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This article explores the role of fossil organic carbon (FOC) weathering in global biogeochemical cycles. FOC is a unique type of organic carbon that has accumulated and fossilized in the Earth's lithosphere over time. Recent studies have shown that FOC is easily reacted, mobilized, and transformed under surface conditions, releasing CO2 and impacting global biogeochemical cycles. However, there are challenges in understanding FOC weathering, including limited data for calibrating its kinetics and the influence of factors like rock types, tectonic activities, geomorphic processes, and climate. The article suggests that future research should focus on studying FOC weathering in different environments and developing proxies to reconstruct past weathering. It also emphasizes the importance of understanding the connection between FOC weathering and the biogeochemical cycles of other nutrient elements. [Extracted from the article]

It is generally accepted that the glacial‐interglacial variations of the East Asian winter monsoon (EAWM) are controlled by the volume of the Northern Hemisphere ice sheets (NHIS), but the fact that they exhibit different evolution patterns during glacial inceptions is often overlooked. By generating an independent chronology framework and integrating multi‐proxy records from the loess sections on the central Chinese Loess Plateau, here we show that the rapid intensifying of the EAWM during glacial inceptions reflects millennial perturbations in the large‐scale atmospheric circulation in East Asia in response to insolation‐triggered abrupt North Atlantic cooling. This climate teleconnection between North Atlantic and East Asia is found to be particularly effective only when the NHIS reaches a critical large size. Our integrated multi‐proxy records thus highlight the key role of ice volume in modulating the response of the EAWM to insolation‐triggered North Atlantic cooling during the interglacial‐glacial transitions. Plain Language Summary: The strength of the East Asian winter monsoon is thought to be dynamically linked to the volume of the Northern Hemisphere ice sheets during the Quaternary glacial‐interglacial cycles. Nevertheless, paleoclimatic records generally indicate a rapid shift in the East Asian winter monsoon intensity in the mid‐way of the gradual build‐up of the Northern Hemisphere ice sheets, meaning that our current understanding of the East Asian winter monsoon dynamics remains elusive. By generating an independent chronology framework and integrating multi‐proxy records from the loess sections on the central Chinese Loess Plateau, here we show that the rapid intensifying of the East Asian winter monsoon during glacial inceptions, previously demonstrated as a direct response to the build‐up of the Northern Hemisphere ice sheets, actually reflects millennial perturbations in the large‐scale atmospheric circulation in East Asia caused by insolation‐triggered abrupt North Atlantic cooling when Northern Hemisphere ice sheets reach a critically large size. Our results thus offer new insights into how the climate teleconnections between high‐ and middle‐latitudes of the Northern Hemisphere have controlled the East Asian winter monsoon during glacial inceptions. Key Points: Microcodium 87Sr/86Sr record captures the cooling trend in East Asia at the interglacial‐glacial transitionsDecoupled evolution of East Asian winter monsoon and temperature occurred during glacial inceptionsIce volume modulates the response of East Asian winter monsoon to insolation‐triggered North Atlantic cooling during glacial inceptions [ABSTRACT FROM AUTHOR]

Earth's climate system has experienced substantial millennial‐scale oscillations characterized by abrupt changes superimposed on orbital‐scale changes. However, the dynamic connection between millennial and orbital timescales remains elusive. Here, we provide a summer monsoon precipitation δ18O record spanning from ∼8 to ∼60.5 ka based on the oxygen isotopic composition of microcodium from loess deposits on the Chinese Loess Plateau. This record shows distinct precessional variations (23 ka) punctuated by prominent millennial‐scale oscillations. It is generally consistent with speleothem δ18O and other loess‐based records, reflecting the East Asian summer monsoon changes. More importantly, our result also shows that large increases in the magnitude of millennial‐scale variability correspond to the Northern Hemisphere summer insolation minimum. We propose that precession‐induced low‐latitude summer insolation modulates the amplitudes of millennial‐scale summer monsoon variability by changing the mean monsoon state during the last glaciation. Plain Language Summary: Understanding the dynamic connections between different timescales is crucial to predicting future climate variability. Here, we provide a summer monsoon precipitation δ18O record based on the oxygen isotopic composition of microcodium from loess deposits on the Chinese Loess Plateau, showing that large increases in the magnitude of millennial‐scale variability correspond to Northern Hemisphere summer insolation minimum. We propose that low‐latitude summer insolation modulates the amplitudes of millennial monsoon variability during the last glaciation. Our work provides clues for deciphering the dynamic connections between orbital and millennial timescales. Key Points: A summer precipitation δ18O record on the Chinese Loess Plateau during the last glaciation was reconstructed based on microcodium δ18OThe record shows distinct precessional variations punctuated by millennial‐scale oscillations, consistent with other monsoon recordsThe magnitude of millennial‐scale East Asian summer monsoon variability was found to be modulated by low‐latitude insolation during the last glaciation [ABSTRACT FROM AUTHOR]

Silicate weathering, which is of great importance in regulating the global carbon cycle, has been found to be affected by complicated factors, including climate, tectonics and vegetation. However, the exact transfer function between these factors and the silicate weathering rate is still unclear, leading to large model–data discrepancies in the CO 2 consumption associated with silicate weathering. Here we propose a simple parameterization for the influence of vegetation cover on erosion rate to improve the model–data comparison based on a state-of-the-art silicate weathering model. We found out that the current weathering model tends to overestimate the silicate weathering fluxes in the tropical region, which can hardly be explained by either the uncertainties in climate and geomorphological conditions or the optimization of model parameters. We show that such an overestimation of the tropical weathering rate can be rectified significantly by parameterizing the shielding effect of vegetation cover on soil erosion using the leaf area index (LAI), the high values of which are coincident with the distribution of leached soils. We propose that the heavy vegetation in the tropical region likely slows down the erosion rate, much more so than thought before, by reducing extreme streamflow in response to precipitation. The silicate weathering model thus revised gives a smaller global weathering flux which is arguably more consistent with the observed value and the recently reconstructed global outgassing, both of which are subject to uncertainties. The model is also easily applicable to the deep-time Earth to investigate the influence of land plants on the global biogeochemical cycle. [ABSTRACT FROM AUTHOR]

It has been suggested that dust generation was closely linked to the development of global ice sheets and/or cooling. This feature has allowed Asian dust to be a potential chronostratigraphic tool in North Pacific Ocean (NPO) sediments. The orbital-scale age control in NPO sediments is usually established by adjusting the benthic-foraminiferal δ18O to the global δ18O stack (LR04). However, it would become difficult if the sediments did not contain enough foraminifera. This study investigates Sr and Nd isotopes, trace elements, mineralogy and grain size of the 'operationally defined aeolian dust' (ODED) extracted from the sediments recovered at Ocean Drilling Program (ODP) site 1209B on the Shatsky Rise in the NPO covering the past five glacial–interglacial cycles. The geochemical results show that the ODED at site 1209B is actually a mixture of Asian dust and volcanic ash. The variation of Nd isotope mimics the cycles of glacial–interglacial ice sheets as revealed by the global benthic foraminifera's oxygen isotope stack (LR04) over the past 500 ka. The low (high) ϵNd values corresponded with the cool (warm) periods. We propose that ϵNd variation reflects the evolving aeolian dust in site 1209 sediments. The excellent agreement between ϵNd values at site 1209B and LR04 stack over the past 500 ka allows establishing the orbital-timescale age control by tuning ϵNd to the LR04 curve. We thus propose that Nd isotope provides a chronostratigraphic technique in NPO sediments, especially for sediments with a limited amount of foraminifera. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • miR-1284 is downregulated in CC tissues and cell lines. • Upregulation of miR-1284 suppressed CC progression and enhanced chemosensitivity of CC cells. • HMGB1 is a tumor promoter in cervical cancer. • HMGB1 is negatively regulated by miR-1284. • HMGB1 can reverse the effects of miR-1284 on the progression and chemosensitivity of CC cells. Abstract Background Chemotherapy is one of the commonest therapeutic method for cervical cancer. There are some common chemotherapy drugs, such as cisplatin, docetaxel, paclitaxel and selenium nanoparticle. microRNAs (miRNAs) have been verified to be regulators in various human cancers. This study aims to investigate the effects of miR-1284 on the cisplatin sensitivity of cervical cancer cells. Methods The levels of miR-1284 in different tissues and cell lines were detected through using qRT-PCR analysis. Kaplan Meier analysis was utilized to analyze the influence of miR-1284 expression on the overall survival rate of cervical cancer patients. The biological effects of miR-1284 on the progression and chemosensitivity of cervical cancer were tested through conducting functional assays. Mechanism investigations were used to prove the binding relation between miR-1284 and HMGB1. Rescue assays were applied to demonstrate the effects of miR-1284-HMGB1 axis on chemosensitivity of cervical cancer cells. Results miR-1284 was down-expressed in cervical cancer tissues and cell lines. Patients with low level of miR-1284 had low overall survival rate. Upregulation of miR-1284 suppressed proliferation and invasion, while promoted apoptosis. Moreover, upregulated miR-1284 enhanced sensitivity of cervical cancer cells to cisplatin. HMGB1 was a target gene of miR-1284. HMGB1 reversed the effects of miR-1284 on the progression and chemosensitivity of cervical cancer cells. Conclusion miR-1284 enhances sensitivity of cervical cancer cells to cisplatin via targeting HMGB1. [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]

