Rees and Trace Element Evidences

atmosphere

Article Tracing the Provenance of Long-Range Transported Dust Deposition in Cryospheric Basins of the Northeast Tibetan Plateau: REEs and Trace Element Evidences

Ting Wei 1,2, Zhiwen Dong 1,3,*, Shichang Kang 1,4,* and Sven Ulbrich 3

1 State Key Laboratory of Cryosphere Sciences, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China; [email protected] 2 University of Chinese Academy of Sciences, Beijing 100049, China 3 Institute for Geophysics and Meteorology, University of Cologne, D-50923 Cologne, Germany; [email protected] 4 CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China * Correspondence: [email protected] (Z.D.); [email protected] (S.K.)

Received: 7 September 2018; Accepted: 17 November 2018; Published: 23 November 2018

Abstract: Based on cryoconite and snow dust samples collected from various glaciers and snowpacks in northeast Tibetan Plateau (NETP) margin and surrounding areas, this study investigated the rare earth element (REE) and trace element composition of long-range transported (LRT) dust in glacier surfaces at the NETP locations, in order to trace its source areas and the transport over the region. Results showed that the deposited dust in NETP mainly originated from the adjacent Qaidam Basin, Badain Jaran and Taklimakan Deserts based on the similarity in (La/Sm)N, Th/YbN and Nb/YbN ratios. However, most samples collected at Miaoergou Glacier (MG) located in the Tianshan Mountains showed very different rare earth elements (REEs) ratios from the above locations attributed to the dominant contribution of LRT dust emitted by the southern Gobi Deserts. We found that large central Asian deserts rarely contributed LRT dust to Yuzhufeng (YG) in the hinterland Tibetan Plateau (TP). Taking the region as a whole, it was found that most of the glacier and snowpacks showed mixed dust sources and inputs from different parts of surrounding central Asian deserts that are characterized by different mineralogical settings. Geochemical data indicated that the NETP region acts as an important channel for aeolian transport from large Asian deserts into Loess Plateau and eastern regions, with atmospheric circulations bringing plenty of dust particles deposition to the high-altitude glacier surface in NETP margin. This work is of great importance in providing a new complete view of LRT aeolian emission and transport over the NETP region.

Keywords: northeast Tibetan plateau margin; long-range transported aeolian dust; glacier snowpack; asian dust transport channel; REE and trace element geochemistry

1. Introduction The northeast Tibetan Plateau (NETP) and south Gobi Deserts in Mongolia, known as the active dust areas, are the primary contributors to the adjacent sand deserts and the Loess Plateau [1,2]. Previous studies showed that the aeolian deposited in the Badain Jaran Desert and Loess Plateau are predominantly derived from the Qilian Mountains and NETP margin initially via fluvial processes and wind erosion and/or deflation by westerly winds [2–5]. Meanwhile, the south Gobi, one of the major Asian dust emission sources, was identified as the dominant dust source for Loess Plateau and Ordos Plateau [6,7]. Geochemical composition of dust materials deposited in high mountain glaciers

Atmosphere 2018, 9, 461; doi:10.3390/atmos9120461 www.mdpi.com/journal/atmosphere Atmosphere 2018, 9, 461 2 of 13 can be used to improve understanding in transport routes and atmospheric cycle of aeolian dust in modern and ancient times [4]. Previous studies have revealed dust transport from the NETP and south Gobi Deserts into Loess Plateau during the historical processes [4,5,8,9]. However, the current regional aeolian cycle and transport routes of long-range transported (LRT) dust in high elevation from the surrounding Asian deserts to the NETP region remains unclear. Very limited research focused on understanding LRT dust in high latitudes from the Asian deserts to the NETP region owing to its remote and the lack of large range ﬁeld investigation, which is of great importance as the high elevation transport of LRT dust could provide clear atmospheric environment and dust routes information on a large scale. Due to glaciers existing on high mountain regions, glacier snowpack in the NETP can thus receive aeolian transported in the middle and upper troposphere through atmospheric circulation [9–12]. Thus, mountain glaciers in NETP region could represent a valuable area to trace the aeolian transport route from the central Asian deserts and also Tibetan Plateau (TP) surface crust [13–17]. Moreover, rare earth element (REE) and trace elements are demonstrated to be powerful tools for tracing the dust origin based on their obvious differences in regional distribution of desert sands [18]. Due to their low solubility of particulate forms, REEs are generally in the particulate phase during atmospheric transport [19]. These properties make REE fractionation with very little change during weathering and diagenesis. In this study, large range ﬁeldwork sampling were launched at the various glacier locations in the NETP region, including the Lenglongling Glacier (LG), Qiyi Glacier (QG), Dabanshan Snowpack (DS), Jingyangling Snowpack (JS) and Ober Ridge Snowpack (OS) in the Qilian Mountains, and Yuzhufeng Glacier (YG) in the Kunlun Mountains, and also the Miaoergou glacier (MG) in adjacent eastern Tianshan Mountains, which together are called as a pan-NETP region (Figure1). The objective of this study is to investigate the REE and trace element compositions on cryoconite and snow dust deposited on the glaciers and further to trace the provenance of LRT Asian dust disposition on the NETP glaciers, providing a better understanding on dust transport process over the region. Moderate Resolution Imaging Spectroradiometer Aerosol Optical Depth (MODIS AOD) (http://giovanni.sci. gsfc.nasa.gov)[20] and wind vector data in the region were also used to demonstrate the potential dust transport source and routes.

