changes of the deserts in northern central china during the last glacial cycle: implications for...
TRANSCRIPT
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!