The homeostatic balance of Earth's long-term carbon cycle and the equable state of Earth's climate are maintained by negative feedbacks between the levels of atmospheric CO 2 and the chemical weathering rate of silicate rocks. Though clearly demonstrated by well-controlled laboratory dissolution experiments, the temperature dependence of silicate weathering rates, hypothesized to play a central role in these weathering feedbacks, has been difficult to quantify clearly in natural settings at landscape scale. By compiling data from basaltic catchments worldwide and considering only inactive volcanic fields (IVFs), here we show that the rate of CO 2 consumption associated with the weathering of basaltic rocks is strongly correlated with mean annual temperature (MAT) as predicted by chemical kinetics. Relations between temperature and CO 2 consumption rate for active volcanic fields (AVFs) are complicated by other factors such as eruption age, hydrothermal activity, and hydrological complexities. On the basis of this updated data compilation we are not able to distinguish whether or not there is a significant runoff control on basalt weathering rates. Nonetheless, the simple temperature control as observed in this global dataset implies that basalt weathering could be an effective mechanism for Earth to modulate long-term carbon cycle perturbations. [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]

Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits (the Xiashu loess) in the lower reaches of the Yangtze River. Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau (CLP) have been proposed. Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique. This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess. The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior. Instead, the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River, indicating the dominance of proximal dust source. Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China, possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate. [ABSTRACT FROM AUTHOR]

Abstract: Trace element compositions of microcodium are applied for the first time as possible paleo-proxies based on a case study on the Chinese Loess Plateau (CLP). The Mg/Ca and Sr/Ca ratios of the microcodium picked from the Holocene paleosol across the CLP show distinct positive correlation over large range of nearly one order of magnitude. Higher Mg/Ca and Sr/Ca ratios of microcodium are recorded in the sites on the northwestern CLP where less monsoonal rainfall is received. Similar large variation of the positively correlated Mg/Ca and Sr/Ca ratios has also been observed for the stream water on the CLP with the same spatial pattern. The Mg/Ca and Sr/Ca ratios of the microcodium seem to be largely controlled by the composition of soil solution as reflected by stream water rather than partition coefficient. Rayleigh distillation, and thus evolving composition of soil solution as a result of progressive precipitation of secondary calcite, is responsible for the large variation and positive correlation of the Mg/Ca and Sr/Ca ratios for both the microcodium and stream water. We propose that the bio-remains in Chinese loess may become inactive when the soil water is extracted to a degree, and then be calcified into microcodium by the infiltration of freshwater that is mixed with the highly evolved soil solutes. Thus, the Mg/Ca and Sr/Ca ratios of microcodium may record the paleo-precipitation amount by reflecting the mixing ratio between the highly evolved soil solutes with higher Mg/Ca and Sr/Ca ratios and the fresh soil water with lower Mg/Ca and Sr/Ca ratios. [Copyright &y& Elsevier]

Abstract: The age distribution of detrital zircon has been used to trace sediment sources. Existing datasets show great similarity of zircon ages between the loess on the Chinese Loess Plateau (CLP) and the sediments from the North Tibetan Plateau (NTP), implying that eolian dust is delivered from the NTP to the CLP by westerly winds or via the Yellow River. However, NTP dust can also be transported by northwesterly winds from the Alxa arid lands (AALs), where materials are received from both the NTP and the Gobi Altay Mountains (GAMs). Here we report U–Pb zircon ages for AALs sands and NTP and CLP loess. The results show that the zircons in the AALs are mixed from NTP and GAMs zircons. NTP loess is mainly derived from local sources. Mixing of materials from the NTP and GAMs defines the zircon ages of the loess on the CLP better than the pure NTP source. No temporal and spatial heterogeneities of zircon ages have been observed for the loess on the CLP, which suggests that the well-mixed materials in the AALs likely have an eolian source. [Copyright &y& Elsevier]

• Oxygen isotope alteration rate of continental crust retrieved from zircon record. • Oxygen isotope alteration rate of continental crust is controlled by weathering. • Weathering history is linked to major evolution events of the Earth system. Weathering plays a significant role in the Earth system through the exchange of material among the lithosphere, atmosphere, hydrosphere, and biosphere. Variation of continental weathering in deep-time, however, remains elusive. This work investigates continental weathering recorded by detrital zircon. Zircon can record the oxygen isotopic composition (δ 18 O) of its parent crust at the time of crystallization, the value of which principally reflects the time-integrated effect of crustal alteration. The Hf isotopes and U-Pb isotopes of zircon also help to constrain the alteration history between crust generation and zircon crystallization. A new algorithm is introduced to reconstruct the average δ 18 O alteration rate of continental crust (R δ 18O-CC) through time by solving a set of linear equations based on a large population of detrital zircons with varying temporal coverage across the history of crustal alteration. A nearly three-billion-year history of R δ 18O-CC from 3.2 Ga to 0.3 Ga can be reconstructed using more than 5,000 globally distributed detrital zircons with coupled U-Pb-Hf-O isotopic records. The reconstructed R δ 18O-CC shows an overall bell-shape long-term evolution centered at ∼2 Ga superposed with variations that are coupled with supercontinental assembly cycles. The long-term evolution of the reconstructed R δ 18O-CC seems to be correlated with solid-earth CO 2 degassing expected from the age distribution of deleted mantle and the supercontinental cycles. Thus, the R δ 18O-CC is interpreted to reflect weathering considering the control of solid-earth CO 2 degassing on the total weathering flux of continental crust. However, independent evidence on the solid-earth CO 2 degassing is unavailable, interpreting R δ 18O-CC as a weathering record requires further testing. Nevertheless, this work provides an example of how the time-integrated signal, with large noise-to-signal ratio, preserved in geological archives can be deconvolved using a large dataset. The result also demonstrates the great potential that weathering history may have in reconstructing the operation of the Earth system across deep-time. [ABSTRACT FROM AUTHOR]