2. Materials and Methods

2.1. Sampling A total of 36 cryoconite and snow dust samples were collected at different elevations along the high mountain glaciers and snowpacks in June and August 2017. Among those glaciers and snowpacks, DS, LG, QG, JS, and OS are located in the Qilian Mountains. YG is located in the Kunlun Mountains (inner TP) and is adjacent to the Qaidam Desert. MG is located in the eastern Tianshan Mountains and is close to the south Gobi Deserts in Mongolia, one of the largest dust emission sources in the world (Figure1). We also collected samples in MG for comparison with dust samples from the NETP region. In addition, 7 local surface crust samples were collected at nearby regions including Golmud, Hami, and the glacier basins to ﬁnd out local dust contribution to those glaciers and snowpacks. The detailed information of sampling locations was listed in Table1. Atmosphere 2018, 9, 461 3 of 13 Atmosphere 2018, 9, x FOR PEER REVIEW 3 of 13

Figure 1. Location map showing the location of study area and sampling sites. MG, QG, YG, OS, Figure 1. Location map showing the location of study area and sampling sites. MG, QG, YG, OS, JS, JS, DS, and LG refer to Miaoergou Glacier, Qiyi Glacier, Yuzhufeng Glacier, Ober Ridge Snowpack, DS, and LG refer to Miaoergou Glacier, Qiyi Glacier, Yuzhufeng Glacier, Ober Ridge Snowpack, Jingyangling Snowpack, Dabanshan Snowpack and Lenglongling Glacier, respectively. Jingyangling Snowpack, Dabanshan Snowpack and Lenglongling Glacier, respectively. Table 1. Description for cryoconite and surface snow dust sampled from the glacier and snowpacks in Tablethe NETP 1. Description and eastern for Tianshan cryoconite Mountains. and surface snow dust sampled from the glacier and snowpacks in the NETP and eastern Tianshan Mountains. Latitude Longitude Altitude Sample Location Mountains Type Latitude Longitude Altitude NumberSample Location Mountains (N) (E) m a.s.l Type (N) (E) m a.s.l Number Dabanshan 4 Snow dust Qilian Mountains ◦ 0 ◦ 2556–3625 DabanshanSnowpack (DS) Qilian 37 21 101 24 2556– 4 Snow dust 37°21′ 101°24 1 Surface crust Snow dust SnowpackLenglongling (DS) Mountains 3625 8 1 Surface crust Qilian Mountains ◦ 0 ◦ 0 3232–3992 Cryoconite Glacier (LG) 37 30 101 53 Snow dust Lenglongling Qilian 3232– 18 Surface crust 37°30′ 101°53′ SnowCryoconite dust Glacier (LG) Mountains 3992 9 Qiyi Glacier (QG) Qilian Mountains 39◦140 97◦450 3883–4750 1 CryoconiteSurface crust 1 SurfaceSnow crust dust QiyiMiaoergou Glacier Qilian 3883– 9 Snow dust Tianshan Mountains39°1442′ ◦590 97°4594◦16′ 0 3100–3320 5 Cryoconite Glacier(QG) (MG) Mountains 4750 Cryoconite Yuzhufeng 1 SnowSurface dust crust Kunlun Mountains 35◦410 94◦160 4342–4720 8 MiaoergouGlacier (YG) Tianshan 3100– CryoconiteSnow dust 42°59′ 94°16′ 15 Snow dust GlacierOber Ridge (MG) (OS) MountainsQilian Mountains ◦ 0 ◦ 0 36853320 Cryoconite 37 59 100 55 1 Surface crust YuzhufengJingyangling Kunlun 4342– Snow dust Qilian Mountains35°41 37′ ◦480 94°16101◦09′ 0 3469 28 Snow dust GlacierSnowpack (YG) (JS) Mountains 4720 Cryoconite ◦ ◦ 0 Golmud KunlunQilian Mountains 36 19 95 13 2963 11 SurfaceSnow crust dust ◦ 0 ◦ 0 Ober RidgeHami (OS) MountainsTianshan Mountains 37°5942′ 78 100°5593 44′ 26923685 11 SurfaceSurface crust crust Jingyangling Qilian 37°48′ 101°09′ 3469 2 Snow dust SnowpackBefore sampling,(JS) Mountains all containers and collecting tools were cleaned following the successive nitric acid immersion with fourKunlun different concentrations [21]. Then, we wore clean polypropylene suits and Golmud 36°19 95°13′ 2963 1 Surface crust gloves during samplingMountains to avoid contamination and ensure the accuracy of the laboratory measurement, and used the precleanedTianshan stainless-steel shovels to collect the snow and cryoconite samples. After that, Hami 42°78′ 93°44′ 2692 1 Surface crust all samples were storedMountains in clean 30 mL polyethylene bottles and acidiﬁed with ultra-pure nitric acid (0.5% v/v) to dissolve the trace elements together with atmospheric particles and to prevent the elementsBefore adhering sampling, onto all thecontainers walls of and the collecting bottles. Ultimately, tools were the cleaned collected following samples the were successive kept frozen nitric aciduntil immersion the analysis with at thefour Analytical different Laboratoryconcentrations of Beijing[21]. Then, Research we wore Institute cleanof polypropylene Uranium Geology. suits andDuring gloves the experimentalduring sampling analysis to avoid process, contamination protective clothing and ensure and footwear the accuracy had to of be used.the laboratory measurement, and used the precleaned stainless-steel shovels to collect the snow and cryoconite samples. After that, all samples were stored in clean 30 mL polyethylene bottles and acidified with

