2-GRL-Lu-Joe-2005Nov

Late Quaternary aeolian activity in the Mu Us and Otindag dune fields (north China)and lagged response to insolation forcing

Huayu Lu,1,2Xiaodong Miao,3Yali Zhou,1,4Joseph Mason,3James Swinehart,4

Jiafu Zhang,5Liping Zhou,5and Shuangwen Yi1,6

Received4September2005;revised7October2005;accepted11October2005;published11November2005.

[1]Dune fields in parts of northern China contain important stratigraphic records of late Quaternary change in the East Asian monsoon.In this study,33new optically stimulated luminescence(OSL)ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet-dry climate variation in the Mu Us and Otindag dune fields of north China.The results indicate dune activity and dry climate in the last few hundred years,14ka to about7–8ka,and50ka to60ka.The dunes were mainly stable,implying a wetter climate,between about7–8ka and 2.4ka.These results imply a lag of several thousand years between peak summer insolation at10–11ka and high summer monsoon rainfall after7–8ka.In the investigated regions,the monsoon climate may not respond directly to orbital forcing over millennial time https://www.wendangku.net/doc/7a14258918.html,nd surface feedbacks may account for lagged dune field response. Citation:Lu,H.,X.Miao,Y.Zhou,J.Mason,J.Swinehart, J.Zhang,L.Zhou,and S.Yi(2005),Late Quaternary aeolian activity in the Mu Us and Otindag dune fields(north China)and lagged response to insolation forcing,Geophys.Res.Lett.,32, L21716,doi:10.1029/2005GL024560.

1.Introduction

[2]Deserts and dune fields cover approximately 1,000,000km2in arid and semiarid regions of northern and northwestern China[Zhu et al.,1988].Parts of these dry lands are highly sensitive to change in the East Asian monsoon,because they lie near the northern limit of monsoon precipitation.When the monsoon circulation is stronger,rainfall increases in these dry lands,and enhanced vegetation cover limits aeolian activity.When the monsoon weakens and vegetation cover is reduced,strong northerly or westerly winds can drive dune migration and dust production.

[3]The Chinese loess record indicates that the monsoon varies in response to orbital forcing at timescales of104yr [Ding et al.,2002;Lu et al.,2004].Orbital variation influences the monsoon through changes in summer inso-lation;high summer insolation enhances land-sea tempera-ture contrasts,strengthening the monsoon[An et al.,2000]. Controls on the monsoon at millennial timescales are less well understood.Recent work in north China suggests that during the Holocene,the onset of a wet climate occurred several thousand years after the summer insolation peak at 10–11ka[Xiao et al.,2002,2004;Peng et al.,2005].Other investigations indicate that Holocene changes in the East Asian monsoon were asynchronous across China[An et al., 2000]or phase-reversed to the Indian monsoon[Hong et al., 2005].These conclusions are challenged,however,by stalagmite records from south China[e.g.,Yuan et al., 2004;Wang et al.,2005]and a lake record from NE Tibetan Plateau[Shen et al.,2005],all indicating rapid monsoon response to insolation forcing in the early Holocene. [4]Climatic change in the dry lands of China is poorly understood in part because of inadequate age control[Dong, 2002].Time constraints for paleoclimatic change have been based mainly on correlation with the loess time series[Dong et al.,1988;Dong,2002],or radiocarbon dating of soil organic matter or other materials,often yielding conflicting results[Gao et al.,1993;Li et al.,1995,2000;Jin et al., 2004].In this study,we directly dated aeolian deposition using OSL dating,a promising method widely used in other dry lands[e.g.,Lancaster et al.,2002;Goble et al.,2004; Stokes et al.,2004],but with limited previous application in China[Li et al.,2002;Han and Sun,2004].

2.Study Areas and Methods

[5]The timing of aeolian activity was investigated in two dune fields near the present limits of significant monsoon rainfall(Figure1).The Mu Us dune field has an area of 38,940km2,a modern mean annual precipitation(MAP)of 250–400mm and mean annual temperature(MAT)of6.0–9.0°C,and is a mosaic of partially to fully active small transverse ridge dunes and largely stable sand sheets.The Otindag dune field(area of29,220km2,MAP of200–350mm,and MAT of0–3°C)is dominated by partially active compound parabolic dunes.

