Deserts in Northern China

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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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Western deserts: <150mm Eastern deserts: 200-450mm Helan Mts. Annual precipitation

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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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Holocene Soil (11ka) LGM Loess (21-11ka) Loess Section

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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 Direct evidence for desert advance during the LGM (S0) (L1-1,) (L1-2) (L1-3) (L1-4) (L-5) (S1)

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

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Eolian section within deserts LGM Sand Holocene Soil

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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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Rocky desert Grassland Sand dunes Loess deposits Wind erosion areas Sand deposition Loess deposition North South Spatial differentiation of landscapes along a north-south transect in the last glacial

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110 30 40 Holocene Optimum(8-4ka) Sun, Ding, Liu (1998) Episodes

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Holocene Soil LGM Sand Deposits Holocene soil eroded and LGM sand exposed

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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 LGM Loess Coarse-grained upper Holocene loess

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130 120 110 40 118 119 49 48 WG HLD 44 43 114 116 SGDL SY Desert Loess 50 Hunlun Buir Desert Hunshandake Desert (m) 0 0.5 1.0 1.5 2.0 WG 0 0.5 1.0 1.5 2.0 2.5 HLHD 0 1 2 3 SGDL 0 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

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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 Closed Agriculturally-used

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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!

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