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As the largest river in Shanxi Province, the Fen River is the main water source for regional economic and ecological development. Water deficiency and industrialization have led to serious water pollution in the Fen River. The major and trace elements of seasonal river waters were measured to determine the spatiotemporal variations and assess the water quality as well as its controlling factors in the Fen River. Trace elements are divided into high abundance elements (B, Ba, Li, and Mn) and low abundance elements (As, Cu, Fe, Ni, Rb, Se, U, and V). The spatial variation of trace elements is obvious, with low values upstream, intermediate values downstream, and very high values midstream. The average values of the trace elements showed different seasonal variations, with high values of As, B, Ba, Mn, and Rb in the wet season, high Cu, V, and Li values in the dry season, and minor seasonal variations of Fe, Ni, Se, and U concentrations. Principal component analysis (PCA) and correlation analysis (CA) showed natural origins of Ba, Mn, Ni, and U, anthropogenic input of As, B, Cu, Li, Rb, Se, and V. According to the results of absolute principal component sore-multivariate linear regression (APCS-MLR), the major pollution sources in the Fen River basin were related to human activities. The land use type significantly influenced the concentrations of trace elements, with high values in the cropland and low values in the forest. The water quality index (WQI) values were higher in the midstream and wet season. In comparison with other rivers in the world, the pollution of the Fen River is at a moderate level. Health risk assessment showed that As, Ba, Mn, Ni, V, and Se were the potential pollutants damaging in the Fen River, especially for children. This study highlights the importance of seasonal sample analysis and can provide vital data for water quality conservation in the Fen River basin.

Barium (Ba) isotopes have been used to trace water mass mixing and export productivity in the oceans. However, the sources, isotopic signature and seasonal variation of dissolved Ba in large rivers remain poorly constrained. In order to improve our understanding of sources and fractionation of riverine Ba isotopes at the continental scale, weekly sampling of river water was carried out in the middle Yellow River over the full hydrological year of 2013. Dissolved Ba was mainly sourced from silicate dissolution, whose flux was correlated with physical erosion rate in this arid to semi-arid basin, largely covered by loess. More than half of the annual dissolved Ba flux was transported during the monsoon season (June to mid-September), in particular during a storm event period (accounting for 4% of the annual dissolved Ba flux in 4 days). The dissolved Ba isotopic composition (δ138Barw) ranged from +0.17‰ to +0.46‰, all higher than δ138Ba of loess (0.00 ± 0.04‰). The seasonal variation in δ138Barw is best explained via an adsorption model of light Ba isotopes onto solids in the river, which is sensitive to erosion of loess, in particular during the storm event and the spring-time ice melting intervals, with a potential role of barite precipitation in groundwater during the dry seasons. With one to three orders of magnitude higher particulate matter fluxes during the monsoon seasons in rivers such as the Yellow River, desorption of Ba could result an unaccounted strong variation of Ba concentration and isotopic composition in coastal environments, which further study requires.

Originally described from a sample collected in the Pamir Mountains at the end of the nineteenth century, Cyclotella lacunarum Hustedt is a centric diatom species that is not-well defined and seldom reported in the scientific literature. Our investigations revealed that the type locality of this taxon, now referred to as Lindavia lacunarum (Hustedt) Nakov et al., is actually in western China and not in Tajikistan, as wrongly assumed previously. Light microscope (LM) and scanning electron microscope (SEM) observations of the type material and of modern material collected at the type locality allowed us to emend the description of this species. Its most remarkable character is that it possesses central fultoportulae with only two satellite pores instead of three as generally reported for similar species of Lindavia. Lindavia lacunarum was then compared to two similar populations of Lindavia collected from high elevation lakes in Tajikistan and Nepal. These two populations were originally identified as Cyclotella/Lindavia lacunarum and represent the only reported occurrences of this taxon outside its type locality. The population from Tajikistan differs from L. lacunarum by having cells of smaller size, with an almost flat valve face and has been described as a new variety Lindavia lacunarum var. karakulensis var. nov. The Nepalese population is more clearly differentiated from L. lacunarum by having a different type of colliculate pattern in the central area and significantly lower density of central fultoportulae and is therefore described as a new species, Lindavia nepalensis sp. nov.

Antarctic ice core records show that climate change and atmospheric CO2 concentration (aCO2) are closely related over the past 800 thousand years. However, the interpretation of their sequential, and hence the causal relationship has long been controversial. In this study, we revisit this long-standing scientific issue based on 88 well-dated high-resolution climate proxy records derived from ice cores, marine deposits, and stalagmites. We composite global and hemispheric stacks of the last deglacial climate index (DCI) using a normalization scheme instead of a more conventional area-weighting and mixing scheme to enable a better detection of temporal variations. Rampfit and Breakfit techniques are employed to detect the trend transitions in each composited DCI series and in the recently constructed centennial-scale aCO2 over the period from 22 to 9 thousand years before present. We detect a clear lead of DCI change over aCO2 variation on both global and hemispheric scales at the early stage of the deglaciation, suggesting that the variation of aCO2 is an internal feedback in Earth's climate system rather than an initial trigger of the last deglacial warming. During the periods of the Bolling-Allerod and the Younger Dryas, the climate system appeared to have been constrained by a fast coupling mechanism between climate change and aCO2 with no obvious asynchrony. The northern and southern hemispheric DCI stacks exhibit a seesawing pattern that can be linked to the influences of Atlantic meridional overturning circulation (AMOC) strength, revealing an important role of AMOC in regulating the global climate in the course of the last deglaciation.

The multiple collector inductively coupled plasma mass spectrometer (MC-ICP-MS) is booming to be a high-precision, fast, and accurate instrument in measuring lithium (Li) isotopes. Modified highly sensitive Jet sample and X skimmer cones have largely upgraded analytical sensitivity and reduced sample consumption with distinct instrumental mass bias behaviors. Herein, four available combinations of the sample and skimmer cones [Jet sample cone + X skimmer cone (Jet + X), Standard sample cone + X skimmer cone (Standard + X), Standard sample cone + H skimmer cone (Standard + H), and Jet sample cone + H skimmer cone (Jet + H)] were tested for their effects on peak shape, sensitivity, mass bias behavior, and accuracy and precision of Li isotopic measurements in solution mode. The results showed that all four combinations were able to attain an ideal peak shape by adjusting the associated parameters, with a positively linear relation between 7Li (and 6Li) signals and Li concentrations. For a given Li concentration, the sensitivities were enhanced 3–7 times using the Standard + X, the Jet + H, and the Jet +X combinations compared to that of using the Standard + H. The enhanced sensitivity is attributable to more plasma ions introduced into the mass spectrometer through the Jet and X cones. Mass bias is distinct for different cone combinations, with a slight difference with various Li concentrations, indicating the neccesity of concentration match during measurement. Among the four cone combinations, the best reproducibility can be obtained by using the Standard + X cones to determine precise and accurate Li isotopes for samples. Furthermore, a pretreatment by 5% HNO3 and 0.1% HF, and then 2% HNO3 prior to analyses can minimize the memory effect of Li.

