YJARE : 2103 ARTICLE IN PRESS - Home | Lehigh Universityziy2/pubs/Zhao2008JAE.pdfa MOE Key Laboratory of Western China’s Environmental Systems, College of Earth and Environmental

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61

ARTICLE IN PRESSYJARE : 2103

Contents lists available at ScienceDirect

Journal of Arid Environments

Journal of Arid Environments ] (]]]]) ]]]–]]]

0140-19

doi:10.1

� CorE-m

PleasTeng

journal homepage: www.elsevier.com/locate/jaridenv

Holocene vegetation and climate change from a lake sediment recordin the Tengger Sandy Desert, northwest China

Yan Zhao a,�, Zicheng Yu a,b, Fahu Chen a, Jiajia Li a

a MOE Key Laboratory of Western China’s Environmental Systems, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, Chinab Department of Earth and Environmental Sciences, Lehigh University, 31 Williams Drive, Bethlehem, PA 18015, USA

a r t i c l e i n f o

Article history:

Received 18 December 2007

Received in revised form

21 April 2008

Accepted 23 June 2008

Keywords:

Arid China

Fossil pollen

Holocene climate change

Lithology

Qingtu paleolake

63/$ - see front matter & 2008 Published by

016/j.jaridenv.2008.06.016

responding author. Tel.: +86 9318912337; fax

ail address: [email protected] (Y. Zhao).

e cite this article as: Zhao, Y., et al.,ger Sandy Desert, northwest China.

a b s t r a c t

We present lithology and fossil pollen data from a 384 cm sediment section from Qingtu

paleolake in arid northwest China and discuss their environmental interpretations. The

chronology was controlled by four accelerator mass spectrometry (AMS) radiocarbon

dates on peat and bulk lake sediments. Lithology changes suggest a general sequence of

local environment shifts from a non-lake environment before 7200 cal yr BP, through a

shallow lake during 7200–3500 cal yr BP and a marsh during 3500–3000 cal yr BP, to a

sandy desert after 3000 cal yr BP. Fossil pollen assemblages suggest a steppe desert

during 7200–5200 cal yr BP, a period of rapid switches between upland and lowland

pollen types from 5200 to 3000 cal yr BP, and a desert since 3000 cal yr BP. Both lithology

and pollen data indicate that in a generally arid context, climate was extremely dry in

the early Holocene, relatively wet at 7200–5200 cal yr BP, highly variable during

5200–3000 cal yr BP, and dry again after 3000 cal yr BP. The climate change around

Qingtu Lake was likely controlled by the interplay of the East Asian summer monsoon,

the mid-latitude westerlies and local topography around the Tibetan Plateau.

& 2008 Published by Elsevier Ltd.

1. Introduction

Northwest China, in the east margin of arid Central Asia, is located at the boundary between the East Asian summermonsoon and the Northern Hemisphere’s westerly winds (Lehmkuhl and Haselein, 2000). As a result, the region is sensitiveto changes in the large-scale westerly and monsoonal circulation systems. Some studies have indicated that Holoceneclimatic changes in this region were mostly influenced by expansion and contraction of the summer monsoonal circulation(e.g. An et al., 2000; Jiang et al., 2006; Zhou et al., 2001). However, due to the interplay between the subtropical monsoonsystem and the mid-latitude westerlies, the region might have experienced complex pattern of climate change during theHolocene, neither a direct response to the westerlies nor to summer monsoon.

The Tengger Sandy Desert immediately to the northeast of the Tibetan Plateau has an average elevation of 1300 m abovesea level, while the Tibetan Plateau and bordering Qilian Mountains have elevations ranging from 3500 to 5000 m. Thisdrastic difference in topography within a few hundred kilometers could have a large impact on regional climate change byaffecting uplifting/subsiding air masses (Broccoli and Manabe, 1992). At the present, the region lies near the northernmargin of the influence of the East Asian summer monsoon. These physiographic settings of the study region suggest thatsedimentary records should provide sensitive records of regional climate, in responding to the interactions of these factors.

Elsevier Ltd.

: +86 9318912330.

Holocene vegetation and climate change from a lake sediment record in theJournal of Arid Environments (2008), doi:10.1016/j.jaridenv.2008.06.016

www.sciencedirect.com/science/journal/yjarewww.elsevier.com/locate/jnlabr/yjaredx.doi.org/10.1016/j.jaridenv.2008.06.016mailto:[email protected]/10.1016/j.jaridenv.2008.06.016Original Text:Sesert

Original Text:-cm

Original Text:palaeolake

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61


1000km

TibetanPlateau

90° 100° 110° 120°80°E

30°

20°

40°

50°N

BLWL

BYC

MDWDDW

DGC Qilian MoutainsQinghai

Lake

Shiya

ng R

iver

TenggerDesert

BadanJaranDesert

QTL

Hei R

iver

43

EJL

100km100°E

39N°

37N°

41N°

HS

SJC

BDK

5▲

▲▲▲

▲1

2

102°E 104°E

Fig. 1. Location of the study region and site. (A) Map showing the location of the study region (open square) in China. Six other paleoclimate sitesmentioned in the text: WL, Wulun Lake; BL, Bosten Lake; DDW, Dadiwan; MDW, Midiwan; BYC, Bayanchagan; and DGC, Dongge Cave. (B) Satellite image

showing the location of the study site (solid square) at Qingtu Lake (QTL) in Gansu, China and other paleoclimate sites (solid circles) in the region

discussed in the text (SJC, Sanjiaocheng section; HS, Hongshui River section; BDK, Biandukou; EJL, Eastern Juyan Lake) and five nearby climate stations

(white triangles; 1: Wushaoling at 3045 m a.s.l.; 2: Qilian at 2787 m; 3: Gulang at 2072 m; 4: Wuwei at 1531 m; and 5: Minqin at 1367 m).

Y. Zhao et al. / Journal of Arid Environments ] (]]]]) ]]]–]]]2

2. Study region and study site

The Shiyang River originates from the Qilian Mountains to the south, runs through the northwest end of the TenggerSandy Desert, and has a catchment area of 41,163 km2 (lat. 371020–391170N, long. 1001570–1041570E). The Tengger SandyDesert is one of the major deserts with active sand dunes in northwest China (Fig. 1). Qingtu Lake (lat. 3910401500N, long.10313604300E, elevation 1302 m a.s.l.) was a terminal lake in the Shiyang River Basin, which is totally dried up at the present.