Abstract: The thick deposits of eolian dust on the Chinese Loess Plateau provide a rare opportunity to explore the past changes of surface processes in response to climatic and tectonic oscillations. Here we report a 22Ma-long Nd and Sr isotopic records of the eolian sources. Decreasing ε Nd values and increasing 86Sr/87Sr ratios of the eolian deposits has been observed from early Miocene to about 7Ma, which indicates growing material contribution from Qilian Mountains relative to the Gobi Altay Mountains. The source shift during 22–7Ma is interpreted to reflect the erosional response of the Qilian Mountains to its surface uplift. Between 7Ma and 1.2Ma, the results show relative constant Nd and Sr isotopic compositions of the eolian deposits, and thus suggest a constant source contribution between Qilian Mountains and Gobi Altay Mountains. Synchronized uplift of the two mountain ranges during this period may explain the constant ratio of source contribution. Since 1.2Ma, Nd and Sr isotopic records indicate that the relative debris input from Qilian Mountains drops rapidly. As large-scale topographic changes would not be expected in such a short time period, the source shift since 1.2Ma might be by the differing erosional responses in Qilian Mountains and Gobi Altay Mountains to the development of full glacial climate after the middle Pleistocene transition. This work shows that combined Nd and Sr isotopic signatures of the dust records are valuable proxies to monitoring past surface processes on the million years time scale. [Copyright &y& Elsevier]

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: It is generally accepted that progressive cooling of global climate since the Late Cretaceous results from decreasing partial pressure of atmospheric CO2 (pCO2). However, details on how and why the carbon cycle evolved and how it would affect pCO2 have not been fully resolved. While the long-term decline of pCO2 might be caused by the decrease of volcanic degassing through the negative feedback between pCO2 and silicate weathering, seafloor spreading, the major control of CO2 degassing, seems to have remained relatively constant. Alternative explanation, known as ‘uplift driven climate change’ hypothesis, proposes that tectonic uplift may have enhanced the sink of atmospheric CO2 by silicate weathering, and thus produced the decline of pCO2. However, increasing weathering sink of CO2 could deplete atmosphere all of its CO2 within several million years while holding volcanic outgassing constant. In this work, major fluxes of long-term carbon cycle are calculated based on a reverse model constrained by marine C, Sr and Os isotopic records and the spreading rate of sea floor. Weathering of island basalt and continental silicate rocks are separated in the new model. The results indicate a long-term decline of island basalt weathering in consistent with the global cooling trend over the past 100 million years. Dramatic changes of the CO2 fluxes associated continental silicate weathering, reverse weathering, volcanic degassing and the growth of organic carbon reservoir have been observed. Disturbance of atmospheric CO2 cycle by these fluxes seems to be maintained by the concomitant adjustments of island basalt weathering that were sensitive to the pCO2 controlled environment factors such as temperature and runoff. The negative feedbacks between pCO2 and weathering of island basalt might have played a significant role in stabilizing the long-term carbon cycle. [Copyright &y& Elsevier]

The precise determination of Cd isotope ratios via multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has made the widespread application of Cd isotopes possible. However, previous studies are complicated by the chemical purification method and molecular interferences from Zn (e.g.70Zn36Ar+, 68Zn38Ar+, and 66Zn40Ar+ on 106Cd+, 70Zn38Ar+ and 68Zn40Ar+ on 108Cd+, 70Zn40Ar+ on 110Cd+). Separation of Zn from Cd requires the usage of a toxic reagent (HBr) and is also complicated by the relatively high procedural Zn blank especially when only a very small amount of Cd is available. Here we present a high-precision Cd isotope measurement method using double spike MC-ICP-MS, which avoids the molecular interferences from Zn introduced by both sample and chemical purification. A 111Cd–113Cd double spike pair optimized for the 111Cd, 112Cd, 113Cd, and 114Cd inversion was used to correct for the mass bias. Elemental doping experiments suggest that the measured Cd isotope data were not significantly affected when the measured solution has, Zn/Cd < 103, Pd/Cd < 102, Fe/Cd < 10−2, In/Cd < 10−3, Sn/Cd < 10−1, Zr/Cd < 10−2, Nb/Cd < 10−1, Mo/Cd < 10−2, Ru/Cd < 10−2, Ga/Cd < 10−2, Ge/Cd < 10−2, Se/Cd < 10−1, and As/Cd < 10−1. We thus modified the chemical purification method by removing the HBr step and eluting Zn and Cd together. The minimum requirement of sample size for precise measurement of stable Cd isotope ratios was tested to be as low as 10 ng. The measurements of pure Cd solutions (BAM I012 Cd and HPS Cd) give a long-term intermediate precision for δ114/110Cd relative to NIST SRM 3108 of 0.05‰. We further validated our method by measuring different reference materials covering a relatively wide range of Zn/Cd (∼9 to 1239), the results of which agree within uncertainty with previous studies. Our study thus provides an efficient and precise way to determine stable Cd isotope ratios of geological samples with relatively low Cd concentrations. [ABSTRACT FROM AUTHOR]

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]

The North China and the neighbouring Mongolia in Asian Interior is characterized by extremely dry climate, resulted in one of the world's major dust emission centres. Deciphering the source region of Asian dust is critical for revealing the mechanism of the dust production, interpreting the paleo-environmental records of eolian deposits, predicting the overall environmental effects of dust, and setting the strategies for the control of contemporary dust storms. This paper summarizes the geochemical methods applied to the source tracing of Asian dust. Nd-Sr isotopes were the most extensively studied source tracer of Asian dust and have been successfully applied in many cases. Geochemistry of detrital monomineral shows great theoretical advantages in source tracing and deserves further studies. The short-range transportation of Chinese loess with direction similar to that of the prevailing near surface wind is revealed. Source tracing also shows that the Asian dust has two ultimate material sources from the northern margin of the Tibetan Plateau and the Central Asian Orogen, which confirms the importance of mountain processes in the production of silt eolian particles. Based on the recent progresses on the source tracing of Asian dust, discussions are expanded on the natural background of Asian dust storms and potential anthropogenic influence, the materials evolution of the source regions of Asian dust and its relationships with climate changes and Tibetan uplift, and the role of Tibetan uplift in the Asian dust system. [ABSTRACT FROM AUTHOR]

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]

Abstract: Eolian deposits of loess on the Chinese Loess Plateau are investigated to decipher the influence of sequentially changed monsoon climate on silicate weathering process. Detailed hydrochloric acid dissolution experiments are applied to establish a sensitive proxy for silicate weathering. Combined elemental and mineralogical studies show that the minerals which are susceptible to incipient chemical weathering can be totally dissolved in hot hydrochloric acid (80°C, 3mol/L) after 4h, while other stable minerals are nearly unaffected. Thus, the hydrochloric acid dissolvable fractions (ADF) of loess and paleosol are more sensitive than bulk samples in the weathering reaction. Since Mg is tend to be leached out from the ADF while Al is conserved during the incongruent weathering, Mg/Al ratio of the ADF (Mg/AlADF) could indicate the weathering intensities of the Mg-bearing minerals, mainly chlorite. The Mg/AlADF of the modern soils on the Chinese Loess Plateau is closely correlated to the local precipitation amounts, suggests that the intensity of summer monsoon is a key factor in the weathering of Mg-silicate. The silicate weathering intensity of the loess-paleosol deposits of past 130Kyrs shows strong procession cycle of ∼ 23Kyrs coupled by glacial-interglacial variation. The ∼ 23Krys cycles are coherent to the variations of the intensity of summer monsoon, while the ∼ 100Kyrs glacial-interglacial variation may relates to the changes in winter monsoon. Phased intensification of East Asian summer monsoon, and thus enhanced silicate weathering and atmosphere CO2 drawdown, in response to the uplift of Tibetan Plateau, may be another mechanism relating the late Cenozoic tectonics to global cooling. [Copyright &y& Elsevier]