Sedimentary records from remote regions contain pollutants derived dominantly from atmospheric input, and thus have the potential to trace past atmospheric pollution history. Based on seventeen sediment records from relatively remote areas of China, atmospheric Pb pollution history during the last century was studied. These records suggest only occasionally slight pollution before ~1950 and display synchronous Pb enrichment processes since the 1950s, implying the start of widespread atmospheric Pb pollution in China. This corresponded well with the beginning of socio-economic development after the establishment of the People's Republic of China. However, owing to the Chinese Cultural Revolution, a roughly unchanged atmospheric Pb status was found in the 1960-70s except on the Qinghai-Tibetan Plateau, where atmospheric Pb still increased gradually caused by long-range atmospheric transport of pollutants from southwest Asia. In ~1980-2000, atmospheric Pb experienced the greatest increase, resulting from rapid development of extensive economy after the Reform and Opening-up in 1978. After ~2000, atmospheric Pb generally stopped increase due to the phasing out of leaded gasoline, but it remained high, with the highest in Southwest China, medium in Northeast China, central North China and the Qinghai-Tibetan Plateau, and the lowest in the southeast Mongolia Plateau and West China. This study reveals spatio-temporal variations of atmospheric Pb in inland China under the influence of recent human activities, providing an important supplement for understanding global Pb pollution in the Anthropocene.

The upper continental crust (UCC) is an important reservoir of Ba within the Earth. We report high precision (≤±0.05‰, 2SD) Ba isotopic data for 71 samples (including granites, granodiorites, loess, glacial diamictites, and river sediments) to constrain the Ba isotopic composition of the UCC. I-type granites from the Fogang batholith, Southeastern (SE) China, exhibit variable δ137/134Ba (−0.16‰ to 0.01‰), which may be due to isotopic fractionation during the latest stages of magmatic differentiation. The δ137/134Ba of S-type granites from Darongshan-Shiwandashan, SE China (−0.03‰ to 0.11‰) correlate with ɛNd (t), likely reflecting mixing of heterogeneous crustal source materials. Five A-type granites with high SiO2 contents (∼76 wt%) from Nankunshan, SE China have remarkably low δ137/134Ba (−0.47‰ to −0.33‰), which possibly arose from magmatic differentiation or assimilation of crustal materials with light Ba isotopic compositions. Loess from northwestern China has homogeneous δ137/134Ba (−0.02‰ to 0.03‰) that shows no correlation with bulk compositions, sample locations, or degree of chemical weathering, suggesting that loess is representative of the average Ba isotopic composition of the UCC. Three river sediments from northern China have δ137/134Ba similar to that of loess. The δ137/134Ba of glacial diamictites vary with CIA values: those with high CIA (≥60) have heterogeneous δ137/134Ba (−0.19‰ to 0.35‰), while those with low CIA ( √ n , n = 71), which is similar to the average Ba isotopic composition of the upper mantle, but significantly lower than δ137/134Ba of seawater.

The eastern margin of the Tibetan Plateau represents one of the morphologically most active regions on Earth, where the interplay of recent crustal deformation and subsequent fluvial landscape adjustment has affected the course of continental-scale rivers by river piracy events. Based solely on field observations, such an event has been hypothesised for two of the largest tributaries of the Yangtze River: the Jialing and Hanjiang Rivers. To test this hypothesis, we employ a novel combination of independent methods including a provenance study based on age distributions of detrital zircons from both modern riverbeds and river terraces and a morphometric analysis of river channels and drainage divides. We supported the morphometric analysis with a time-dependent numerical model describing the evolution of river channel long profiles and drainage divides in a succession of river capture events. Analysed zircon ages show clearly distinguishable distributions for the modern Jialing and Hanjiang Rivers, but similar distributions for the recent Hanjiang River up to its topmost terraces. This suggests that the capture of the Hanjiang headwaters by the Jialing River is unlikely to have taken place during the last 1.2 million years. However, several knickpoints in the main stem and the tributaries of the Jialing River cluster at an elevation of about 900 m and separate steeper (downstream) from less steep channel segments (upstream), which is consistent with the morphological expression of a major capture event. χ mapping indicates drainage divide asymmetry at catchment scale with on average steeper rivers on the Jialing side, whereas Gilbert metrics show a symmetric divide at hillslope scale. This numerical model explains this apparent contradiction by the travel time of capture-related knickpoints from the capture point towards the watershed, where χ mapping indicates divide asymmetry immediately after the river capture, while Gilbert metrics are only affected as soon as the knickpoints reach the channel heads and the divide effectively starts moving. Based on knickpoint travel distances and constraints on regional incision / uplift rates, we estimate the possible date of river capture to be the Pliocene. This is earlier than the formation of the terraces investigated in the provenance study but recent enough that most of the drainage divides are still unaffected and currently almost stable. Only the wind gap located in the almost dry valley connecting the two competing drainage systems is likely to have shifted towards the Hanjiang side. We suggest that this resulted in the capture of another important tributary of the Hanjiang River (the Heishui River) by the Jialing drainage system. Our results illustrate the complex evolution of drainage networks along the eastern margin of the Tibetan Plateau, and highlight the importance for combining provenance and morphometric analyses in regions of active landscape rejuvenation where river captures are likely to occur.

The sediment sequences retained by landslides and check dams on the Chinese Loess Plateau (CLP) are ideal for tracing historical catchment erosion, hydrological events and land use. This study explored a geochemical proxy to plot visible and non-visible deposition couplets in a sediment sequence from the CLP, in order to better trace soil erosion associated with historical rainstorms. An intact sediment sequence core (JB-2) was acquired in a palaeolandslide-dammed reservoir in Jingbian County, Shaanxi Province. The high-resolution elemental distribution of the entire core was generated by an Anaatech XRF Core Scanner. The water content and grain size were analysed in discrete samples of the representative core section. The Rb/Zr ratio was recommended as a high-resolution geochemical proxy for plotting the deposition couplets. Annual freeze–thaw layers among the couplets were then identified by the correlation between the Ca/Zr and Fe/Zr ratios. As a result, 41 deposition couplets and 18 annual freeze–thaw layers were identified in the JB-2 sediment sequence, indicating that 41 rainstorms occurred over 18 years during the survival of the reservoir. Furthermore, the ranges of couplet and annual specific sediment yields were 0.06–3.09 × 104 t km−2 and 0.06–3.42 × 104 t km−2 year−1 in the JB-2 reservoir, respectively. High annual specific sediment yields were the combined consequence of high annual rainfall frequency and the sediment yields associated with the rainstorm intensities. This study highlights the use of high-resolution plots of deposition couplets for providing a basis for the reconstruction of recent and contemporary soil erosion records and for determining the implication of past rainstorm intensities and frequencies on the CLP.

Evaluating the effects of soil and water conservation on the Chinese Loess Plateau (CLP) during the past 60 years depends mainly on understanding the historical processes of soil erosion fluxes and their mechanism. However, little was known about the historical variation in soil erosion and its driving factors due to the lack of few ideal geological carriers on the CLP. A representative Heshui (HS) landslide-dammed reservoir that formed 200 years ago was drilled with a 31.39 m length sediment sequence. The HS sequence was composed of 165 deposition couplets with 56 annual freeze–thaw layers based on the elemental distributions by X-ray fluorescence core scanners. Mean couplet and annual specific sediment yields (CSSY and ASSY) were 1.44 × 104 t/km2 and 1.28 × 104 t/km2/yr, respectively. The HS sequence was deposited over CE 1811–1996, which was dated by multi-methods crossing among 137Cs activities, annual freeze–thaw layers, CSSY, recent rainfall records, and historical flood index grades. Besides, the threshold value of hydrological events that generated sediments in the HS reservoir was greater than 40 mm. As a result, there were eight periods of high ASSY between CE 1811 and 1996, although the total tendency of the ASSY was decreased, especially under the management of soil and water since the 1960s on the CLP. Interannual change of monsoon storms under El Nino-Southern Oscillation events was the primary factor affecting the variations in ASSY and storms in the HS region. Besides, human activities, such as policies and wars, also had significant influences on the historical soil erosion processes in this region. These results not only shed light on the historical changes in soil erosion fluxes and corresponding hydrological events during the past 200 years in the plateau-gully area of the CLP, but the active mechanisms under the different driving factors were also better understood.

