Changes of the Deserts in Northern Central China during the last

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Changes of the Deserts in Northern Central China
during the last Glacial Cycle Implications
for Causes 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)
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Desrtified Land 3436 km2/year
Causing tremendous environmental and social
problems
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Causes for the desert-forming are not fully
understood Natural processes or human
activities? Or both?
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What measures should be taken to stop the
desert-forming process?
If geological records can provide any
implication for it?
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Helan Mts.
Annual precipitation
Western deserts lt150mm Eastern deserts 200-450mm
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Temporal and spatial changes of the deserts in
the last glacial-interglacial period
Paleo-records Wind-blown loess deposits in the
Loess Plateau Loess-sand deposits in the
loess-deserts border Sand-soil deposits from
within the deserts
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Loess Section
Holocene Soil (11ka)
LGM Loess (21-11ka)
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Relationship between Loess grain-size and the
distance of the Loess Plateau to the deserts
Shorter distance
Longer distance
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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
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Sampling sites in the Loess Plateau
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Map of the LP and deserts in northern China
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Loess-Sand-Soil Section Along the Border
(S0)
(L1-1,)
(L1-2)
(L1-3)
(L1-4)
(L-5)
(S1)
Direct evidence for desert advance during the LGM
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LGM
LGM
LGM
LGM
LGM
LGM
LGM
LGM
Grain-size records of the loess sections along
the transitional area of the Loess Plateau to
the deserts
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Eolian section within deserts
Holocene Soil
LGM Sand
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Rocky desert in the northern part
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Dry grasslands in the northern part
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sand-dunes in the middle part
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Loess deposits in the southern part
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North
South
Loess deposition
Wind erosion areas
Sand deposition
Rocky desert Grassland
Loess deposits
Sand dunes
Spatial differentiation of landscapes along a
north-south transect in the last glacial
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Holocene Optimum(8-4ka)
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110
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Sun, Ding, Liu (1998) Episodes
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Holocene soil eroded and LGM sand exposed
Holocene Soil
LGM Sand Deposits
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Influence of climate deterioration after the
Holocene Optimum on the desert expansion?
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A 14-ka pollen diagram at Daihai near desert
9-3.5 ka, tree pollen over 20, almost absent
aftermath
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Ancient lake level
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Holocene
Coarse-grained upper Holocene loess
LGM Loess
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OSL Dating Results
118
119
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HLD
WG
130
120
110
Hunlun Buir Desert
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48
40
114
116
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Loess
Desert
Hunshandake Desert
SY
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SGDL
WG
SGDL
HLHD
SY
(kyr)
(kyr)
(kyr)
(kyr)
(m)
(m)
(m)
(m)
0
0
0
0
0.040.01
1.560.14
1.050.10
0.5
0.5
1.250.14
1
3.500.36
1
1.0
1.0
2.480.29
1.850.18
2
1.670.18
1.5
1.5
2
9.861.36
13.40.5
2.0
2.0
3
12.41.2
2.5
11.11.3
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Aeolian sand
Paleosol
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We do have geological evidence for late Holocene
drying up of the land, which may have important
impacts on the recent desert-forming processes.
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Is the climate deterioration the most important
cause for the current desert-forming?
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Sand-dunes stabilized by planting trees for over
a decade
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Vegetation recovered by natural processes after
the closure of the area for four years
Agriculturally-used
Closed
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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.
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Thank you!