Dust Source Areas Research Articles

Thermodynamic and dynamic behavior in a recent dust precipitation event in north China

The dynamic and thermodynamic characteristics of a dust precipitation event that took place on May 11, 2020 in North China are analyzed. With the invasion of cold air from Lake Baikal (107°E, 53°N), the arid area in the southeast of Mongolia (107°–108°E, 47°–48°N) was in a region with a large potential pseudo-equivalent temperature gradient, where interactions between cold and warm air led to instability of the atmospheric stratification, and became the dust source area. Meanwhile, a low-pressure cyclone formed over the area (122.3°E, 47.5°N) to the east of the dust source area. Under the joint action of the westerlies, the cyclone developed and supplied forces to the vertical ascent and transportation of dust. Strong winds carried the dust along the southeast direction to China. As the cyclone strengthened, the cold and humid air from Lake Baikal arrived and supplied water vapor for precipitation over Beijing. On the whole, the low-pressure cyclone provided momentum and water vapor for this dust–precipitation event. It is found that the horizontal helicity belt can be an indicator for the prediction of the dust transport pathway. The quick increase in surface dust concentration to its peak was closely related to the increase in downward movements in the layers above 700 hPa.

Provenance tracing of long-range transported dust over the Northeastern Arabian Sea during the southwest monsoon

One of the major pathways for dust supply to surface water of the Arabian Sea is via wet deposition, which is significant during southwest Monsoon (June-September). Aeolian dust supplies macro and micronutrients, which can impact on several marine biogeochemical processes. Here we report, major elements and rare earth elements (REEs) content as well as mineralogical and Sr-Nd isotopic composition of particulate collected from wet deposition (WDP) during the southwest monsoon period over the Northeastern Arabian Sea (NEAS) (Goa; 15.4° N, 73.8° E) in 2013. The collected WDP samples are classified into three categories based on changing wind regime, namely: (1) beginning of monsoon (BM; June); (2) mid of monsoon (MM; July-August) and (3) end of monsoon (EM; September). Our result highlights a significant temporal variability in REEs pattern showing a decreasing trend of Lan/Ybn and relatively higher Eu*/Eu anomaly during mid of monsoon compared to beginning and end of monsoon period. High palygorskite (P) with moderate smectite (S) is observed for beginning of monsoon and majority of mid monsoon samples, however, high smectite with moderate palygorskite and negligible palygorskite and smectite abundance is observed for few of mid monsoon and end of monsoon samples, respectively, indicating change in dust sources during the southwest monsoon period. We also observed temporal variability in 87Sr/86Sr (0.7090–0.7193) and εNd (−2.3 to −9.1) isotopic compositions wherein less radiogenic 87Sr/86Sr and relatively more positive εNd is exhibited by mid of monsoon samples compared to those observed in beginning and end of monsoon collections. The seasonal variability in geochemical tracers are related to changes in the dust source areas which are identified as (1) the Arabian Peninsula contributing significantly in beginning of monsoon and majority of mid monsoon samples; (2) Northeastern Africa contributing to some of the mid monsoon samples and (3) Southwest Asia and Thar Desert in end of monsoon samples. These source identification using geochemical tracers are corroborated by the satellite images (CALIPSO and aerosol index maps) and back-trajectory analyses.

Quantitative estimation of provenance contributions to loess deposits in Eastern China and implication for paleo-dust storm activity

Improvement in the current knowledge regarding the provenance of loess deposits could clarify complex depositional processes, as well as provide new insights into the paleo-dust storm history in dust source areas. In this study, a comprehensive analysis of the size-differentiated geochemical compositions and zircon UPb ages of the examined loess deposits assisted in deepening the provenance identification of the Xiashu loess in Eastern China. It was first reported that the fine-grained components of the Xiashu loess were mainly derived from the arid region of the Asian interior via the paleo-dust storms, as supported by consistent geochemical compositions of <5 μm components between the Xiashu loess and the Luochuan loess. It has been demonstrated that the geochemical compositions of the 10–20 μm and 20–50 μm components and the zircon (> 40 μm) UPb age distributions of the Xiashu loess were very similar to the Yangtze River sediments, revealing that the >10 μm components of the Xiashu loess were sourced from the local floodplains of the Yangtze River's downstream regions. Furthermore, a new method of combination of provenance results of the size-differentiated fractions and quartz grain-size contents was proposed to quantitatively estimate the Xiashu loess sources. Results of the quantitative evaluations showed that at least 82.43% of the components in the Xiashu loess were the result of nearby-source transport processes and approximately 9.64% were from distant-source transport processes. We thus conclude that the activities of local ancient dust storms dominated the aeolian deposition system in the eastern plain of the Yangtze River Delta. However, it was determined that the long-range transported dust via ancient sandstorms in Asian inland cannot be ignored because fine-grained dust has important impacts on climate, ecological environment, and human health.