Tracing erosion flux within a single catchment is one of the major targets for the Earth’s Critical Zone science. The sedimentary succession in landslide-dammed reservoirs within the Chinese Loess Plateau (CLP) serves as a valuable archive of past erosion history. Deposition couplets and annual freeze–thaw layers were firstly identified for the sedimentary succession of the Jingbian reservoir on the northern CLP with high-resolution XRF core scanning. The deposition couplets in the reservoir since 1963 A.D. were further dated with 137Cs activity. We found consistent one-to-one correspondence between couplet specific sediment yield and storm intensity. The reconstructed soil erosion history highlights the control of storm intensity and frequency on loess erosion on the northern CLP in the past hundreds of years.

A new araphid diatom, Diatoma kalakulensis sp. nov., was discovered in Lake Kalakul, located in the Pamir Mountains in north-western China. The morphology and ultrastructure of this new species are described on the basis of observations made under light and electron microscopy. Compared to Diatoma tenuis, Diatoma kalakulensis is characterized by longer valves, higher stria density, wider apical ends and the position of its rimoportula.

Arid and semi-arid areas in inner Asia contribute lots of mineral dust in the northern hemisphere, but dust flux evolution in the past is poorly constrained. Based on particle sizes and elemental compositions of a sediment core from Lake Qinghai on the northeastern Tibetan Plateau, dust fluxes during ∼1518–2011 A.D. were reconstructed based on 18–100 μm fractions of the lake sediment. The dust fluxes during the past ∼500 years ranged between 100 and 300 g/m 2 /yr, averaging 202 g/m 2 /yr, experiencing four stages: Stage 1 (∼1518–1590s), the flux was averaged 165 g/m 2 /yr, much lower than that in the Stage 2 (1590s–1730s, 254 g/m 2 /yr); similarly, an average flux of 169 g/m 2 /yr in the Stage 3 (1730s–1950s) was followed by an increased flux of 259 g/m 2 /yr in the Stage 4 (1950s–2011). During the first three stages the fluxes were dominated by natural dust activities in arid inner Asia, having a positive relation with wind intensity but a poor correlation with effective moisture (or precipitation) and temperature. The high dust flux in Stage 2 was due to relatively strong wind during the maximum Little Ice Age, whereas the remarkably high flux in 1950s–2011 was resulted from recent increasing human activities in northwestern China. The dust record not only documents past dust fluxes on the northeastern Tibetan Plateau but also reflects evolutions and mechanisms of dust activity/emission in inner Asia during the past ∼500 years.

RATIONALE Lithium (Li) isotopes have increasingly been applied as tracers in Earth and planetary sciences and their effectiveness relies upon accurate and precise Li isotopic data. Nowadays, multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) combined with chromatographic purification is the most common strategy for obtaining Li isotopic ratios in natural samples, with a long-term internal precision better than 0.3‰ in most laboratories. However, there is a large discrepancy in the Li isotopic compositions of the same reference materials determined by MC-ICP-MS among international laboratories (e.g. ca 3.5‰ difference for measurements of homogeneous seawater), which has been attributed to insufficient recovery of Li during chromatographic purification. Despite this recognition, the exact impact of Li recovery during purification on Li isotopic determinations by MC-ICP-MS has never been quantified. METHODS We employed a normal distribution function to model Li elution curves and quantified the Li isotopic fractionation resulting from Li recovery during chromatographic purification. Furthermore, we compared the calculated and measured relative recovery (R) with the Li isotopic ratios determined by ICP-MS to validate our theoretical calculation. RESULTS The theoretical calculations showed that R should be higher than 99.8% in order to avoid observable Li isotopic fractionation during chromatographic purification at IEECAS. This idea is further supported by the better long-term external precisions for data with R ≥ 99.8% compared with previous values of 99.5% ≤ R

A sediment record reveals a 2-year delayed response following the 2008 Wenchuan earthquake, attributed to monsoon rainfall., Infrequent extreme events such as large earthquakes pose hazards and have lasting impacts on landscapes and biogeochemical cycles. Sediments provide valuable records of past events, but unambiguously identifying event deposits is challenging because of nonlinear sediment transport processes and poor age control. Here, we have been able to directly track the propagation of a tectonic signal into stratigraphy using reservoir sediments from before and after the 2008 Wenchuan earthquake. Cycles in magnetic susceptibility allow us to define a precise annual chronology and identify the timing and nature of the earthquake’s sedimentary record. The grain size and Rb/Sr ratio of the sediments responded immediately to the earthquake. However, the changes were muted until 2 years after the event, when intense monsoonal runoff drove accumulation of coarser grains and lower Rb/Sr sediments. The delayed response provides insight into how climatic and tectonic agents interact to control sediment transfer and depositional processes.

Erosion of organic carbon from the terrestrial biosphere and sedimentary rocks plays an important role in the global carbon cycle across a range of timescales. Over geological timescales (>104 years), erosion and burial of particulate organic carbon (POC) from the terrestrial biosphere (POCbiosphere) is an important CO2 sink, while oxidation of organic carbon derived from sedimentary rocks (petrogenic, POCpetro) releases CO2 to the atmosphere. Over decadal to millennial timescales, the balance between POCbiosphere production and degradation affects atmospheric CO2 concentrations. To better constrain the controls on erosional carbon transfers, here we quantify POCbiosphere and POCpetro fluxes in a mountain range with relatively low runoff, the Longmen Shan, which drains the eastern margin of the Tibetan Plateau. We measure total organic carbon content ([OCtotal]) and the carbon isotopic compositions (13C/12C expressed as δ13C; 14C/12C expressed as fraction modern or Fmod) of organic matter in suspended sediments collected from six gauging stations on the Min Jiang, a tributary of the Yangtze River, from 2005 to 2012. We find that POCpetro has a large range of δ13C, from -26.2‰ to -13.2‰. This POCpetro mixes with POCbiosphere to set the δ13C of POC in river sediments. Binary mixing models reveal the possibility of aged POCbiosphere at two gauging stations which drain the high elevations of the eastern Tibetan Plateau, with modelled Fmod values of 0.82 ± 0.09 and 0.84 ± 0.08. This is consistent with prior suggestions of aged biospheric carbon being eroded from the Plateau. The annual POCpetro yields range from 0.04 ± 0.02 tC km-2 yr-1 to 1.69 ± 0.56 tC km-2 yr-1 across the five study catchments, with basin average yield that appears to be linked to catchment average slope as a likely proxy for erosion rate. Here, the variability in the petrogenic organic carbon content of rocks masks the signal of the weathering and oxidation of this rock-derived organic carbon. The annual POCbiosphere yields range from 0.21 ± 0.04 tC km-2 yr-1 to 3.33 ± 0.57 tC km-2 yr-1. These values are towards the lower end of those measured in mountain ranges around the world, which we suggest not only reflects the relatively low erosion rates of the Longman Shan, but also the low annual runoff (

During the Last Glacial Maximum (LGM; ~20,000 years ago), the global ocean sequestered a large amount of carbon lost from the atmosphere and terrestrial biosphere. Suppressed CO2 outgassing from the Southern Ocean is the prevailing explanation for this carbon sequestration. By contrast, the North Atlantic Ocean—a major conduit for atmospheric CO2 transport to the ocean interior via the overturning circulation—has received much less attention. Here we demonstrate that North Atlantic carbon pump efficiency during the LGM was almost doubled relative to the Holocene. This is based on a novel proxy approach to estimate air–sea CO2 exchange signals using combined carbonate ion and nutrient reconstructions for multiple sediment cores from the North Atlantic. Our data indicate that in tandem with Southern Ocean processes, enhanced North Atlantic CO2 absorption contributed to lowering ice-age atmospheric CO2., Atmospheric CO2 is governed by CO2 gains (e.g., via Southern Ocean outgassing) and losses (e.g., via North Atlantic absorption). Using a novel method to estimate air–sea CO2 exchange signals, the authors show that North Atlantic CO2 absorption became more efficient and contributed to lowering atmospheric CO2 during ice ages.