[6]Most long-term variation of aeolian activity in both study areas is likely due to variation in effective moisture (precipitation minus evapotranspiration),causing changes in vegetation cover,though significant human impacts are possible since2000ka[Sun,2000].Ten aeolian sediment sections were sampled(Figure1),most of them far from major floodplains or other sediment sources that could locally influence aeolian activity independent of regional climate change.From these sections,33OSL ages were obtained and more than200samples were measured for grain-size distribution,organic material content and magnetic susceptibility(Figures2and3).

GEOPHYSICAL RESEARCH LETTERS,VOL.32,L21716,doi:10.1029/2005GL024560,2005 1State Key Laboratory for Loess and Quaternary Geology,Institute of

Earth Environment,Chinese Academy of Sciences,Xi’an,China.

2Institute for the Environment,Brunel University,Uxbridge,UK.

3Department of Geography,University of Wisconsin-Madison,Madison,

Wisconsin,USA.

4Institute of Agriculture and Natural Resources,School of Natural

Resources,University of Nebraska at Lincoln,Lincoln,Nebraska,USA.

5School of Earth and Space Science,Peking University,Beijing,China.

6Graduate School of the Chinese Academy of Sciences,Beijing,China.

Copyright2005by the American Geophysical Union.

0094-8276/05/2005GL024560$05.00

[7]OSL dating was carried out at the University of Nebraska-Lincoln and Peking University,using similar procedures in both laboratories [Goble et al.,2004].1Luminescence measurements were made with both Ris?and Daybreak OSL systems on coarse quartz grains (90–125m m or 90–160m m),isolated by wet sieving,heavy liquid flotation,and hydrofluoric acid treatments.The Single Aliquot Regeneration method was used [Murray and Wintle ,2000],with dose rates estimated by the con-centrations of U,Th,K,and Rb as well as moisture content,using the methods of Aitken [1998].

[8]Grain size measurements were made by laser diffrac-tion with a Malvern Mastersizer,after pretreatment as described by Lu and An [1997].Organic matter content was determined by titration of ground samples with potassium dichromate.Magnetic susceptibility (MS)was measured with a Bartington MS2magnetic meter.

3.Results and Discussion

3.1.Timing of Aeolian Activity and Paleoclimatic Interpretations

[9]Alternation of aeolian sand,paleosols and/or loess at the study sites (Figure 2)is clearly indicative of variation in the extent of aeolian activity,vegetation cover,and effective

moisture [Dong et al.,1988;Dong ,2002].Aeolian sand beds often display wind-ripple lamination indicating active sand transport with limited vegetation cover.The paleosols represent wetter conditions with much less aeolian activity.These buried soils have greater organic matter content,MS,and silt and clay content than sediment above or below,indicating enough stability and vegetation cover for organic matter accumulation,pedogenic MS enhancement,and trapping of fine-grained dust (Figure 2).The thicker paleosols (e.g.HSHN,Figure 2)appear to be cumulative soils,built up by short-lived local sand movement during periods of general stability [e.g.Goble et al.,2004].Coarse loess beds at some study sites probably record intermediate climate conditions.

[10]The high deposition rate of aeolian sediment in the study areas should capture millennial-scale climatic epi-sodes that the loess-paleosol sequences cannot [Lu et al.

,

Figure 1.(a)Location of study areas within China;(b)and (c):Study site locations.Gray shades =aeolian sand;hachures =thick loess;cross-hachures =mountains.1

Auxiliary material is available at ftp://https://www.wendangku.net/doc/7a14258918.html,/apend/gl/

2005GL024560.

Figure 2.Examples of stratigraphic sections used in this study,with OSL ages and other measurements.See color version of this figure in the HTML.

