Loess Deposits Research Articles

Multivariate Controls of Water–Carbon Coupling Relationship Under Various Land Use Types in the Thick Loess Deposits

ABSTRACTPrior studies have conducted extensive investigations of the water–carbon coupling relationship for aboveground vegetation and shallow soils, but the characteristics and multivariate controls in deep soils have not been fully explored. This has important implications for better understanding the water and carbon cycles of ecosystems. In this study, we attempted to examine the water–carbon coupling relationship in 18 m profiles under farmland (F), grassland (G), willow (SP), and poplar (P) in China's Loess Plateau. Specially, the multivariate controls of the water–carbon coupling relationship at diverse depths and scales were explored via the wavelet analysis. Individually, the conversion from F to G, SP, and P decreased the soil water storage within the 0–15 m by 553 (22% of F), 557 (22%), and 943 mm (38%). Land use change had little impact on soil organic or inorganic carbon. Even so, the poplar, compared with the willow, resulted in higher vertical variations in deep water and carbon. Furthermore, land use conversion increased the coherence between soil water and carbon in the whole layer. In comparison to F, which was dominated by water retention, G, SP, and P exhibited dominant carbon sequestration. The poplar reduced the root‐mean‐square deviation between soil water and organic carbon from 0.29 (F) to 0.13 in the 6‐ to 15‐m layer and between soil water and inorganic carbon from 0.32 (F) to 0.20 in the 0‐ to 2‐m layer. Sand content and electrical conductivity both played negative roles in maintaining water and carbon in the 6‐ to 15‐m and 0‐ to 15‐m layers at different scales, respectively. This study endeavors to present a novel viewpoint on land use management, with the potential to enhance ecosystem services in water‐limited and land‐degradation regions.

Characterizing and Modeling Infiltration and Evaporation Processes in the Shallow Loess Layer: Insight from Field Monitoring Results of a Large Undisturbed Soil Column

Frequent agricultural irrigation events continuously raise the groundwater table on loess platforms, triggering numerous loess landslides and significantly contributing to soil erosion in the Chinese Loess Plateau. The movement of irrigation water within the surficial loess layer is crucial for comprehending the mechanisms of moisture penetration into thick layers. To investigate the infiltration and evaporation processes of irrigation water, a large undisturbed soil column with a 60 cm inner diameter and 100 cm height was extracted from the surficial loess layer. An irrigation simulation event was executed on the undisturbed soil column and the ponding infiltration and subsequent evaporation processes were systematically monitored. A ruler placed above the soil column recorded the ponding height during irrigation. Moisture probes and tensiometers were installed at five depths to monitor the temporal variations in volumetric water content (VWC) and matric suction. Additionally, an evaporation gauge and an automatic weighing balance measured the potential and actual evaporation. The results revealed that the initially high infiltration rate rapidly decreased to a stable value slightly below the saturated hydraulic conductivity (Ks). A fitted Mezencev model successfully replicated the ponding infiltration process with a high correlation coefficient of 0.995. The monitored VWC of the surficial 15 cm-thick loess approached a saturated state upon the advancing of the wetting front, while the matric suction sharply decreased from an initial high value of 65 kPa to nearly 0 kPa. The monitored evaporation process of the soil column was divided into an initial constant rate stage and a subsequent decreasing rate stage. During the constant rate stage, the actual evaporation closely matched or slightly exceeded the potential evaporation rate. In the decreasing rate stage, the actual evaporation rate fell below the potential evaporation rate. The critical VWC ranged from 26% to 28%, with the corresponding matric suction recovering to approximately 25 kPa as the evaporation process transitioned between stages. The complete evaporation process was effectively modeled using a fitted Rose model with a high correlation coefficient (R2 = 0.971). These findings provide valuable insights into predicting water infiltration and evaporation capacities in loess layers, thereby enhancing the understanding of water movement within thick loess deposits and the processes driving soil erosion.