To evaluate the roles of climate and hydrology in continental-scale silicate weathering, we applied Li isotopes to the Yellow River and systematically investigated seasonal Li flux, Li isotopic compositions and potential sources. We collected samples from the middle reaches of the Yellow River weekly over the full hydrological year of 2013. We find that the dissolved Li is mainly derived from silicates and evaporites in the arid to semi-arid Yellow River basin. Silicate weathering of loess during the monsoonal season dominates the Li flux in the middle reaches of the Yellow River, with a positive relationship between dissolved Li flux and physical erosion rate. Evaporite contribution for riverine Li was relatively constant in the middle reaches of the Yellow River but slightly increased after the storm event, with an average proportion of ∼25%, which might represent the proportion of evaporite contribution to global oceans. Seasonal variations in the riverine Li isotopic compositions are dominantly controlled by temperature with a fractionation gradient as −0.182‰ per °C over the full year with deviations likely driven by re-dissolution of suspended particulate matter, extreme hydrological events, and groundwater contribution. Temperature dependent δ7Li value variation of river water inputted into oceans indicates that Cenozoic climate cooling itself may be able to explain ∼2‰ of the 9‰ rise of Cenozoic seawater δ7Li value (Misra and Froelich, 2012). The seasonal variation in riverine Li isotopes highlights that erosion and weathering of loess may provide valuable clues on secular chemical weathering and seawater δ7Li variation spanning a range of time scales.

Chinese eolian deposits have been investigated intensively to reconstruct East Asian monsoon changes at tectonic to millennial timescales. However, high-resolution elemental proxies sensitive to rapid monsoon changes remains sparse. Here we present multiple elemental ratios of the Linxia loess sequence generated by scanning and conventional X-ray fluorescence (XRF) to assess East Asian monsoon variability at glacial-interglacial to sub-orbital timescales. The results show that 11 elements (Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr and Ba) can be reliably measured by XRF scanning of loess cores, albeit with relatively lower precision and increased noise levels (due to variable water content and matrix effects) when compared to XRF scanning of dry and homogenized powder samples. Seven elements (Ca, Fe, Ti, Mn, Zr, Rb and Sr), measured by XRF scanning of the core face and powder samples show high correlation (R2 > 0.7, n = 100) with those measured by conventional XRF methods, and thus can be considered as robust indicators for chemical weathering and grain-size sorting. We employ element ratios of Ca/Ti and Rb/Sr to reflect precipitation-induced weathering intensity, and the Zr/Rb ratio and mean grain size to infer the sorting effects related to winter-monsoon winds. These element ratios exhibit significant glacial-interglacial fluctuations, similar to records of magnetic susceptibility and mean grain size. Precessional- to millennial-scale monsoon changes are also persistent in our high-resolution elemental proxies, consistent with those in Gulang loess elemental ratios and Hulu/Sanbao speleothem δ18O records. Our results suggest that high resolution XRF scanning elemental ratios of Chinese loess have great potential for evaluating co-evolution of orbital- and millennial-scale monsoon variations.

Land use change is one of the dominant driving factors of hydrological change at the watershed scale. Thus, understanding the hydrological responses to land use changes can facilitate development of sustainable water resource management. The land use of the Wei River (the largest tributary of the Yellow River) Basin (WRB) has changed greatly due to the large-scale ecological restoration program in the Chinese Loess Plateau (e.g., grain-for-green program), causing dramatic impacts on the water cycle. This study was to simulate the impacts of land use and land cover change (LUCC) on the key hydrological components, using the Soil and Water Assessment Tool (SWAT). We investigated the spatiotemporal changes of LUCC from 1980 to 2010 in terms of four sub-regions (i.e., three subbasins and one mid-downstream area) and three landforms (i.e., mountain, hill, and plain), respectively. Then, we quantified the spatial heterogeneity of hydrological responses to land use change scenarios. Our LUCC analysis showed that cropland declined by about 0.8%, from 58,776 km2 in 1980 to 57,519 km2 in 2010, whereas the forest and grassland areas correspondingly increased 552 km2 and 16 km2, respectively. The urban area changed more dramatically in the middle and lower reaches of the Wei River owing to the faster socioeconomic development in this region than the rest areas. In mountain area, the main types of land use were forest and grassland, and the main transformation was from cropland to forest land and grassland. The area of cropland in plain could be over 50%, and it was mainly converted to urban land. The hydrological simulation indicated that LUCC from 1980 to 2010 caused 5.3% of decrease in the water yield and 6.2% increase in soil water content, but there was nearly no change in evapotranspiration (ET). Scenarios about slopping land use conversion (SLC) program showed that the conversion of cropland to grassland or forest (i.e., grain-for-green) resulted in negative effects on soil water content and water yield, with a greater effect by the reforestation. In addition, we found that the change of ET was clear in areas where cropland with slope > 15° was converted to grassland or forest, suggesting slope is also an important factor for hydrological responses to LUCC. This study can provide valuable decision support for land use planning and water resources protection in the WRB.

Silicate weathering via CO2 consumption is considered to regulate the long-term climate change. Discriminating silicate versus carbonate weathering from sedimentary records is helpful to understand the coupling relationship between weathering and past climate. However, owing to the paucity of well-dated and continuous records of weathering and erosion, the relationship between silicate and carbonate weathering and their links with mountain uplift and glacial-interglacial climate remain elusive. Geochemical analysis of a 666 m core from the Heqing basin, a paleolake situated at the southeastern margin of the Tibetan Plateau, demonstrates silicate versus carbonate weathering and erosion changes under Indian summer monsoon (ISM) conditions spanning the entire Pleistocene, via respective tracing between Rb/Sr and Al/Na ratios. The Rb/Sr record is interpreted as reflecting a competition between clayey silicate-origin Rb versus carbonate-origin Sr fluxes, whereas Al/Na ratio is a balance between weathering and erosion of silicate minerals, both pacing the glacial-interglacial cycles of the ISM. During interglacials, strong silicate weathering intensity reflected by low Al/Na values is mainly controlled by warmer temperatures, with the reduced variability during 1.82–0.92 Ma, recalling the pacing of the Arabian Sea surface temperature amplitudes. Within glacials, the weak carbonate leaching and clay erosion within the older and younger intervals are interrupted by strong clay erosion within the middle interval. In conclusion, the Heqing Rb/Sr and Al/Na records reveal the sensitivity of catchment weathering and erosion to ISM changes over glacial-interglacial timescales with warmer temperature enhancing silicate weathering and clay formation during interglacials and greater physical erosion during glacials.

Landslide-dammed reservoirs are widespread on the Chinese Loess Plateau (CLP). Due to the contrasting seasonality of the monsoonal hydroclimate, sediment sequences in landslide-dammed reservoirs are characterized by deposition couplets of eroded loess with annual freeze-thaw layers that are ideal objects to reconstruct catchment erosion processes, hydrologic events, land use and human activity history. Identifying annual freeze-thaw layer from the deposition couplets in a given year is crucial for dating sediment sequences and for reconstructing erosion history using sediments because they are considered to be the boundary of the last hydrological event in an individual year. Using high-resolution XRF core scanning, grain size and mineralogy, fine-grained layers were identified in two representative core sections from the Jingbian and Heshui landslide-dammed reservoirs on the northern and southern CLP. The results show that both annual and intra-annual fine-grained layers have high Ca, Fe, and Mn contents but low Si contents and are dominated by clays, calcite and fine silt as a result of sorting and stratification during deposition. However, Ca exhibits two distinct trends with Fe (and Mn) in these fine-grained layers from both core sections. The steeper slopes of the relationship between them reflect further concentrations of both Ca and Fe (and Mn) that potentially result from freeze-thaw processes. The fine-grained layers with high concentrations of Ca and Fe and high slopes of their correlations are therefore identified as the annual freeze-thaw layers. The identification of annual freeze-thaw layers in landslide-dammed reservoir sediment sequences by high-resolution XRF core scanning provides new insights into their formation and mobile elemental enrichment processes as well as dating of the sediment sequences.

