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The aeolian loess deposits in northeastern China have substantial potential for reconstructing the paleoclimate in the East Asian monsoon boundary zone. Identifying the source of the aeolian dust is crucial to interpret the paleo‐proxies recorded in the loess deposits in northeastern China; however, traditional geochemical tracers such as Nd and Sr isotopes cannot discriminate between the potential source areas, that is, the Otindag Sandy Land, Horqin Sandy Land, and Hulun Buir Sandy Land regions. In this study, the (234U/238U) activity ratio is used to constrain the provenance of the loess deposits in northeastern China. The (234U/238U) of the studied loess‐paleosol sequences (from 0.935 to 0.910) decreases with increasing depositional age (from 10 to ∼1,000 ka), which is consistent with predictions from uranium isotope comminution age model. A derived (234U/238U) of 0.935 ± 0.003 for the newly deposited loess (zero depositional age) is most similar to that of the Otindag Sandy Land positioned at a proximal upwind direction, suggesting that the Otindag Sandy Land is the most likely source of the aeolian dust that formed the loess deposits in northeastern China. A transportation time of 432 ± 65 ka was calculated for these deposits, indicating extensive mixing of the fine dust in the source regions, which could partially explain the relative homogeneity of loess deposits in northeastern China. The transportation time longer than several glacial‐interglacial cycles suggests that reconstructions of regional paleoclimate on orbital timescales should be viewed with caution because the potential influence of climatic changes could largely be buffered. Plain Language Summary: The activity ratio of the uranium isotopes (234U and 238U) in fine‐grained particles can be used to determine the "comminution age", or the amount of time since the production of fine sediment particles (≤50 μm) from the breakdown of bedrock by weathering. The (234U/238U) activity ratio provides a new approach to track the age and origin of dust particles. In this study, we measure the (234U/238U) composition of the loess deposits in northeastern China and surface sand samples in potential source areas to better understand the transport of aeolian dust in the region. We find that the Otindag Sandy Land, which is in the proximal upwind direction, is the main source region for the loess deposits in northeastern China and that the dust materials have been resided in the source region for around 432 ± 65 thousand years before aeolian transport and deposition. Our results shed light on the transport and depositional history of loess in northeastern China and provide valuable information for reconstructing paleoclimate using the loess deposits in this region. Key Points: The (234U/238U) activity ratio of a loess sequence in northeastern China is consistent with a uranium isotope comminution age modelLoess deposits found in northeastern China have a long residence time of 432 ± 65 ka in the source regionsThe Otindag Sandy Land in the proximal upwind direction is the main source region for the studied loess sequence [ABSTRACT FROM AUTHOR]

Orbital‐scale East Asian Summer Monsoon (EASM) variations inferred from loess deposits in northern China and speleothems from southern China display different dominant periods, complicating our understanding of monsoon response to insolation and ice‐volume forcings. Here we integrate a new microcodium δ18O record from a high‐resolution last interglacial loess profile with previously published data and provide a composite microcodium δ18O record on the Chinese Loess Plateau (CLP) since the last interglacial. The composite microcodium δ18O record displays distinct precessional cycles, consistent with speleothem δ18O records, but with different amplitude contrast (particularly during the peak interglacials). We propose that both loess and speleothem δ18O records exhibit covariations at precessional timescale oscillations. The discrepancy between loess and speleothem from southern China can be attributed to the influences of other processes besides summer precipitation on the proxies. A slight difference in amplitude between microcodium and speleothem δ18O records implies that the EASM is also influenced by inland surface boundary conditions, which has important impacts on the occurrence of EASM precipitation. Therefore, microcodium δ18O from the Chinese loess–paleosol sequences can be regarded as a representative proxy of EASM precipitation in northern China and then a reliable proxy reflecting the variation of EASM intensity. [ABSTRACT FROM AUTHOR]

