three sediment cores from the Alpha Ridge, central Arctic Ocean, were analyzed for proxies of sediment transport and depositional mechanisms. The identified end-member grain-size components - clayey EM1, fine-silty EM2, and silty-sandy EM3 - are interpreted as proxies of sea ice transport, near-bottom current, and iceberg inputs, respectively. The sea-ice and iceberg transport proxies, EM1 and EM3, have opposing patterns peaking in the interglacials/interstadials and glacials/stadials, respectively. The near-bottom current proxy EM2 shows an overall gradual decrease with secondary variations indicating current slow-down during intervals of enhanced iceberg discharge. EM3 peaks during Marine Isotope Stages (MIS) 12, 10, 8, and MIS 7 stadials co-occur with high Ca content indicative of iceberg inputs from the Laurentide ice sheet via the Beaufort Gyre. Other EM3 peaks, notably during MIS 6 and MIS 4/3 likely originated from the Siberian margin based on elevated Zr content, thus indicating expanded Eurasian ice sheet and the Transpolar Drift extension towards the central Arctic Ocean. High coherences in the spectral analysis between the sea ice and iceberg proxies versus the global ice volume and orbital parameters on the 100-kyr and 23-kyr time bands illustrate the strong responses of sea ice and glaciations to eccentricity and precessional cycles. A persistent precessional impact of low latitude processes on high Arctic environment indicates a potential link to the low latitudes via atmospheric moisture and heat transport.

Grain-Size End-Members of Anguli-Nuur Lake Core Sediments: Evidence for Moisture Variability in Northern China since the Last Deglaciation

The common methods used for grain-size analysis have their own deficiencies and limitations in terms of explaining the genesis of grain-size components. In this study, the end-member modeling analysis method is applied to multi-mode grain-size distributions of core sediment from Anguli-nuur lake to help to understand the sediment provenance, transport processes and sedimentary environment. Four optimal end-members are unmixed, and three transport-deposition processes are revealed, including the runoff, wave and aeolian processes. The humidity index synthesized by the runoff and aeolian end-members in the core sediment is used to reconstruct the humidity variability in the East Asian monsoonal domain since the last deglaciation. Our record shows that the patterns of humidity variability are coincidentally linked with the monsoonal precipitation index from the same core and stalagmite record in southern China. The Holocene optimum is identified in early and middle Holocene. In addition, a series of millennial- and multi-centennial-scale dry events documented in our record are well correlated with the ice-rafted debris events in the North Atlantic. The results reveal that the grain-size record from Anguli-nuur lake is sensitive in response to moisture variability in northern China.

Millennial variability of terrigenous transport to the central–southern Peruvian margin during the last deglaciation (18–13 kyr BP)

Abstract. Reconstructing precipitation and wind from the geological record could help researchers understand the potential changes in precipitation and wind dynamics in response to climate change in Peru. The last deglaciation offers natural experimental conditions to test the response of precipitation and wind dynamics to high-latitude forcing. While considerable research has been done to reconstruct precipitation variability during the last deglaciation in the Atlantic sector of South America, the Pacific sector of South America has received little attention. This work aims to fill this gap by reconstructing types of terrigenous transport to the central–southern Peruvian margin (12 and 14∘ S) during the last deglaciation (18–13 kyr BP). For this purpose, we used grain-size distribution in sediments of marine core M77/2-005-3 (Callao, 12∘ S) and core G14 (Pisco, 14∘ S). We analyzed end-members (EMs) to identify grain-size components and reconstruct potential sources and transport processes of terrigenous material across time. We identified four end-members for both Callao and Pisco sediments. In Callao, we propose that the changes in the contributions of EM4 (101 µm) and EM2 (58 µm) mainly reflect the hydrodynamic energy and diffuse sources, respectively, while the variations in EM3 (77 µm) and EM1 (11 µm) reflect changes in the eolian and fluvial inputs, respectively. In Pisco, where there are strong winds and an extensive coastal desert, changes in the contribution of EM1 (10 µm) reflect changes in river inputs, while EM2 (52 µm), EM3 (75 µm), and EM4 (94 µm) reflect an eolian origin. At millennial scale, our record shows an increase in the fluvial inputs during the last part of Heinrich Stadial 1 (∼16–14.7 kyr BP) at both locations. This increase was linked to higher precipitation in the Andes related to a reduction of the Atlantic Meridional Overturning Circulation and meltwater discharge in the North Atlantic. In contrast, during the Bølling–Allerød interstadial (∼14.7–13 kyr BP), there was an eolian input increase, associated with stronger winds and lower precipitation that indicate an expansion of the South Pacific Subtropical High. These conditions would correspond to a northern displacement of the Intertropical Convergence Zone–South Pacific Subtropical High system associated with a stronger Walker circulation. Our results suggest that variations in river discharge and changes in surface wind intensity in the western margin of South America during the last deglaciation were sensitive to Atlantic Meridional Overturning Circulation variations and the Walker circulation on millennial timescales. In the context of global warming, large-scale increases in precipitation and fluvial discharge in the Andes as a result of a declining Atlantic Meridional Overturning Circulation and southward displacement of the Intertropical Convergence Zone should be considered.