Mean annual precipitation at nearby Minqin meteorological station (at 1367 m a.s.l., 110 km southwest of the study site)is about 115 mm and is highly variable seasonally, most of which falls as rain during the summer months (Fig. 2A); themean annual temperature is 7.8 1C; and the potential evaporation is about 2640 mm. In the Shiyang River Basin,precipitation increases with elevation (Fig. 2B). The distribution of modern vegetation in this region (Hou, 2001; Huang,1997) is strongly related to precipitation and to elevation: forest at 42500 m, alpine meadow at 2350–2500 m, desertsteppe at 2000–2350 m and desert at o2000 m. The vegetation surrounding Qingtu Lake is dominated by desert plants, e.g.Chenopodiaceae (including Salsola abrotanoides, Kalidium gracile, Haloxylon ammodendion, and Ceratoides compacta),Ephedra przewalskii, Nitraria spp., Tamarix chinensis, Ajania fruticulosa and Kerelinia caspica.

Several studies on Late Quaternary paleoenvironments in the Tengger Desert have been published (e.g. Pachur et al.,1995; Zhang et al., 2004a). Evidence from sediment structure, geochemical composition, and ostracods suggest that theremight be a mega-paleolake at 39,000–23,000 14C year BP in the Tengger Desert (Pachur et al., 1995). The stratigraphicevidence shows that no lakes existed in the Tengger Desert during the last glacial maximum (LGM) centered around18,000 14C yr BP (Zhang et al., 2004a). The paleolakes started to develop again around 12,000 14C yr BP. The extent of theHolocene paleolakes, primarily migratory lakes, was smaller than that of the Late Pleistocene paleolakes represented bystratified lake deposits, alternating with fluvial and eolian deposits, indicating a long-term oscillation trend toward aridconditions (Pachur et al., 1995; Zhang et al., 2004a). However, the detailed climate history in this region is still poorlydocumented and understood, as these records are mostly based on geomorphic evidence from terrace deposits that mayhave dating controls and discontinuous deposition problems.

Three papers focusing on climate change in the Shiyang River drainage along the northwestern edge of the TenggerDesert have been published in recent years (Chen et al., 2006; Ma et al., 2004; Shi et al., 2002), but these authors presenteddifferent interpretations of climate changes. Shi et al. (2002) reconstructed the lake evolution of the terminal area of theShiyang River drainage based on the investigations of geomorphology and sedimentology, and radiocarbon dates, grain sizeand carbonate of the sediments from nine sections. The chronologies were based on conventional radiocarbon dates frombulk carbonate-rich organic and carbonate. They interpreted high carbonate as low lake level and dry climate. The resultssuggested a coalescent open lake in the terminal area, indicating moist early Holocene; and closed shallow carbonate lakesand swamps during the middle and Late Holocene, showing an aridification trend. Previously published pollen recordsfrom two sections in this region were from near river and tributary channel (Chen et al., 2006; Ma et al., 2004; Zhang et al.,2000; Zhu et al., 2003). A pollen record from Hongshui section (see location in Fig. 1) suggested that the climate was thewarmest and wettest during 7400–5650 cal yr BP, fluctuated during 5650–4450 cal yr BP, and humid during 4450–3500 cal

Please cite this article as: Zhao, Y., et al., Holocene vegetation and climate change from a lake sediment record in theTengger Sandy Desert, northwest China. Journal of Arid Environments (2008), doi:10.1016/j.jaridenv.2008.06.016

dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:°02’-

Original Text:°17’

Original Text:°57’-

Original Text:°57’

Original Text:° 04’15”

Original Text:°36’43”

Original Text:) was

Original Text:º

Original Text:-2500

Original Text:-2350

Original Text:.

Original Text:, Tamarix

Original Text:late

Original Text:palaeoenvironments

Original Text:-23

Original Text:year

Original Text:palaeolakes

Original Text:year



Original Text:Shi et al., 2002; Ma et al., 2004

Original Text:late

Original Text:5650

Original Text:4450

Original Text:3500

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61


Fig. 2. Regional climate data. (A) Mean monthly precipitation and temperature at Minqin climate station (from 1953 to 2001), about 110 km southwest ofQingtu Lake. Mean annual precipitation is 115 mm, and mean annual temperature is 7.8 1C. (B) Relationship between elevation and annual precipitationfrom five climate stations in the study region. Elevation of Qingtu Lake is 1302 m.

Y. Zhao et al. / Journal of Arid Environments ] (]]]]) ]]]–]]] 3

yr BP. However, the pollen results from Sanjiaocheng section (inferred mainly by montane tree pollen from the QilianMountains) suggested a dry Mid-Holocene during 7100–3800 cal yr BP, and a wetter early and Late Holocene (Chen et al.,2006). We here present pollen and lithology results for a dried-up lake (Qingtu Lake) sediment sequence to discuss lakedevelopment, major vegetation and climate changes.

3. Materials and methods

3.1. Sampling and dating methods

A 384-cm-long section (QTL-03) was excavated in October 2003 in the dried-up Qingtu Lake. The profile was describedin the field and subsampled at 2 cm intervals. Due to the absence of plant macrofossils, five samples of bulk organic matterwere radiocarbon dated using accelerator mass spectrometry (AMS) at AMS Dating Laboratory at Beijing University(PKUAMS, Beijing, China) (Table 1). Samples at 40 and 374 cm are from organic-rich peat layers; others are from organicmatter in carbonate layers. Graphite sample preparation at PKUAMS is based on direct CO2 catalytic reduction on ironpowder, as described by Vogel et al. (1987). The d13C values were measured by a VG Sira-24 mass spectrometer forfractionation correction. All dates were calibrated to calendar years before present (present ¼ 1950 AD) based on IntCal04dataset (Reimer et al., 2004), using the program Calib Rev. 5.01. The age-depth model was based on linear interpolations ofcalibrated ages (Fig. 3). Calibrated ages were used throughout the paper.

3.2. Magnetic susceptibility, grain size and carbonate content analysis

Magnetic susceptibility (MS) was measured on Bartington Instruments’ MS2B susceptibility meter. Analysis ofcarbonate content was done using a Bascomb calcimeter. Grain-size analysis was determined using a Mastersizer 2000


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:mid

Original Text:3800

Original Text:late

Original Text:cm

Original Text:rich

Original Text:data set (

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61


Table 1AMS radiocarbon dates and calibrated ages from Qingtu Lake (section QTL-03), northwest China

Laba number Sample depth

(cm)

Material dated d13C (%, VPDB) 14C date7S.E.(yr BP)

2s range (cal BP)c Median age(cal yr BP)c

LAM06-065 40 Peat �28.8 2835735 2857–3042 2950LAM06-033 118 Organic matter �36.2 2675740b 2744–2853 2799LAM06-066 206 Organic matter �30.1 3860735 4222–4412 4317LAM06-067 374 Peat �24.1 6285735 7159–7278 7219LAM06-034 380 Organic matter �33.4 11,445750 13,209–13,401 13,305

a AMS Dating Lab at Beijing University (PKUAMS), Beijing.b Date is too young and rejected.c Calibrated based on CALIB rev. 5.01 using IntCal04 calibration dataset (Reimer et al., 2004).