2004].However,since dune migration requires both depo-sition and erosion,unconformities are common in dune field sections,and long,continuous stratigraphic records are seldom preserved.This problem can be overcome by dating aeolian activity at multiple sites,ultimately producing a relatively complete,high-resolution record of climatic change.This study is an initial step toward that goal.For example,at the DBY section (Figure 2),we infer limited dune activity and soil development at 7.4ka,extensive local dune activity at 12.7–13.7ka,loess influx at 37.7ka and dune activity 52.5–https://www.wendangku.net/doc/7a14258918.html,bination of these results with data from other sites yields a regional record of wet-dry climate variation.

[11]Our data from the Mu Us and Otindag dune fields indicate deposition of aeolian sand at approximately 0–0.3ka,7.2–8.7ka,9.8–10.5ka,11–11.6ka,12.7ka,13.7ka,52.5ka,and 57.5ka BP (Figure 3).Ages obtained from within cumulative paleosols indicate general stability,with occasional local sand deposition,between 2.4ka and 8ka.Loess deposition is dated to 0.71ka,0.95ka,7.2ka,18.7ka,37.7ka,and 41.2ka BP (Figure 3).Thus extensive aeolian activity occurred between 14ka and about 8.5ka,but there was widespread soil development and limited aeolian activity from 7–2.4ka (Figure 3).The absence of evidence for sand deposition between the last glacial maximum (21ka)and 14ka may reflect enhanced vegeta-tion cover in a cooler climate with less evaporation,or simply our limited sample size.

[12]Previous research on these dune fields presents a complex picture (Figure 3),but suggests widespread aeolian activity between about 14ka and 7–8ka,interrupted by brief episodes of stability and soil development at some sites.Dune field stability was clearly widespread between about 7–8ka and 2.4ka,though locally interrupted by dry episodes,and multiple episodes of activity occurred after 2.4ka.Overall,previous research is in broad agreement with our results,but suggests that our data set is not large

enough yet to capture some millennial-or centennial-scale climatic events.A high-resolution lake record located between our two study areas also concludes that a wetter period occurred during 7900–3100ka [Peng et al.,2005]https://www.wendangku.net/doc/7a14258918.html,g of Climatic Change in the Dune Fields Behind Insolation Forcing

[13]If the monsoon rainfall in our study areas responds directly to insolation forcing with minimal lag,then the dunes should have become stabilized during or shortly after peak summer insolation,around 10–11ka [Berger and Loutre ,1991].In fact,our data indicate widespread dune activity at that time,and long-term stability only after about 7–8ka.Dune activity at 52ka and 57ka also coincided with intermediate to high summer insolation,although much more work is needed to adequately date this earlier arid interval.

[14]Our results provide additional evidence that peak monsoon strength lagged peak summer insolation in some dry lands of north China,but as noted above,data from south China and the northeast Tibetan Plateau do not indicate a similar lag [Yuan et al.,2004;Wang et al.,2005;Shen et al.,2005].Regional climates across China,although more or less related to the East Asian,South Asian and/or Tibetan Plateau monsoons,and to changes in the westerlies,may not respond synchronously to insolation forcing.Most likely,insolation is not the only control on the monsoon,and other mechanisms such as ice sheet extent and vegetation or soil feedbacks may have significant effects at millennial time scales.For example,increased evaporation brought on by increased solar radiation and warmer temperatures in the early Holocene may have been sufficient to decrease effective moisture and so result in increased aeolian activity in our study areas,even if monsoon strength increased.Once a large area of mobile sand had developed,there could also be positive feedback between increased albedo and reduced precipitation,

the

Figure 3.OSL ages from this study,compared to previous work and summer insolation.References for previous work:1.Sun et al.[1998];2.Li et al.[2002];3.Xiao et al.[2002];4.Zhou et al.[2001];5.Jin et al.[2004];6.Dong [2002];7.Gao et al.[1993];8.Li et al.[2000];9.Li et al.[1995].Boxes are individual ages.See color version of this figure in the HTML.

inverse of an effect proposed for the Sahara during the early-middle Holocene[Kutzbach et al.,1996].

4.Conclusions

[15]Our results provide strong evidence for widespread early Holocene aeolian activity in the Mu Us and Otindag dune fields,implying a lag of several thousand years between insolation forcing and changes in the monsoon climate. When our data are combined with previous research,there is also evidence for wet-dry variation at suborbital timescales. Thus,there may not be a simple relationship between wet-dry climatic variation in north China and insolation forcing at millennial timescales.Much more work is needed to better understand the mechanisms and spatial patterns of late Quaternary monsoon variation,using more complete records of aeolian activity in north China.

