Changes of the Deserts in Northern Central China during the lastGlacial Cycle: Implications forCauses of Recent Desert-Forming Process

Z.L. Ding, J.M. Sun, S.L. Yang and T.S. Liu

(Institute of Geology and Geophysics, CAS, Beijing)

Desrtified Land : 3436 km2/year

Causing tremendous environmentaland social problems

Heavy AgricultureHeavy Agriculture OvergrazingOvergrazing

Causes for the desert-forming are not fully understood: Natural processes or human activities? Or both?

What measures should be taken to stop the desert-forming process?

If geological records can provide any implication for it?

Western deserts: <150mmEastern deserts: 200-450mm

Helan Mts.

Annual precipitation

Temporal and spatial changes of the deserts in the last glacial-interglacialperiod

Paleo-records:Wind-blown loess deposits in the Loess PlateauLoess-sand deposits in the loess-deserts borderSand-soil deposits from within the deserts

Holocene Soil(11ka)

LGM Loess(21-11ka)

Loess Section

Relationship between Loess grain-size and the distanceof the Loess Plateau to the deserts

Desertexpansion

Desertretreat

Coarse loessgrain-size

Fine loessgrain-size

Shorter distance

Longer distance

Loess grain-size links to monsoon

Northward move of monsoon rainfall belt

Northward retreat of desert margin

Increase in the distance of deserts to the LP

Fine-sized eolian loess deposited in the Plateau

Sampling sites in the Loess Plateau

6 0 4 0 2 0

H o n g d eM d (m )

5 0

4 0

3 0

2 0

1 0

0

Dep

th(m

)6 0 4 0 2 0

H u a n xia nM d (m )

4 0

3 0

2 0

1 0

0

6 0 4 0 2 0

M uboM d(m )

4 0

3 0

2 0

1 0

0

4 0 3 0 2 0 1 0

Qu ziM d (m )

3 0

2 5

2 0

1 5

1 0

5

0

4 0 2 0

Q ingyangM d(m )

2 5

2 0

1 5

1 0

5

0

4 0 3 0 2 0 1 0

B aim apuM d(m )

2 5

2 0

1 5

1 0

5

0

3 0 2 0 1 0

X ifengM d(m )

2 0

1 5

1 0

5

0

3 0 2 0 1 0

N ingxianM d(m )

2 0

1 5

1 0

5

0

3 0 2 0 1 0

B inxianbe iM d(m )

2 0

1 5

1 0

5

0

2 1 1 4 7

B inxianM d(m )

2 0

1 5

1 0

5

0

2 4 1 8 1 2 6

YongshouM d(m )

1 5

1 0

5

0

2 0 1 5 1 0 5

Y a n g lin gM d (m )

1 5

1 0

5

0

Dep

th(m

)

S0

S1

S2-1

L1-1L1-2

L1-3

L1-4

L1-5

L2-1L2-2

L2-3

L2-4L2-5

S0

S1

S2-1

L1-1L1-2

L1-3

L1-4

L1-5

L2-1

L2-2

L2-3L2-4

L2-5

S0

S1

S2-1

L1-1

L1-2L1-3

L1-4

L1-5

L2-1

L2-2

L2-3L2-4

L2-5

S0

S1

L1-1

L1-2

L1-3 L1-4

L1-5

S0

S1

S2-1

L1-1

L1-2L1-3

L1-4

L1-5

L2-1L2-2

L2-3L2-4

L2-5

S0

S1

S 2-1

L1-1L1-2

L1-3

L1-4

L1-5

L2-1

L2-2

L2-3L2-4

L2-5

S0

S1

S2-1

L1-1

L1-2L1-3

L1-4

L1-5

L2-1

L2-2

L2-3L2-4

L2-5

S0

S1

S2-1

L1-1

L1-2

L1-3L1-4

L1-5

L2-1L2-2

L2-3

L2-4

L2-5

S0

S1

S2-1

L1-1

L1-2

L1-3L1-4

L1-5

L2-1

L2-2

L2-3L2-4

L2-5

S0

S1

S2-1

L1-1L1-2

L1-3L1-4

L1-5

L2-1L2-2

L2-3L2-4

L2-5

S0

S1

S2-1

L1-1

L1-2

L1-3

L1-4

L1-5

L2-1L2-2

L2-3

L2-4L2-5

S0

S1

S2-1

L1-1

L1-2

L1-3L1-4

L1-5

L2-1

L2-2

L2-3L2-4

L2-5

Map of the LP and deserts in northern China

101

272484554

1011113010

887759

Age(ka)

Eolian sand Loess Soil

Holocene Soil

LGM Eolian Sand

Loess Horizon

Last Interglacial Soil

Loess-Sand-Soil Section Along the Border

Direct evidence for desert advance during the LGM

(S0)