2835±35

2675±40

3860±35

6285±3511445±150

14C date(Cal yr BP)

Peat Silty marl Fine sandMarl

Depth(cm)

Median grainsize (µm)

Hiatus

Age-depth model

Qingtu Lake, Gansu( )2950

( )2799

( )4317

( )7219

( )13305

Coarse sand

Age (cal yr BP)Carbonate (%)MS (10-8m3/g)

Fig. 3. Sediment lithology and chronology at Qingtu Lake, northwest China. (A) Lithology and AMS dating horizons; (B) magnetic susceptibility; (C)median grain size; (D) carbonate (%); and (E) age-depth model of section QTL-03.


(Malvern Instruments) after organic matter and carbonate were removed by H2O2 and HCl, respectively. All these analyseswere done at 2-cm intervals.

3.3. Pollen analysis

Pollen subsamples of ca. 20 g were taken at mostly 4 cm intervals from the section. The subsamples were treated with amodified acetolysis procedure (Fægri and Iversen, 1989), including HCl, NaOH, HF and acetolysis treatments, and finesieving to remove clay-sized particles. The concentrate was mounted in glycerol gel. A known number of Lycopodiumclavatum spores (batch no. 938934) were initially added to each sample for calculation of pollen concentration (Maher,1981). Each pollen sample was counted under a light microscope at 400� magnification in regularly spaced traverses;1000� magnification was used for critical identification. Pollen sums are usually 4300 terrestrial pollen grains.Identifications followed Wang et al. (1995) aided by the modern reference collections. Pollen percentages were calculatedbased on the total pollen sum. Pollen diagrams were plotted using TGView 2.0 (E. Grimm of Illinois State Museum,Springfield, IL, USA).


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:Magnetic Susceptibility

Original Text:Median

Original Text:Carbonate (%);

Original Text:Age

Original Text:(‰-VPDB

Original Text:E

Original Text:445

Original Text:209

Original Text:401

Original Text:305

Original Text:data set (

Original Text:-cm

Original Text:#

Original Text:×

Original Text:magnification

Original Text:-spaced

Original Text:×

Original Text:magnification

Original Text:Illinois

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61



4. Results

4.1. Lithology

The lithology of QTL-03 changes from basal sand to marl and to surface sand, with multiple layers of peat and silty marlwithin marl section (Fig. 3A). The section below 380 cm consists of coarse fluvial sand. Between 380 and 100 cm, thesediment is mainly composed of carbonate (mostly 70–80%) containing numerous mollusk shells, with two silty marllayers of low carbonate at 215–206 cm and 170–160 cm. The upper section above 100 m contains three peat layersalternated with silty marl and marl layers, capped by fine eolian sand of high magnetic susceptibility.

4.2. Chronology

Although the dates were on bulk organic matters, carbon isotope values of �28.8% and �24.1% for peat samples at 40and 374 cm indicate terrestrial origin of organic matter, so we do not expect a significant old carbon effect, if any, at thesetwo critical horizons. There is a dating reversal at 40 cm (2835735 14C BP) and 118 cm (2675740 14C BP). Accepting bothdates would result in an age model that has about 500 years difference in the last 4000 years. We rejected the date at118 cm from marl layer that is rich in carbonate as it was more likely problematic due to its low organic matter content.There is obviously a sediment hiatus around 380 cm as bracketed by two dates of 13,300 and 7200 cal yr BP (Fig. 3E). Theremight be another hiatus around 100 cm (3000–3500 cal yr BP) based on the sharp lithology change from marl to peat andeventually to sand. Despite the low number of dates, the two reliable dates at 40 and 374 cm on terrestrial peat shouldprovide adequate chronology for our discussion of major environmental change during the Mid- and Late Holocene atmulti-millennial timescale.

4.3. Fossil pollen assemblages

We identified a total of 50 pollen types in 88 samples from section QTL-03. A summary percentage pollen diagram isshown in Fig. 4. Artemisia (up to 87%), Chenopodiaceae (up to 70%), and Asteraceae (excluding Artemisia) (up to 84%)switched dominance throughout the sequence. Poaceae (up to 15%), Ephedra (up to 15%) and Nitraria (up to 30%) aresecondary dominant regional and local pollen types. Tree pollen are generally o2% through the pollen sequence, but reachup to 27% at 5200–4300 cal yr BP (252–204 cm). Aquatic pollen types include Potamogeton, Alisma and Sparganium, all beingo1%, while Typha is up to 8%.

The percentage pollen diagram is divided into four pollen assemblage zones, with subzones when necessary, based onstratigraphically constrained cluster analysis (CONISS) (Grimm, 1987; Fig. 4).

0

1000

2000

3000

4000

5000

6000

7000

Age

(cal

yr B

P)

Picea

20 20 20 20 20 20 2 6 10 14100 200400 80040 60

Pinus

Sabin

a

Betul

aQu

ercus

UlmusRa

nunc

ulus

Poac

eae

Artem

isia

Aster

acea

e

Chen

opod

iacea

e

Nitrar

ia

Ephe

dra

Polle

nsum

Typh

a

Zone

Hiatus

QTL-1

QTL-2

QTL-3

QTL-4a

QTL-4b

(x1000 grains/g) Total sum of squares

CONISS

80 20 20 20

A/C

ratio

Conc

entra

tion

Mountain plants

Percentage pollen diagram from Qingtu Lake, northwestern ChinaRegional and local plants

Polyg

onum

Cype

racea

emurtcilahTCarbonate (%)

400 80 40 60 80 4060 80

Fig. 4. Percentage pollen diagram of section QTL-03 at Qingtu Lake, northwest China. Selected taxa shown.