Three North African dust source areas and their geochemical fingerprint

North Africa produces more than half of the world's atmospheric dust load. Once entrained into the atmosphere, this dust poses a human health hazard locally. It also modifies the radiative budget regionally, and supplies nutrients that fuel primary productivity across the North Atlantic Ocean and as far afield as the Amazonian Basin. Dust accumulation in deep sea and lacustrine sediments also provides a means to study changes in palaeoclimate, particularly those associated with rainfall climate change. Systematic analysis of satellite imagery has greatly improved our understanding of the trajectories of long-range North African dust plumes, but our knowledge of the dust-producing source regions and our ability to fingerprint their contribution to these export routes is surprisingly limited. Here we report new radiogenic isotope (Sr and Nd) data for sediment samples from known dust-producing substrates (dried river and lake beds), integrate them with published isotope data and weight them for dust source activation. We define three isotopically distinct preferential dust source areas (PSAs): a Western, a Central and an Eastern North African PSA. More data are needed, particularly from the Western PSA, but our results show a change in PSA dust source composition to more radiogenic Nd- and less radiogenic Sr-isotope values from west to east, in line with the overall decreasing age of the underlying bedrock. Our data reveal extreme isotopic heterogeneity within the Chadian region of the Central PSA, including an extremely distinctive geochemical fingerprint feeding the Bodélé Depression, the most active dust source on Earth. Our new analysis significantly improves the reliability by which windblown dust deposits can be geochemically fingerprinted to their distant source regions.

Estimating air pollution levels by numerical simulation depending on wind flow speed and dust source area

Research aim is to estimate atmospheric pollution levels in the town of Apatity, by numerical simulation, depending on the discrete arrangement of dust sources at the tailing dump closest to the town and the speed of wind flow. Methodology. For computer 3D modeling, the COMSOL software was used. To calculate the aerodynamic properties the approach of incompressible fluid and standard (k–ε)-model of turbulence were used. The spread of dust pollution has been modeled by numerically solving the convective-diffusion equation of impurity transfer taking into account the deposition rate. Numerical experiments were performed for wind flow speeds between 5 and 23 m/s and a discrete representation of the dust source area between 2 and 10 ha. Results. The spatial distributions of the model's aerodynamic properties and the interval (and total) distributions of dust pollution were obtained. The Starye Apatity area is most exposed to atmospheric pollution. Atmospheric pollution levels were analyzed and generalized to functional dependencies, depending on the values of the model's variable parameters. It is shown that the calculated dependencies between the maximum dust concentration and the dust source area can be described by linear functions, which allows predicting the critical dust source area, at which the level of air pollution reaches the threshold limit value. It is demonstrated that the dependence of the maximum dust concentration on wind flow speed at fixed dust source area values can be approximated by a power-law function. Summary. A generalized analytical formula has been derived that allows predicting maximum dust concentrations in the town of Apatity depending on the discrete locations of dust sources at the tailing dump and the speed of wind flow.

Iron Mineralogy in the Chinese Deserts and Mongolian Gobi: Impact for the Biogeochemical Cycle

Deserts are the major source of the dust greatly impact the biogeochemical cycles. However, quantitatively evaluating iron forms in the dust source areas is still a challenge due to large uncertainty in the iron mineralogy. Here we investigate iron mineralogy of 19 surface sand samples collected from seven deserts along the arid zone in North China and Mongolia.