Abstract: Silicate Nd–Sr isotopes of the fine-grained fractions of the 10 major deserts and sandy lands in North China and the loess in Chinese Loess Plateau were systematically investigated. Wide ranges in Nd–Sr isotopic compositions have been observed. The results of the <75μm silicate fractions show that the Nd–Sr isotopic compositions of each desert are quite homogeneous and unique. According to the geographic distribution of the deserts and their Nd–Sr isotopes of both the <75 and <5μm silicate fractions, three isotopic regions of Chinese deserts can be identified: (A) the deserts on the northern boundary of China, with the highest ε Nd(0)>−7.0; (B) the deserts on the northern margin of Tibetan Plateau, with ε Nd(0) ranging from −11.9 to −7.4; and (C) the deserts on the Ordos Plateau, with the lowest ε Nd(0)<−11.5. The distribution of the threes isotopic regions is controlled by the tectonic setting in North China, which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the Nd–Sr isotopic signatures of these deserts could be quit stable over the past million years on the sub-tectonic time scales if there is any desert at those times. The Nd–Sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region B, suggesting that the main source regions of the last glacial loess in the Chinese Loess Plateau are Badain Jaran Desert, Tengger Desert, and Qaidam Desert. Also, the comparison between the Nd–Sr isotopes of the <5μm silicate fractions of the deserts and the ancient dust falls in the North Pacific and Greenland show that the Asian end members of these dust falls are derived most from the deserts in the isotopic region B and less from those in the isotopic region C. [Copyright &y& Elsevier]

Abstract: Oxygen isotopic compositions of rhizoconcretions and land snail shells were measured to reconstruct the δ 18O profiles of paleorainwater (δ 18Op) for well-dated loess-paleosols in Luochuan, China. To assess the paleoclimatic significance of δ 18Op, factors that control the spatial and temporal δ 18O variations of rainwater in East Asian monsoon regions were investigated. Modern records indicate that the spatial δ 18O variations of modern rainwater (δ 18Om) are closely related to near surface temperature (T) and the amount of precipitation (P). In order to separate the effects of T and P on the δ 18Om, a linear relationship between δ 18Om, T and the natural logarithm of P is established by multiple regressing analyses: The δ 18O of paleorainwater over the past 130 Ka in Luochuan area is calculated by the modern-spatial δ 18O–T–P relationship using estimated T and P from other paleoclimate records. The calculated δ 18O match well to those reconstructed from the authigenic carbonates, which implies that the spatial and temporal δ 18O variations of rainwater in East Asian monsoon regions have similar δ 18O–T–P relationships and the authigenic carbonates in Chinese loess-paleosol sequences can serve as valid records of δ 18Op. As an application of the δ 18O–T–P relationship, P variation in the past 130 ka in Luochuan was evaluated. The reconstructed P is in good agreement with other studies using different approaches. Our results suggest higher precipitation in Marine Isotope Stages 1, 3 and 5, reflecting intense summer monsoon influences during these periods of time. [Copyright &y& Elsevier]

Abstract: The knowledge of how and why marine 87Sr/86Sr ratios changed helps understand the impacts of many processes on the global biogeochemical cycle in the geological past. Here we examine the possible influence of global cooling on the evolution of marine 87Sr/86Sr curve by a kinetic approach. The importance of mica weathering is emphasized due to its high content of radiogenic strontium and low activation energy in weathering reaction. Since the activation energy determines the sensitivity of weathering rate in response to temperature changes, global cooling will increase the 87Sr/86Sr ratio of continental flux by relatively preferential weathering of mica. Based on the average strontium contents and 87Sr/86Sr ratios of the mica minerals in the exposed upper continental crust, a kinetic model is established to survey the response of riverine 87Sr/86Sr to the changes of global temperatures. The model result indicates that the increase of riverine 87Sr/86Sr caused by global cooling can solely account for most of the increase in seawater 87Sr/86Sr since 3.4 Myr B.P. This finding emphasizes that the weathering kinetics is an important mechanism relating the global climate change to marine 87Sr/86Sr curve; and the marine 87Sr/86Sr curve should be used with great care in the climate-weathering-tectonic connections. [Copyright &y& Elsevier]

Length‐weight relationships (LRWs) were determined for three fish species from the Hainan Island, China. Fish specimens were sampled across the Nandu River and Changhua River from May 2017 to June 2018 with benthic fyke‐nets (stretched mesh size: 0.4 cm), multi‐mesh gillnets (stretched mesh size ranging from 1.0 to 12.5 cm) and electrofishing. Relationships between length and weight were fitted very well for all species (all R2>0.95). The b values of the LRW equations ranging from 2.938 for Liniparhomaloptera qiongzhongensis to 3.259 for Toxabramis houdemeri. [ABSTRACT FROM AUTHOR]

Existing feature models used in thermal infrared (TIR) tracking struggle to get strong discriminative features of TIR objects, because TIR image has few details and low contrast. This characteristic makes the existing TIR tracking methods easy to drift to similar distractors. To tackle this problem, we introduce a novel diverse fine-grained feature network for TIR tracking. Our proposed method emphasizes extracting fine-grained features from multiple local regions of the target to improve its ability to discriminate against distractors. Specifically, our feature model consists of a specific-designed fine-grained feature network architecture and an auxiliary diversity loss function. Firstly, the fine-grained feature network explores the subtle clues of the infrared target through a mask suppression mechanism. This mechanism can force the network to learn subtle cues of the target. Secondly, to guarantee the learned fine-grained features are various, we propose a diversity loss to force all fine-grained features to be unique. These two modules help the feature model learn diverse fine-grained features from two complementary aspects. To verify the effectiveness of the two modules, we evaluate them on four benchmarks. The relevant experimental results prove that our proposed method achieves the best performance compared to the state-of-the-art methods. • Infrared fine-grained features can improve the performance of target tracking. • The network can extract infrared fine-grained features without labels. • The proposed DFG loss can improve the diversity of fine-grained features. • Infrared targets require strong features because of the lack of details. [ABSTRACT FROM AUTHOR]

Asian dust delivers highly reactive iron (FeHR) to the Pacific Ocean, affecting marine biogeochemical cycles and Earth's climate. Tracing the source of dust deposited in the Pacific is vital for assessing global nutrient cycles but poses challenges. This work applies the (234U/238U) activity ratio to determine the pre‐deposition time and provenance of dust in North Pacific Ocean sediments (Ocean Drilling Program site 1209B). Results indicate a consistent dust pre‐deposition time (134 ± 10 ka) over the past 300,000 years, except during Marine Isotope Stage 7 when volcanic ash input shortened it to 31 ± 19 ka. Comparing the dust pre‐deposition times to those of the potential source deserts, we identify the dust transported to the North Pacific Ocean was primarily from the Taklamakan Desert, which contains higher FeHR content than other deserts. This finding enhances our understanding of soluble Fe supplied to the oceans, especially in dust circulation models. Plain Language Summary: Unraveling the provenance of aeolian dust deposited in the oceans is critical for understanding marine biogeochemical cycles, past climate changes, and dust transport mechanisms. Here we measured the (234U/238U) activity ratio of marine sediments in the North Pacific Ocean to understand the source and pre‐deposition time of dust deposited in the Pacific. The source of dust in the Pacific has remained debated because of the non‐unique geochemical signatures of possible source regions and the complexity introduced by the volcanic ash. The (234U/238U) of the dust fraction in marine sediments informs the source‐to‐sink transport time for dust particles, providing a new source tracer. We compared the (234U/238U)‐derived pre‐deposition time, Nd isotopes, grain size, magnetic susceptibility and aeolian dust flux of the North Pacific marine sediments to those of potential dust source regions, and identify the Taklamakan Desert as a major source delivering dust to the North Pacific. Our work highlights the (234U/238U) and associated particle pre‐deposition time as a promising tool for tracing sources of dust in marine sediments, holding profound implications for our understanding of global dust‐nutrient cycles. Key Points: Uranium isotope‐based pre‐deposition time serves as a novel tool to trace the provenance of Asian dust transported to the North Pacific OceanDust pre‐deposition time at site 1209B remains relativity stable (134 ± 10 ka), but decreases during MIS 7 due to volcanic ash inputTaklimakan Desert is the major source of dust delivered to the North Pacific Ocean, supplying dust with highly reactive iron [ABSTRACT FROM AUTHOR]