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:-80

Original Text:-206

Original Text:-160

Original Text:-28

Original Text:‰

Original Text:-24

Original Text:‰

Original Text:cm

Original Text:±

Original Text:±

Original Text:300

Original Text:-3500

Original Text:cm

Original Text:mid

Original Text:late

Original Text:4300

Original Text:-204

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61



4.3.1. Zone QTL-1 (374–252 cm; 7200–5200 cal yr BP)

The pollen assemblages were dominated by Artemisia (60–70%), Chenopodiaceae (�25%) and Poaceae (�15%). A/C ratiowas about 3. This zone had a total pollen concentration of about 30,000–40,000 grains/g. The basal sand sample (380 cm;13,300 cal yr BP) has low Artemisia (only 15%) and high Chenopodiaceae (34%), with very low pollen concentration of�1000 grains/g.


Pollen assemblages were characterized by Chenopodiaceae (�50%), Artemisia (20–40%) and Asteraceae (up to �80%). A/C ratio was mostly o1. Ranunculaceae and Ephedra had high peaks in this zone. Tree pollen was at its highest value in thiszone, mainly from Pinus (up to 26%) and Picea. Pollen concentration was around 1000 grains/g.


Artemisia increased and reached the maximum value of 87% while Chenopodiaceae decreases to �15%. A/C ratio reaches410. Poaceae was up to 10% in this zone. Pollen concentration was 1000–5000 grains/g.


Pollen assemblages were characterized by consistently low Artemisia (mostly 10–20%). Nitraria reached the highestvalue (�32%). A/C ratio was o1. Two subzones were divided at 3000 cal yr BP (44 cm) based mostly on change inChenopodiaceae and Asteraceae. At subzone QTL-4a (100–40 cm; 3500–3000 cal yr BP), Asteraceace dominated pollenassemblages (�95%), with pollen concentration of 500–3000 grains/g. At subzone QTL-4b (40–0 cm; 3000–0 cal yr BP),pollen assemblages were characterized by Chenopodiaceae (�70%), with a total pollen concentration at its lowest value ato600 grains/g.

5. Discussion

5.1. Lake development and local environmental change

At Qingtu Lake, the coarse sand deposit before 7200 cal yr BP suggests a non-lake environment at the site likely under adry climate during the early Holocene. The date of 13,300 cal yr BP from the sand deposit indicates a sediment hiatus of6000 year duration, going back to the Late glacial. The peat layer of high organic matter and low carbonate during7200–7100 cal yr BP represent a wetland environment, when the terminal depression began to become wet. During7100–3500 cal yr BP, marl sediments with high carbonate content and uniform grain size indicate a stable and shallow lakeenvironment, except two silty marl layers at 4400 and 4000 cal yr BP suggesting variable and lower lake levels. Between3500 and 3000 cal yr BP, a highly variable local environment was suggested by rapidly changing lithology of peat, silty marland eolian sand, with large variations of magnetic susceptibility and grain size. Since 3000 cal yr BP, the lake was dried up atthe coring site as inferred by eolian sand deposit.

Our environmental interpretations of lithology data above are different from Shi et al. (2002), as they interpreted highcarbonate representing dry environment. However, our pollen results as discussed below from the same section at QingtuLake generally supported our lithologic interpretation that high carbonate represent wetter and ‘‘steppe’’-dominatedenvironment.

5.2. Holocene regional vegetation history

We focused on the abundance of Artemisia, Chenopodiaceae, Ephedra, Nitraria, Asteraceae and Poaceae as reflectingvegetation change in this study. Artemisia is representative of steppe, while Chenopodiaceae, Ephedra and Nitraria are thetaxa that are traditionally used to represent desert (El-Moslimany, 1990; Herzschuh et al., 2004; Liu et al., 1999). Asteraceaepollens at QTL-03 likely come from A. fruticulosa based on the surface pollen results in the Shiyang River Basin (Zhu et al.,2003) and on our vegetation investigation in the field. A. fruticulosa is widespread in gravel valleys in the regions of desertand steppe desert (Wang, 1988). We speculate that the abrupt increase of A. fruticulosa pollen around 4300 cal yr BP andduring 3500–3000 cal yr BP at QTL-03 might suggest the expanding of A. fruticulosa in the floodplain after flooding. Anincrease of Poaceae can indicate an expansion of steppe over desert, suggesting relatively moist environments based onsurface pollen spectra from Inner Mongolia, Xinjiang and the Tibetan Plateau (Cour et al., 1999; Herzschuh et al., 2003; Li,1998; Li et al., 2005; Shen et al., 2006; Yu et al., 2001; Zhao et al., 2007).

The summary pollen diagram shows clear vegetation changes during the Holocene (Fig. 4). Vegetation was desertcharacterized by Chenopodiaceae, Artemisia and Ephedra before 7200 cal yr BP. A steppe desert dominated mainly byArtemisia and Chenopodiaceae, with high vegetation cover as inferred from pollen concentration, developed during7200–5200 cal yr BP. Vegetation appeared to be highly variable during 5200–3000 cal yr BP showing rapid switchesbetween highland and lowland pollen types: desert dominated by Chenopodiaceae, Asteraceae (likely Ajania) and Ephedraat 5200–4300 cal yr BP, steppe desert dominated by Artemisia during 4300–3500 cal yr BP, and desert/steppe desert


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:-70

Original Text:(~

Original Text:(~

Original Text:000 –

Original Text:000

Original Text:300

Original Text:~

Original Text:(~

Original Text:- 40

Original Text:~

Original Text:~

Original Text:-5000

Original Text:20

Original Text:(~

Original Text:40

Original Text:3000

Original Text:(~

Original Text:3000

Original Text:0

Original Text:0

Original Text:(~

Original Text:300

Original Text:late

Original Text:7100

Original Text:– 3500

Original Text:Liu et al., 1999

Original Text:jania

Original Text:jania

Original Text:jania

Original Text:3000

Original Text:jania

Original Text:Li, 1998

Original Text:Yu et al., 2001

Original Text:5200

Original Text:3000

Original Text:4300

Original Text:3500

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61



dominated by Asteraceae type (likely Ajania), Artemisia and Nitraria 3500–3000 cal yr BP. A desert vegetation dominated byChenopodiaceae returned after 3000 cal yr BP after the lake dried up at the coring site.