Properties of dust source material and volcanic ash in Iceland

AbstractThe volcanic origin, primarily basaltic, of most of the surface material in Iceland influences its physical properties and appearance. Size distributions, shape analyses and melting experiments were made for surface material collected in high‐erosion dust source areas and fresh volcanic ash deposits to determine whether they differ from one another and from dust from other major dust sources. The major differences found between Icelandic dust and dust from other major dust sources in the world, such as the Sahara, are in the particle shapes, lower density and darker colour. Icelandic dust particles greater than 20 μm retain volcanic morphological properties that are also found in fresh volcanic ash. Dust and fresh volcanic ash particles less than 20 μm are crystalline and blocky in nature, similar to the dust from other global source regions. The finer grained (&lt;20 μm) Icelandic particles will have similar suspension and transport behaviours and be similarly hazardous to health and infrastructure as non‐Icelandic dust. The coarser particles (&gt;20 μm) will have different suspension and transport behaviours than other dusts due to the volcanic morphology. Icelandic surface material has between 5% and 30% glassy particles compared to fresh volcanic ash which has more than 50% glassy particles. Glassy particles were observed to melt at a lower temperature than the mineral grains; and, as a result, volcanic ash is found to be more threatening to aircraft engines than the typical dust from Iceland. Icelandic dust was observed to be blocky, or plate‐like in the respirable size fraction, suggesting similar health hazards as dust from other regions.

Changing nature of Saharan dust deposition in the Carpathian Basin (Central Europe): 40 years of identified North African dust events (1979–2018)

Several billion tonnes of mineral dust is emitted, and transported through winds every year from arid-semiarid areas. North African dust hot spots located in the Sahara are responsible for 50–70% of the global mineral dust budget. Dust-loaded air-masses originated from these sources can be transported over long distances and can also affect remote areas, such as North and South Americas, Europe, and the Middle East.In this study, we analysed 218 identified Saharan dust events (SDEs) in the Carpathian Basin (Central Europe) during 1979 to 2018. Systematic identification of SDEs and analyses of dust emission, dust source area activity, dust transporting wind systems, and transport routes revealed that different synoptic meteorological patterns are responsible for SDEs, and these are occurring mostly in spring and summer. The characteristic synoptic meteorological background of episodes was also identified, and three major types of atmospheric pressure-system patterns were distinguished.In recent years, several intense wintertime dust deposition events have been recorded in Central Europe. All of the identified unusual episodes were characterised by severe washout of mineral dust material and were related to very similar synoptic meteorological situations. Enhanced southward propagation of a high-latitude upper-level atmospheric trough to north-western Africa and orographic blocking of Atlas Mountains played an essential role in the formation of severe dust storms, whereas the long-range transport was associated with the northward branch of the meandering jet. The occurrence and southerly penetration of high-latitude upper-level atmospheric trough to low-latitudes and the increased meridionality of the dominant flow patterns may be associated with enhanced warming of the Arctic, leading to more meandering jet streams.Particles size of sampled dust material of some intense deposition episodes were very coarse with a considerable volumetric proportion of > 20 µm particles.

Long-term aerosol optical depth trend over Iran and identification of dominant aerosol types

The paper focuses on analysis of long-term changes of aerosol optical depth (AOD) over Iran. It describes contributions of dominant aerosol in the aerosol load over Iran covering the period 1980–2018. For this purpose, a long-term AOD dataset from the reanalysis-based Modern Era Retrospective Analysis for Research and Applications (MERRA-2), the satellite-based Moderate Resolution Imaging Spectroradiometer (the new version of MODIS/Terra and Aqua) as well as a new AOD product (MERRA-2 MODIS merged) were used. The ground-based AOD measurements of the five Aerosol Robotic Network (AERONET) sites used for validation demonstrated better consistency of the MERRA-2 MODIS merged (MMM) product. Analysis of these datasets demonstrated high AOD in the southwest of Iran because of the proximity to the major source areas of natural mineral dust in spring and summer. In contrast, low AOD was mostly observed along the high elevation lands in the northern and western highlands. The trend analysis of AODs revealed differences between the AOD datasets, but agree on the positive trends over southwestern Iran and negative trend in northern Iran. Classification of major aerosol types indicated that the clean marine and mixed aerosols were the dominant aerosol types during the cold and hot seasons, respectively, and the increase of desert dust around 2010 was another obvious result in spring and summer. Our results indicate that the variation in dust aerosol has a key role in determining the AOD long-term changes in Iran which has contributed in regional climate change and environmental evolutions.