There has been a growing interest in using cadmium (Cd) isotopes to trace the source of Cd contamination and Cd cycling in the Earth surface. Yet it remains technically challenging to precisely and efficiently determine the Cd isotopic compositions of samples with extremely low Cd concentrations due to the imperfect separation of Cd from the matrix and the interference caused by resin-derived organics when TRU Spec resin was used. In this study, we present a two-stage column chromatography system (AG-MP-1M resin + UTEVA resin) for Cd purification. Here, a Prefilter resin combined with UTEVA resin effectively purifies Cd from Sn after the separation of Cd by AG-MP-1M column while keeping the phosphorous organic compounds to an acceptable level. In contrast to TRU Spec resin, which is prone to leaking through the Prefilter resin, we find that UTEVA resin is effectively retained by the Prefilter resin, thus avoiding the P-related anomalous shifts in the Cd isotope measurement (P/Cd < 1). UTEVA resin also exhibits a comparable capacity for purifying Cd from Sn and Mo when compared to TRU Spec resin. The recovery of the two-stage column system is generally higher than 99% and the procedural blank accounting for sample digestion and chemical purification is lower than 20 pg. The Cd isotopic compositions of several reference materials are determined using double spike MC-ICP-MS, with a 111Cd–113Cd double spike pair optimized for the 111Cd, 112Cd, 113Cd, and 114Cd inversion. The δ114/110Cd values of these reference materials relative to NIST SRM 3108 agree within analytical uncertainty with previous studies. The long-term external precision of δ114/110Cd determined based on replicated measurements of BCR-2 is 0.04‰ (n = 10, 2 SD) for a minimum sample size of 10 ng. Our study thus provides an efficient two-stage column system for determining the Cd isotopic compositions of geological samples with relatively low Cd concentrations. [ABSTRACT FROM AUTHOR]

The rare earth elements (REEs) in loess sediments may preserve key information of paleoenvironmental changes in East Asia but remain poorly explored. Here we present the REE compositions of sequentially leached phases of loess sediments from a 16 m long loess-paleosol sequence collected from Weinan at the southern margin of the Chinese Loess Plateau (CLP). The REEs associated with carbonates, easily reducible oxides, reducible oxides, clay minerals, and the residual silicate minerals were sequentially leached with Na-acetate, hydroxylamine-HCl, Na-dithionite/Na-citrate, 12 mol L−1 HCl and concentrated HF-HNO 3 solutions. The results show that the REE concentrations of different phases vary in the loess-paleosol layers and are most enriched in the easily reducible phase (except for the residual phase), which is likely explained by the association of REEs with Mn-oxides. Significant Eu anomalies can only be found in the carbonate and easily reducible phases, with the carbonate phase being characterized by appreciable positive Eu anomalies and the easily reducible phase being characterized by negative Eu anomalies, indicating the incorporation of Eu2+ into secondary carbonates that leaves the authigenic Mn-oxides with depleted Eu relative to other REEs. The carbonate phase shows significant negative Ce anomalies, which is likely due to the preferential removal of Ce4+ by Mn oxides before the formation of secondary carbonates. Nevertheless, appreciable positive Ce anomalies for the easily reducible phase can only be found at the bottom of the paleosol S1 while significant negative Ce anomalies were found within the paleosol S1, indicating the downward leaching of Ce4+ that shows stronger complexation with the organic matters than REE3+ in the soil solution. This may partly account for the negative Ce anomalies previously found in the paleosols. Overall, our results suggest a two-stage evolution of Eu and Ce anomalies of the carbonate phase, with the first stage controlled by the formation of both Mn-oxides and secondary carbonates and the second stage dominated by the precipitation of secondary carbonates. The comparison of carbonate Eu and Ce anomalies with other paleoclimatic proxies indicates that the combination of Eu and Ce anomalies of the carbonate fraction of loess may be applied as novel proxy records of climate change in East Asia. [ABSTRACT FROM AUTHOR]

Over the last decade, there has been a growing interest in using lithium (Li) isotopes in marine carbonates to trace chemical weathering and clay formation in the Earth's history. Yet it remains technically challenging to precisely and efficiently determine the Li isotope composition in carbonate samples due to the imperfect Li separation led by the matrix effect and the extremely low Li concentration in carbonates relative to the analytical threshold of sample size. For such high matrix and low-Li samples, here we present an efficient dual-column chromatography system for Li purification. The dual-column system has a large loading capacity, fixed Li elution range of merely 12 mL, complete Li recovery (>99.5%) and relatively efficient total elution time (7 hours). The procedural blank is 0.036 ± 0.002 ng accounting for sample dissolution and chemical purification, and the Na/Li mass ratio of the Li cut is below 0.5. High precision and accurate Li isotope measurement is performed efficiently with a small sample-sized protocol developed on a MC-ICP-MS (Neptune plus) connected with an APEX 2-IR desolvator. The whole procedure is validated by analyzing a series of certified reference materials. The long-term external precision of δ7Li determined based on L-SVEC and a high-purity Li solution is 0.6‰ (2SD) and 0.9‰ (2SD) for a minimum sample size of 7.5 ng. [ABSTRACT FROM AUTHOR]

• We find a trend of decreasing 87Sr/86Sr with groundwater age in a sandstone aquifer. • We consider Sr from silicates in HAc leachate of rocks to obtain 87Sr/86Sr of calcite. • Sr isotopes reveal that groundwater has higher degree of weathering than most rivers. • Low 87Sr/86Sr of old groundwater reveals deep aquifers can be important carbon sinks. • The ratio of silicate to calcite weathering decreases with content of dissolved CO 2. Sr isotopes have been widely used to quantify silicate versus carbonate weathering reflected in rivers, but there is no such study in groundwater, which is restricted by the difficulty of accurately determining the Sr contents and isotopic ratios of the two endmembers in silicate-dominated aquifers. In a sandstone catchment, we find rainwater, modern groundwater in the recharge area, and old groundwater in the discharge area have contrast 87Sr/86Sr ratios, with mean values of 0.710784, 0.711448, and 0.710269, respectively. If we follow previous studies and use the acetic acid leachate of sandstone to represent the calcite fraction, the resulting 87Sr/86Sr ratio cannot explain most groundwater samples. By considering the simultaneous dissolution of calcite and silicates in the acetic acid leachate, we find the typical 87Sr/86Sr ratio of calcite equals 0.709113, which well explains the 87Sr/86Sr ratios of all groundwater samples. The 87Sr/86Sr ratios of groundwater in the recharge area with abundant dissolved CO 2 are contributed by three endmembers (rainwater, silicate and calcite), whereas those of old groundwater in the discharge area with low dissolved CO 2 as well as low Cl− and SO 4 2− can be explained by two endmembers (calcite and groundwater in the recharge area). Based on strontium isotopic budget, we find the equivalent concentrations of CO 2 consumption by silicates and calcite in groundwater are both larger than those in river waters studied in previous studies, and the majority of dissolved CO 2 in groundwater can be fixed by carbonate weathering as long as the residence time is long enough. This study enhances understanding of the roles of silicate and carbonate weathering during long-time groundwater circulation. [ABSTRACT FROM AUTHOR]

The flux of dust deposition to the ocean and its impact on marine biological productivity are outstanding issues of the Earth's climate system. The North Pacific gyre (NPG) is the Earth's largest ecosystem and is important for marine nitrogen fixation, which is sensitive to Asian dust-regulated surface nutrient stoichiometry. Meanwhile, it is one of the least studied regions in the global ocean during the late Pleistocene, because of the extremely slow sediment accumulation and lack of biological material preservation. 232Th and 230Th concentrations recorded by hydrogenetic ferromanganese crusts in the deep NPG provide a novel and quantitative proxy of dust deposition and export productivity in this region. For this purpose, we have established an in situ U – Th isotope analytical technique on hydrogenetic ferromanganese crusts collected from the deep NPG. Iron, Mn, and Co of our samples have also been analyzed to constrain the impact of dust dissolution on the Fe geochemical cycle. Remarkably, variability of the 232Th-based dust flux over the last ∼900 ky exhibits a striking resemblance to grain-size records of the Chinese loess deposits and sea-level reconstructions but clearly decouples from the global temperature evolution. On orbital time scales, dust storms over the NPG are apparently sensitive to effects related to continental ice sheet sizes but decoupled from major global cooling during the early glaciation. While our 232Th data indicate a 2- to 3-fold variability of glacial – interglacial dust flux, scavenging of Fe, Mn, and Co in the deep NPG is much less variable through the late Pleistocene. We suggest that variable dust fluxes have a limited impact on the inventory of dissolved Fe in the deep waters of NPG, even though the scavenging of Fe has likely been regulated by glacial – interglacial paleoceanography. The paired 230Th-scavenging-based biological productivity tracks gyre sea surface temperature rather than dust flux during the last glacial cycle. We observe no correlation between dust flux and export productivity in the NPG, indicating that dust-derived Fe is not the productivity-limiting factor on orbital time scales in this region. Instead, these results imply that changes in gyre mixing and mode water formation might have led to increased supply of phosphorous and thus enhanced glacial biological carbon sequestration, with potentially stronger nitrogen fixation under higher eolian input. [ABSTRACT FROM AUTHOR]