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ultra-pure nitric acid (0.5% v/v) to dissolve the trace elements together with atmospheric particles and to prevent the elements adhering onto the walls of the bottles. Ultimately, the collected samples were kept frozen until the analysis at the Analytical Laboratory of Beijing Research Institute of

AtmosphereUranium2018 Geology., 9, 461 During the experimental analysis process, protective clothing and footwear4 ofhad 13 to be used.

2.2. Rees and Trace ElementsElements AnalyzedAnalyzed REEs areare aa groupgroup ofof 1414 elements elements including including La, La, Ce, Ce, Pr, Pr, Nd, Nd, Sm, Sm, Eu, Eu, Gd, Gd, Tb, Tb, Dy, Dy, Ho, Ho, Er, Er, Tm, Tm, Yb, Yb, Lu. TheLu. The selected selected trace trace elements elements in this in study this study included included Nb, Zr, Nb, Th, Zr, Y, Sc.Th, Aiming Y, Sc. Aiming to break to down break the down silicates the andsilicates other and salts, other all samplessalts, all were samples digested were with digested ultra-pure with HNO ultra-pure3–HF in HNO poly tetra3–HF ﬂuoroethylenein poly tetra (PTFE)fluoroethylene screw–top (PTFE) bombs screw–top at 100 ◦C forbombs 24 h onat a100 hotplate °C for until 24 noh residueon a hotplate was detected. until no Then residue the totally was dissolveddetected. Then samples the totally were transferred dissolved samples to clean were capped transferred PTFE bottles to clean using capped a Finnpipette PTFE bottles to mark using the a volume,Finnpipette and to were mark diluted the volume, with 5% and HNO were3 (3 diluted mL) for with inductively 5% HNO coupled3 (3 mL) plasma-mass for inductively spectrometry coupled (ICP–MS,plasma-mass Thermo spectrometry Scientiﬁc (ICP–MS, Element/XR, Thermo Waltham, Scientific USA) Element/XR, analysis. Waltham, USA) analysis.

2.3. Tem-Edx MeasurementMeasurement Analyses of thethe snowpack/cryoconitesnowpack/cryoconite individual individual particles particles were conducted using a JEM–2100F (JEOL,(JEOL, Tokyo, Japan)Japan) transmissiontransmission electron microscopemicroscope (TEM) operated at 200 kV. The analyses involved conventional and high-resolution imaging using bright field ﬁeld mode, electron diffraction, and energy-dispersiveenergy-dispersive X–rayX–ray spectrometryspectrometry (EDX)(EDX) [[22,23].22,23]. Laboratory TEM–EDX analysis was performed onon thethe individual individual cryoconite cryoconite particles particles ﬁltered filtered on calcium-coatedon calcium-coated carbon carbon (Ca–C) (Ca–C) TEM grids.TEM Thegrids. TEM The instrument TEM instrument had the advantageshad the advantages of high-resolution of high-resolution (up to 20 nm), (up and to the20 “transmission”nm), and the feature“transmission” for individual feature particle for individual analysis, particle when combined analysis, withwhen EDX combined analysis with for theEDX particle analysis elemental for the compositionparticle elemental (Figure composition2). (Figure 2).

Figure 2.2. TEM–EDXTEM–EDXmeasurement measurement of of individual individual particles particle ins thein the glacier glacier snowpack snowpack and cryoconiteand cryoconite dust indust northeast in northeast TP, (a )TP, aggregated (a) aggregated clay mineral clay mineral and black and carbon black carbon (BC) particles (BC) particles in LG, ( bin) CaSOLG, (4b)mineral CaSO4 aggregatedmineral aggregated particles particles in DS, (c in) Mixed DS, (c organic) Mixed matterorganic and matter aluminosilicate and aluminosilicate particles particles in QG; (ind) QG; Silicate (d) andSilicate ﬂy and ash aggradedfly ash aggraded particles particles in MG; in (e) MG; Aluminate (e) Aluminate mineral mineral particles particles in YG; (inf) SootYG; ( andf) Soot Fe-rich and mineralFe-rich mineral aggregates aggregates in YG. Thein YG. mixture The ofmixture mineral of andmineral organic and andorganic BC also and showed BC also LRT showed source LRT of glaciersource of surface glacier dust. surface dust.