(L1-1,)(L1-2)

(L1-3)(L1-4)

(L-5)(S1)

5 0 4 0 3 0 2 0 1 0

X inzhuangyuanMd(m)

3 5

3 0

2 5

2 0

1 5

1 0

5

0

De

pth

(m

)

5 0 4 0 3 0 2 0 1 0

JiyuanMd(m)

4 0

3 5

3 0

2 5

2 0

1 5

1 0

5

04 0 3 0 2 0 1 0

L ijiayuanMd(m)

2 5

2 0

1 5

1 0

5

06 0 4 0 2 0

H ongdeM d(m )

3 0

2 5

2 0

1 5

1 0

5

06 0 4 5 3 0 1 5

Zichang M d(m )

2 0

1 6

1 2

8

4

04 0 0 2 0 0 0

YulinM d(m )

1 6

1 2

8

4

04 0 2 0

W upuM d(m )

1 6

1 2

8

4

06 0 4 0 2 0

Xingxian M d(m )

2 8

2 4

2 0

1 6

1 2

8

4

0

L1

S0

S1

L1

S0

S1

L1

S0

S1

L1

S1

L1

S0

S1

L1

S0

S1

L1

S0

S1

L1

S0

S1

Grain-size records of the loess sections along the transitional area of the Loess Plateau to the deserts

LGMLGM LGM

LGMLGM

LGM LGMLGM

Eolian section within deserts

LGM Sand

Holocene Soil

Rocky desert in the northern part

Dry grasslands in the northern part

sand-dunes in the middle part

Loess depositsin the southernpart

Rocky desertGrassland Sand dunes Loess deposits

Wind erosionareas

Sanddeposition

Loessdeposition

North South

Spatial differentiation of landscapes alonga north-south transect in the last glacial

40

30

Present

mountains

desertGobi desert

Study sites

908070 130100 110

30

40

120

LGM(20-10ka)

110

30

40

Holocene Optimum(8-4ka)

Sun, Ding, Liu (1998)Episodes

Holocene Soil

LGM Sand Deposits

Holocene soil eroded and LGM sand exposedHolocene soil eroded and LGM sand exposed

Influence of climate deteriorationafter the Holocene Optimum onthe desert expansion?

温度

/℃降水量

/%

时间 /KaBP

Precip

itation(

%)

Tem

peratu

re

Age (ka)

Holocene climate change estimated fromthe pollen record of Qinghai lake (Shi, 1992)

A 14-ka pollen diagram at Daihai near desert

9-3.5 ka, tree pollen over 20%, almost absent aftermath

Ancient lake level

Holocene

2 5 2 0 1 5 1 0

LuochuanMd(m)

2

1

0

20 15 10

T ongchuanMd(m)

4

3

2

1

0

16 8

Y aoxianMd(m)

3

2

1

0

12 8

LantianMd(m)

2

1

0

30 20 10

L ijiayuanMd(m)

4

3

2

1

0

De

pth

(m)

1 5 1 0 5

S hiz iMd(m)

2

1

0

25 20

L ingbaoMd(m)

2

1

0

L1-1

S0

L1-1

S0

L1-1

S0 S0

L1-1

S0

L1-1

S0

L1-1

S0

L1-1

LG

M L

oess

Coarse-grained upper Holocene loess

130120110

40

118 119

49

48

WGHLD

44

43

114 116

SGDLSY

DesertLoess

50

Hunlun Buir Desert

Hunshandake Desert

(m) 0

0.5

1.0

1.5

2.0

WG0

0.5

1.0

1.5

2.0

2.5

HLHD0

1

2

3

SGDL0

1

2

3

SY

Aeolian sand Paleosol

0.04±0.01

1.85±0.18

13.4±0.5

1.56±0.14

2.48±0.29

12.4±1.2

1.05±0.10

3.50±0.36

9.86±1.36

1.25±0.14

1.67±0.18

11.1±1.3

(m) (m) (m)(kyr) (kyr) (kyr) (kyr)

OSL Dating Results

We do have geological evidence for lateHolocene drying up of the land, whichmay have important impacts on the recent desert-forming processes.

Is the climate deterioration the mostimportant cause for the currentdesert-forming?

Sand-dunes stabilized byplanting trees for over adecade

Vegetation recovered bynatural processes after theclosure of the area forfour years

Closed

Agriculturally-used

Major Conclusions

1. The recent desert-forming in the eastern deserts of northern China occurs mainly as the re-activation of the sand dunes formed in the LGM because of the erosion of the thin Holocene soil.2. Although the post-Holocene Optimum climate deterioration may play a part in recent desert-forming, unreasonable human activities appear to be the most important cause for it. 3. The sand-dunes can be stabilized simply after the land is closed up for a couple of years.

Thank you!