The Mg/Ca ratio of seawater increased from ∼1.5 to its present value of 5.4 over the Neogene, indicating a fundamental imbalance in the Mg–Ca cycle during the late Cenozoic. The imbalance in Mg–Ca cycles since the late Cenozoic, however, is contrasted by an arguable constancy in the Mg isotope compositions of seawater (δ 26 Mg sw) reconstructed from several low-resolution carbonate records. Addressing such Cenozoic Seawater Conundrum requires reliable seawater Mg isotopic records. The Xisha Islands in the South China Sea host large Cenozoic dolostone sequences that record seawater chemistry over the past 23 Myr. This study reports the Mg isotopic and trace elemental compositions of island dolostones in the well-studied Xike-1 drill core from the Xisha Islands. Petrographic, C–O–Sr isotopic, and paleomagnetic data from the drill core samples collectively support a "fluid-buffered", syn-depositional origin for the dolostones. The dolostones from the Xike-1 core have a narrow range of δ 26 Mg (− 2.83 ‰ ± 0.12 ‰), confirming that δ 26 Mg sw have been stable around the modern value (−0.83‰) since the late Cenozoic. This record provides a new opportunity to better understand the Mg–Ca cycle during the late Cenozoic. We ran numerical models of global seawater Mg–Ca contents and δ 26 Mg sw with the most recently published flux and isotope fractionation data. The results show that the contrast between the constancy of δ 26 Mg sw values and the dramatic increase in seawater Mg/Ca ratios cannot be explained by a single mechanism (i.e., a decrease in the rate of phyllosilicate formation on the seafloor alone). Instead, processes involving different Mg fluxes need to be coupled to explain the observed trends in Mg content and isotopic compositions of Cenozoic seawater. The solution to the Cenozoic Seawater Conundrum includes simultaneous decreases in the rates of both clay formation and dolomitization on the seafloor, or an increase in the rate of both continental weathering together with decreased seafloor clay formation. Our study underlines the sensitivity of the Mg cycle to the interactions between climate, continental weathering, and seafloor processes during the late Cenozoic. • Seawater δ 26 Mg sw values can be reconstructed from tropical island dolostones. • Record of Xisha Island dolostones shows a stable δ 26 Mg sw for the past 23 million years. • A sharp contrast between stable δ 26 Mg and rising Mg/Ca of seawater in the late Cenozoic. • Changes in dolomitization intensity canceled the Mg isotope effect of changes in clay formation intensity. [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]

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]

Radiogenic uranium isotope disequilibrium (234U/238U) has been used to trace a variety of Earth surface processes, and is usually attributed to direct recoil of 234Th and preferential dissolution of radioactively damaged lattices at the mineral surface. However, the relative contribution of these two mechanisms in the natural environment remains unresolved, making it hard to use the extent of disequilibrium to quantify processes such as weathering. This study tests the contribution of preferential dissolution using well-characterized weathered moraines and river sediments from the southeastern Tibetan Plateau. The observations show that weathering of recent moraines where the contribution from direct recoil is negligible and is not associated with depletion of 234U at the mineral surface. It suggests a limited role for preferential dissolution in this setting. We attribute this lack of preferential dissolution to a near-to-equilibrium dissolution at the weathering interfaces, with little development of etch pits associated with radioactively damaged energetic sites. [ABSTRACT FROM AUTHOR]

The observed stability of Earth's climate over millions of years is thought to depend on the rate of carbon dioxide (CO2) release from the solid Earth being balanced by the rate of CO2 consumption by silicate weathering. During the Cenozoic era, spanning approximately the past 66 million years, the concurrent increases in the marine isotopic ratios of strontium, osmium and lithium suggest that extensive uplift of mountain ranges may have stimulated CO2 consumption by silicate weathering, but reconstructions of sea-floor spreading do not indicate a corresponding increase in CO2 inputs from volcanic degassing. The resulting imbalance would have depleted the atmosphere of all CO2 within a few million years. As a result, reconciling Cenozoic isotopic records with the need for mass balance in the long-term carbon cycle has been a major and unresolved challenge in geochemistry and Earth history. Here we show that enhanced sulphide oxidation coupled to carbonate dissolution can provide a transient source of CO2 to Earth's atmosphere that is relevant over geological timescales. Like drawdown by means of silicate weathering, this source is probably enhanced by tectonic uplift, and so may have contributed to the relative stability of the partial pressure of atmospheric CO2 during the Cenozoic. A variety of other hypotheses have been put forward to explain the 'Cenozoic isotope-weathering paradox', and the evolution of the carbon cycle probably depended on multiple processes. However, an important role for sulphide oxidation coupled to carbonate dissolution is consistent with records of radiogenic isotopes, atmospheric CO2 partial pressure and the evolution of the Cenozoic sulphur cycle, and could be accounted for by geologically reasonable changes in the global dioxygen cycle, suggesting that this CO2 source should be considered a potentially important but as yet generally unrecognized component of the long-term carbon cycle. [ABSTRACT FROM AUTHOR]

Projecting future changes in effective precipitation under global warming, which requires constraints on both the precipitation and evapotranspiration, is still challenging in the semi‐arid region of East Asia. Here we present proxies, based on Sr/Ca and 87Sr/86Sr of soil carbonate, to reconstruct the evolution of both effective precipitation and temperature from a high‐resolution loess profile in the East Asian monsoon marginal area covering the last interglacial period as a geological analog for future conditions. We find that intervals with a stronger summer monsoon are characterized by lower effective precipitation during Marine Isotope Stage (MIS) 5 due to a larger increase in evapotranspiration than in monsoonal precipitation in response to higher temperature. The greater response of the effective precipitation to temperature than summer monsoon intensity during MIS 5 thus suggests the risk of further aridification in the semi‐arid region of East Asia under climate warming. Plain Language Summary: The potential shortage of water resources in the semi‐arid regions of East Asia under climate warming may pose serious social issues in this highly‐populated area. Projecting changes in water resources in this region requires knowledge of how both monsoonal precipitation and evapotranspiration would respond to a warming climate. Here we present records of effective precipitation and temperature from the East Asian monsoon margins during Marine Isotope Stage (MIS) 5 when a similar degree of warming to future projections has been documented globally. The results show that warm intervals during MIS 5 were characterized by strong summer monsoon conditions but low effective precipitation, indicating greater response of evapotranspiration than monsoonal precipitation to climate warming. Our results thus suggest the possibility of water shortages in the future semi‐arid region of East Asia. Key Points: Microcodium Sr/Ca ratio is a proxy for effective precipitation while microcodium 87Sr/86Sr is sensitive to local temperatureEvolution of both effective precipitation and temperature during Marine Isotope Stage (MIS) 5 has been reconstructedEffective precipitation in the East Asian monsoon margins is controlled by both temperature and monsoonal precipitation amount during MIS 5 [ABSTRACT FROM AUTHOR]