Magnetism and Grain-Size Distribution of Particles Deposited on the Surface of Urban Trees in Lanzhou City, Northwestern China.

Studies on the variation in the particulate matter (PM) content, Saturation Isothermal Remanent Magnetization (SIRM), and particle grain-size distribution at a high spatial resolution are helpful in evaluating the important role of urban forests in PM removal. In this study, the trees located in dense urban forests (T0) retained more PM than trees located in open spaces (T1–T4); the SIRM and PM weight of T0 were 1.54–2.53 and 1.04–1.47 times more than those of T1–T4, respectively. In addition, the SIRM and PM weight decreased with increasing distance to the road, suggesting that distance from pollution sources plays a key role in reducing the air concentration of PM. The different grain-size components were determined from frequency curve plots using a laser particle-size analyzer. A unimodal spectrum with a major peak of approximately 20 μm and a minor peak between 0.1 and 1 μm was observed, indicating that a large proportion of fine air PM was retained by the needles of the study trees. Additionally, more <2.5 μm size fraction particles were observed at the sampling site near the traffic source but, compared to a tree in a row of trees, the percentage of the >10 μm size fraction for the tree in the dense urban forest was higher, indicating that the particles deposited on the needle surface originating from traffic sources were finer than those from natural atmospheric dust. The exploration of the variation in the PM weight, SIRM, and grain size of the particles deposited on the needle surface facilitates monitoring the removal of PM by urban forests under different environmental conditions (e.g., in closed dense urban forests and in open roadside spaces), different distances to roads, and different sampling heights above the ground.

Palynological evidence indicates the paleoclimate evolution in southeast China since late marine isotope stage 5

Four coastal cores collected from Fujian province in southeast China revealed new palynological evidence of vegetation, sea level, and climate changes since the late marine isotope stage (MIS) 5. A comparison between modern and fossil pollen assemblages, using scanning electron microscopy and 45 dating samples ensured an accurate interpretation of pollen data. The evergreen Quercus-dominated pollen assemblage indicated that a relatively warm subtropical climate prevailed during the last glaciation, whereas large amounts of Tsuga pollen indicated distinct cooling during early MIS2. Marine dinocysts revealed three transgressional intervals in the Holocene, early MIS3, and late MIS5, which corresponded to a globally sea-level rising. Richer pollen from tropical and subtropical broad-leaved trees and higher sand content in grain-size components confirmed a warm climate during the early MIS1 and early MIS3, and strong river flow associated with heavy precipitation during late MIS5, reflecting the sensitive response of the land climate to high summer insolation. During the early MIS3 period, the reconstructed optimum climate was consistent with the sea surface temperature records in the west Pacific and northern South China Sea and summer monsoon signal from terrestrial records, implying that high summer insolation strongly affected the climate of East Asia.

New insights into loess formation on the southern margin of the Chinese Loess Plateau