Tree pollen (mostly from Pinus and Picea) at section QTL-03 appears to have been transported from the mountains and isnot representative of local vegetation around the study site. Pollen transport by wind and rivers has been confirmed bymodern surface pollen studies in this region (Zhu et al., 2003). The high percentages of Pinus and Picea during5200–4300 cal yr BP in the section QTL-03 probably resulted from overrepresentation of transported tree pollen from themountains, due to very low local pollen production as indicated by the extremely low pollen concentration during thisperiod. Or alternatively, high input of transported tree pollen reflected an increase of river runoff from the mountain.Ranunculus pollen at section QTL-03 could also have been transported from meadow in the high elevation mountain, sohigh Ranunculus percentage during 5200–3500 cal yr BP was not indicative of local vegetation. The abrupt increase of A.fruticulosa pollen at around 4300 cal yr BP and during 3500–3000 cal yr BP aforementioned followed the high abundances oftree or Ranunculus, supporting the speculation about the expanding of A. fruticulosa in the floodplain after increased riverrunoff from the mountains.

The lacustrine section QTL-03 showed different pollen spectra from Hongshui section (Ma et al., 2004) and Sanjiaochengsection (Chen et al., 2006) in the Shiyang River Basin, which contain averagely ca. 40–55% tree pollen (mainly from Picea,Pinus and Sabina) throughout the Holocene. Modern surface pollen sample analysis indicated that both sections near riverchannel contain abundant tree pollen transported by rivers from the Qilian Mountains (Ma et al., 2004; Zhu et al., 2003).The Qilian Mountains have elevations averaging 44000 m, while the Tengger Sandy Desert has an elevation of 1300 m (Fig.1). If both high elevation and low elevation vegetation respond to the same precipitation change, then the general moisturepatterns should be the same at both locations. However, if stream flow was dependent on glacial melting rates in thesummer, then summer temperature might have played a major role in river flow, and consequently the river’s ability totransport tree pollen from highlands. So we speculate that the difference between our record and the other two previouslypublished records (Chen et al., 2006; Ma et al., 2004) is due to different changes in temperature and precipitation betweenhigh and low elevations. In any case, because their records contain more tree pollen, abundant river-transported pollenlikely obscure signals from regional and local vegetation, especially at Sanjiaocheng site.

5.3. Inferred climate change and possible mechanism

The lake development history and vegetation change suggest the following sequence of Holocene climate change in ageneral arid context (Table 2). The climate was extremely dry before 7200 cal yr BP as inferred from dried-up lake andsediment hiatus. The moistest climate occurred at 7200–5200 cal yr BP, suggested by stable lake level, steppe desert anddenser vegetation. A highly variable climate from 5200 to 3000 cal yr BP was indicated by rapid switches betweenmountain and lowland pollen types. The dry climate persisted since 3000 cal yr BP as indicated by eolian sand depositionand dried-up lake, though coarse resolution analysis does not permit detailed reconstructions.

The Holocene temporal pattern of climate changes at Qingtu Lake has also been documented at Eastern Juyan Lake(Herzschuh et al., 2004) in nearby region (see Fig. 1 for location), which showed the general dry–wet–dry pattern duringthe Holocene (Fig. 5B). However, the climate pattern at Qingtu was obviously out of phase with the records from QinghaiLake on the Tibetan Plateau and Biandukou at the edge of Qilian Mountains (Yu et al., 2006; Fig. 5C), which are likelyinfluenced by the East Asian summer monsoon. At Qinghai Lake, ca. 450 km southwest of Qingtu Lake, but at very differentelevations (3200 m vs. 1367 m), both oxygen isotopes of lacustrine carbonate (Lister et al., 1991) and pollen record (Shen etal., 2005) suggested a wet climate in the early and middle Holocene induced by stronger summer monsoon. At Biandukou,multi-proxy record of magnetic, optical and geochemical properties showed that a generally humid early Holocene andstrong aridification after 4700 cal yr BP (Yu et al., 2006). Many other records from semi-arid regions and the Loess Plateau(e.g. Dadiwan, An et al., 2003; Bayanchagan, Jiang et al., 2006; Midiwan, Li et al., 2003) also appear to correlate well withthose well-dated records from Qinghai Lake (Lister et al., 1991; Shen et al., 2005) and Dongge Cave in southwest China asreported by Wang et al. (2005) (Fig. 6C), which show strong early and Mid-Holocene summer monsoon (see Fig. 1A forlocations of these records). However, at sites further north and west of Qingtu Lake mostly influenced by the westerlies, adifferent pattern appears to emerge. Chen et al. (2008) reviewed the Holocene moisture change in arid Central Asia basedon pollen and other independent climate proxies. Most sites experienced maximum effective moisture between 8000 and4000 cal BP in the Mid-Holocene and a slightly wet climate around 2000 cal BP (Fig. 6B). For example, at Hulun Lake inXinjiang, a pollen record showed a drying climate in the early Holocene, a relatively wet climate during 7000–5000 cal

Table 2Summary of evidences for moisture change at Qingtu Lake (section QTL-03), northwest China

Time intervals (ka) Moisture change Evidences for moisture change

3–0 Very dry Eolian sand, high percentage of Chenopodiaceae (desert indicator) pollen

5.2–3 Highly variable High variations in carbonate content and pollen percentages

7.2–5.2 Stable and wet High carbonate percentage, high percentage of Artemisia (steppe indicator) pollen

47.2 Very dry Sand deposit, sedimentary hiatus


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:-0 ka

Original Text:very

Original Text:eolian

Original Text:-3 ka

Original Text:highly

Original Text:high

Original Text:-5

Original Text:ka

Original Text:stable

Original Text:high

Original Text:ka

Original Text:very

Original Text:sand

Original Text:4300

Original Text:3500

Original Text:jania

Original Text:3000

Original Text:jania

Original Text:-55

Original Text:Ma et al., 2004

Original Text:5200

Original Text:doesn’t

Original Text:-wet-

Original Text:the

Original Text:, Dadiwan

Original Text:mid

Original Text:mid

Original Text:5000

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61


Variable

Dry

Wet

Dry

QingtuLake

0

1

5

6

7

8

9

10

11

12

Age

(ka)

WulunLake

Wet

Dry

Wet

BostenLake

Dry

Variable

Dry

Variable

Wet

Dry

Wet

Dry

Biandukou QinghaiLake

Dry

Wet

Dry

Eastern JuyanLake

Out-of-phase monsoon pattern Monsoon pattern Westerly pattern

2

4

3

Nodata

Fig. 5. Correlations of wet-dry climate intervals from paleoclimate sites in northwest China. (A) Qingtu Lake (this study); (B) Eastern Juyan Lake(Herzschuh et al., 2004); (C) Biandukou (Yu et al., 2006); (D) Qinghai Lake (Shen et al., 2005); (E) Wulun Lake (Yang and Wang, 1996); and (F) Bosten Lake

(Huang, 2006).