2.4. Quality Control of Chemical Analysis 2.4. Quality Control of Chemical Analysis The blank samples from both the laboratory and ﬁeld work were also measured using the same The blank samples from both the laboratory and field work were also measured using the same procedure. Result of the blank analyses showed that there was negligible contamination (<5%), procedure. Result of the blank analyses showed that there was negligible contamination (<5%), during the sampling, storage, and transportation. Elemental concentrations were quantiﬁed using during the sampling, storage, and transportation. Elemental concentrations were quantified using external calibration standards. For analytical precision, the corresponding RSD(relative standard external calibration standards. For analytical precision, the corresponding RSD(relative standard deviation) values of all element concentrations measured in the reference material were found to be less than 5%. Atmosphere 2018, 9, x FOR PEER REVIEW 5 of 13

deviation) values of all element concentrations measured in the reference material were found to be less than 5%. Atmosphere 2018, 9, 461 5 of 13 2.5. Data Analysis and Geochemical Parameters

2.5. DataThe Analysis REE and and trace Geochemical element Parameters compositions in those locations of the NETP glacier and snowpack wereThe measured. REE and REE trace abundance element compositions in chondrites, in the those most locations primitive of thesubstance NETP glacierfrom solar and system, snowpack was wereused measured. to eliminate REE the abundance odd-even ineffect chondrites, and standa therdize most the primitive element substance compositions from solar[24]. In system, detail, was(La/Yb) usedN to ratio eliminate can reflect theodd-even the different effect degree and standardizebetween Light the Rare element Earth compositions Element (LREE) [24]. and In detail, Heavy (La/Yb)Rare EarthN ratio Element can reflect (HREE). the differentThe (La/Sm) degreeN ratio between can represent Light Rare theEarth difference Element of LREE, (LREE) with and a Heavypositive N Rarecorrelation Earth Element between (HREE). the ratio The (La/Sm)and the Ndifferentialratio can represent degree. theMoreover, difference (Gd/Yb) of LREE, may with indicate a positive the correlationdifferential between degree theof the ratio HREE and and the differentialit is negative degree.ly correlated Moreover, with (Gd/Yb)the differentialN may indicatedegree. Also, the differentialEu/Eu* = degree(EuN/ (Sm of theN * HREEGdN) 1/2 and), could it is negatively indicate correlatednot only the with sedimentary the differential environment degree. Also, but Eu/Eu* also the 1/2 =parent (EuN/(Sm rockN characteristics* GdN) ), could of dust indicate materials. not only La-Th-Sc the sedimentary composition environment is generally butused also to discriminate the parent rockthe characteristicssediment sources[25,26]. of dust materials. Th/YbN La-Th-Scand Nb/Yb compositionN ratios areis useful generally tools used for the to discriminatediscrimination the of sedimenttectonic sourcessettings[27–29]. [25,26]. Th/Yb Y/Zr Nandand Nb/Zr Nb/Yb ratiosN ratios represent are useful differential tools for the degree discrimination in different of tectonicminerals settingsdue to [different27–29]. Y/Zrmineral-liquid and Nb/Zr distribution ratios represent coefficients differential [27]. degree in different minerals due to different mineral-liquid distribution coefficients [27]. 3. Results and Discussion 3. Results and Discussion 3.1. Geochemical Compositions of Aeolian Materials in Different Locations Of the NETP Glaciers and 3.1.Snowpacks Geochemical Compositions of Aeolian Materials in Different Locations Of the NETP Glaciers and Snowpacks SeveralSeveral REE REE characteristic-parameters characteristic-parameters are usedare hereused to here find outto find the provenance out the provenance of dust deposition of dust ontodeposition the glaciers onto and the snowpacks. glaciers and In general,snowpacks. all samples In general, from MGall samples are uniformly from describedMG are asuniformly lower (La/Sm)describedN (averaging as lower (La/Sm) 2.65), lowerN (averaging Th/YbN and2.65), Nb/Yb lowerN Th/Yb(averagingN and 0.26Nb/Yb andN 0.39,(averaging respectively), 0.26 and and 0.39, a weakrespectively), negativeeven and positivea weak negative Eu anomaly even (averaging positive Eu 0.98), anomaly suggesting (averaging a large discrepancy0.98), suggesting from a other large studydiscrepancy locations from in NETP other region study (Figure locations3). The in elementalNETP region ratios (Figure exhibit 3). similar The elemental REE characteristics ratios exhibit in thesimilar NETP REE locations characteristics (QG, OS, in DS, the JS, NETP LG ), implyinglocations an(QG, identical OS, DS, dust JS, sourceLG ), implying in this region. an identical However, dust thesource ratios in of severalthis region. samples However, from YG the display ratios lower of several (La/Sm) samplesN, higher from Eu/Eu*, YG display but similar lower Nb/Yb (La/Sm)N toN, thehigher NETP Eu/Eu*, locations, but indicating similar Nb/Yb the mixtureN to the LRTNETP dust locations, sources indicating in the region. the Moreover,mixture LRT DS dust shows sources lower in Y/Zrthe region. and higher Moreover, (La/Sm) DSN comparedshows lower to the Y/Zr other and NETP higher locations, (La/Sm) showingN compared theobvious to the other difference NETP existedlocations, between showing those the NETP obvious locations, difference which existed is probably between caused those by NETP mixed locations, source and which routes is probably of LRT dustcaused under by the mixed regional source atmospheric and routes circulations of LRT dust of un fineder dust the particlesregional originatedatmospheric from circulations different areasof fine withdust different particles geochemical originated from settings. different areas with different geochemical settings.