Provenance of late Pleistocene loess in central and eastern Europe: isotopic evidence for dominant local sediment sources

Loess profiles along the Danube River provide a record of long-term Quaternary dust (loess) deposition in central-eastern Europe. Here, Sr–Nd isotopic data from four loess-palaeosol profiles (47 samples) spanning the last two-glacial-interglacial cycles are presented. The isotopic compositions generated by this study are compared with bedrock and sedimentary samples from Europe and North Africa to decipher the sources of sediment. The results demonstrate that over the last 300 ka the alluvial plains of the Danube (which are themselves sourced from surrounding mountain belts) are a local source of material and consequently sediment experiences aeolian transport over relatively short distances. The results dispute the commonly held assumption that the Sahara was a sediment contributor to loess in central-eastern Europe as North African contributions are not needed to explain loess signatures. Consequently, the findings suggest a suppressed southerly wind direction and dominance of the westerly and north-westerly wind systems over the entirety of the record.

Power of Terroir: Case study of Grašac at the Fruška Gora wine region (North Serbia)

Abstract The main goal of this study is to find out if there are any differences between Grašac wines from two different locations of the Fruška Gora Mountain and to further explore why these differences (if they exist) occur. To achieve this, we selected one vineyard in Sremski Karlovci and one in Neštin where we have analyzed the topography features, soil, and climate at both sites as well as the chemical analysis of the wines from these sites from three different vintages (2017–2019). Additionally, a sensory analysis was also done for seven consecutive vintages (2016–2022). The results reveal that the wines from Sremski Karlovci have a higher aroma intensity on the nose and dominant primary fruit aromas while they are young. These characteristics tend to drop quickly with age. On the other hand, Grašac wines from Neštin tend to age better, becoming fuller bodied, more intense, complex, with tertiary aromas on the nose and palate and with a longer finish. The key differences between these two locations are connected to the thick loess deposits and the amount of available water at the analyzed sites.

Mid-Pleistocene aridity and landscape shifts promoted Palearctic hominin dispersals

Population expansions and contractions out of and into Africa since the early Pleistocene have influenced the course of human evolution. While local- and regional-scale investigations have provided insights into the drivers of Eurasian hominin dispersals, a continental-scale and integrated study of hominin-environmental interactions across Palearctic Eurasia has been lacking. Here, we report high-resolution (up to ∼5-10 kyr sample interval) carbon isotope time series of loess deposits in Central Asia and northwest China, a region dominated by westerly winds, providing unique paleoecological and paleoclimatic records for over ~3.6 Ma. These data, combined with further syntheses of Pleistocene paleontological and archaeological records and spatio-temporal distributions of Eurasian eolian deposits and river terraces, demonstrate a pronounced transformation of landscapes around the Mid-Pleistocene Climate Transition. Increased climate amplitude and aridity fluctuations over this period led to the widespread formation of more open habitats, river terraces, and desert-loess landscapes, pushing hominins to range more widely and find solutions to increasingly challenging environments. Mid-Pleistocene climatic and ecological transitions, and the formation of modern desert and loess landscapes and river networks, emerge as critical events during the dispersal of early hominins in Palearctic Eurasia.

Quantitative reconstruction of sedimentary processes, provenance, and binary sources in Horqin Sandy Land, NE China: An integrated approach