Fig. 6. Correlation of Qingtu Lake record with other Holocene moisture records and possible mechanism interpretations. (A) Holocene moisture pattern atQingtu Lake (this study); (B) moisture pattern in arid Central Asia (Chen et al., 2008); (C) oxygen isotope from Dongge Cave (Wang et al., 2005) with lower

values indicating stronger monsoon precipitation; (D) summer insolation at 401N (Berger and Loutre, 1991); and (E) proposed interpretations for QingtuLake moisture record, considering possible interactions between the Tibetan Plateau-induced air subsidence and direct monsoon precipitation.


yr BP and variable climate after 5000 cal yr BP (Yang and Wang, 1996; Fig. 5E). At Bosten Lake, lithology and pollen datashowed that a dry climate in the early Holocene, a wet middle Holocene and a moderately wet and variable climate after3500 cal yr BP (Huang, 2006; Fig. 5F). Comparison with these records suggests that the Qingtu climate pattern is out of


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:Moisture

Original Text:Oxygen

Original Text:Summer

Original Text:Proposed

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61

Q 1



phase at certain times with the sites influenced by summer monsoon (Fig. 6C). Also, the pattern is not simply a reflection ofthe influence of the prevailing westerlies, considering the different Late Holocene climate pattern (Fig. 6B).

The contrasting climate patterns might have arisen from the vertical air dynamics modulated by the difference inelevations of these sites. During the early Holocene, the maximum summer insolation (Berger and Loutre, 1991) enhancedthe Asian summer monsoon (Kutzbach, 1981), leading to high precipitation in the region affected by monsoon. Many recentpaleoclimate studies have shown an intensification of the monsoon in the early Holocene and subsequent weakeningaround 5000–4000 cal yr BP (e.g. An et al., 2000; Morrill et al., 2003; Shao et al., 2006; Wang et al., 2005). For example, atDongge Cave in South China where the climate is influenced by both the SE Asian and Indian monsoons, a decrease inoxygen isotope values in stalagmites at the beginning of the Holocene indicated an increase in summer monsoonal rains, asa result of the onset of an intensified monsoon (Wang et al., 2005). Qingtu Lake is situated in an arid low-lying basin(1302 m a.s.l.) to the northeast of the Tibetan Plateau with an average elevation of ca. 5000 m. This difference in elevationmight have been important in inducing uplifting and subsiding air motions, modifying regional climate patterns. Broccoliand Manabe (1992) found that the heating and upward motion of air over the Tibetan Plateau causes strong air subsidenceto the northwest and north of the Plateau, inducing dry climate. Observational data during the 1979 monsoon season (He etal., 1987) also supports the hypothesis that the intense heating and upward motion over the plateau is accompanied bysubsidence as compensating flow over the surrounding areas. This uplifting and subsiding dynamic mechanism has beenconsidered as an explanation for the spatial pattern of Holocene wet–dry climate periods in Central Asia (Herzschuh, 2006)and in the Qaidam Basin on the Tibetan Plateau (Zhao et al., 2007, 2008). As a result, the enhanced air subsidence duringthe early Holocene at the maximum summer insolation might have caused dry climate at Qingtu Lake.

During the Mid-Holocene, summer monsoon became weaker due to the decreasing summer insolation. At Dongge Cave,an increase in oxygen isotope values in stalagmites during the Mid-Holocene indicated a decrease in summer monsoonalrains (Wang et al., 2005). A similar drying trend occurred at Qinghai Lake (Lister et al., 1991; Shen et al., 2005). A weakeneduplifting on the Tibetan Plateau would cause less subsiding air flow in the surrounding lowland regions, causing a dryPlateau and a wet lowland relationship. This uplifting and subsiding mechanism between highlands and lowlands might beresponsible for a relatively wet climate during 7200–5200 cal yr BP around Qingtu Lake. The Late part of the middleHolocene experienced large climate fluctuations during 5200–3000 cal yr BP around Qingtu Lake, which also correspondedwith the greatest transported tree pollen and Ranunculus pollen from Qilian Mountain. This highly variable transitionperiod might have been caused by the great contrast of climate changes in highland and lowland regions, induced by thecompeting factors of subsiding dry airflow versus direct monsoon precipitation.

A general drying trend in the Late Holocene around Qingtu Lake inferred from our multi-proxy data has beendocumented at many records from northwest China. For example, climate became drier after 3000 cal yr BP at Daihai Lake(Xiao et al., 2004), after 3900 cal yr BP at Eastern Juyan Lake (Herzschuh et al., 2004), after 4700 at Biandukou (Yu et al.,2006), and after 4200 cal yr BP at Qinghai Lake (Shen et al., 2005). This drying pattern has also been documented by higheroxygen isotope values in stalagmites from eastern China (e.g. Shao et al., 2006; Wang et al., 2005; Zhang et al., 2004b). Thedry Late Holocene in the Qingtu Lake region was possibly in response to weakened monsoon induced by decreased summerinsolation and subsequent less precipitation.

In summary, the possible controlling factors on the major environmental change in the Qingtu Lake region are shown inFig. 6. Before 7200 cal yr BP, strong summer insolation caused enhanced air subsidence and dry climate in the lowlandregions surrounding the Tibetan Plateau, including Qingtu Lake. During 7200–5200 cal yr BP, less subsiding air flow causedby weaker summer insolation and relative strong monsoon caused a relatively wet climate at Qingtu Lake. The interactionsbetween subsiding air flow and direct monsoon precipitation at the lowlands during 5200–3000 cal yr BP might beresponsible for the variable climate. After 3000 cal yr BP, subsiding influence continued to decrease due to decreasedinsolation and at the same time direct monsoon precipitation became weak as well, causing a dry climate.

Uncited reference

Liu et al. (1998).

Acknowledgments

We thank Dr. D.S. Xia, Mr. J.X. Chao, Dr. M.R. Qiang and Dr. H. Zhao for field and laboratory assistance. This project wassupported by the National Natural Science Foundation of China (Grants nos. 40771212 and 40528001) and NSFC InnovationTeam Project (No. 40721061). The final version of the manuscript was prepared when the senior author was a VisitingResearch Scientist in the Department of Earth and Environmental Sciences at Lehigh University (Bethlehem, PA, USA),partially supported by a US National Science Foundation grant (to Yu).

References

An, Z.S., Porter, S.C., Kutzbach, J.E., Wu, X.H., Wang, S.M., Liu, X.D., Li, X.Q., Zhou, W.J., 2000. Asynchronous Holocene optimum of the East Asian monsoon.Quaternary Science Reviews 19, 734–762.


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:late

Original Text:).