The Loess Plateau has been identified as one of the most important areas for dust particles deposition and considered as one of the key areas for studying the global climate change and regional responses. In this study, a continuous loess profile, located on the southern margin of the Loess Plateau, was selected to analyze microstructure of the loess and palaeosol. Combined with the end-member model and principal factor analysis, the dust transport and loess formation processes were reconstructed. Magnetic susceptibility and grain-size analyses suggest considerable differences between the loess and the palaeosol. The parametric decomposition model was used to decompose the grain-size components into 3 end-members, revealing the transport force of westerly circulation and winter monsoon and pedogenesis after deposition that affected the loess formation. The microstructure analysis reflects the loess is different from the palaeosol in terms of skeleton particles, contact modes, type and morphology of pores. More meso- and minipores and smaller fractal dimension of pores is observed in loess than palaeosol, preserving the climatic information during the formation of loess layers. The principal factor analysis of grain-size components and parameters shows that factor Ⅰ indicates the two important transport force of westerly circulation and winter monsoon. While factor Ⅱ reflects a kind of compound force, the combined effect of high airflow transport and pedogenesis. Based on these, the conceptual model of loess formation in the Weihe Basin is established under different climates between glacial and interglacial. The findings are helpful to understand the regional climatic environmental evolution, formation of loess landform and evolution of the atmospheric circulation system in East Asia.

Response of grain-size components of loess-paleosol sequence to Quaternary climate in the Southern Loess Plateau, China

A new, thick, and complete loess-paleosol sequence is a good response to climate changes. In this paper, the distribution and parameters of grain size in the Xiushidu (XSD) sequence in the southern Loess Plateau were systematically investigated. A comparative analysis of the sediment granularity with different areas was also conducted. The results show that the XSD sequence is primarily constituted by coarse silt (52.18%), clay (21.71%), and fine silt (20.27%), and the contents of colloidal particles (3.63%) and fine sand (2.21%) are relatively small. The contents of 1~5 μm and < 5 μm show a slight increase from S9 to S5, while the contents are clear downward from L5 to L0, indicating that the climate is gradually getting colder after S5. Grain-size distribution curves show a bimodal pattern for loess/paleosol. The grain-size component and peak pattern illustrate that dust materials were not only transported by wind but also experienced pedogenesis. Moreover, the changes of grain-size indicator Mz values indicate climatic instability. Comparing with the Beglitsa, Oitak (AYTK), Lanzhou (LZ), Pengyang (PY), Luochuan (LC), and XSD sequences, we can infer that the XSD sequence not only has experienced the strong pedogenesis and the warm and humid climate but also has influenced by the Himalayas, the Tibetan Plateau, the QM, and the LPM. These analyses help to clarify the climatic and environmental context of loess-paleosol sequence deposition phases and regional environmental evolutions.

Grain-size end-members and environmentally sensitive grain-size components: A comparative study in the mud shelf depocenters off southern Brazil

The current study aims to do a comparative analysis of the results obtained with two End-Member (EM) grain-size modeling techniques (AnalySize and BasEMMA) and the Environmental Sensitive Grain-Size (ESGS) modeling for sediment samples collected in the mudbelts of the southern Brazilian shelf. The methods were compared using grain-size data from the south Brazilian shelf, and the results are discussed here. It is the first time that the concept of ESGS, in its present form, is utilized outside China. The results show that despite its relative ease of use, the ESGS is not fully comparable to the EM analyses, and only two grain-size ESGS classes were recognized as analogous to EMs. The comparison of the AnalySize and BasEMMA procedures also revealed significant differences between the techniques. A comparative analysis between the two EM techniques revealed advantages in the BasEMMA, especially in the better correlation of the end-members with the original grain size distribution. The analysis of the geographical distribution of the EM abundances allowed point sources of sandy populations to be recognized as well as the contribution of the Rio de la Plata as a source of silty sediments to be inferred.

Quantitative reconstruction of the East Asian Winter Monsoon evolution over the past 100 years: Evidence from high-resolution sedimentary records of the inner continental shelf of the East China Sea

The East Asian Monsoon (EAM) is a regional factor affecting the East Asian climate and the oceanographic processes of the marginal seas along the Western Pacific. Finding proxies for the EAM intensity and reconstructing the interannual and interdecadal variations of the EAM using high-resolution records are necessary to improve our understanding of the EAM’s role in the global climate system and for predicting climate change. In this paper, high-resolution sedimentary records of sedimentary core C0702 obtained from the inner continental shelf of the East China Sea were comprehensively analyzed using a laser particle size analyzer, an ItraxTM core scanner, and a 210Pb and 137Cs radionuclide analyzer to explore potential proxies for the East Asian Winter Monsoon (EAWM). By combining the obtained results with instrumental observations of the EAM, we established a quantitative formula for the EAWM, which enables to reconstruct the evolution trend of the EAWM during the past 130 years. The sensitive grain-size component F2, with a grain-size range of 14.35–230 µm, and principal component PC1 of the sedimentary deposits of the East China Sea inner shelf can be used as EAWM proxies. The evolution of EAWM in 1880–1950 could be roughly divided into two stages: a weak EAWM period from 1882 to 1900 and a strong EAWM period from 1900 to 1945. This study improves our understanding of the variations in the EAWM on interannual and interdecadal temporal scales.