Earthquakes play a fundamental role in the evolution of Earth's topography through co-seismic uplift and subsidence, as well as erosion through widespread landslides induced by ground motion. Earthquake-induced landslides can result in exceptional increases in the transfer of mass from landscapes, supplying sediment to rivers where impacts can last for decades or longer. Landslides can also erode vegetation and soils, in addition to exposing freshly ground rock mass, which can both result in regionally significant carbon transfers. Recent work has sought to quantify the fluxes, rates, and temporal patterns of the impacts on earth surface processes generated by these tectonic events. In this review, we focus on the impacts of earthquake-induced landslides on erosion and sediment flux, river water chemistry, and carbon export through the lens of the well-studied 2008 Wenchuan earthquake. We then discuss these themes in the context of works from the 1999 Taiwan Chi-Chi earthquake, 2015 Nepalese Gorkha earthquake, and New Zealand historical earthquakes, altogether highlighting an important role of earthquake-induced landslides in erosion and weathering along tectonically active mountain ranges. We suggest that more monitoring, geochemical tracing, paleo-records, and/or modelling studies are needed to compare the processes and fluxes of catchment erosion and weathering before and after earthquake events, which will help to deepen our understanding not only of the impacts of earthquake-induced landslides on earth surface processes, but also the linkage among high magnitude events, continental erosion and weathering, and the long-term global carbon cycle. [ABSTRACT FROM AUTHOR]

• U-Sr-Be isotopes are used to quantify the impacts of landslides on weathering and erosion. • Landslides contribute 33.1% ± 16.2% (1SE) to the riverine solutes in the Wenchuan area. • Landslides contribute 43.4% ± 20.8% (1SE) to the riverbed sediment in the Wenchuan area. • Catchments with different levels of landslide propensity show distinct uranium isotopes. In active mountains, landslides are the primary agent of erosion that readily generates materials with high weatherability. Understanding the linkage between landslide activity, erosion, and chemical weathering is critical for assessing how tectonic uplift affects the carbon cycle and Earth's climate. However, quantifying the contribution to chemical weathering and erosion fluxes from landslides remains challenging because of the lack of effective tracers related to landslide activities. Recent studies suggest that a suite of isotopic tracers, including the U, Sr and Be isotopes, have the potential to trace solutes and materials associated with landslide activities. Here we use three isotope ratios (234U/238U, 10Be/9Be, 87Sr/86Sr) to quantify the contribution to solid and solute fluxes from landslides in the tectonic-active eastern Tibetan mountains. We focus on 22 small catchments (drainage area < 50 km2) draining the epicentral region of the 2008 Wenchuan earthquake using samples collected in 2018 and 2019. Landslide seepage water and landslide sediment samples are used to constrain the landslide-weathering end-member. Tree branch and regolith topsoil samples are used to characterize the weathering end-member of regolith. We show that the U-Be-Sr isotopes can trace the solutes and solids sourced from landslide debris and quantify that landslides contribute 33.1 ± 16.2% (1SE) to the riverine solutes and 43.4 ± 20.8% (1SE) to the riverbed silt-sized sediment. These proportions are lower than the landslide-derived proportions in high-order catchments immediately (1 to 4 years) after the Wenchuan earthquake, which may relate to changes in landslide-material inputs across drainage networks and/or weathering processes over time. We also find that across 87 catchments with variable basin areas (from <1 km2 to ∼20,000 km2) draining the broad eastern Tibetan mountains, the 234U/238U activity ratio of river water and silt-sized riverbed sediment shows distinct characteristics for the catchments grouped by mean slope angles (mean slope angles shallower versus steeper than a common threshold angle of 32°). These findings suggest that U isotopes are a promising tracer of landslide-sourced solutes and materials. Overall, our work provides a case study showing that a multi-isotope approach can be used to quantify the impacts of landslides on erosion and weathering, providing new insights into how tectonic activities could affect the carbon cycle. [ABSTRACT FROM AUTHOR]

Basalt weathering is one of many relevant processes balancing the global carbon cycle via land–ocean alkalinity fluxes. The CO2 consumption by weathering can be calculated using alkalinity and is often scaled with runoff and/or temperature. Here, it is tested if the surface age distribution of a volcanic system derived by geological maps is a useful proxy for changes in alkalinity production with time. A linear relationship between temperature normalized alkalinity fluxes and the Holocene area fraction of a volcanic field was identified using information from 33 basalt volcanic fields, with an r2=0.93. This relationship is interpreted as an aging function and suggests that fluxes from Holocene areas are ∼10 times higher than those from old inactive volcanic fields. However, the cause for the decrease with time is probably a combination of effects, including a decrease in alkalinity production from material in the shallow critical zone as well as a decline in hydrothermal activity and magmatic CO2 contribution. The addition of fresh reactive material on top of the critical zone has an effect in young active volcanic settings which should be accounted for, too. A comparison with global models suggests that global alkalinity fluxes considering Holocene basalt areas are ∼60 % higher than the average from these models imply. The contribution of Holocene areas to the global basalt alkalinity fluxes is today however only ∼5 %, because identified, mapped Holocene basalt areas cover only ∼1 % of the existing basalt areas. The large trap basalt proportion on the global basalt areas today reduces the relevance of the aging effect. However, the aging effect might be a relevant process during periods of globally intensive volcanic activity, which remains to be tested. [ABSTRACT FROM AUTHOR]

Abstract The ratio between the activity of dissolved 234U and 238U in river water, (234U/238U) Riv , shows promise for tracing weathering processes. It has been suggested that preferential 234U release generates a high (234U/238U) Riv under low weathering intensity while congruent weathering, as expected for high weathering intensity, would release uranium with a secular equilibrium (234U/238U) Riv of 1. However, weathering intensity depends on the combination of exposure age of weathering interfaces and dissolution rate, complicating the use of (234U/238U) Riv as a tool in weathering studies. This work attempts to resolve the weathering dynamics reflected by (234U/238U) Riv using catchment scale denudation rate (D) as a first order approximation for the age of weathering interfaces. A global dataset (n = 653), including 132 new measurements from Chinese catchments, indicates changing responses of (234U/238U) Riv to D. Higher values (>1.5) and larger variability of (234U/238U) Riv are observed in catchments both with high (>3 mm/yr) and low D (<0.1 mm/yr). In contrast, the lowest values (approaching secular equilibrium) and the least variable (234U/238U) Riv are associated with catchments of medium to high D (0.3–2 mm/yr). The observed pattern can be explained by a model that involves competing uranium release from active- and inactive-weathering interfaces in response to a shifting weathering regime, from kinetically-limited to supply-limited. (234U/238U) Riv decreases with decreasing D under a kinetically-limited weathering regime due to the increasing contribution of congruent weathering relative to the preferential dissolution of 234U from radioactively damaged sites as D decreases. In contrast, (234U/238U) Riv increases with decreasing D under a supply-limited weathering regime because the minerals that remain under these conditions continue to release 234U to solution by recoil, while contributing little to the dissolved 238U because of their slow dissolution rate. A much deeper depth of the weathering interface is suggested for catchments with high D due to higher weathering contribution from deep fractures relative to the poorly developed surface regolith. A young age of ∼10 kyrs is constrained by the model for complete dissolution of exposed weathering-active minerals, which implies a rapid shifting from kinetically-limited to supply-limited weathering regime and limited influence of weathering on the calculation of comminution age based on (234U/238U) in sediments. A site-specific dissolution rate that is consistent with those estimated from weathering profiles is also constrained, which suggests that the discrepancy between field and laboratory weathering rate may largely be controlled by the difference in chemical affinity associated with stagnant micro-pores, low permeability, and high rock/fluid ratios rather than the passivation of weathering interfaces. Highlights • We observed changing responses of riverine dissolved (234U/238U) value to changes in catchment denudation rates. • The observation reflects shifting weathering limitation regimes. • We proposed a model that captures most variability of the riverine (234U/238U). • Site-specific dissolution rates ∼3 orders of magnitude lower than laboratorial experiments are constrained. [ABSTRACT FROM AUTHOR]