The sensitivity of multi-collector inductively coupled plasma mass spectrometers (MC-ICP-MS) can be significantly improved using different sample and skimmer cones with different orifice diameters and angles. In this study, an MC-ICP-MS with three typical combinations of sample and skimmer cones [(H skimmer cone + standard sample cone (Standard + H), X skimmer cone + standard sample cone (Standard + X) and X skimmer cone + Jet sample cone (Jet + X)] was used to measure the boron isotopes, and the effect of the different combinations of sample and skimmer cones on the sensitivity of the MC-ICP-MS and the underlying physical principles were investigated. The results suggest that more ions can be introduced into sample cones with larger orifices, which results in increased sensitivity. Compared with standard skimmer cones (which have cylindrical entrances and trumpet-shaped exits), X skimmer cones (which have trumpet-shaped entrances and exits) can provide more space for ion beams to entrance the skimmer⿿s orifice after they are subjected to the space-charge effect.

Hydrochemistry methods were used to decipher the weathering and geochemical processes controlling solute acquisition of river waters in the dry season in the middle Loess Plateau (MLP), one of the most severely eroded areas and turbid riverine systems in the world. River waters were neutral to slightly alkaline with pH varying from 7.6 to 9.6. The total dissolved solids decreased from northwest to southeast with a mean value of 804 mg/l, much higher than the global average and other large rivers in China. Ternary diagram showed that river waters were dominated by Na+, HCO3−, and Cl− with the main water-type of HCO3−–Cl−–Na+. Saturation index values, Mg2+, Ca2+, and HCO3− analyses indicated the preferential Ca2+ removal by calcite precipitation. Gibbs plots and stoichiometry plots indicated that the dissolved solutes were mainly derived from rock weathering with minor anthropogenic and atmospheric inputs. Samples in the northwestern basin are also influenced by evaporation. A forward model of mass budget calculation showed that, owing to high soluble characteristics, evaporite dissolution was a major feature of river waters and contributed 41% to the total dissolved cations on average, while carbonate and silicate weathering contributed 28%,and 25% on average, respectively. Besides evaporite dissolution, cation exchange is also responsible for the high concentrations of Na+ in river water. Spatial variations showed that evaporite dissolution and silicate weathering were higher in the northern basin, whereas carbonate weathering was higher in the southern basin. Different from most rivers in the world, the physical erosion rates (varying from 117.7 to 4116.6 t/km2y) are much higher than the chemical weathering rates (varying from 3.54 to 6.76 t/km2y) in the MLP because of the loose structure of loess and poor vegetation in the basin. In the future, studies on comparison of water geochemistry in different seasons and on influence of different types of land use and soil salinization on water geochemistry, denudation rates, and water quality should be strengthened in the MLP. These results shed some lights on processes responsible for modern loess weathering and also indicate the importance of time-series sampling strategy for river water chemistry. Copyright © 2016 John Wiley & Sons, Ltd.

Long-term trends of atmospheric compositions are significant for assessing the influence of human activities on the atmosphere and protecting the atmospheric environment. In this study, based on heavy metal concentrations and Pb isotope ratios in a well-dated sediment core from a remote alpine lake in central North China, anthropogenic fluxes of As, Cd, Sb, and Pb were reconstructed and heavy metal evolutions in the atmosphere were revealed in the last 200 years. The heavy metals in the atmosphere were generally natural origins before 1980 A.D. Since the 1980s they began to increase gradually, but they increased the most in the 1990s resulting from rapid developments of rough and high energy-consuming industries in North China. After entering the 21st century the industries still developed rapidly, but the atmospheric Pb ceased increase and the As and Sb even decreased in the 2000s due to (1) phasing out of leaded gasoline and (2) implementing stricter industrial emission standards in 2000 A.D. in China. However, in the 2000s the atmospheric heavy metals still kept at a relatively high level and even likely began to increase again in the 2010s. Considering the lake relatively remote and seldom affected by local human activities, the results likely reflect heavy metal evolutions in the regional background atmosphere of central North China at the annual/decadal timescale in the last 200 years.

Investigation of the weathering of silicate minerals is helpful to understand the process of soil development, cycling of nutrient elements, and potential applications in fixation of carbon dioxide from the atmosphere through carbonate precipitation. In this study, weathering experiments of calcium-montmorillonite were conducted using Paenibacillus sp. strain SB-6 for 70 days. The results indicated that the Si4+, Al3+, Ca2+ and Na+ concentrations in the medium of the biotic experiments were evidently higher than those of the abiotic experiments, and that Paenibacillus sp. could help the transformation of partial montmorillonite into an illite–montmorillonite mixed-layer. In the process of illitization, K+ went into the interlayer of montmorillonite and hydrated Ca2+ and Na+ released from it. In the late stage of the experiments, the Ca2+ released from montmorillonite combined with carbonate ions generated by the bacterial metabolism, forming calcite.

Evaluating the influence of earthquakes on erosion, landscape evolution, and sediment-related hazards requires understanding fluvial transport of material liberated in earthquake-triggered landslides. The location of landslides relative to river channels is expected to play an important role in postearthquake sediment dynamics. In this study, we assess the position of landslides triggered by the Mw 7.9 Wenchuan earthquake, aiming to understand the relationship between landslides and the fluvial network of the steep Longmen Shan mountain range. Combining a landslide inventory map and geomorphic analysis, we quantify landslide-channel connectivity in terms of the number of landslides, landslide area, and landslide volume estimated from scaling relationships. We observe a strong spatial variability in landslide-channel connectivity, with volumetric connectivity (ξ) ranging from ~20% to ~90% for different catchments. This variability is linked to topographic effects that set local channel densities, seismic effects (including seismogenic faulting) that regulate landslide size, and substrate effects that may influence both channelization and landslide size. Altogether, we estimate that the volume of landslides connected to channels comprises 43 + 9/−7% of the total coseismic landslide volume. Following the Wenchuan earthquake, fine-grained ( 90% of the total landslide volume) may be more significantly affected by landslide locations.

Grain-size compositions of lake sediments can provide direct information on changes in transporting mechanism and sedimentary environment. Various grain-size parameters have been employed to reconstruct hydrological conditions within the lake and dust influx from outside the lake. Here we present the grain-size results of a 5-m core retrieved from Lake Qinghai, northeastern Tibetan Plateau in order to address the links between Holocene depositional process and climatic change. Our results indicate that two parameters (skewness and grain-size ratio of 8–50/2–8 μm) are sensitive to hydrodynamic changes in Lake Qinghai, which are further linked to the strength of the Asian summer monsoon. Variations of these two parameters reveal that summer monsoon intensity weakened gradually from early to late Holocene, superimposed by persistent centennial variability with dominant periods at 0.35, 0.23 and 0.12 kyr. Comparison of grain-size variations with solar activities and North Atlantic cooling events reveals that solar forcing likely plays an important role in driving centennial monsoon variability.