Characteristics of dust devil and its dust emission in northern margin of the Taklimakan Desert

Abstract Dust aerosol has significant impacts on weather, climate, ecology, and global matter cycling, and dust devils are an important source of dust aerosol. The Taklimakan Desert is a major dust source area in East Asia, yet the characteristics of dust devils and their dust emissions are unclear in this region. In this study, the characteristics of dust devils at the northern margin of the Taklimakan Desert were analyzed. Existing equations for estimating dust emission by dust devils were revised based on our observed data, and dust emissions were estimated for the study area. The results showed that dust devils in the study area mainly occurred between March and September, which accounted for 90.9% of the total number of occurrence days in the year. Dust devil occurrence days displayed clear seasonal variation, ranked in the following descending order: summer > spring > autumn > winter. Dust devils tended to occur more frequently during the day, with relatively high occurrences from around 12:00 to 16:00 local standard time (LST) with peak occurrence 14:00–15:00 LST. Of the observed dust devils, 72.5% had a duration of 4 min or less while only 5.9% lasting for more than 6 min. The average annual dust emission from dust devils in the study area was approximately 1.96 t/km2. The occurrence of dust devils and the calculated amounts of dust emitted were closely related to surface temperature and thermodynamic efficiency.

Hybridized neural fuzzy ensembles for dust source modeling and prediction

Dust storms are believed to play an essential role in many climatological, geochemical, and environmental processes. This atmospheric phenomenon can have a significant negative impact on public health and significantly disturb natural ecosystems. Identifying dust-source areas is thus a fundamental task to control the effects of this hazard. This study is the first attempt to identify dust source areas using hybridized machine-learning algorithms. Each hybridized model, designed as an intelligent system, consists of an adaptive neuro-fuzzy inference system (ANFIS), integrated with a combination of metaheuristic optimization algorithms: the bat algorithm (BA), cultural algorithm (CA), and differential evolution (DE). The data acquired from two key sources – the Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue and the Ozone Monitoring Instrument (OMI) – are incorporated into the hybridized model, along with relevant data from field surveys and dust samples. Goodness-of-fit analyses are performed to evaluate the predictive capability of the hybridized models using different statistical criteria, including the true skill statistic (TSS) and the area under the receiver operating characteristic curve (AUC). The results demonstrate that the hybridized ANFIS-DE model (with AUC = 84.1%, TSS = 0.73) outperforms the other comparative hybridized models tailored for dust-storm prediction. The results provide evidence that the hybridized ANFIS-DE model should be explored as a promising, cost-effective method for efficiently identifying the dust-source areas, with benefits for both public health and natural environments where excessive dust presents significant challenges.

A Method for Estimating the Threshold Wind Speed for Dust Emissions as a Function of Soil Moisture

A method is proposed to estimate the threshold wind speed for dust emissions as a function of soil moisture in arid regions. This method, which is applicable at the local scale, employs a model of the surface heat budget to estimate the spatial distribution of thermal inertia-derived soil moisture (TISM) and an analytical footprint model to estimate dust source areas. It incorporates readily available satellite and meteorological data. The soil moisture inside the dust source area is estimated for individual dust phenomena observed at a synoptic surface observation site, and then, together with the corresponding observed wind speed, the threshold wind speed as a function of soil moisture is found by employing the parametrization of Fecan et al. (Ann Geophys 17:149–157, 1999). This relationship represents the local dust climatology at the observation site, although the data include some outliers. The results show that readily available data for the natural environment can be used, as an alternative to wind-tunnel data, with the parametrization used to derive the threshold wind-speed relation. The derived relation indicates the TISM and wind speed at which the probability of a dust phenomenon is 10%. Moreover, the threshold wind-speed results are not sensitive to the principal footprint-model parameters. The TISM standard error of approximately 0.04 m3 m−3 could significantly affect the results under dry and weak-wind conditions, but this sensitivity can be avoided if the soil clay content or the soil type at the observation point is known.

Provenance of loess deposits and stepwise expansion of the desert environment in NE China since ~1.2 Ma: Evidence from Nd-Sr isotopic composition and grain-size record