FigureFigure 3. 3.Bivariate Bivariate plots plots and and spatial spatial distributions distributions of of geochemical geochemical compositions compositions of of snow snow dust dust and and cryoconitecryoconite samples samples from from the the glaciers glaciers and and snowpacks snowpacks in in the the Tianshan Tianshan Mountains Mountains and and northeast northeast Tibetan Plateau. (a) (La/Sm)N versus Nb/Zr; (b) Nb/YbN versus Th/YbN;(c) Y/Zr versus Eu/Eu*; (d) (La/Sm)N versus Eu/Eu*. Atmosphere 2018, 9, 461 6 of 13

In total, there is large spatial difference existed in trace elements and REE composition among MG, YG, and the other Qilian Mountains sites (QG, LG, DS, JS, OS). The climatic conditions (atmospheric circulation, prevailing wind, etc.) and surrounding deserts environment are the main reasons for the large difference of dust provenance among these locations. In specific, the climatic conditions of MG situated in the eastern Tianshan Mountains, is with westerlies prevailing around all the year. YG is different from MG with more precipitation (maximum precipitation in summer) and is controlled by westerlies and also the summer/winter monsoon over the plateau surface. Another factor is the topography of the area. MG is surrounded by the Gobi Deserts in central Asia, and to the south lies the Taklimakan Desert, which contributes with a large dust flux to the northern Hemisphere [30], and the LRT dust may have even been transported to the Loess Plateau through the eastern Tianshan and the NETP region. Southern and Northern Gobi Deserts in Mongolia and in also north China are both adjacent to the glaciers in the Tianshan Mountains, which will certainly influence the central Asia dust transport route to the MG basin. The YG, located in the downwind of the Qaidam Basin and the Kumtag Desert, is also likely to be affected by the arid deserts of the TP surface crust because of the expanded desert on the northern plateau during recent years [15]. The glaciers in the Qilian Mountains (e.g., QG, LG, DS, OS, and JS) are geographically close to the Badain Jaran and Tengger Deserts, which also have plenty of dust emission and then transport to the Loess Plateau and more eastern regions [3]. Regional climate background and dust source distribution may have together caused the complicated dust transport routes in the pan-NETP region. Therefore, various arid deserts source to the glaciers lead to the different geochemical element compositions of LRT dust deposited on the glaciers and snowpacks.

3.2. LRT Dust in NETP Region and Its Relationship with Large Scale Regional Atmospheric Circulation

The Bivariate diagrams of (La/Sm)N, (La/Yb)N, Eu/Eu* and (Gd/Yb)N ratios of samples from the glaciers and snowpacks for comparing of the sampling locations with potential dust sources are shown in Figure4. The different locations of the Qilian Mountains (QG, LG, DS, and OS) show very similar dust geochemistry with the large deserts, such as Qaidam Basin, Badain Jaran and Taklimakan deserts. Moreover, many samples of the above locations show the similar REE and trace element geochemistry to the NETP surface crust (Figure4), which is largely different from the western TP (such as higher (La/Sm)N and (La/Yb)N). It is probable that the Badain Jaran and Tengger Deserts are the major sources for dust inputs of LG, QG, JS, and OS, as the similarity of (La/Sm)N, (La/Yb)N, Eu/Eu* and (Gd/Yb)N ratios between them, which is also demonstrated by La-Th-Sc and TiO2–Zr–Al2O3 diagram (see Figure5). Besides, REE data of NETP glacier is mainly close to that of the east of the TP surface crust dust. Therefore, the Qaidam Basin, Badain Jaran and Taklimakan deserts and NETP surface crust dust are the possible LRT dust source over the Qilian Mountains in addition to the local dust source in the glacier basin. Atmosphere 2018, 9, x FOR PEER REVIEW 7 of 13 Atmosphere 2018, 9, 461 7 of 13 Atmosphere 2018, 9, x FOR PEER REVIEW 7 of 13

Figure 4. Bivariate diagrams of (La/Sm)N, (La/Yb)N, Eu/Eu* and (Gd/Yb)N ratios of samples from the glaciers and snowpacks, and the comparison with that of central Asian deserts sands, including FigureFigureSouth 4.4. BivariateBivariate Gobi from diagramsdiagrams References ofof (La/Sm)(La/Sm) [31,32];NN, ,(La/Yb) (La/Yb)TaklimakanN,N Eu/Eu*, Eu/Eu* Desert and and (Gd/Yb)finer (Gd/Yb) fracN tionratiosN ratios from of samples of[33,34]; samples from Badain from the Jaran theglaciers glaciersDesert and and finersnowpacks, snowpacks, fraction and from and the [3,34]; the comparison comparison Qaidam withBasin with that and that ofTengger of central central Desert Asian Asian fromdeserts deserts [34]; sands, Eastern includingincluding and western SouthSouthTP GobiGobi from fromfrom [34,35]. ReferencesReferences Color icons [[31,31,3232]; and]; TaklimakanTaklimakan gray icons DesertDesertrefer to ﬁnerfiner snow fractionfrac dust/cryoconitetion fromfrom [[33,34];33, 34samples]; BadainBadain and JaranJaran local dust DesertDesertsamples, ﬁnerfiner fractionfraction respectively.( from [[3,34];3,a34) (La/Sm]; QaidamQaidam)N versus Basin (Gd/Yb) andand TenggerTenggerN; (b) (La/Sm) DesertDesert fromNfrom versus [[34];34 ];(La/Yb) EasternEasternN; ( andandc) (La/Yb) westernwesternN versus

TPTP fromfromEu/Eu*; [[34,35].34,35 (].d) ColorColor(La/Sm) iconsiconsN versus andand grayEu/Eu*.gray iconsicons referrefer toto snowsnow dust/cryoconitedust/cryoconite samplessamples andand locallocal dustdust samples,samples, respectively.(a) (La/Sm)N)N versusversus (Gd/Yb) (Gd/Yb)N; N(b;() (La/Sm)b) (La/Sm)N versusN versus (La/Yb) (La/Yb)N; (c) N(La/Yb);(c) (La/Yb)N versusN versusEu/Eu*; Eu/Eu*; (d) (La/Sm) (d) (La/Sm)N versusN Eu/Eu*.versus Eu/Eu*.