Water resources play a key role in the development of regional economy and stability of ecosystem in the middle Loess Plateau, China. Spatial variability of fluoride (F−) and its geochemical control with other dissolved ions in the middle Loess Plateau were discussed. Samples were neutral to weak alkaline (pH = 7.4–9.6) with little variation of ion concentrations between river water and groundwater. The F− concentrations ranged from 0.2 to 3.1 mg/L, with an mean value of 0.9 mg/L. Approximately 31% of samples in northern and southern part of the study area were HCO3−–Na+ water type with F− levels higher than the Chinese Drinking Water Standard of 1.0 mg/L. About 12% samples in the central part were HCO3−–Ca2 + water type with F− content lesser than recommended value for caries control of 0.5 mg/L. The Quaternary deposits in the study area were the mainly F− sources of natural waters, and rainwater also contributed some F−. The alkaline characteristic of natural waters favored desorption of F− from hydrous metal oxides in loess, the climate of the study area, cation exchange, and CaCO3 precipitation further increased F− concentrations in natural waters in the middle Loess Plateau. Moreover, the chemical data analyzed in the principal component analysis (PCA) also indicated that climate coupled with geochemical processes was the main controlling factor for high F− in natural waters in the area. For the supply of high quality drinking water with safe F−, short-term and long-term action plans as well as awareness/education programs for the public were advocated.

A large area of the continents is covered by loess that is subject to fast erosion, but detailed research is lacking about processes influencing the hydrogeochemistry in loess-covered regions. This study presents the first δ 18 O and δD, and major ion contents of various waters (rain, rivers, lake, springs and wells) from Daihai Lake catchment on the Chinese Loess Plateau (CLP). In combination with historical hydrological and meteorological data during the past 60 years, we investigate factors affecting water chemistry and lake evolution on the CLP, and thereby provide insight into hydrogeochemical processes under semi-arid climatic conditions. On the northeast CLP, river and groundwaters show elevated TDS (450 and 461 mg/L, respectively), about ~ 4 times higher than the global river mean value. Their water chemistry is dominantly influenced by carbonate weathering. Lake waters show even higher TDS at 5758 mg/L, ~ 50 times of the global mean, which is attributed to strong evaporation and associated with precipitation of calcite and dolomite. The order of carbonate (calcite and dolomite) saturation indexes follows lake water > river water > groundwater. Downstream rivers to the west of Daihai Lake are characterized by elevated SO 4 2 − , indicating high lake levels in the past. Comparison of δ 18 O, δD, TDS and ion contents of river and groundwaters implies that shallow groundwaters are derived from surface runoff via fast infiltration, a hydrological process different from limited infiltration of groundwater on the Tibetan Plateau. Water quality assessment indicates that all river and 79% of well waters belong to moderately hard to hard-fresh waters, suitable for drinking and irrigation of plants with moderate salt tolerance. In contrast, all lake and spring waters and 21% of well waters belong to very bad water quality, and hence are not suitable for irrigation or drinking. Owing to intensified human activities under drying and warming climate, the lake water level of Daihai declined by 4.83 m from 1955 to 2003, and started to accelerate since 1980. As a result, TDS and Cl − increased by 1.8 times and Mg/Ca rose by 156 times from 1953 to 2010. Our data show that environment degradation poses a great threat to human occupation on the CLP. Considering the uniformity of loess, hydrogeochemical processes between surface and groundwaters on the loess regions may represent a widespread status of the CLP.

It has been proposed that the riverine Mg isotopes are sensitive to primary mineral dissolution and the formation of secondary minerals and are served as an effective tracer for chemical weathering. Glacial comminution can produce fresh mineral surfaces that provide easily leached cations to the rivers and thus could potentially modify the riverine Mg isotopic behavior. However, the mechanism controlling riverine Mg isotopes under glacial environment is poorly constrained. Here we investigated Mg and Sr isotopic compositions of river and spring waters, bedrocks and sediments within the glacial-covered Muztag catchment in the northeastern Pamir Plateau. The δ26Mg and 87Sr/86Sr values of dissolved loads along the mainstream increased from −1.56‰ and 0.713050 at the glacier margin to −1.12‰ and 0.713855 at the downstream, respectively, both showing strong negative correlation with elevation. The lower δ26Mg but higher molar Ca/Mg and Ca/Na ratios of glacial river waters than those of non-glacial rivers indicate a preferential dissolution of carbonates under glacial environment, further supported by a negative liner correlation between δ26Mg and carbonate weathering proportion. In contrast, the high δ26Mg but low Ca/Mg and Ca/Na ratios at the downstream reflect an increased input of silicate weathering. Saturation state modelling suggests little chance of secondary mineral formation and limited impact on the Mg isotopic behavior in glacial rivers, characterized by low ionic concentrations and short water residence time. These observations, together with complied data from other glacial rivers, suggest preferential carbonate weathering under glacial environment could directly release low Mg isotopes to river water, different from the process of Mg isotopic fractionation by secondary mineral formation. Our findings would provide insight in carbonate weathering regulating riverine Mg isotopic evolution and its potential influence on global carbon cycle, in particular under present warming scenario.

Boron (B) is an essential micronutrient for plant growth. Lack of valid methods for pretreatment and measurement of δ11B in plant restrict applications of it in the biosphere. Dry ashing, one step cation exchange and micro-sublimation were combined to separate and purify boron (B) in plant tissues. The low procedure blank, high B recovery and the accurate δ11B values of the plant reference materials demonstrate that this method is suitable and valid for B pretreatment and δ11B measurement in plant samples by MC-ICP-MS. Based on this method, the δ11B in different plants (Brassica napus, Chenopodium album L, moss, lichen, and Nostoc commune) was analyzed. For Brassica napus, δ11B increased gradually from root to leaf, and then decreased to rapeseed. For the same parts, the δ11B increased from the lower parts to the higher parts. This variation may be due to the B(OH)3 transporter of NIP6;1 and the incorporation of B into the cell. The reason for lower δ11B values in shell and rapeseed compared to those in leaves presumably is to the preferred transport of borate in the phloem. The largest δ11B fractionation between leaf and root in Brassica napus and Chenopodium album L was + 24.2‰ and + 26.6‰, respectively. The large variation and fractionation of δ11B within plants indicates that δ11B is a good tracer to study the B translocation mechanisms and metabolism within plants. The δ11B in Nostoc commune, lichen, and moss showed variations of -4.1‰ to + 21.5‰, − 9.4‰ to + 7.3‰, and − 18.3‰ to + 11. 9‰, respectively. In the same site, δ11B in different plants ranked Nostoc commune>moss>lichen and δ11B in mosses growing in different environment ranked soil>tree>rock. Rain and soil available B are the main B sources for these plants. The δ11B in Nostoc commune, lichen, and moss may be a useful tracer to study the atmospheric B input. In the future, plants culture experiments under certain environments and studies from molecular level are necessary to decipher the variation of δ11B and fractionation mechanisms within plants.

Experiments involving boron incorporation into brucite (Mg(OH)2) from magnesium-free artificial seawater with pH values ranging from 9.5 to 13.0 were carried out to better understand the incorporation behavior of boron into brucite and the influence of it on Mg/Ca-SST proxy and δ11B-pH proxy. The results show that both the concentration of boron in deposited brucite ([B]d) and its boron partition coefficient (Kd) between deposited brucite and final seawater are controlled by the pH of the solution. The incorporation capacity of boron into brucite is almost the same as that into corals, but much stronger than that into oxides and clay minerals. The isotopic compositions of boron in deposited brucite (δ11Bd) are higher than those in the associated artificial seawater (δ11Bisw) with fractionation factors ranging between 1.0177 and 1.0569, resulting from the preferential incorporation of B(OH)3 into brucite. Both boron adsorptions onto brucite and the precipitation reaction of H3BO3 with brucite exist during deposition of brucite from artificial seawater. The simultaneous occurrence of both processes determines the boron concentration and isotopic fractionation of brucite. The isotopic fractionation behaviors and mechanisms of boron incorporated into brucite are different from those into corals. The existence of brucite in corals can affect the δ11B and Mg/Ca in corals and influences the Mg/Ca-SST proxy and δ11B-pH proxy negatively. The relationship between δ11B and Mg/Ca in corals can be used to judge the existence of brucite in corals, which should provide a reliable method for better use of δ11B and Mg/Ca in corals to reconstruct paleo-marine environment.