The U 234 / 238 U ratio of fine particles can record the time since their separation from bed rock because of the disruption of uranium series equilibrium introduced by the recoil of daughter 234 Th nuclei (precursor of 234 U) out of particle surfaces during the decay of 238 U. Application of the uranium comminution age method, which has great potential in tracing production and transportation of sediments is however complicated by the weathering dissolution of U 234 depleted particle surfaces, the difficulty in determining the fraction of recoiled nuclei, and the precipitation of exogenetic U 234 . Here we minimize these complications by using a newly developed precise size separation using electroformed sieve, and a chemical protocol that involves reductive and oxidative leaching. Eolian deposits collected from the Chinese Loess Plateau (CLP) were used to test the validity of our method. Possible effects of weathering dissolution were also evaluated by comparing samples with different weathering intensities. The results show decreasing 234 U/ 238 U ratios in fine eolian particles with increasing sedimentation age, agreeing well with the theoretical prediction of the comminution age model. This successful application of the uranium comminution age approach to the eolian deposits on the CLP is also aided by a stable dust source, the low weathering intensity, the lack of consolidation, and the well-defined age model of the deposits. A transportation time of 242 ± 18 ka was calculated for the eolian deposits, which indicates a long residence time, and thus extensive mixing, of the dust particles in source regions, partly explaining the stable and homogeneous composition of the eolian dust over glacial–interglacial cycles. [ABSTRACT FROM AUTHOR]

Records from natural archives show that the strength of the East Asian summer monsoon (EASM) strongly depends on the orbital configuration of the Earth. However, the dominant orbital cycles driving EASM have been found to be spatially different. Speleothem stable oxygen isotopic records from southern China, which are believed to reflect large-scale changes in the Asian monsoon system, are dominated by climatic precession cycles. Further north, on the Chinese Loess Plateau (CLP), loess-and-paleosol sequences, which are argued to be controlled by monsoon intensity, are in pace with global ice volume changes dominated by obliquity, and after the mid-Pleistocene transition by 100-kyr cycles. To understand these critical discrepancies, here we apply a novel proxy based on the trace metal compositions of pedogenic carbonate in the eolian deposits on the CLP to reconstruct summer precipitation over the last 1.5 million years. Our reconstructions show that summer precipitation on the CLP is dominantly forced by obliquity not in pace with the ice-volume-imprinted loess-paleosol sequences before and after the mid-Pleistocene transition or with the precession-paced speleothem oxygen isotopic records. Coupled with climate model results, we suggest that the obliquity-driven variations of summer precipitation may originate from the gradient of boreal insolation that modulates the thermal contrast between the Asian continent and surrounding oceans. [ABSTRACT FROM AUTHOR]

The skeletons of aragonitic corals carry essential information about oceanic environmental changes in the past. However, coral-based geochemical proxies are sensitive to vital effect and post-depositional diagenetic processes, which have not been well understood for deep-sea corals. In this study, we have investigated the mineralization and early diagenetic process of the dendroid stem of a dead deep-sea scleractinian coral sample (Madrepora oculata) collected by Remote Operated Vehicle (ROV) from a seamount in the Caroline Ridge, western Pacific. Despite being only ~270 years old, as dated by the U-series disequilibrium method, this sample already has extensive diagenesis including a visible chalky layer. The outermost chalky layer and the adjacent pristine skeleton of the sample were characterized by multiple mineralogical (SEM, XRD, EBSD, Raman Spectroscopy) and geochemical (ICP-OES, LA-ICP-MS, IR-MS, MC-ICP-MS) techniques. Skeletal stable C and O isotopes display strong linearity, with a trend pointing toward the theoretical isotopic composition of inorganically-precipitated aragonite from local seawater. This observation suggests that the epithecal mineralization of M. oculata is far from equilibrium with seawater and can be quantitatively explained by bio-mineralization models developed for solitary scleractinian corals. We further show that chalking of the outer layer, a common feature in sub-fossilized deep-sea corals, is caused by microbial-driven boring and μm-scale dissolution voids at an average rate of 3.5 μmol/cm2/y (scaled to the skeleton surface) without notable secondary infillings or mineralogical alternations. The higher average δ13C and δ18O of the chalky part than the pristine part might be due to the preferential dissolution of carbonate relatively depleted in 13C and 18O during alteration, and/or reduced isotope fractionation from seawater during coral mineralization of the outer layer. The chalky layer shows significantly higher Mn/Ca and Th/Ca ratios than the pristine part, characterized by Th/Mn ratios similar to that of the dissolved component of local seawater. Our study suggests that the incorporation of external Th into the coral skeleton is most likely associated with organic binding rather than detrital contamination, secondary carbonate mineral formation, adsorption onto surfaces of chalky aragonite or ferromanganese oxides, with important implications for coral U-series geochronology. [ABSTRACT FROM AUTHOR]

Deciphering the sources of eolian dust on the Chinese Loess Plateau (CLP) is fundamental to reconstruct paleo-wind patterns and paleo-environmental changes. Existing datasets show contradictory source evolutions of eolian dust on the CLP, both on orbital and tectonic timescales. Here, the silicate Sr and Nd isotopic compositions of a restricted grain size fraction (28-45 μm) were measured to trace the source evolution of the CLP since ~2.7 Ma. Our results revealed an unchanged source on orbital timescales but a gradual source shift from the Qilian Mountains to the Gobi Altay Mountains during the past 2.7 Ma. Both tectonic uplift and climate change may have played important roles for this shift. The later uplift of the Gobi Altay Mountains relative to the Qilian Mountains since 5 ± 3 Ma might be responsible for the increasing contribution of Gobi materials to the source deserts in Alxa arid lands. Enhanced winter monsoon may also facilitate transportation of Gobi materials from the Alxa arid lands to the CLP. The shifting source of Asian dust was also reflected in north Pacific sediments. The finding of this shifting source calls for caution when interpreting the long-term climate changes based on the source-sensitive proxies of the eolian deposits. [ABSTRACT FROM AUTHOR]

Abstract: We use new and published data representing a 20 million long record to discuss the systematics of interpreting planktic foraminiferal B/Ca ratios. B/Ca-based reconstructions of seawater carbonate chemistry and atmospheric pCO2 assume that the incorporation of boron into foraminiferal tests can be empirically described by an apparent partition coefficient, (). It has also been proposed that there is a species-specific relationship between KD and temperature (). As we discuss, although these relationships may be robust, there remain significant uncertainties over the controls on boron incorporation into foraminifera. It is difficult to be certain that the empirically defined correlation between temperature and KD is not simply a result of covariance of temperature and other hydrographic variables in the ocean, including carbonate system parameters. There is also some evidence that KD may be affected by solution ratios (i.e., pH), or by . In addition, the theoretical basis for the definition of KD and for a temperature control on KD is of debate. We also discuss the sensitivity of pCO2 reconstructions to different KD –temperature calibrations and seawater B/Ca. If a KD –temperature calibration is estimated using ice core pCO2 values between 0 and 200ka, B/Ca ratios can be used to reasonably approximate atmospheric pCO2 between 200 and 800ka; however, the absolute values of pCO2 calculated are sensitive to the choice of KD –temperature relationship. For older time periods, the absolute values of pCO2 are also dependent on the evolution of seawater B concentrations. However, we find that over the last 20Ma, reconstructed changes in declining pCO2 across the Mid-Pleistocene Transition, Pliocene glacial intensification, and the Middle Miocene Climate Transition are supported by the B/Ca record even if a constant coretop KD is used, or different KD –temperature calibrations and models of seawater B evolution are applied to the data. The inferred influence of temperature on KD from coretop data therefore cannot itself explain the structure of a published pCO2 reconstruction (). We conclude the raw B/Ca data supports a coupling between pCO2 and climate over the past 20Ma. Finally, we explore possible implications of B/Ca-based pCO2 estimates for the interpretation of other marine pCO2 proxies. [Copyright &y& Elsevier]