Records of Asia Summer Monsoon (ASM) from the Chinese loess and the speleothem display distinct features. The very different proxies that were applied to the two archives may be responsible for this discrepancy. A direct comparison between the speleothem and the loess records under the same proxy system of rainwater δ 18 O may help to resolve this puzzle. Here we show that the calcified microcodium in the loess deposits may record the oxygen isotopic composition of the summer rainwater. A microcodium based δ 18 O record covering the past 140 kyrs was generated, which shows similar magnitude of the overall variation to that of the speleothem records. However, much weaker precession variability was registered in the microcodium record during the last interglacial period. Instead, the microcodium δ 18 O record is more consistent with the widely used summer monsoon proxy of magnetic susceptibility in the loess deposits with clear glacial-interglacial pattern. This similarity may originate from the low sedimentation rate of the interglacial paleosol layer that preferentially record the peak ASM signals on the precession band. It is also possible that the orbital variability of ASM between the North China and South China is inherently different with more ice-volume related influence in the north. A longer microcodium δ 18 O record in sequences of higher sedimentation rate and a reliable record of summer rainfall may help to resolve these possibilities. [ABSTRACT FROM AUTHOR]

We analyzed the Sr/Sr ratios of basaltic rocks and basin water in Xuyi, China, and found a big difference, which may challenge conventional wisdom on the contribution of basalt weathering in end-member analysis. Results of an in-house weathering experiment suggest that rainwater and dust are not responsible for the difference. By isolating the major minerals in basalt, we found that plagioclase has much higher Sr/Sr ratios than bulk basalt and basin water, which might explain the difference in Sr/Sr ratios of basalt and basin water. We infer that low-temperature hydrothermal alteration increased the Sr/Sr ratios of plagioclase. Future analyses of end-member contribution in a mixed-rock basin should take into account that basin water and plagioclase have higher Sr/Sr ratios than basaltic rocks. [ABSTRACT FROM AUTHOR]

Here we present (U/U) data from river sediments collected on the Tibetan Plateau. The (U/U) ratios of a specific grain size fraction show good correlation with erosion rates, which were determined by in-situ-produced cosmogenic nuclides. This correlation has previously been observed in a wide range of geomorphic settings, suggesting that (U/U) ratios of fluvial sediments have great potential to quantify erosion rates. [ABSTRACT FROM AUTHOR]

Abstract: Carbonate in the eolian deposits on the Chinese Loess Plateau carries a significant amount of information on the evolution of paleo-environment. However, the paleo-proxies based on total carbonate are largely complicated by the coexistence of primary and secondary carbonate. This work provides a new method to quantify the relative proportion of primary and secondary carbonate in these eolian deposits according to the Mn/Ca and Mg/Ca ratios of bulk carbonate. The carbonate associated Mg and Mn, which can be extracted by selective dissolution using diluted weak acid, are mostly derived from primary carbonate because the secondary carbonate contains very little Mg and Mn. The amounts of Mg and Mn associated with carbonate could thus serve as proxies for the pedogenic dissolution of primary carbonate, which reflect clear glacial–interglacial changes of summer monsoon. A positive correlation between the Mn/Ca and Mg/Ca ratios of bulk carbonate has been observed, indicating binary mixing between secondary carbonate with the low Mn/Ca and Mg/Ca ratios and primary carbonate with high Mn/Ca and Mg/Ca ratios. The high Mn/Ca and Mg/Ca ratios of primary carbonate endmember also indicate Alxa arid lands as the main source of eolian deposits on Chinese Loess Plateau. The Mn/Ca and Mg/Ca ratios of carbonate could be employed as a quick method to check the purity of the secondary carbonate used for paleo-environmental studies and help to interpret the paleo-proxies based on the bulk carbonate. The results reveal significant amount of primary carbonate included in the traditionally believed pure authigenic carbonate phases such as carbonate concretion, rhizolith, and the fine grain sized carbonate. The new method also helps to appraise the control of the relative portion of primary and secondary carbonates on the stable carbon and oxygen isotopes of bulk carbonate. High Mg/Ca ratio and low Mn/Ca ratio of the carbonate in red clay formation is observed, which confirms the existence of authigenic dolomite. [Copyright &y& Elsevier]