Environmentally sensitive grain-size component records and its response to climatic and anthropogenic influences in Bosten Lake region, China

Using 137Cs and 210Pb dating and multi-proxy evidence from a 41-cm sediment core from Bosten Lake in China, the responses of sediment grain size to environmental changes were reconstructed over the past 150 years. After the end of the Little Ice Age, the climate of the Bosten Lake region became warmer and drier, and the lake water level decreased. The results indicated that the lowest water storage periods occurred at approximately 1920–1930 AD. Decreases in the Siberian High intensity and water vapour transport from the Indian Ocean during this period led to a reduction in the water vapour supply, which resulted in reduced lake levels in the period 1920–1930 AD. Then, the lake was at a high level until the 1960s. The water storage then declined in the 1960s. Since the 1960s, the contents of total organic carbon and total nitrogen have significantly decreased, which is closely related to the significant decline in water level and increased water salinity caused by enhanced water demands. Increased irrigation water demand as a result of expanding cultivated areas and climate change, coupled with a reduced input of water vapour, resulted in the worst water environment in approximately 1980–1990 AD. Since the late 1980s, the water level of the lake has risen, and the lake primary productivity of Bosten Lake has improved. Through the application of statistical methods to grain size data from Bosten Lake combined with the abovementioned data on climate change and human activities, two major potential factors influencing the grain size of terrigenous clastic material were revealed. The first factor, consistent with a grain size of 3.31 μm, is related to the recent increase in agricultural acreage in the Bosten Lake watershed and may reflect increases in atmospheric dust. The second factor, correlated with grain sizes of 11.48 μm and 69.18 μm, can be used to reflect changes in the lake hydrological state. It is suggested that the grain sizes of these lake sediments sensitively reflect changes in the hydrological characteristics of the basin and can be used to reconstruct the history of climate change and human activities.

Variations in the East Asian winter monsoon from 3500 to 1300 cal. yr BP in northern China and their possible societal impacts

Changes in paleoenvironments from 3500 to 1300 cal. yr BP have been documented by a high-resolution grain-size and organic carbon isotope record in core Z8 from the Shandong mud wedge in the southern Yellow Sea (YS). The sensitive grain-size component, sorting coefficients and δ13Corg values were used to identify the paleohydrologic variations and the intensity of the East Asian winter monsoon (EAWM). The coarse fraction of sediment, together with organic isotope and sea surface temperature (SST) data, shows a weak EAWM during 3500–2300 cal. yr BP, a gradual increase in the EAWM from 2300 to 1700 cal. yr BP and an enhanced EAWM since 1700 cal. yr BP. Superimposed on this general trend, several prominent short-lived strong EAWM episodes peaked at approximately 3300, 3100, 2900, 2750, 2620, 2220, 1900, 1700 and 1400 cal. yr BP. The paleoenvironmental record matches ancient Chinese historical climate records as well as socioeconomic changes, with lower economic levels occurring during stronger EAWM episodes. The results show that prosperous stages of ancient Chinese dynasties mainly occurred in weak EAWM periods, while collapses and/or changes in ancient Chinese dynasties generally occurred during cold periods with a strong EAWM. We suggest that the persistent short-lived strengthening of the EAWM could have exerted a remarkable influence on ancient agricultural societies through decreases in both winter temperature and monsoonal precipitation.

Geoacoustic provinces of the northern South China Sea based on sound speed as predicted from sediment grain sizes

The determination of geoacoustic provinces has important applications in assessing the responses of sedimentary environment and processes. Suitable geoacoustic provinces have not yet been identified in the northern South China Sea, which is an excellent study site for examining sediment acoustic properties. To determine the geoacoustic provinces of sediments in the northern South China Sea, 270 position samples were collected and analysed. Two-parameter empirical equations linking sediment grain-size components to sound speed were applied to sediments from the continental shelf and slope to accurately calculate sound speed in seafloor sediments, especially in the absence of site-specific acoustic data. Based on the ratios of sound speed within the sediments, two geoacoustic provinces are identified. Province I, which is characterized by low sound speed, primarily consists of fine-grained sediments discharged from the Pearl River. Province II, which is characterized by high sound speed, can be further divided into Province II-A and Province II-B. Province II-A is composed of mixed modern and relict sediments originating from the Pearl River and the southwest coast of Taiwan during a Pleistocene drop in sea level. Province II-B consists of coarser relict sediments caused by sea level change during the late Quaternary.