The Quaternary wind-blown Chinese loess-paleosol sequence, which developed as a product of the intensification of Northern Hemisphere glacial-interglacial cycles, is a major source of information on aridification of the Asian interior. In northeastern (NE) China, extensive loess deposits occur that have great potential for reconstructing the long-term paleoclimatic evolution of the region. Despite existing geochemical data indicate that the probable major source areas for these loess deposits were the nearby Horqin and Otindag deserts, it is still unclear that whether there was a long-term change in the detrital source of these loess deposits. In addition, the aridity history and long-term desert evolution of NE China are currently poorly understood. In the present study, we measured the silicate Nd and Sr isotopic composition of the 28–45 μm grain-size fraction from multiple loess sections (NYZG, SBH, and TDJZ). The results show that the loess deposits of the three sites were dominantly sourced from the Otindag sandy desert and that this source remained constant for the past 1.2 Ma. Notably, the 87Sr/86Sr ratios are influenced mainly by variations in the content of clay-sized material present in the form of aggregates or adhering to the surface of coarser particles. Therefore, caution is needed in the use of 87Sr/86Sr ratios of the 28–45 μm fraction as a tracer of eolian dust, when the clay minerals are not completely removed during the pretreatment process. The grain-size variability of the three sections indicates that stepwise enhancement of aridification in the Otindag sandy desert occurred at 1.2 Ma, 0.9 Ma, and 0.7 Ma, which coincided respectively with the beginning of the Mid-Pleistocene transition (MPT), an extremely cold event at ~0.9 Ma within the MPT, and the establishment of a full glacial climate at the termination of the MPT. This finding supports the hypothesis that the growth of high-latitude ice sheets was the major driver of the long-term aridification of Asian dust source areas.

Mechanism for enhanced eolian dust flux recorded in North Pacific Ocean sediments since 4.0 Ma: Aridity or humidity at dust source areas in the Asian interior?

Abstract Eolian material within pelagic North Pacific Ocean (NPO) sediments contains considerable information about paleoclimate evolution in Asian dust source areas. Eolian signals preserved in NPO sediments have been used as indices for enhanced Asian interior aridity. We here report a detailed eolian dust record, with chemical index of alteration (CIA) and Rb/Sr variations, for NPO sediments from Ocean Drilling Program Hole 885A over the past 4.0 m.y. CIA and Rb/Sr co-vary with the dust signal carried by combined eolian hematite and goethite concentrations. Changes in CIA around the intensification of Northern Hemisphere glaciation (iNHG) event at ca. 2.75 Ma indicate that dust production in source areas was associated mostly with physical and chemical weathering before and after the iNHG event, respectively. We here attribute the eolian flux increase into the NPO across the iNHG event mainly to increased availability of wind-erodible sediment in dust source areas derived from snow and glacial meltwater runoff, which resulted from glacial expansion and enhanced snowfall in the mountains surrounding the Tarim region in response to global cooling. Our results provide a deeper understanding of Asian interior environmental changes in response to global paleoclimate changes, where dust source areas became intermittently moister rather than more arid in response to global cooling.

Sr-Nd isotopic characteristics of the Northeast Sandy Land, China and their implications for tracing sources of regional dust

The Sr-Nd isotopic study of the Northeast Sandy Land (NESL), China is of great significance for a thorough understanding of the dust system in this area. The 162 bulk (<63 μm) and 86 size-fractioned samples of surface eolian sands and river sands in the NESL are very suitable to be added to the elaborate Sr-Nd isotopic composition dataset. The results are as follows. The Nenjiang River drainage system (NR) in the Songnen Sandy Land (SNSL) and the Hulun Buir Sandy Land (HLSL) are characterized by more radiogenic Nd values relative to the other areas within the NESL whereas the Onqin Daga Sandy Land (ODSL), the Horqin Sandy Land (HQSL) and the Songhua River drainage system (SR) exhibit a clear overlap of Sr-Nd isotopic composition. Nd isotopic composition (especially in the ODSL) exhibits significant dependency on time effect, indicating instability of geochemical composition in the dust source areas. Sr isotopic composition is slightly affected by grain size with very small variations of size-separated 87Sr/86Sr values, yet Nd isotopic composition exhibits clear grain size-dependent variability. The substantial proportion of Sr-Nd isotopic values show enrichment in the coarse-grained fraction, which is accounted for by source-rock control. Both the HLSL and the NR to the northwest of Harbin play very little role in contribution to eolian dust deposits in the Northeast Plain, either in the geological past or now, whereas Sr-Nd geochemical composition alone is insufficient to unequivocally distinguish exact provenance of the eolian dust deposits in this region. The integrated consideration, as expected, revealed the derivation of the eolian dust deposits. The eolian loess and the modern dust-storm deposits in Harbin share significantly different source areas: Harbin loess is the product of spring dust-storm weather and has a mixed source with the SR being the main dust contributor, whereas 2011 Harbin dust-storm deposits were derived from the ODSL and beyond which also provided minor amounts of fine dust particles to Harbin loess.