As the largest semi-fixed dune field in China, the Horqin Sandy Land (HSL) provides a valuable opportunity to study the surface processes and paleoenvironmental evolution of drylands in the monsoon region. However, limited data and a single qualitative approach hinder our understanding of the sediment erosion and transport process of the HSL. The ability to trace and quantify sediment provenance of the HSL is increasingly needed to properly understand the source-to-sink processes, and to accurately interpret aeolian–fluvial interactions in terms of a comprehensive database and multidisciplinary approach perspective. This study integrates previously existing grain-size, heavy mineral, element geochemistry, Sr-Nd-Hf isotopic, and zircon-geochronological databases with new petrographic, TIMA automation heavy mineral data and statistical analysis. Together, the high degree of recycling of HSL severely limits the provenance identification of element fingerprints, although these elements are largely inherited from the parent rocks and are not affected by chemical weathering. The heavy minerals, Sr-Nd-Hf isotopes, and zircon U-Pb age composition together reveal that the HSL sediments are a binary mixture of the Palaeozoic-Mesozoic igneous rocks in the Great Xing’an Range (GXR) and the Precambrian metamorphic rocks in the Yanshan Mountains. The isotopic end-element mixing models, multidimensional scaling (MDS) diagrams and inverse Monte Carlo models of detrital zircon ages indicate that GXR and Yanshan Mountains account for ∼ 60 % and ∼ 40 % of the source contributions, respectively. Under the strong influence of the northwest to west winds controlled by the Mongolia-Siberian High, detrital material from the GXR is consistently transported to the interior of the dune field and intensively reworked. The Laoha River and the Yangxumu River originating from the Yanshan Mountains provide stable detrital sources for the HSL. In addition, the transverse flow of the Xilamulun River and the West Liao River has provided sufficient space and sediment for the dunes, which is conducive to the full mixing of materials inside the dune field. The sediment in the southeast of HSL shows an obvious Yanshan Mountains source dominance and a grain-size dependence. The coarse fractions (>63 μm) mainly modified from the river channel sand and alluvial plain of the Yangxumu River (∼75.8 %), while the fine fractions (<63 μm) have a strong affinity with the loess deposit of Yanshan Mountains (∼52.4 %). The fluvial-lacustrine deposits during the last glacial maximum served as a temporary transit station, providing a direct dust source for the modern dunes in the HSL region. Aeolian–fluvial interaction controls the geomorphology and landscape evolution of the HSL in the monsoon region; however, it is challenging to derive insights into the landscape evolution from studying surface samples.

To Investigate the Impact of Land Use Change on the Potential Groundwater Recharge on Hillslope With Deep Loess Deposits

ABSTRACTAccurately estimating groundwater recharge in hilly areas with limited water and thick vadose zones is challenging. This study investigated the impact of land use changes on groundwater recharge at a hillslope scale of Yuanzegou Watershed in China's Loess Plateau. Three adjacent hillslopes were selected for three different land uses: arbor (jujube, Ziziphus jujuba Mill.), subshrub (native grass, Artemisia gmelinii), and crop (millet, Setaria italica). Soil cores (as deep as 10–16/18 m) were collected at each of the three landscape positions on a hillslope. Reported tritium profiles in the watershed were used to estimate the net chloride input into vadose zone on hillslope associated with inverse chloride mass balance (CMB) method/chloride accumulation method (CAM). Soil water content and chloride profiles in the study were measured to determine recharge rates at each landscape position beneath different vegetation types. For the first time, we evaluated the actual chloride input into vadose zone on hillslopes as 540.2 ± 23.8 mg m−2 yr.−1, excluding the impact of runoff. Then, estimated recharge rates ranged from 42.7 ± 3.5 to 62.4 ± 4.7 mm yr.−1, consistent with nearby studies. Results showed that groundwater recharge does not change with landscape position except for higher value on upslope beneath subshrub hillslope. In contrast, groundwater recharge did significantly reduce by 12.9% ± 5.4% and 26.5% ± 4.5% after conversion from cropland to subshrub/arbor on the hillslope, respectively. Our findings contribute to understanding the ecohydrological effects of land use changes on groundwater recharge on hillslope and help to select suitable afforested vegetation for greening efforts in water‐limited hilly areas, with a priority on groundwater safety.

Land snail Δ47 thermometry using cultured and European natural populations of Clausilia pumila, Succinella oblonga and Trochulus hispidus