[16]Acknowledgments.We thank Dong Guangrong for inspiring us to initiate this work,Stephen Stokes for patient guidance in the field,Chen Huizhong,Li Xiaoze,Li Sen,Yang Liping,Qiang Xiaoke,Wen Lingjuan, Wang Xianyan and Sun Xuefeng for field and lab assistance,and two anonymous reviewers for helpful comments.Research supported by NSFC (contracts40325007,40121303)and US NSF(BCS-0352683,BCS-0352748,ATM-0502489and ATM-0502511).

References

Aitken,M.J.(1998),An Introduction to Optical Dating:The Dating of Quaternary Sediments by the Use of Photon-Stimulated Luminescence, Oxford Univ.Press,New York.

An,Z.S.,S.C.Porter,J.E.Kutzbach,X.H.Wu,S.M.Wang,X.D.Liu, X.Q.Li,and W.J.Zhou(2000),Asynchronous Holocene optimum of the east Asian monsoon,Quat.Sci.Rev.,19,743–762.

Berger,A.,and M.F.Loutre(1991),Insolation values for the climate of the last10million years,Quat.Sci.Rev.,10,297–317.

Ding,Z.L.,E.Derbyshire,S.L.Yang,Z.W.Yu,S.F.Xiong,and T.S.Liu (2002),Stacked2.6-Ma grain size record from the Chinese loess based on five sections and correlation with the deep-sea d18O record,Paleoceano-graphy,17(3),1033,doi:10.1029/2001PA000725.

Dong,G.R.(2002),Climate and Environment Changes in Deserts of China—Selected Papers of Dong Guangrong’s Research Group(in Chinese),China Ocean,Beijing.

Dong,G.,S.Gao,J.Jin,and B.Li(1988),The formation,evolution and cause of the Mu Us desert in China,Sci.China,Ser.B,32,33–45. Gao,S.Y.,et al.(1993),A preliminary study of paleoclimate changes at margins of Chinese eastern deserts in the Holocene(in Chinese),Sci. China,Ser.B,23,202–208.

Goble,R.J.,J.A.Mason,D.B.Loope,and J.B.Swinehart(2004),Optical and radiocarbon ages of stacked paleosols and dune sands in the Nebraska Sand Hills,USA,Quat.Sci.Rev.,23,1173–1182.

Han,P.,and J.M.Sun(2004),A research of optically stimulated lumines-cence dating on Otindag desert(in Chinese),Quat.Sci.,24,461. Hong,Y.T.,B.Hong,Q.H.Lin,Y.Shibata,M.Hirota,Y.X.Zhu,X.T. Leng,Y.Wang,H.Wang,and L.Yi(2005),Inverse phase oscillations between the east Asian and Indian Ocean summer monsoons during the last12,000years and paleo-El Nin?o,Earth Planet.Sci.Lett.,231,337–346.

Jin,H.L.,Z.Z.Su,L.Y.Sun,Z.Sun,H.Zhang,and L.Y.Jin(2004), The palaeoclimate changes during the Holocene in Otindag desert(in Chinese),Chin.Sci.Bull.,49,1532–1536.

Kutzbach,J.,G.Bonan,J.Foley,and S.P.Harrison(1996),Vegetation and soil feedbacks on the response of the African monsoon to orbital forcing in the early to middle Holocene,Nature,384,623–https://www.wendangku.net/doc/7a14258918.html,ncaster,N.,G.Kocurek,and A.Singhvi(2002),Late Pleistocene and Holocene dune activity and wind regimes in the western Sahara desert of Mauritania,Geology,30,991–994.

Li,B.S.,D.D.Zhang,H.L.Jin,Z.Wu,M.C.Yan,W.Sun,Y.Z.Zhu,and D.H.Sun(2000),Paleo-monsoon activities of Mu Us desert,China since150ka B.P.—A study of the stratigraphic sequences of the Mi-langgouwan section,Salawusu River area,Palaeogeogr.Palaeoclimatol. Palaeoecol.,162,1–16.