Historical records of heavy metals from remote areas are important for assessing temporal pollution trends of the regional atmosphere. Based on comparison analyses of heavy metals, Pb isotopes, and total carbon in sediment cores from two relatively remote lakes on the southeast Mongolian Plateau, atmospheric heavy metal pollution trends during ∼1900–2016 were reconstructed. The current anthropogenic fluxes of Zn, Cd and Pb in the region are 11.7, 0.104 and 2.44 mg m−2 yr−1, respectively, close to those in Lake Sayram in West China, but lower than most other records in China. Anthropogenic metal fluxes and 206Pb/207Pb ratios suggest that (1) before ∼1950 atmospheric metal pollution was negligible in the region; (2) since ∼1950, the pollution became detectable but was relatively slight until ∼1980, corresponded with the beginning of socio-economic development after the foundation of China in 1949 and the rapid development after the Reform and Opening-up in 1978; and (3) since ∼2000, atmospheric Pb stopped increasing because of the phasing out of leaded gasoline. Based on comparison and fitting analyses with other sediment records, a similar four-stage evolution picture of atmospheric heavy metals in China over the last century was uncovered. This study indicates rapid increase trends of atmospheric heavy metals in China since ∼1980 associated with economic development.

In the extreme arid region of the Tarim River Basin (TRB), groundwater is the most valuable resource for people's lives and regional ecology. Major ion concentrations of groundwater were analyzed to decipher hydrochemistry, temporal and spatial variations, solute sources, and controlling factors of the groundwater within the TRB. Groundwaters in this area were neutral to alkaline in nature and most of them were hard-brackish waters, dominated by Na, Ca, Mg, Cl, and SO4 ions. The total dissolved solid (TDS) varied over two orders of magnitude with a mean value of 2044 mg/L in wet season and 3091 mg/L in dry season, about 1–2 times higher than those in river water in this area. Hydrochemical types and chemical compositions of groundwaters showed zonal distribution. Mineral dissolution and evaporation were the main processes responsible for high solutes in groundwater. Ion exchange between Na on clay minerals and Ca (Mg) in groundwater increased Na+ concentrations. Groundwater was oversaturated with respect to dolomite, calcite and aragonite, and under-saturated with respect to gypsum and halite. A forward model of mass budget calculation showed that evaporite dissolution, carbonate weathering, silicate weathering, and atmospheric input contributed 58 ± 14%, 25 ± 12%, 13 ± 2%, and 4 ± 2% of the total dissolved cations on average in wet season, and 68 ± 13%, 20 ± 12%, 10 ± 2%, and 2 ± 1% in dry season for the whole basin, respectively. Spatial variations of rock weathering were significant, with higher evaporite dissolution in the southern basin, and higher carbonate weathering in the northern basin. Although anthropogenic inputs were minor, the majority of samples were not suitable for drinking with reference to TDS, F− and/or SO 4 2 − . These results can enhance the understanding of hydrochemical characteristics in desert environments and provide information for the material sources of Lop Nor.

In order to reveal the seasonal variations of river water chemistry and its controlling factors in the middle reaches of the Yellow River, river water samples were collected weekly from the Longmen hydrological station over the whole year of 2013. Major cation and anion compositions were measured. The major ionic compositions of the dissolved load exhibited distinct seasonal variability over the one year period, reflecting seasonal differences in relative inputs from various sources and weathering reactions within the catchment. A forward model was used to calculate the apportionments of rain, anthropogenic, silicate, evaporite, and carbonate origins on a seasonal basis. The contributions of both rain and anthropogenic sources to the middle Yellow River were less than ~ 12% in average, with little seasonal variations in 2013. The calculations showed that silicate sources had a relatively large impact on water chemistry during the pre- and early-monsoon seasons, though both silicate and carbonate weathering increased greatly during the monsoon season. The high silicate input during the pre- and early-monsoon seasons was attributed to the waters potentially derived from plateau headstream, glacial melting, and soil pore. Meanwhile, the dominated contributions of evaporites and carbonates in the late- and post-monsoon seasons were resulted from their rapid dissolution from the loess plateau through physical erosion acceleration along with high water discharge, because widespread loess is characterized by easy denudation and high carbonates and evaporites. Our densely time-series data also highlighted a significant impact of extreme hydrological events on water chemistry in semi-arid area. During the ice melting interval in the springtime, more silicate-origin ions entered the river from melting water, whereas during the stormy event interval in the peak monsoon, more carbonates and evaporites reached the Yellow River from the loess plateau via accelerated physical erosion. Our data shed further light on processes responsible for seasonal variation of river chemistry of the Yellow River and modern loess weathering.

There is ongoing debate over how the water level and composition of the water in Lake Qinghai changed in the past and might change in future. This study of the microchemistry of otoliths from ancient naked carp explores the chemistry of a relict lake isolated from Lake Qinghai during the Little Ice Age (LIA). A close correlation between the ages measured on fish bone and otoliths by AMS-14C, and by optically stimulated luminescence on overlying sediments, confirms a high water level in Lake Qinghai before 680–300 years ago. The contrasting compositions of the ancient otoliths relative to modern otoliths and waters indicate that the relict lake became enriched in 18O, Mg, Li, B and to a lesser extent Ba, but depleted in 13C, owing to strong evaporation, authigenic carbonates precipitation, (micro-)organism activity, and less fresh water input after it was isolated. If there were long-term fresh water input, however, a reverse trend might occur. The most important observation is that, because the waters have been supersaturated with respect to carbonates, authigenic carbonate precipitation would result in low but consistent Sr/Ca ratios in the lakes, as recorded by both the ancient and modern otoliths. The geochemical records of ancient versus modern biogenic carbonates provide insights into the long-term hydroclimatic evolution processes of an inland water body.

An understanding of topsoil geochemistry within a watershed helps to identify the influence of natural processes and anthropogenic activities in the environment. Fifteen elements were measured in 73 topsoil samples (top 30 cm) from the Lake Qinghai catchment, NE Qinghai–Tibetan Plateau (QTP) in 2009, to investigate geochemical patterns, identify possible sources and explore the implications of chemical weathering. Compared with their content in the upper continental crust (UCC), a deficit of Cu and Zn and an enrichment of Pb were identified in the study area. Enriched Ca levels were observed in alpine soil and pedocal, solonchak and aeolian sand soils, whereas there was a loss in hydromorphic and semi-hydromorphic soils. High Na in marsh solonchak indicated the possible presence of evaporites. Cluster analysis (CA) and principal component analysis (PCA) indicated the dominance of carbonate and the accumulation of P, possibly from grassland litterfall in topsoil. Some human activities have exerted an influence on virgin topsoil, as revealed by GIS mapping. The implications for chemical weathering, based on a chemical index of alteration (CIA) and an Al2O3–(CaO* + Na2O)–K2O (A–CN–K) diagram were characterised by a major carbonate control of the primary weathering stage under cold-dry climatic conditions with Ca and/or Na removal.