Figure 5. Cont.

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Figure 5. TiOTiO2–Zr–Al–Zr–Al22OO33 andand La–Th–Sc La–Th–Sc diagrams diagrams ternary ternary of of cryo cryoconiteconite and and snow snow dust dust collected collected in the various glaciers and snowpacks. Literature data of intrusive intrusive rocks from potential dust source areas in thethe Tarim BasinBasin [ 36[36],], the the South South Gobi Gobi [32 [32],], the the Qaidam Qaidam Basin Basin [37 [37]] and and the the Badain Badain Jaran Jaran desert desert [38] [38] are alsoare

alsoincluded included for comparison. for comparison. (a) TiO (a2) –Zr–AlTiO2–Zr–Al2O3 of2O cryoconite3 of cryoconite and snowand snow dust compositions;dust compositions; (b) La–Th–Sc (b) La– Th–Scof cryoconite of cryoconite and snow and dustsnow compositions dust compositions by comparison by comparison with those with ofthose potential of potential dust sources. dust sources.

Compared with with the the Qilian Qilian Mountain Mountain locations locations (e.g., (e.g., QG, QG, LG, LG, DS, DS, and and OS), OS), samples samples from from YG YG in thein the Kunlun Kunlun mountains mountains have have lower lower (La/Yb) (La/Yb)N Nratioratio and and higher higher Eu/Eu* Eu/Eu* (Figure (Figure 4b–d)4b–d) but similarsimilar (Gd/Yb)NN values.values. This This suggests suggests mixed mixed sources sources for for LRT LRT dust dust deposi depositedted onto onto the the NETP NETP glaciers from the Qaidam and and Badain Badain Jaran Jaran Deserts, Deserts, together together with with mineral mineral particles particles from from the the Taklimakan Taklimakan Deserts. Deserts. Furthermore, the distinct similarity is shown inin the ternary diagramsdiagrams ofof La-Th-ScLa-Th-Sc andand TiOTiO22–Zr–Al–Zr–Al22O3 (Figure 55),), indicatingindicating aa likelike compositioncomposition betweenbetween QaidamQaidam BasinBasin andand YG.YG. Moreover,Moreover, thethe surfacesurface crustcrust (e.g., Golmud crust dust) is also another source for dust input into YG snowpack, due to their similar similar geochemical compositions (Figure 4 4).). Compared to the above study sites, MG cryoconi cryoconitete in the eastern eastern Tianshan Tianshan Mountains indicates relatively lowerlower (La/Sm)(La/Sm)N,, (Gd/Yb) (Gd/Yb)NN andand (La/Yb) (La/Yb)N Nratios,ratios, but but shows shows less less negative negative and and even even positive positive Eu anomaly (Figure(Figure4 ),4), suggesting suggesting very very different different LRT LRT dust dust sources sources for for the the MG MG basin. basin. Moreover, Moreover, the MG the MGgeochemistry geochemistry data isdata very is close very to close southern to southe Gobi Deserts,rn Gobi asDeserts, showing as similarshowing (La/Sm) similarN, (La/Yb)(La/Sm)N,, (La/Yb)Eu/Eu*N, and Eu/Eu* (Gd/Yb) and N(Gd/Yb)ratios.N This ratios. might This indicate might thatindicate the southernthat the southern Gobi Deserts Gobi could Deserts represent could representan important an important potential source potential for regionalsource for LRT regi dustonal emission LRT dust from emission north to from NETP. north Moreover, to NETP. the Moreover,REE ratios derivedthe REE from ratios MG derived local crust from show MG higher local (La/Sm) crust showN, (La/Yb) higherN and(La/Sm) (Gd/Yb)N, (La/Yb)N, andN lower and (Gd/Yb)Eu/Eu*,N, implying and lower its Eu/Eu*, smallcontribution implying its tosmall the contribution glacier basin. to Fromthe glacier these basin. results, From we these can find results, that wemineral can find dust that deposition mineral ondust the deposition investigated on glaciersthe investigated is dominated glaciers by LRTis dominated aeolian dust by fromLRT aeolian central dustAsian from deserts, central besides Asian smalldeserts, contribution besides small from contribution local dust from in the local glacier dust basin.in the glacier Also, as basin. shown Also, in asFigure shown2, the in LRTFigure dust 2, the probably LRT dust originated probably from orig differentinated from arid different desert areas arid combined desert areas with combined various withpollutant various particles, pollutant such particles, as black carbonsuch as (BC) black and carbon organic (BC) carbon and organic (OC), in carbon the glaciers (OC), and in the snowpacks. glaciers and snowpacks.The southern Gobi Desert is confirmed to be the dominant arid area exchanging crustal materials withThe the surroundingsouthern Gobi areas. Desert It has is been confirmed recognized to thatbe the the southerndominant Gobi arid (including area exchanging the Gobi Desertscrustal −1 materialsin western with China) the surrounding is a major dust areas. emission It has been source recognized due to rare that precipitation the southern (<50Gobi mm(including yr )[ 39the], Gobilow vegetation Deserts in coverwestern (10% China) even is zero)], a major extremely dust emission dry climate source conditions,due to rare precipitation as well as stronger (< 50 mm surface yr−1) [39],wind low speed vegetation in springtime cover (24–30 (10% m/s).even zero)], Dust emission extremely from dry the climate Gobi Deserts conditions, are lifted as well up to as more stronger than >3surface kilometers wind speed by cold in front springtime passage (24–30 from northwest m/s). Dust direction, emission and from then the are Gobi entrained Deserts toward are lifted southeast up to moredirection than over >3 thekilometers eastern Tianshanby cold front Mountains passage [39 from]. Therefore, northwest not onlydirection, is south and Gobi then identified are entrained as one towardof the major southeast sources direction for the over Chinese the Loesseastern Plateau Tiansh [4an,6 ],Mountains but is also [39]. a major Therefore, contributor not only for materials is south Gobitransport identified to the as NETP one glaciers,of the major suggesting sources the for possiblethe Chinese LRT dustLoess transport Plateau [4,6], route but from is thealso southern a major contributor for materials transport to the NETP glaciers, suggesting the possible LRT dust transport