Abstract: The magnetic properties of soil have been increasingly applied as a rapid and economic way to monitor environment pollution. Sediments from a growing islet in the lower reach of Yangtze River as well as the suspended particles in the surrounding river water were used to identify anthropogenic influence on the magnetic susceptibility (MS) of the Yangtze River sediment. Results show that newly deposited sediments in 2004 have significantly higher MS (~150×10−8 m3 kg−1) on average than that of the ancient deposit (~50×10−8 m3 kg−1). Scanning electron microscope (SEM) of the extracted magnetic particles from newly deposited sediments and fly ash samples indicates large contribution of fly ash for the samples with elevated MS. Dependence of MS on grain size is evident, which enable calculation of the MS of suspended particles from river sediment. A value of 32×10−8 m3 kg−1is inferred for the suspended particles in ancient Yangtze River. The records from 2004 to 2010 indicate progressive increase in the MS of the suspended particles in Yangtze River from 67 to 96×10−8 m3 kg−1, which is much higher than that of the ancient. Mass balance calculation based on the increasing MS suggests that at least 7% of the fly ash produced within the catchment of Yangtze River was released into the environment. [Copyright &y& Elsevier]

Abstract: We have systematically collected samples in the possible source regions (the deserts and sandy lands of North China, northeastern past of the Tibetan Plateau, Chinese Loess Plateau and southern part of Mongolia) of the East Asian dust. Based on Nd–Sr isotopic ranges, the source regions can be divided into four isotopic regions: Region A1: the Gurbantunggut Desert in Junggar basin and Hunlun Buir sandy land in northeastern China; Region A2: the Hunshandake sandy land, Horqin sandy land and southern part of Mongolia; Region B: the Taklimakan Desert in Tarim basin, northeastern past of the Tibetan Plateau, Chinese Loess Plateau, Badain Jaran Desert and Tengger Desert in Alashan Plateau; Region C: the Hobq Desert and Mu Us Desert in the Ordos Plateau. Through comparison of Nd–Sr isotopes, it can be inferred that the sediments of the north-central Pacific and dust particles in the Greenland ice cores are mainly derived from Region B. Dusts of East Asian dust storm are derived mostly from Region B also, and less from Region A2. The materials of dust storm at Beijing area in April 2006, originated largely from the Hobq Desert and Mu Us Desert in the Ordos Plateau. The floating dust at Beijing area in April 2006, is the mixing of dust of distant deserts and local dust at Beijing area. Loess of the Chinese Loess Plateau may largely originate from Region B. [Copyright &y& Elsevier]