Clumped isotope composition (Δ47) of aragonitic shells of terrestrial molluscs allow the quantitative reconstructions of continental paleotemperatures from loess-paleosol records of the last 2.5 million years, but it needs testing the method under controlled laboratory conditions and using natural populations. In this study the stable carbon, oxygen and clumped isotope compositions of cultured individuals and field-collected specimens of three species (Clausilia pumila, Succinella oblonga and Trochulus hispidus), widespread in Quaternary loess deposits in Europe, were measured in the Debrecen (ATOMKI) and ETH Zürich laboratories. Our data of cultured snails demonstrate that shells of the three species record Δ47 signatures close to equilibrium conditions with mostly positive (C. pumila), both positive/negative (T. hispidus), and mostly negative (S. oblonga) offsets on the order of 0.0158 ± 0.0105 ‰ (mean offset±1 SD) compared to the Anderson et al. (2021) unified calibration. Calcification temperatures (TΔ47) derived from C. pumila shells were found to be in excellent agreement with chamber temperatures of 12, 18 and 24 °C, especially in the ATOMKI laboratory (mean T offset: 2.1 ± 2.2 °C, 1 SD), while the other two species exhibited larger discrepancies on the order of 5–8 °C (mean offset). Single shell-based mean TΔ47 values of field-collected molluscs indicated growth temperatures spanning values from the frost-free period to summer season, or even above summer maxima. The sites of natural populations, characterized by different climate conditions, could be grouped using the aridity index (AI) with values of 0.96–1.06 representing mean temperature of the frost-free period (TFFP), and AI ranging either from 0.85 to 0.91 or 1.14 to 1.51 reflecting mean summer season or July temperatures (TJJA/TJ). Multi-shell TΔ47, obtained by homogenizing the material of 3–5 shells of C. pumila and T. hispidus, reflect TJJA in most cases. We observed a dependence of the shell oxygen isotope compositions of the three species on oceanity/continentality with more negative/positive values characteristic for more continental/oceanic sites, likely due to moisture source distance and depletion of rainfall in 18O towards the continental interior. In addition, deviation of body fluid δ18O values (derived from δ18Oshell and Δ47shell) from seasonal precipitation δ18O is also controlled by an additional temperature effect, being independent of the climate zone of the collection site, but co-varying with the site-specific difference between single shell TΔ47 and TJJA.

Quantifying Pleistocene loess provenance in midcontinental North America using a mixing model: Implications for glacial lobe evolution along the southern Laurentide ice sheet

Abstract Quaternary glaciations have significantly impacted the midcontinental North American landscape, leaving behind a proglacial sediment record of glacial lake deposits, glacio-fluvial sand and gravel, and windblown loess. This paper aims to expand upon a previous study using detrital zircon provenance analysis to investigate midcontinental North American loess provenance in relation to the glacial history of the southern Laurentide ice sheet during the middle to late Pleistocene. The study incorporates previously published detrital zircon data from last glacial tills (representing the Huron-Erie Lobe, Lake Michigan Lobe, Green Bay Lobe, Superior Lobe, Des Moines Lobe, and James Lobe), middle to late Pleistocene loess from several sites along the Illinois and Mississippi River valleys, and suspended sediment load inputs from the Missouri River and Arkansas River. A statistical mixing model (DzMix version 2.2) was used to estimate the relative proportions of glacial and nonglacial sources to Wisconsin Episode, Illinois Episode, and pre–Illinois Episode age loess. We show that mixing models that include the modern suspended sediment loads of the Missouri and Arkansas Rivers significantly improve (up to 23% increase in cross-correlation value) the source characterization of Wisconsin Episode (last glacial) and Illinois Episode (penultimate glacial) loess deposits within the Mississippi River drainage basin. These river sources are dominant inputs for certain loess sites (as much as 51%), but their relative contributions are not static across time and space, which has implications for temporal and spatial differences in relative sediment source estimates and glacial and fluvial sediment transport evolution. Specifically, differences in relative sediment proportion estimates among Wisconsin, Illinois, and pre–Illinois Episode loess support previous evidence for the persistence of a Quebec-Labrador ice dome source through multiple glacial cycles, even with the inclusion of river sources in updated mixing models. Illinois and pre–Illinois Episode loess in the southern portion of our study area received ~20% detrital zircon input from sources similar to the present-day Missouri and Arkansas Rivers, suggesting that these river systems were contributing a significant amount of detritus to the lower Mississippi River valley region during the middle Pleistocene.