Original Text:4000

Original Text:Wang et al., 2005

Original Text:-dry

Original Text:mid

Original Text:mid

Original Text:5200

Original Text:late

Original Text:3000

Original Text:late

Original Text:Zhang et al., 2004b; Wang et al., 2005

Original Text:late

Original Text:-5200

Original Text:-3000

Original Text:Acknowledgements

Original Text:#

Original Text:#

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

55

57

59

61



An, C.B., Feng, Z.D., Tang, L.Y., 2003. Evidence of a humid mid-Holocene in the western part of the Chinese Loess Plateau. Chinese Science Bulletin 48,2472–2479.

Berger, A., Loutre, M.F., 1991. Insolation values for the climate of the last 10 million years. Quaternary Science Reviews 10, 297–317.Broccoli, A.J., Manabe, S., 1992. The effects of orography on midlatitude Northern Hemisphere dry climates. Journal of Climate 5, 1181–1201.Chen, F.H., Chen, B., Zhao, Y., Zhu, Y., Madsen, D., 2006. Holocene environmental change inferred from high-resolution pollen records from inland lake

deposits, arid China. The Holocene 16, 675–684.Chen, F.H., Yu, Z.C., Yang, M.L., Ito, E., Wang, S.M., Madsen, D.B., Huang, X.Z., Zhao, Y., Sato, T., Birks, H.J.B., Boomer, I., An, C.B., Wünnemann, B., 2008.

Holocene moisture evolution in Arid Central Asia and its out-of-phase relationship with Asian monsoon history. Quaternary Science Reviews 27,351–364.

Cour, P., Zheng, Z., Duzer, D., Calleja, M., Yao, Z., 1999. Vegetational and climatic significance of modern pollen rain in northwestern Tibet. Review ofPalaeobotany and Palynology 104, 183–204.

El-Moslimany, A.P., 1990. The ecological significance of common nonarboreal pollen: examples from dryland of the Middle East. Review of Palaeobotanyand Palynology 64, 343–350.

Fægri, K., Iversen, J., 1989. Textbook of Pollen Analysis, fourth ed.. Wiley, London.Grimm, E.C., 1987. CONISS: a Fortran 77 program for stratigraphically constrained cluster analysis by the method of incremental sum of squares.

Computers & Geosciences 13, 13–35.He, H.Y., McGinnis, J.W., Song, Z.S., Yanai, M., 1987. Onset of the Asian summer monsoon in 1979 and the effect of the Tibetan Plateau. Monthly Weather

Review 115, 1966–1995.Herzschuh, U., 2006. Palaeo-moisture evolution in Monsoonal Central Asia during the last 50,000 years. Quaternary Science Reviews 25, 163–178.Herzschuh, U., Kürschner, H., Ma, Y.Z., 2003. The surface pollen and relative pollen production of the desert vegetation of the Alashan Plateau, western

Inner Mongolia. Chinese Science Bulletin 48, 1488–1493.Herzschuh, U., Tarasov, P., Wünnemann, B., Hartmann, K., 2004. Holocene vegetation and climatic of the Alashan Plateau, NW China, reconstructed from

pollen data. Palaeogeography, Palaeoclimatology, Palaeoecology 211, 1–17.Hou, X., 2001. Vegetation Atlas of China. Science Press, Beijing (in Chinese).Huang, D., 1997. Vegetation in Gansu. Gansu Science and Technology Press, Lanzhou.Huang, X.Z., 2006. Holocene climate variability of arid central Asia documented by Bosten Lake, Xinjiang, China. PhD Dissertation, Lanzhou University.Jiang, W.Y., Gao, Z.T., Sun, X.J., Wu, H.B., Chu, G.Q., Yuan, B.Y., Hatté, C., Guiot, J., 2006. Reconstruction of climate and vegetation changes of the lake

Bayanchagan (Inner Mongolia): Holocene variability of the East Asian monsoon. Quaternary Research 65, 411–420.Kutzbach, J.E., 1981. Monsoon climate of the early Holocene: Climate experiment using the earth’s orbital parameters for 9000 years ago. Science 214,

59–61.Lehmkuhl, F., Haselein, F., 2000. Quaternary paleoenvironmental change on the Tibetan Plateau and adjacent areas (Western China and Western

Mongolia). Quaternary International 65/66, 121–145.Li, W.Y., 1998. Quaternary Vegetation and Environment of China. Science Press, Beijing (in Chinese).Li, X.Q., Zhou, W.J., An, Z.S., Dodson, J., 2003. The vegetation and monsoon variations at the desert-loess transition belt at Midiwan in northern China for

the last 13 ka. The Holocene 13, 779–784.Li, Y.C., Xu, Q.H., Zhao, Y.K., Yang, X.L., Xiao, J.L., Chen, H., Lu, X.M., 2005. Pollen indication to source plants in the eastern desert of China. Chinese Science

Bulletin 50, 1632–1641.Lister, G.S., Kelts, K., Chen, K., Yu, J., Niessen, F., 1991. Lake Qinghai, China: closed-basin lake levels and the oxygen isotope record for ostracoda since the

latest Pleistocene. Palaeogeography, Palaeoclimatology, Palaeoecology 84, 141–162.Liu, K., Yao, Z.J., Thompson, L.G., 1998. A pollen record of Holocene climatic changes from Dunde ice cap, Qinghai-Tibetan Plateau. Geology 26, 135–138.Liu, H.Y., Cui, H.T., Pott, R., Speier, M., 1999. The surface pollen of the woodland-steppe ecotone in southeastern Inner Mongolia, China. Review of

Palaeobotany and Palynology 105, 237–250.Ma, Y.Z., Zhang, H.C., Pachur, H.-J., Wuennemann, B., Li, J.J., Feng, Z.D., 2004. Modern pollen-based interpretations of mid-Holocene palaeoclimate at the

southern margin of the Tengger Desert, northwestern China. The Holocene 14, 841–850.Maher, L.J., 1981. Statistics for microfossil concentration measurements employing samples spiked with marker grains. Review of Palaeobotany and

Palynology 32, 153–191.Morrill, C., Overpeck, J.T., Cole, J.E., 2003. A synthesis of abrupt changes in the Asian summer monsoon since the last deglaciation. The Holocene 13,

465–476.Pachur, H.-J., Wünnemann, B., Zhang, H.C., 1995. Lake evolution in the Tengger Desert, Northwestern China, during the last 40,000 years. Quaternary

Research 44, 171–180.Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, C.J.H., Blackwell, P.G., Buck, C.E., Burr, G.S., Cutler, K.B., Damon, P.E., Edwards, R.L.,

Fairbanks, R.G., Friedrich, M., Guilderson, T.P., Hogg, A.G., Hughen, K.A., Kromer, B., McCormac, F.G., Manning, S.W., Ramsey, C.B., Reimer, R.W.,Remmele, S., Southon, J.R., Stuiver, M., Talamo, S., Taylor, F.W., van der Plicht, J., Weyhenmeyer, C.E., 2004. Intcal04 terrestrial radiocarbon agecalibration, 0–26 cal kys BP. Radiocarbon 46, 1029–1058.