New insights on sources contributing dust to the loess record of the western edge of the Pampean Plain during the transition from the late MIS 2 to the early Holocene

High-resolution studies of palaeorecords located closer to the dust source areas of South America are relevant for increasing the knowledge on past climatic conditions in the Southern Hemisphere. In this sense, the Pampean loess archives can offer explicit records of dust source, transport, and deposition in the region, providing new insights which may be used to better understand the role of dust in future climate change scenarios. In this work, we studied a loess sequence located at the westernmost Pampean Plain. The studied sequence covers a span of time from the late Marine Isotope Stage (MIS 2) period up to the early Holocene. Loess samples from this record have two grain-size populations, indicating more than one dust source area. The dominance of a coarse-silt subpopulation during the transition from the late MIS 2 to the early Holocene suggests that proximal dust sources were dominant at that time. Two of the most proximal dust sources were analyzed as probable contributors to the Lozada site: sediments derived from the Eastern Pampean Ranges and sediments derived from the shorelines of the Mar Chiquita Lake. The geochemical data suggest that neither area was a significant dust source to the eastern Pampean Plain during the studied interval. Instead, our geochemical data suggest a dominant supply from a southern and relatively closer area, linked to the foothills of the Andes, and the increased activation during the early Holocene of a more distant source to the north in the Puna region, which contributed finer loess.

African dust deposition in Puerto Rico: Analysis of a 20-year rainfall chemistry record and comparison with models

Dust deposition represents an important flux of rock-derived nutrients such as phosphorus to ecosystems on highly weathered soils. Direct measurements of terrestrial dust deposition and its spatial variability are rare, yet they are essential for testing models of dust deposition processes and understanding the biogeochemical effects of dust. Long-term records of precipitation chemistry are available in the Luquillo Mountains of Puerto Rico, which are downwind of the world's largest dust source in Africa. We analyzed 20-year datasets of openfall, throughfall, and wet-only precipitation chemistry with weekly resolution at two different locations in the Luquillo Mountains to evaluate spatial and temporal variability of dust inputs and compare the observational records with models. Based on rainwater dissolved silica and total suspended solids content, the measured dust flux varied by a factor of 2 over a distance of 10 km despite similarities between sites in elevation and rainfall amount. In comparison with simulated dust deposition from ten models in the Aerosol Comparisons between Observations and Models (AeroCom) project, the empirical rainfall chemistry agrees well with the mean of the models on the seasonal distribution of wet dust distribution. Both the data and the models show a summer maximum in wet dust deposition that is consistent with variation in transport pathways and the dust source area emission strength based on environmental conditions in the Sahel region. The rainfall chemistry record and AeroCom models also agree in terms of attributing ~70% of the total dust deposition overall to dry deposition, although the range of uncertainty in the models is large. The results indicate value in combining long-term analysis of rainfall chemistry with data from satellites and models, and highlight the need for accurate ground-based metrics for dry deposition to improve understanding and modeling of dust deposition processes. The dataset complements earlier studies that characterize the dust plume originating from Northern Africa and its impact on ecosystems in South America and the Caribbean.

Vertical distributions of airborne microorganisms over Asian dust source region of Taklimakan and Gobi Desert

Airborne microorganisms transported by dust events from Asian Deserts influence climate changes, ecosystem dynamics and human health in the westerly-wind blowing areas of East Asia. However, the vertical transport of airborne microorganisms was not understood in detail. We collected aerosols at high altitudes (800 m and 500 m) and ground levels (5 m and 10 m) at Asian dust-source area, such as the Taklimakan and Gobi Deserts, for analyzing compositions and abundances of the airborne microorganisms that are distributed vertically over desert area. Assessment of the dust particles using an optical particle counter and microscopic observation counts demonstrated that the mineral and microbial particles remained suspended at altitudes of over 300 m and decreased to half to one-tenth of concentrations compared to those at the ground level. High-throughput sequencing of 16S rRNA genes (bacterial taxonomic marker) revealed that the airborne bacterial communities were mixed vertically at the altitudes of some hundreds of meters over both the sites and were predominantly composed of the phyla Actinobacteria, Firmicutes, Bacteroidetes, and Proteobacteria. In contrast, using sequencing analysis of internally transcribed spacer regions (fungal taxonomic markers), the fungal community structures over both the sites were different at high altitudes and ground levels. Sequences belonging to the phylum Ascomycota increased at high altitudes and comprised those of a commonly detected mold that includes the genera Cladosporium and Alternaria and is thought to be resistant to atmospheric stressors. Our results indicate that airborne bacterial communities are easily mixed vertically over dust-source desert, while stressor-tolerant fungi of airborne Ascomycota remain at high altitudes of desert atmosphere.