Aeolian dust dynamics in southern Central Asia revealed by the multi-timescale loess records in southern Tajikistan

Dust activity in Central Asia (CA) holds significant scientific interest due to their broad social and environmental impacts. Loess deposits in CA serve as crucial natural archives, recording regional atmospheric characteristics and dust dynamics. The oldest loess in CA has been discovered in southern Tajikistan. However, debates persist regarding the wind dynamics of the Tajikistan loess deposition, which motivates our current study. By analyzing grain sizes of the last glacial loess and previous loess records since 800 ka, we determined that the Tajikistan loess consisted of post-storm floating dust and fine-grained dust transported by the westerlies. The reduced grain sizes may indicate less frequent dust storms. Our results provided explanation for the influence of global ice volume changes on the dust dynamics in southern Tajikistan, primarily by modulating sea-level pressure differences between the Caspian Sea and Hindu Kush/Pamirs. These ice volume changes also intensified rapid atmospheric fluctuations in CA, suggesting a sensitive response of the latter to glacial boundary conditions. Moreover, although precipitation variations may influence dust activities, their impact appears to be minimal. Collectively, our findings offer vital insights into the formation of loess strata and the development of extensive modern loess landforms in southern CA.

Vegetation and environmental changes on the Northeast China Plain during warm periods since MIS 3

Understanding past terrestrial ecosystem responses to climate changes is vital for future predictions, but research in densely populated plains is limited due to insufficient materials. This study focuses on vegetation and environmental changes in the Northeast China Plain since Marine Isotopic Stage (MIS) 3 using pollen analysis from core WCZK03. The findings reveal significant shifts in vegetation that correspond to climatic events. During MIS 3 (52–29 cal ka BP), the region was predominantly a lake environment with vegetation transitioning from grassland dominated by Poaceae, Chenopodiaceae and Artemisia to conifer-broadleaf mixed forests as the climate ameliorated. The Last Glacial Maximum (29–17 cal ka BP) was characterized by loess deposits, followed by drought-tolerant grassland (17.0–11.3 cal ka BP) dominated by Artemisia and Chenopodiaceae in the plain. The onset of the Holocene witnessed the expansion of conifer and broad-leaved deciduous forests in hilly areas and the retreat of grassland in the plain. The sedimentary sequence shows transitions from fluvial-lacustrine deposits to loess-like and black soil deposits, showing significant environmental changes. This study suggests that changes in vegetation on the Northeast China Plain were closely related to regional climate patterns and were more responsive to climate changes than the surrounding mountainous areas.

Exploring the limits of the provenience postulate: chemical and mineralogical characterization of Bronze Age ceramics from the Great Hungarian Plain

Determining the provenience of archaeological objects relies on the so-called “provenience postulate,” namely, that sources of these objects are more compositionally distinct from each other than they are internally variable. For ceramics, it can be relatively straightforward in geologically heterogeneous environments to determine where vessels were produced, and whether they were traded or not. In geologically homogeneous regions, this can be far more complicated. In this study, we mineralogically and chemically compare Bronze Age ceramics (primarily Middle Bronze Age) from five archaeological sites on the Great Hungarian Plain to a large regional clay sample. The Great Hungarian Plain is comprised almost entirely of Pleistocene loess deposits, yet prior compositional studies have identified patterned variability between ceramics from different sites. Our results show that chemical variation in the region is continuous and clinal, making it difficult to strictly apply the provenience postulate to identify distinct production locations. However, we show that this clinal chemical variability can be used to make broad statements about whether most ceramics at any given site were produced relatively locally or were obtained from further distances (c. 50 km or more). We show that while production at most of our study sites was likely relatively localized, in one instance (the tell at Berettyóújfalu-Herpály-Földvár), many ceramics may have been obtained from other Bronze Age communities, including those in the Körös River drainage.