Li,S.,W.Sun,X.Z.Li,and B.Zhang(1995),Sedimentary characteristics and environmental evolution of Otindag sandy land in Holocene(in Chinese with English abstract),J.Desert Res.,15,323–331.

Li,S.H.,J.M.Sun,and H.Zhao(2002),Optical dating of dune sands in the northeastern deserts of China,Palaeogeogr.Palaeoclimatol.Palaeo-ecol.,181,419–429.

Lu,H.Y.,and Z.S.An(1997),Pretreatment methods in loess-palaeosol granulometry,Chin.Sci.Bull.,42,237–240.

Lu,H.Y.,F.Q.Zhang,X.D.Liu,and R.Duce(2004),Periodicities of palaeoclimatic variations recorded by loess-paleosol sequence in China, Quat.Sci.Rev.,23,1891–1900.

Murray,A.S.,and A.G.Wintle(2000),Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol,Radiat. Meas.,32,57–73.

Peng,Y.J.,J.L.Xiao,T.Nakamura,B.L.Liu,and Y.Inouchi(2005), Holocene east Asian monsoonal precipitation pattern revealed by grain-size distribution of core sediments of Daihai Lake in inner Mongolia of north-central China,Earth Planet.Sci.Lett.,233,467–479.

Shen,J.,X.Liu,S.Wang,and R.Matsumoto(2005),Palaeoclimatic changes in the Qinghai Lake area during the last18,000years,Quat. Int.,136,131–140.

Stokes,S.,R.M.Bailey,N.Fedoroff,and K.E.O’Marah(2004),Optical dating of aeolian dynamism on the West African Sahelian margin,Geo-morphology,59,281–291.

Sun,J.M.(2000),Origin of aeolian sand mobilization during the past2300 years in the Mu Us desert,China,Quat.Res.,53,78–88.

Sun,J.M.,G.M.Yin,Z.L.Ding,T.S.Liu,and J.Chen(1998),Thermo-luminescence chronology of sand profiles in the Mu Us Desert,China, Palaeogeogr.Palaeoclimatol.Palaeoecol.,144,225–233.

Wang,Y.J.,H.Cheng,R.L.Edwards,Y.Q.He,X.G.Kong,Z.S.An,J.Y. Wu,M.J.Kelly,C.A.Dykoski,and X.D.Li(2005),The Holocene Asian monsoon:Links to solar changes and North Atlantic climate, Science,308,854–857.

Xiao,J.L.,T.Nakamura,H.Y.Lu,and G.Y.Zhang(2002),Holocene climate changes over the desert/loess transition of north-central China, Earth Planet.Sci.Lett.,197,11–18.

Xiao,J.L.,Q.H.Xu,T.Nakamura,X.L.Yang,W.D.Liang,and Y.Inouchi (2004),Holocene vegetation variation in the Daihai Lake region of north-central China:A direct indication of the Asian monsoon climatic history, Quat.Sci.Rev.,23,1669–1679.

Yuan,D.X.,et al.(2004),Timing,duration,and transitions of the last interglacial Asian monsoon,Science,304,575–578.

Zhou,W.J.,J.Head,and L.Deng(2001),Climate changes in northern China since the late Pleistocene and its response to global change,Quat. Int.,83–85,285–292.

Zhu,Z.,S.Liu,and X.Di(1988),Desertification and Rehabilitation in China,Int.Cent.for Educ.and Res.on Desertification Control,Lanzhou, China.

àààààààààààààààààààààà

H.Lu,S.Yi,and Y.Zhou,SKLLQG,Institute of Earth Environment, Chinese Academy of Sciences,Xi’an710075,China.

J.Mason and X.Miao,Department of Geography,University of Wisconsin-Madison,Madison,WI53706,USA.(mason@geography.wisc. edu)

J.Swinehart,IANR,School of Natural Resources,University of Nebraska at Lincoln,Lincoln,NE68588-0517,USA.

J.Zhang and L.Zhou,School of Earth and Space Science,Peking University,Beijing100871,China.