Shao, X.H., Wang, Y.J., Cheng, H., Kong, X.G., Wu, J.Y., 2006. Holocene monsoon precipitation abrupt change and centennial variation from spelethomrecord at Shennongjia. Chinese Science Bulletin 51, 80–86.

Shen, J., Liu, X.Q., Wang, S.M., Matsumoto, R., 2005. Palaeoclimatic changes in the Qinghai Lake area during the last 18,000 years. Quaternary International136, 131–140.

Shen, C.M., Liu, K., Tang, L.Y., Overpeck, J.T., 2006. Quantitative relationships between modern pollen rain and climate in the Tibetan Plateau. Review ofPalaeobotany and Palynology 140, 61–77.

Shi, Q., Chen, F.H., Zhu, Y., Madsen, D., 2002. Lake evolution of the terminal area of Shiyang River drainage in arid China since the last glaciation.Quaternary International 93–94, 31–43.

Vogel, J.S., Nelson, D.E., Southon, J.R., 1987. 14C background in an accelerator mass spectrometry system. Radiocarbon 29, 323–333.Wang, J.T., 1988. The steppes and deserts of the Xizang Plateau (Tibet). Plant Ecology 75, 135–142.Wang, F.X., Qian, N.F., Zhang, Y.L., 1995. Pollen Flora of China. Science Press, Beijing (in Chinese).Wang, Y.J., Cheng, H., Edwards, R.L., He, Y.Q., Kong, X.G., An, Z.S., Wu, J.Y., Kelly, M.J., Dykoski, C.A., Li, X.D., 2005. The Holocene Asian monsoon: links to

solar changes and North Atlantic climate. Science 308, 854–857.Xiao, J.L., Xu, Q.H., Nakamura, T., Yang, X.L., Liang, W.D., Inouchi, Y., 2004. Holocene vegetation variation in the Daihai Lake region of north-central China: a

direct indication of the Asian monsoon climatic history. Quaternary Science Reviews 23, 1669–1679.Yang, X.D., Wang, S.M., 1996. The vegetation and climatic environmental changes in Hunlun Lake and Wulun Lake during Holocene. Oceanologia at

Limnologia Sinica 27, 67–71 (in Chinese).Yu, G., Tang, L.Y., Yang, X.D., Ke, X.K., Harrison, S.P., 2001. Modern pollen samples from alpine vegetation on the Tibetan Plateau. Global Ecology &

Biogeography 10, 503–519.Yu, Y.T., Yang, T.B., Li, J.J., Liu, J.F., An, C.R., Liu, X.Y., Fan, Z., Lu, Z.Y., Li, Y.P., Su, X., 2006. Millennial-scale Holocene climate variability in the NW China

drylands and links to the tropical Pacific and the North Atlantic. Palaeogeography, Palaeoclimatology, Palaeoecology 233, 149–162.Zhang, H.C., Ma, Y.Z., Wünnemann, B., Pachur, H.-J., 2000. A Holocene climatic record from arid northwestern China. Palaeogeography, Palaeoclimatology,

Palaeoecology 162, 389–401.Zhang, H.C., Peng, J.L., Ma, Y.Z., Chen, G.J., Feng, Z.-D., Li, B., Fan, H.F., Chang, F.Q., Lei, G.L., Wünnemann, B., 2004a. Late Quaternary palaeolake levels in

Tengger Desert, NW China. Palaeogeography, Palaeoclimatology, Palaeoecology 211, 45–58.


dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:pollen analysis

Original Text:4th

Original Text:John

Original Text:and Sons

Original Text:PhD Dissertation

Original Text:vegetation

Original Text:environment

Original Text:Closed

Original Text:Links

Original Text:Vegetation

Original Text:Climatic Environmental Changes

1

3

5

7

9



Zhang, M., Yuan, D., Lin, Y., Qin, J., Li, B., Cheng, H., Edwards, R.L., 2004b. A 6000-year high-resolution climatic record from a stalagmite in Xiangshui Cave,Guilin, China. The Holocene 14, 697–702.

Zhao, Y., Yu, Z.C., Chen, F.H., Ito, E., Zhao, C., 2007. Holocene vegetation and climate history at Hurleg Lake in the Qaidam Basin, northwest China. Review ofPalaeobotany and Palynology 145, 275–288.

Zhao, Y., Yu, Z.C., Chen, F.H., Liu, X.J., Ito, E., 2008. Sensitive response of desert vegetation to moisture change based on annually-resolved pollen recordfrom Gahai Lake in the Qaidam Basin, northwest China. Global and Planetary Change, doi:10.1016/j.gloplacha.2007.12.003.

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

Zhu, Y., Xie, Y.W., Cheng, B., Chen, F.H., Zhang, J.W., 2003. Pollen transport in the Shiyang River drainage, arid China. Chinese Science Bulletin 48,1499–1506.


dx.doi.org/10.1016/j.gloplacha.2007.12.003dx.doi.org/10.1016/j.jaridenv.2008.06.016Original Text:.

Holocene vegetation and climate change from a lake sediment record in the Tengger Sandy Desert, northwest ChinaIntroductionStudy region and study siteMaterials and methodsSampling and dating methodsMagnetic susceptibility, grain size and carbonate content analysisPollen analysis

ResultsLithologyChronologyFossil pollen assemblagesZone QTL-1 (374-252cm; 7200-5200calyrBP)Zone QTL-2 (252-204cm; 5200-4300calyrBP)Zone QTL-3 (204-100cm; 4300-3500calyrBP)Zone QTL-4 (100-0cm; 3500-0calyrBP)

DiscussionLake development and local environmental changeHolocene regional vegetation historyInferred climate change and possible mechanism

Uncited referenceAcknowledgmentsReferences

Documents

YJARE : 2103 ARTICLE IN PRESS - Home | Lehigh Universityziy2/pubs/Zhao2008JAE.pdfa MOE Key Laboratory of Western China’s Environmental Systems, College of Earth and Environmental