Late Neogene aridification and wind patterns in the Asian interior: Insight from the grain-size of eolian deposits in Altun Shan, northern Tibetan Plateau

A well-preserved and continuous Neogene red clay deposit, the Caihonggou section, was recently discovered in the eastern Xorkol Basin, in the Altun Shan area at the northern margin of the Tibetan Plateau. We report detailed grain-size analyses for the Caihonggou red clay and also for the Shilou red clay section of the Chinese Loess Plateau in east-central China. Although the grain sizes are similar and can be modeled as two-component mixtures, the temporal variation of grain size and the proportions of grain-size components are very different between the Caihonggou and Shilou sections, indicating that their transportation and deposition processes and/or source areas were completely different. The fine component of the Caihonggou red clay was transported by high-level westerlies, whereas the coarser particles were carried by lower-level westerlies coming from the Taklimakan Desert, as indicated also by previous detrital zircon provenance analysis. A range of grain-size parameters for the Caihonggou section indicate that since about 8 Ma, and particularly between 8 and 6 Ma, the westerly winds strengthened, and the aridity of the Asian interior increased.

Palaeoenvironmental implication of grain-size compositions of terrace deposits on the western Chinese Loess Plateau

Sedimentary sequences that developed on river terraces have been widely investigated to reconstruct high-resolution palaeoclimatic changes since the last deglaciation. However, frequent changes in sedimentary facies make palaeoenvironmental interpretation of grain-size variations relatively complicated. In this paper, we employed multiple grain-size parameters to discriminate the sedimentary characteristics of aeolian and fluvial facies in the Dadiwan (DDW) section on the western Chinese Loess Plateau. We found that wind and fluvial dynamics have quite different impacts on the grain-size compositions, with distinctive imprints on the distribution pattern. By using a lognormal distribution fitting approach, two major grain-size components sensitive to aeolian and fluvial processes, respectively, were distinguished from the grain-size compositions of the DDW terrace deposits. The fine grain-size component (GSC2) represents mixing of long-distance aeolian and short-distance fluvial inputs, whilst the coarse grain-size component (GSC3) is mainly transported by wind from short-distance sources. Thus GSC3 can be used to infer the wind intensity. Grain-size variations reveal that the wind intensity experienced a stepwise shift from large-amplitude variations during the last deglaciation to small-amplitude oscillations in the Holocene, corresponding well to climate changes from regional to global context.

A multi-proxy climatic record from the central Tengger Desert, southern Mongolian Plateau: Implications for the aridification of inner Asia since the late Pliocene

Aridification of the Asian interior is one of the most significant paleoenvironmental events during the Cenozoic. However, continuous paleoclimatic records from desert interiors are scarce because of the lack of outcrops, erosion and discontinuous sediment accumulation. Here we report a multi-proxy climatic record for the last ∼3.55 Ma from paleomagnetically-dated drilling core WEDP01 from the central Tengger Desert, which is one of the most important sediment source areas for Northern Hemisphere atmospheric dust and the Chinese Loess Plateau. Analysis of grain-size components indicates the onset of continuous dust deposition at 2.6 Ma and desert formation at 0.9 Ma. In addition, analysis of major element content and sediment color reveals a stepwise process of increasing aridification and significant cooling in the Tengger Desert area. Simultaneous aridification events in northwest China during the Quaternary were probably induced by the uplift of the Tibetan Plateau. Northern Hemisphere glaciation may have been another important factor for Asian aridification; meanwhile, the increased dust emission from sources such as the Tengger Desert may provide a positive feedback mechanism for global cooling.

Geochemical evidence for the provenance of aeolian deposits in the Qaidam Basin, Tibetan Plateau

Abstract The main purpose of this study is to analyse the material source of different grain-size components of dune sand in the Qaidam Basin. We determined the trace and rare earth element (REE) compositions and Sr-Nd isotopic compositions of the coarse (75–500 μm) and fine (