Dynamic landscape response to Younger Dryas and earliest Holocene cooling events in the European Eastern Alps (Austria)

In classic loess areas research into dust deposition and concomitant environmental changes has a long history and numerous well-investigated loess-palaeosol sequences provide insights into Late Quaternary landscape responses to climatic change on orbital to centennial time scales. This contrasts with mountain regions, where an understanding of dust deposition under rapidly changing climatic and environmental conditions is much less developed. Here we describe two sediment records from the Austrian Alps that provide rare evidence for intramontane loess accumulation. Dust deposition has been numerically constrained to the Younger Dryas (YD) to earliest Holocene interval, making these sites the first proof of significant intramontane aeolian activity during this time interval in the Eastern Alps.At study site 1, located in the Northern Calcareous Alps, a loess layer 10–20 cm in thickness and laterally exposed over more than 300 m is sandwiched into an alluvial-fan succession. Two optically-stimulated luminescence ages of quartz and four radiocarbon ages of charcoals indicate loess accumulation during the Younger Dryas to earliest Holocene. This laterally extensive loess drape suggests much drier climatic conditions compared to today, which is corroborated by palynological investigations. Macro- and micro-charcoal particles within the loess indicate regional wildfires that might have exaggerated climatically induced sedimentary processes. The second site is a Mesolithic site located ∼30 km southeast of site 1. At site two, redeposited till and pebbly scree are sharply overlain by a few centimetre thick light-grey loess layer, which is capped by the archaeological living floor hosting 14C dated fireplaces suggesting human presence as early as 10.9 ± 0.2 cal ka BP. These radiocarbon ages in combination with single-grain IRSL dating of feldspar at site two suggests concomitant aeolian deposition at site 1 and 2.Recently, a widespread drape of loess deposited immediately subsequent to the LGM was described for the same sector of the Eastern Alps (Gild et al., 2018). The present study expands on these findings and provides evidence for the recurrence of loess deposition also during the YD to earliest Holocene, and suggests a highly sensitive response of the geomorphic system in mountain ranges to abrupt post-LGM climate fluctuations. We conclude that, in addition to moraine records of Alpine glaciers and speleothems that accurately chronicle Late Glacial temperature fluctuations, the spatio-temporal pattern of inner-Alpine loess deposits records the mode and sensitivity of landscape responses to such cooling events. Because such aeolian sediment layers can be redeposited or pedologically overprinted, they are often overlooked, and are thus still severely under-researched.

Phosphorus dynamics across a 450 ka vertical chronosequence of loess derived (paleo)soils in central US

Pedogenesis entails profound changes in terrestrial phosphorus (P) dynamics, yet means to understand how time- and climate-induced soil weathering impacts P-cycling over geologic timescales remain relatively limited to space-for-time substitution approaches with multi-site chronosequences. We tested an alternative approach for evaluating terrestrial P dynamics described by the Walker-Syers model by measuring P pools in a ~ 450 ka loess–paleosol sequence. This vertical chronosequence reflects episodic proglacial loess deposition during multiple glaciations and interglacial soil development in central North America in a four-stage loess–paleosol sequence that initiated with the pre-Illinois Episode glaciation. Changes in P pools estimated by sequential fractionation aligned with the Walker-Syers P model for interglacial periods but not glacial periods, possibly reflecting limited soil weathering in cooler and drier conditions of the latter. Total P decreased from 797 to 328 mg/kg with depth and was higher in paleosols than underlying loess parent materials. During glacial periods, primary P increased due to loess deposition and decreased during interglacial periods concomitantly with increased non-occluded and occluded secondary P pools, the extent of which reflected differences in weathering environments of paleoclimatic conditions and loess accumulation rates. That P fractions reflected the Walker-Syers model demonstrates that single-site vertical chronosequences have potential for evaluating long-term soil P dynamics.

Sedimentation rate changes across the Chinese Loess Plateau from luminescence dating of Malan loess in the Sanmen Gorge