Minerals and rocks have distinct Sr87/86Sr and 143Nd/144Nd ratios, depending on their geological origin and ages, and these isotope ratios are less altered than elemental composition during transport in the atmosphere or after deposition as sediments, thus stable isotopes of Sr and Nd have great potential as tracers for provenance and transport of materials. During the hypergene process, Sr isotope ratios of sediments are controlled by their parent rocks, particle sizes and chemical weathering. In general, the higher the Sr isotope ratios of parent rocks, and/or the more the fine-grained fractions, and/or the stronger the chemical weathering, thus the higher the Sr isotope ratios of sediments. On the contrary, there are lower Sr isotope ratios of sediments. Nd isotope ratios of sediments, independent of their particle sizes and chemical weathering, are only associated with parent rocks. For the provenance of the Chinese Loess Plateau, different reseachers drew discordant and even contradictory conclusions by using the method of Sr-Nd isotopic tracing. From the previous Nd isotope data, it is considered that the Tarim Basin, deserts in the central and west parts of Inner Mongolia and the Tibetan Plateau are the main sources of the Chinese Loess Plateau, and are also manufacturers for eolian dust of the Far East regions, together with the Chinese Loess Plateau. Sr isotope ratios of eolian dust are solely affected by wind sorting and weathering-pedogenesis due to its homogeneous composition in the Chinese Loess Plateau. Wind sorting is related to the East Asian winter monsoon but weathering-pedogenesis is mainly associated with the East Asian summer monsoon. Studies on Sr isotopic compositions of the loess-paleosol sequence suggest that 87Sr/86Sr ratios in acid-soluble materials are an index for chemical weathering intensity of the Chinese Loess Plateau, indicating the East Asian summer monsoon variations, whereas 87Sr/86Sr ratios in acid-insoluble materials are significantly controlled by particle sizes, and can be used as a proxy indicator reflecting the East Asian winter monsoon variations. Variations of 87Sr/86Sr ratios in acid-insoluble materials in the past 2.6Ma further demonstrate that the East Asian winter monsoon gradually strengthened since the beginning of the Quaternary period. This result agrees with the prior conclusion that climate gradually cooled since the onset of the Quaternary Ice Age. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) is a major component of the global climate yet, the causes for the past spatiotemporal variability of EASM rainfall, its interactions and impacts remain unresolved. Here we use the Sr–Nd isotopes and rare earth elements composition of dust in a peat record from northeast (NE) China to investigate the relationship between aeolian dust, the East Asian monsoon and Westerly Jet (WJ) over East Asia since the Late Pleistocene (14 cal ka BP). The NE drylands of China dominate the dust fraction (Hunshandake, Horqin; 44–88%) with a contribution from the deserts of NW China (Badain Jaran, Tengger, Taklamakan; 10–44%), suggesting an influence of the WJ. Dust deposition varied during the Holocene, displaying a minimum between 8.0 and 6.0 cal ka BP and two peaks at 5.8–3.8 and 1.7–0.3 cal ka BP. Changes in dust flux are opposite to the East Asian winter monsoon intensity profile, suggesting a limited influence of the winter monsoon. The EASM appears to have played a more significant role in the dust cycle, with increasing dust fluxes corresponding with lower EASM precipitation. Variations in dust flux from NE drylands display shifts reflecting changes in EASM precipitations and dune activity along the EASM margin, where the dust originates from. To account for the influence of the WJ, we propose that the meridional position and intensity of the WJ also affected dust emission in the drylands' region. A more northward position of the WJ allows the EASM front further north, generating more precipitations over the NE drylands, reducing the extent of arid areas, and resulting in less dust emission from dune activity, while the opposite occurs with a strong, more southerly WJ. Anthropogenic activities are likely to have had an increasing impact on the dust cycle over the late Holocene. Nevertheless, the presence of inconsistencies in records, coupled with a simultaneous decline in climatic conditions (mainly precipitations) during the same timeframe, hinders the precise assessment of the influence of human activities on dust emissions in the region. • Aeolian dust in Hani peatland originate mainly from the northeast drylands. • Deserts of the north margin of the Tibetan Plateau also contribute significantly. • Dust deposition follows the general pattern of the East Asian summer monsoon (EASM). • WJ path changes influence EASM dynamics and desert surface conditions in NE China. • EASM-WJ interactions control dust dynamics at the margin of the EASM system. [ABSTRACT FROM AUTHOR]

Abstract: Morphological characters and multi-element isotopic compositions of carbonates from the loess–paleosol sequences in Northwestern China are examined to explore the origin of the minerals. Samples are collected from various sections ranging from Holocene to 0.9Ma within the sequences and fractions with grain sizes >45 and <2μm are separated from the bulk soil and examined by SEM and TEM. The results show that the grains >45μm exhibit an almost perfect spherical shape while those <2μm are dominated by nano-rods having diameters of 30–50nm and lengths of 0.3–2μm, presumably indicating the detrital origin of the coarse fractions and the authigenic characters of the fine ones. Such implications are corroborated by the multi-elemental isotopic compositions of the carbonate minerals. A comparison of the δ13C and δ18O values between minerals and biologically originated samples indicates that the <2μm fractions have a similar composition to those of coexisting land snail shells. Additional differences between the two size fractions also manifest in the ratios of 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, and 87Sr/86Sr. These results suggest the utility of fine carbonate particles in the soil profile in reconstructing a potentially higher resolution δ13C and δ18O time series to elucidate the paleoclimatic fluctuation in the Chinese Loess Plateau during Pleistocene. The discovery of the nano-rod calcite in Chinese loess, together with previous findings of the similar mineral form in Asian dust, strongly suggests the possibility that these highly reactive CaCO3 form may alter the aerosol properties during transport. [Copyright &y& Elsevier]