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Gobiroute Desertfrom the in asouthern large range Gobi scale, Desert which in a could large also range be demonstratedscale, which could by analyzing also be demonstrated aerosol particles by propertiesanalyzing andaerosol meteorological particles properties data (Figures and meteorological6 and7). data (Figures 6 and 7).

FigureFigure 6.6. MODIS Aerosol Optical Depth at 0.55 micronsmicrons for land Mean of dailydaily MeanMean monthlymonthly ((http://giovanni.sci.gsfc.nasa.ghttp://giovanni.sci.gsfc.nasa.govov) )during during each each season season in in 2015–2017 2015–2017 in in the the Tibetan Plateau andand surroundingsurrounding areas.areas.

Figure6 shows the MODIS Aerosol Optical Depth (AOD) in the TP and its surrounding areas, Figure 6 shows the MODIS Aerosol Optical Depth (AOD) in the TP and its surrounding areas, reﬂecting the potential dust sources in the NETP and the adjacent arid regions. AOD in the Taklimakan reflecting the potential dust sources in the NETP and the adjacent arid regions. AOD in the Desert and Gobi-deserts in the northern China are much larger than the TP and Qaidam Basin Taklimakan Desert and Gobi-deserts in the northern China are much larger than the TP and Qaidam during each season from 2014–2016, indicating more strong dust storms in the both arid regions. Basin during each season from 2014–2016, indicating more strong dust storms in the both arid Thus, dust from the Taklimakan and Badain Jaran deserts might be transported to the high mountain regions. Thus, dust from the Taklimakan and Badain Jaran deserts might be transported to the high glaciers (e.g., LG, OS, QG, JS, and DS) through atmospheric circulation. Because of the low AOD found mountain glaciers (e.g. LG, OS, QG, JS, and DS) through atmospheric circulation. Because of the low in Qaidam Basin and the obstruction of the Qilian Mountains, it is very likely that the basin has a AOD found in Qaidam Basin and the obstruction of the Qilian Mountains, it is very likely that the major contribution to glaciers (YG) in the hinterland TP, whereas very less contribution to the glaciers basin has a major contribution to glaciers (YG) in the hinterland TP, whereas very less contribution in NETP. Moreover, the large AOD in south Mongolian Gobi probably means large amounts of LRT to the glaciers in NETP. Moreover, the large AOD in south Mongolian Gobi probably means large dust transported to its downwind glacier areas, such as MG, by the East Asian Winter Monsoon. amounts of LRT dust transported to its downwind glacier areas, such as MG, by the East Asian Figure7 indicates the wind vector data of near surface wind (850 mb) in study areas during each Winter Monsoon. season (winter (December–January–February), spring (March–April–May), summer (Jun–July–August), Figure 7 indicates the wind vector data of near surface wind (850 mb) in study areas during and autumn (September–October–November)), indicating the potential LRT dust source and the transport each season (winter (December–January–February), spring (March–April–May), summer (Jun–July– routes in NETP margin and central Asia. Besides, the surface crust from the TP is ascertained as another August), and autumn (September–October–November)), indicating the potential LRT dust source dust source attributed to active aeolian process and desertification of the TP surface [14,15]. Moreover, the and the transport routes in NETP margin and central Asia. Besides, the surface crust from the TP is inner regions of the TP show very limited dust materials exchange with other arid deserts, such as the ascertained as another dust source attributed to active aeolian process and desertification of the TP Gobi, Badain Jaran, and Tengger Deserts around the NETP. surface [14,15]. Moreover, the inner regions of the TP show very limited dust materials exchange with other arid deserts, such as the Gobi, Badain Jaran, and Tengger Deserts around the NETP.