Abstract The Chinese Loess Plateau (CLP), recognized as the world's largest loess plateau, has been a subject of ongoing debate regarding the continuity of its sedimentary loess sequence due to its intricate depositional environment. In this study, we conducted dating on a 9.8-m-long Malan loess core obtained from the Sanmen Gorge in the southern CLP using optically stimulated luminescence (OSL). The OSL dates indicate loess deposition between 52.4 and 11.3 ka, with no apparent hiatus on a millennial scale, and a sedimentation rate (SR) exhibiting six distinct episodes. Additionally, a comprehensive review of 613 OSL ages from 18 sections at 14 sites across the CLP was conducted. The results reveal loess deposition at most sites shows no apparent hiatus on a millennial scale over the past 60 ka, except for two specific locations. High SR episodes during Marine Isotope Stage (MIS) 3 across the CLP were attributed to heightened dust emissions from the source region and an enhanced dust deposition efficiency, while MIS 2 deposits were influenced by an intensified East Asian winter monsoon. Low SR episodes during MIS 1 at most sites were likely associated with reduced atmospheric transportation and pedogenesis. Spatially heterogeneous SR variations across the CLP might be influenced by local depositional environments.

Quaternary provenance changes in the loess deposits of the western Chinese Loess Plateau: Insights from U-Pb age spectra of detrital zircon

The western region of the Chinese Loess Plateau (CLP) on the western side of the Liupan Mountains connects the Tibetan Plateau with the deserts of the northern arid zones. This region is key for understanding of the coupled relationship between tectonic uplift and surface processes (erosion and climate) on the Tibetan Plateau; however, the variation of Quaternary wind-dust sources in the region remains uncertain, confounding analysis. In this paper, we conduct a source tracing investigation using detrital zircon U-Pb dating of 12 loess layers from the Huining aeolian sedimentary sequence of the western CLP, reconstruct the history of provenance changes during the Quaternary Period, and further explore driving mechanisms. Results show that aeolian dust from the western CLP is mainly from the northeastern margin of the Tibetan Plateau (NTP). At 1.8–1.66 Ma, the main source region was the NTP, which corresponds to the Episode C uplift event of the Tibetan Plateau. The dominant source area transitioned to the Gobi Altay Mountains (GAMs) around 1.5–1.4 Ma. This shift suggests that the tectonic uplift of the Tibetan Plateau had entered a period of stasis following the conclusion of Episode C, leading to increased transport of detrital material from the GAMs by the East Asian Winter Monsoon. After 1.24 Ma, the dominant source region abruptly changed from the GAMs to the NTP and lasted until 0.04 Ma. The topographic fluctuations caused by the Kunhuang Movement appears to have been the main reason for the sudden source change. Based on our results and evidence from previous studies, the source changes that occurred during the Quaternary Period were in response to a combination of tectonic events and climate change. Comparison of zircon age spectra between the eastern and western CLP further support the idea that the Plateau Winter Monsoon was the main transport system for aeolian dust in the western CLP.

Effect of plant roots on the radiocarbon age of loess deposits in arid central Asia

Radiocarbon and OSL dating are the two main approaches used to date aeolian deposits in arid central Asia (ACA). Previous results showed that, compared with OSL dating, the 14C ages of loess deposits in ACA are underestimated when the loess age is beyond ∼25 ka. However, the cause of this radiocarbon age underestimation has not been adequately addressed. In this study, we measured the 14C ages of different dating materials, including pyrolysis volatile (Py-V), pyrolysis residue (Py-R), humin, and total organic carbon fractions from two loess sections in ACA (the Hoalin section in the western Pamir Mountains, and the TLD16 section in the northern Tianshan Mountains). The results show that different dating material yielded different 14C ages for all the loess samples, and all the radiocarbon ages obtained are younger than their corresponding OSL ages. Based on these results, together with a regional comparison of 78 14C ages from ACA with their corresponding OSL ages, we propose that the 14C age underestimation is mainly due to the contamination by the deep penetration of the extended root systems of the plants that grow in arid areas, whereas this effect is less significant in the summer monsoon–dominated Chinese Loess Plateau.