Geochemical characterization of major elements in desert sediments and implications for the Chinese loess source

Mineral dust released from the desert is one of the important components of atmospheric aerosols. Arid and semi-arid deserts, sandy lands in northern China and their adjacent Gobi Desert lands in northern China and neighboring Mongolia (hereinafter referred to as Gobi) are potential sources of mineral dust in Asia. However, there is currently a lack of systematic studies on the characteristics of major elements in the potential mineral dust source area. This study investigates the major elements of 310 surficial sand samples in the stabilized and semi-stabilized dune fields from 12 deserts/sandy land and Gobi in northern China and southern Mongolian Gobi and compiles published data. We identify four regions with distinct geochemical characteristics: (1) Taklimakan, Kumtag and Qaidam deserts in western China; (2) Badain Jaran, Tengger, Hobq, and Mu Us deserts in the central and western regions of northern China; (3) Hulun Buir, Onqin Daga and Horqin sandy lands in northeast China; and (4) Gobi and Gurbantunggut deserts. The spatial distributions of the SiO2 and CaO contents in Chinese deserts are highly variable. The average content of SiO2 generally reflects an increasing trend from west to east, while the average content of CaO shows a decreasing trend from west to east. We demonstrate that the spatial variation of major elements is likely controlled by two key scenarios: the composition of source rocks and the mineral maturity caused by the supply of fresh materials. The SiO2/(Al2O3+K2O+Na2O) ratio of desert sediments is relatively lower in western China and may be caused by high ferric-magnesia and high carbonate minerals; this ratio is relatively higher in the northeast sandy lands and may be linked to a lack of fresh material supply and the presence of high K-feldspar minerals in source rocks. The deserts can be further distinguished by ternary diagrams with SiO2/10-CaO-Al2O3, (K2O+Na2O)-CaO-Fe2O3 and CaO-Na2O-K2O. The comparison of major elements between desert sediments and loess suggests that the western and/or central deserts in China may be the potential provenances of loess on the Loess Plateau.

Fluvial sediments in the Alagxa Plateau as a dust source: iron mineralogical and geochemical evidence

The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a source of eolian silty. The northeastern margin of the Tibetan Plateau is one of the most actively-growing mountain belt on earth, and has large amounts of debris, with masses of fine grained material, which were continuously mobilized and deposited in the Alagxa Plateau by rivers, forming broad alluvial fans. It is possible that the role of fluvial sediments as a source of silty dust in the Alagxa Plateau has been underestimated. In this study, we test this hypothesis by investigating the iron mineralogical and geochemical characteristics of the fluvial sediments and the surface material of the sandy desert in the Alagxa Plateau, and comparing them with paleo-eolian dust deposits (loess) in the adjacent Chinese Loess Plateau (CLP) to investigate the possible linkages among the fluvial sediments, sandy desert and the last glacial loess of the CLP. The results show that sandy desert typically have high contents of goethite, and high ratios of goethite to hematite, similar to the fluvial sediments in the Alagxa Plateau. Based on the major element characteristics, field investigations and the results of previous studies, we found a genetic link between the silt component of the fluvial sediments and the sandy desert in the Alagxa Plateau with high value of Gt (goethite) and similarity of the Gt/(Hm (hematite)+Gt) ratio. But the silt component of the sandy desert main come from the adjacent fluvial sediments. The iron mineralogical characteristics (χ (magnetic susceptibility), χARM (anhysteretic susceptibility), SIRM (saturation isothermal remanent magnetization) and SIRMAF100mT (SIRM demagnetized at 100 mT)) of the CLP samples overlap with those of the fluvial sediments in the Alagxa Plateau, but there is a mismatch with the sandy desert samples. This suggests that the fluvial sediments are the source of a large amount of silty material which could be transported to the CLP. Therefore, we conclude that the fluvial sediment in the Alagxa Plateau is an important source of eolian silt, which is deposited in downwind region, and that this source has been previously underestimated.