HR: 10:55h
AN: C22A-03    [Abstracts]
TI: Evolution of Permafrost on the Qinghai-Tibet Plateau
AU: Jin, H
EM: hjjin@lzb.ac.cn
AF: State Key Laboratory of Frozen Soils Engineering, 326 West Donggang Road, Lanzhou, GS 730000 China
AU: Zhao, L
EM: linzhao@lzb.ac.cn
AF: State Key Laboratory of Frozen Soils Engineering, 326 West Donggang Road, Lanzhou, GS 730000 China
AU: Wang, S
EM: jhj67@hotmail.com
AF: State Key Laboratory of Frozen Soils Engineering, 326 West Donggang Road, Lanzhou, GS 730000 China
AU: * Jin, R
EM: jinrui@lzb.ac.cn
AF: State Key Laboratory of Frozen Soils Engineering, 326 West Donggang Road, Lanzhou, GS 730000 China
AB: Thick permafrost was developed on the QTP during the early and middle Pleistocene with mean annual air temperatures (MAATs) 7 to 8 centigrade colder than today. During 1.1 to 0.6 MaBP, permafrost developed extensively when QTP rose to 3,500 m. The second maximum glaciation occurred during 0.8 to 0.6 MaBP, and permafrost was extensively developed. During the middle Pleistocene climatic warming, permafrost largely retreated. During 330 to 220 KaBP, permafrost was continuous. The Last Glaciation Maximum (LGM) occurred during 30 to 25 kaBP with MAATs 5 to 7 centigrade colder than today, mean annual ground temperatures (MAGTs) colder than -4 to -5 centigrade, and thicknesses of permafrost at 120 to 150 m. The lower limit of permafrost (LLP) extended down to 1,800 m. The post-LGM climate was warming, still with widespread permafrost, LLPs 1,000 m lower than today, and area of permafrost 70-80 per cent greater. During 10.8 to 8.5-7 kaBP, permafrost had retreated with LLPs on the margins up by 300-400 m. Although permafrost degraded, its total area still was 40-50 percent greater. During the Megathermal (8.5-7 to 4-3 kaBP), permafrost had largely retreated. In the interior, persistent downward thawing reached depths of 14 to 16 m. Permafrost survived in islands, or buried, or in mountains. Permafrost degradation in the east was more dramatic. The LLP was 300 to 400 m higher than today, MAATs 2 to 3 centigrade higher, and area of permafrost 40 to 50 percent of that at present. During 4-3 to 1 kaBP, the Neoglaciation resumed the cold climate. The LLP was about 300 m lower and MAATs were about 2 centigrade colder. Permafrost again expanded, and reached to the maximum in the end of the cold period. The area of permafrost was 20 to 30 per cent greater than today. In the interior, permafrost as thick as 30 m was developed. Due to the marginal nature, permafrost thawed to depths of 15 to 20 m during the Megathermal, but the newer permafrost formed during the later cold period was less than 15to 20 m in thicknesses. During 1,000 to 500 aBP, permafrost in marginal areas had largely disappeared, and downward degradation reached to depth of 10 m as a result of several small-scale warming. Two positions of relict permafrost table were identified. The first of late Holocene warming is at depth of 8.35 m, the second of the Megathermal is at depth of 16 m. The LLP, MAATs and permafrost area were 200 to 300 m and 1.5 to 2.0 centigrade higher, and 20 to 30 per cent less, respectively. During the Little Ice Age (500 to 100 aBP), permafrost started to develop again, with increasing areal extent and thickness. A new layer of permafrost of about 10 m was formed by downward freezing of soils, connecting with the second layer relict permafrost table of late Holocene warming. The LLP should be 150 to 200 m lower, the MAATs 0.8 to 1.5 centigrade colder, and area of permafrost 10 per cent greater. Climatic warming have been apparent during the past century, especially during the past 40 a. Seasonal thaw penetration has increased by 25 to 60 cm. The MAGTs have risen by 0.1 to 0.4 centigrade. Permafrost has been shrinking towards the interior, with a reduction of permafrost area of 6 to 8 percent, and the LLP has risen by 40 to 80 m. Permafrost degradation in the periphery island permafrost zones is the most striking. The vertical degradation of permafrost has resulted in taliks of tens of centimeters to 3 m in thicknesses. The MAATs are projected to rise by 2.2 to 2.6 centigrade during the next 50 years, permafrost degradation would be accelerating.
DE: 0700 CRYOSPHERE (4540)
DE: 0702 Permafrost (0475)
DE: 0704 Seasonally frozen ground
DE: 0710 Periglacial processes
DE: 1105 Quaternary geochronology
SC: Cryosphere [C]
MN: Fall Meeting 2005