Aeolian activity in the Yarlung Zangbo River Basin, southern Tibetan Plateau, began at 584 ka: implications for the glaciation of the Tibetan Plateau

Aeolian activity on the Tibetan Plateau (TP) has profound effect on the Asian and global climate. In the southern TP, loess deposition widely occurred associated with the massive glaciers and large rivers, recording the interplay history among the aeolian activity, atmosphere, and cryosphere. However, the initiation age of the loess and the factor controlling the loess formation are still controversial. Here, three drilling cores were retrieved from Linzhi area, in the eastern Yarlung Zangbo River Basin of the southern TP, which reached the bedrock and documented the loess development in the southern TP. Based on the optically stimulated luminescence, electron spin resonance, paleomagnetism dating and relative paleointensity correlation, the basal age of the drilling core was constrained at 584 ka revealing the onset of significant aeolian activity on the southern TP. Synthesize this study and previous work on the loess age across the TP, three stages were identified, namely 3600, 2800–2700, and 1200–600 ka, with the age trending younger from north to south. Extensive loess development on the TP occurred between 1200 and 600 ka, which was mainly ascribed to the global cooling during the mid-Pleistocene Transition. During this time, the ampler glaciers extent significantly expanded, westerly displaced southward and the wind intensity also intensified on the TP, which resulted in the enhancement of dust generation, arid and windy condition, leading to the loess preservation and development on the TP. Moreover, numerous evidences suggested that the glaciers on the TP may significantly developed since 800 ka, then enlarged at 500–600 ka, which may lead to the massive dust/loess input to the TP, Chinese Loess Plateau and north Pacific Ocean.

Identification of climatic tipping points and transitions in Chinese loess grain-size records utilizing nonlinear time series analysis

As one of the most important terrestrial sediments, Chinese loess provides valuable information on regional and global climatic and environmental changes and holds great potential for studying on nonlinear behaviors of the East Asian monsoon system. Utilizing objective and quantitative methods to identify tipping points and climate transitions in paleoclimatic records can help us understand the climatic change in the Chinese Loess Plateau (CLP). This study explores critical tipping points and nonlinear climate transitions within the CLP using the Chiloparts record, a comprehensive 2600-ka paleoclimate dataset. We pinpointed potential tipping points using recurrence quantification analysis and the augmented Kolmogorov-Smirnov test, ultimately leading to 15 critical tipping points. We argued that these 15 tipping points represent some of the most significant climatic changes recorded in the Chinese loess paleoclimate record. Employing recurrence quantification analysis, recurrence networks, and visibility graphs, we also identified several climate transitions and provided some nonlinear information, including the Mid-Pleistocene Transition (MPT) as well as the Mid-Brunhes Transition (MBT). We particularly highlight a significant climatic regime transition around 500 ka that may reflect a nonlinear response to variations in the Atlantic Meridional Overturning Circulation (AMOC). Our research also contributes to the understanding of the complex interplay between loess deposition, environmental change, and tectonic activity, emphasizing the need for further investigations to elucidate the mechanisms driving these transitions.

The usefulness of the magnetic susceptibility of loess paleosol sequences for paleoclimate and stratigraphic studies: The case of the Quaternary Palouse loess, northwestern United States

Worldwide, Quaternary loess-paleosol sequences archive terrestrial paleoenvironmental information. The Palouse loess in the northwestern USA is one such deposit representing at least a million years of sediment accumulation. Loess paleosol sequences are often studied via the magnetic susceptibility of sediments and the changes in susceptibility with depth. However, since variations in magnetic susceptibility can have different underlying causes, the interpretation of the magnetic susceptibility of loess depends on factors specific to each major loess region. We measured the magnetic susceptibility of sediments along depth profiles in a well-studied exposure of the Palouse loess in eastern Washington, USA (the “CLY-2 site,” 46.3131° N, 118.4874° W, WGS84). Our measurements show that the magnetic susceptibility of sediments in the Palouse loess varies systematically and predictably with depth and can be correlated with other magnetic susceptibility profiles at the outcrop scale and at the regional scale. We also measured changes in grain size, elemental abundance, mineralogy, and other magnetic properties to determine the most likely cause of the magnetic susceptibility signal. Based on these results, variations in magnetic susceptibility in the Palouse are likely driven mostly by changes in coarse sediment supply and accumulation of tephra rather than changes in weathering. Magnetic susceptibility is useful as an inexpensive, non-destructive tool for stratigraphic correlation of Quaternary loess deposits in the Palouse, especially in combination with paleosol stratigraphic markers and known tephra deposits.