• First report of Li isotope data in the Cryogenian clastic sedimentary strata. • Negative Li isotopic excursion in the basal Cryogenian interglacial interval. • Low Li isotope values suggested enhanced silicate weathering intensity. • Extensive seawater euxinia was triggered by intense silicate weathering. The Cryogenian Period comprised two episodes of global glaciation (Sturtian and Marinoan glaciations) separated by a non-glacial interval, which was characterized by early radiations of eukaryotic algae and putative metazoans. Geochemical data indicate that the non-glacial interval might be marked by a transient marine oxygenation, nevertheless oceanic redox conditions varied both in time and space. Further, the links between non-glacial climate and marine redox variations are not well constrained. Here we present high-resolution lithium isotope (δ 7 Li), Fe speciation and trace element (Mo and U) data for clastic sedimentary rocks from the Cryogenian interglacial Datangpo Formation, South China, in order to track the evolution of continental chemical silicate weathering and driving factors behind marine redox variability during the Cryogenian non-glacial interval. A significantly negative δ 7 Li excursion of ∼ − 5 ‰ is observed in the basal Datangpo Formation, suggesting a dramatic increase in chemical silicate weathering intensity in the aftermath of the Sturtian glaciation. Expansion and contraction of anoxic-sulfidic conditions, as demonstrated by Fe speciation and trace element (Mo and U) data, mirror changes in silicate weathering intensity. Our study provides evidence that greater nutrient and sulfate availability, due to high silicate weathering intensity associated with increased exposure of fresh rocks and a warm climate, facilitated the spread of euxinic waters over the continental margins of the otherwise ferruginous Cryogenian ocean. [ABSTRACT FROM AUTHOR]

Quantifying microplastic accumulation in aquatic organisms is important for risk assessments in natural habitats. However, studies on the factors influencing microplastic accumulation by fish, particularly in natural water bodies, remain limited. In this study, we monitored the microplastic pollution characteristics in the fish digestive tract and surface water of the Nandu River, the largest river in Hainan, China. Among the 179 fish examined, microplastics were detected in 90.5 %, covering 27 fish species. Moreover, low abundance of microplastics occurred among the different fish, with an average of 3.20 ± 2.60 particles per fish. Fibrous microplastics with a large size (>500 μm) were dominant in both the water column and fish. In this study, fish size, feeding habits, and living habitats did not affect microplastic abundance in fish. Based on the analysis of differences in the abundance and morphological characteristics of microplastics in water column and fish, we suggested that the random intake and differential excretion of microplastics with different characteristics by fish might lead to the homogeneity of microplastic accumulation in different fish. Our study suggest that more attention should be given to the negative effects of microplastics on small fish owing to the higher microplastic exposure per gram weight, and further improvement in microplastic risk assessment methods is required., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Fly ash-the residuum of coal burning-contains a considerable amount of fossilized particulate organic carbon (FOC ash ) that remains after high-temperature combustion. Fly ash leaks into natural environments and participates in the contemporary carbon cycle, but its reactivity and flux remained poorly understood. We characterized FOC ash in the Chang Jiang (Yangtze River) basin, China, and quantified the riverine FOC ash fluxes. Using Raman spectral analysis, ramped pyrolysis oxidation, and chemical oxidation, we found that FOC ash is highly recalcitrant and unreactive, whereas shale-derived FOC (FOC rock ) was much more labile and easily oxidized. By combining mass balance calculations and other estimates of fly ash input to rivers, we estimated that the flux of FOC ash carried by the Chang Jiang was 0.21 to 0.42 Mt C⋅y -1 in 2007 to 2008-an amount equivalent to 37 to 72% of the total riverine FOC export. We attributed such high flux to the combination of increasing coal combustion that enhances FOC ash production and the massive construction of dams in the basin that reduces the flux of FOC rock eroded from upstream mountainous areas. Using global ash data, a first-order estimate suggests that FOC ash makes up to 16% of the present-day global riverine FOC flux to the oceans. This reflects a substantial impact of anthropogenic activities on the fluxes and burial of fossil organic carbon that has been made less reactive than the rocks from which it was derived., Competing Interests: The authors declare no competing interest.