To advance the understanding of the spatial variability of sediment composition and its controlling factors in a large hydrologically closed lake, the spatial distributions in the mineralogy and geochemistry of 18 surface sediment samples along three transects across the deepest part of Lake Qinghai on the northeastern Tibetan Plateau were investigated. The data show (1) that the surface lake sediments are almost the same in the XRD patterns, (2) that the sediments do not have considerable changes in geochemical compositions along three transects and (3) that the standard deviations of the lake sediments are low in grain size, elemental abundances, δ13C and δ18O values of carbonates, and total organic carbon and nitrogen, with the exception of one sample (QH-11) from the westernmost part of the northern sub-basin. These characteristics indicate that the spatial variability of the surface sediment across Lake Qinghai is very low in geochemical and silicate mineralogical compositions, with limited differences in the chemical composition of carbonates associated with river water dilution. Sample QH-11 has anomalously high levels of MgO, a high carbonate content, and positive δ13C and δ18O values in bulk and fine-grained carbonates, probably because of the effect of calcareous tufa. Spatial uniformity in the mineralogical and geochemical compositions of surface sediments in Lake Qinghai can be attributed to the flat topography of the lakebed and stable sediment provenances, the latter dominated by dust deposition and authigenic carbonates. The spatial uniformity and dominance of dust and authigenic aragonite of surface sediments across Lake Qinghai provide a potential record of the hydroclimate in the past, which is associated with changes in the Westerlies and the summer monsoons.

In nature, boron exhibits a large range of isotopic compositions (up to 150‰), which makes it a powerful geochemical tracer. Improving the separation and purification procedures of boron in complex matrices and at low boron contents is a challenge in obtaining high-precision and accurate boron isotope ratios. A method of ion exchange using solid-phase extraction (SPE) for the efficient separation of boron from samples with low boron contents was developed for determining boron isotopes by MC-ICP-MS. The results showed that the total amount of residual boron in the solution after ion exchange decreased from 60 μg at a vacuum pressure of 0.09 MPa to 0 at 0.04 MPa. When the vacuum pressure was between 0.008 and 0.04 MPa boron was not detected in the solution. The flow rate of the solution increased from 50 μL min−1 at a vacuum pressure of 0.008 MPa to 1358 μL min−1 at a vacuum pressure of 0.09 MPa, and the volume of eluent required increased from 300 μL at 0.008 MPa to 600 μL at 0.04 MPa. Therefore, the recommended vacuum pressure was below 0.04 MPa based on these results. The δ11B values of NBS 951 after chemical treatment using SPE were between −0.25‰ and 0.26‰. Using this procedure, boron in river water, rainwater and seawater samples was separated and the B isotope compositions analyzed by MC-ICP-MS. The accuracy and precision of our method were assessed by comparing the measured δ11B values of these samples with published results using positive-ion thermal-ionization mass spectrometry. The improved efficient separation of boron from samples with a low boron content using SPE is applicable to a wide range of boron isotopic separations.

Earthquakes cause widespread landslides that can increase erosional fluxes observed over years to decades. However, the impact of earthquakes on denudation over the longer timescales relevant to orogenic evolution remains elusive. Here we assess erosion associated with earthquake-triggered landslides in the Longmen Shan range at the eastern margin of the Tibetan Plateau. We use the M w 7.9 2008 Wenchuan and M w 6.6 2013 Lushan earthquakes to evaluate how seismicity contributes to the erosional budget from short timescales (annual to decadal, as recorded by sediment fluxes) to long timescales (kyr to Myr, from cosmogenic nuclides and low temperature thermochronology). Over this wide range of timescales, the highest rates of denudation in the Longmen Shan coincide spatially with the region of most intense landsliding during the Wenchuan earthquake. Across sixteen gauged river catchments, sediment flux-derived denudation rates following the Wenchuan earthquake are closely correlated with seismic ground motion and the associated volume of Wenchuan-triggered landslides ( r 2 > 0.6 ), and to a lesser extent with the frequency of high intensity runoff events ( r 2 = 0.36 ). To assess whether earthquake-induced landsliding can contribute importantly to denudation over longer timescales, we model the total volume of landslides triggered by earthquakes of various magnitudes over multiple earthquake cycles. We combine models that predict the volumes of landslides triggered by earthquakes, calibrated against the Wenchuan and Lushan events, with an earthquake magnitude–frequency distribution. The long-term, landslide-sustained “seismic erosion rate” is similar in magnitude to regional long-term denudation rates (∼0.5–1 mm yr−1). The similar magnitude and spatial coincidence suggest that earthquake-triggered landslides are a primary mechanism of long-term denudation in the frontal Longmen Shan. We propose that the location and intensity of seismogenic faulting can contribute to focused denudation along a high-relief plateau margin.

The deep ocean is thought to have played a crucial role in modulating atmospheric CO2 changes, and thus reconstructions of deep ocean conditions can place important constraints on the past global carbon cycle. Some previous studies suggested that foraminiferal U/Ca could be used to infer seawater carbonate chemistry changes, but others showed complications from diagenesis and temperature. A recent down-core study suggested that foraminiferal U/Mn may be used for sedimentary redox-conditions, but no core-top work has been done to investigate factors affecting U/Mn. We investigate controlling factors on U/Ca and U/Mn in two benthic foraminiferal species from 120 global core-tops and three Atlantic sediment cores. Our core-top data reveal no significant correlation between core-top benthic U/Ca and carbonate system parameters. The lack of an influence of deep-water [CO32-] on U/Ca is further supported by our down-core results. Together, our data highlight complications to use benthic U/Ca for deep-water carbonate chemistry reconstructions. Although no correlation is found between core-top U/Mn and hydrographic data, high-resolution U/Mn and U/Ca in core TNO57-21 show similar patterns to authigenic U (aU) and vary in tandem with atmospheric CO2 on millennial timescales. Changes in U/Mn, U/Ca and aU in TNO57-21 may reflect post-depositional diagenesis linked to sedimentary oxygen, which is controlled by subantarctic surface productivity and ventilation of deep South Atlantic in the past. We suggest that benthic U/Mn and U/Ca may be used as auxiliary indicators for past sedimentary redox-conditions and along with other proxies could reflect deep-water oxygenation. This article is protected by copyright. All rights reserved.

A series of paddy soil profiles with approximately 50, 300, 700 and 1000 years of paddy cultivation history and an uncultivated mud beach profile under nearly identical landscape and climate conditions were studied. The signatures of rare earth elements (REEs) were used to identify sediment provenances and parent material uniformity of the studied profiles and to assess long-term paddy management effects on REE mobilization and fractionation. The distribution patterns of samples on a δEu N –ΣREEs plot indicate that the parent materials of paddy soils and the uncultivated soil mainly originate from Yangtze River sediments. The REE chondrite-normalized curve could be used to adequately evaluate parent material uniformity, thus allowing further studies of soil REE changes along a time sequence of paddy cultivation. To understand anthro-pedogenic effects on REE mobilization and fractionation, the REE concentrations of paddy soils were normalized to those of the uncultivated soil. Paddy management resulted in accumulation of all REEs within the upper 100 cm, possibly due to anthropogenic inputs such as irrigation water and phosphate fertilizers. In particular, a distinct positive Ce anomaly was observed. This was likely due to periodic reduction and oxidation processes caused by artificial submergence and drainage. These REE signatures are especially marked in the anthrostagnic epipedon (Ap), as compared with the hydragric horizon (Bg). The positive Ce anomaly increased gradually with increasing paddy cultivation age. This demonstrates the utility of Ce anomaly as a trace of the frequency and intensity of redox conditions. The relative enrichment of all REEs and gradual accumulation with paddy cultivation time in the Ap horizons imply low mobility of REEs in the investigated paddy soils. In conclusion, our study demonstrates the effectiveness of various REE proxies as tracers of sediment provenances and parent material uniformity in present paddy soils. It also reveals the effects of long-term paddy management on REE enrichment and positive Ce anomalies.