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Figure 7. The mean windwind vectorvector datadataof of850mb 850mb wind wind in in the the study study area area during during each each season season from from 2012 2012 to 2017,to 2017, based based on on NCEP/NCAR NCEP/NCAR (National (National Centers Centers for for Environmental Environmental Prediction/ Prediction/ NationalNational Center for Atmospheric Research)Research) reanalysisreanalysis datadata (https://www.esrl.noaa.gov/(https://www.esrl.noaa.gov/),), reflecting reﬂecting the the potential dust transport routes in northeastnortheast TibetanTibetan PlateauPlateau andand centralcentral Asia.Asia.

Taking the region as aa whole,whole, thethe mineralmineral dustdust sourcesource depositeddeposited in the high mountainmountain glaciers and snowpack is very complicated complicated,, asas mostmost ofof thethe glacierglacier snowpacksnowpack showshow mixedmixed LRT dust sources input fromfrom itsits surrounding surrounding deserts. deserts. Demonstrated Demonstrated from from meteorological meteorological data data of AOD of AOD and wind and vectorwind datavector in data the region,in the region, our results our showresults that show the that NETP theregion NETP actsregion as anacts important as an important Channel Channel for aeolian for dustaeolian transport dust transport from central from Asiancentral deserts Asian (e.g.,deserts the (e.g., Qaidam, the Qaidam, Taklimakan, Taklimakan, and Gobi and Deserts) Gobi Deserts) into the Loessinto the Plateau Loess and Plateau surrounding and surrounding areas, bringing areas, plenty bringi ofng dust plenty particles of dust deposition particles to deposition the high-altitude to the glacierhigh-altitude surface glacier in northeast surface margin in northeast of the margin TP. of the TP.

4. Conclusions This study investigates REE and trace elements compositions of cryoconite and snow dust collected fromfrom thethe variousvarious glaciersglaciers in in the the northeast northeast Tibetan Tibetan Plateau Plateau and and eastern eastern Tianshan Tianshan Mountains Mountains to determineto determine LRT LRT dust dust sources sources and and regional regional atmospheric atmospheric circulation circulation in the in NETP.the NETP. Most Most samples samples from glaciers (LG, OS, QG, JS and DS) in the NETP margin display the similar (La/Sm) , Th/Yb and from glaciers (LG, OS, QG, JS and DS) in the NETP margin display the similar (La/Sm)N N, Th/YbNN and Nb/Yb ratios, while largely differe from those of MG and YG. Based on the similarity in geochemical Nb/YbNN ratios, while largely differe from those of MG and YG. Based on the similarity in ((La/Sm) , Th/Yb , Nb/Yb and La-Th-Sc ) and mineralogical composition, we ﬁnd that the major geochemicalN ((La/Sm)N N, Th/YbNN, Nb/YbN and La-Th-Sc ) and mineralogical composition, we find that dustthe major sources dust to sources NETP margin to NETP were margin mainly were derived mainly from derived Qaidam from Basin, Qaidam Badain Basin, Jaran Badain and Taklimakan Jaran and Deserts.Taklimakan However, Deserts. most However, samples most from samples the Miaoergou from the Glacier Miaoergou show Glacier the high show similarity the high in(La/Sm) similarityN, Th/Yb , Nb/Yb and Eu/Eu* to the South Mongolian Gobi, implying the major contribution of the in (La/Sm)N N, Th/YbN N, Nb/YbN and Eu/Eu* to the South Mongolian Gobi, implying the major South Gobi. By comparison of the REEs, trace elements, and mineralogy (TiO –Zr–Al O , La–Sc–Th contribution of the South Gobi. By comparison of the REEs, trace elements, and2 mineralogy2 3 (TiO2– ternary diagrams) in cryoconite and snow dust with the central Asian deserts, the Qaidam Basin is Zr–Al2O3, La–Sc–Th ternary diagrams) in cryoconite and snow dust with the central Asian deserts, identiﬁedthe Qaidam as Basin a source is identified for dust depositionas a source onto for dust YG in deposition the inner onto TP, while YG in large the inner central TP, Asian while deserts large central Asian deserts rarely contributed with LRT dust to the glacier. We find that most of the glacier snowpack samples showed mixed dust sources from different parts of surrounding central Asian

Atmosphere 2018, 9, 461 11 of 13 rarely contributed with LRT dust to the glacier. We ﬁnd that most of the glacier snowpack samples showed mixed dust sources from different parts of surrounding central Asian deserts. The LRT dust provenance in the NETP glacier is also supported from the AOD data and wind ﬁeld in the region.

Author Contributions: Formal analysis, T.W. and S.U.; Investigation, T.W. and Z.D.; Resources, Z.D. and S.K.; Software, S.K.; Writing—Original draft, T.W. Funding: This work was funded by the National Natural Science Foundation of China (41671062, 41721091), the State Key Laboratory of Cryosphere Sciences (SKLCS–ZZ–2018), the Chinese Academy of Sciences (QYZDJ–SSW–DQC039), and the Youth Innovation Promotion Association, CAS (2015347). Acknowledgments: The authors would like also to thank the field work team in summer 2017 on the northeast Tibetan Plateau for their logistical field work. Conflicts of Interest: The authors declare no conflict of interest.

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