5 : ,,,,, ( 1) 1 (a) 1 (b) Fig. 1 Atmospheric circulation above and around Qinghai2Xizang Plateau, 110m, 44m - [15 17

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1 , No. 5 Vol. QUA TERNAR Y SCIENCES September, J ef Vandenberghe 3 (, ;, ;, ;, ),,, CaCO 3, 5e, 5a 5c 3, 13 1,,, [1 5 ] [6 9 ],,,, [10,11 ],,, [12 17 ], : 33 E2mail llqg. ac. cn 3 ( : KZCX KZCX2-305) ( : ) ,

2 5 : ,,,,, ( 1) 1 (a) 1 (b) Fig. 1 Atmospheric circulation above and around Qinghai2Xizang Plateau, 110m, 44m - [15 17]1) ( 3m), (715 YR6Π3,, 1)

3 ),, ; 33m, (10 YR6Π4),, ; 8m, (715 YR5Π4), 4,,, 6, 5cm, 10cm, Bartington MS2,CaCO 3, Malvern Mastersize - S, [18 ],,, 2000,, 215m,, ( 2) 2 CaCO Fig. 2 Stratigraphy, thermoluminescence ( TL) and optically stimulated luminescence (OSL) dates, magnetic susceptibility, CaCO 3 content and grain2size variations with depth of the loess profile of Tuxiangdao, Xining

4 5 : , ( 1) 200m,,, -, 2 825m, 17m 1315m S 1, 20cm, ( 3), 5cm, 10 20cm, 25 50, , 2 G, Fig. 3 Stratigraphy, thermoluminescence ( TL) dates, magnetic susceptibility, frequency2dependent susceptibility and grain2size variations with depth of the loess profile of Panzishan, Xining 3 ( 2 3),

5 ,,, - S 1 Blake [19 ], Blake,, [6,20 ],, [21 ] CaCO 3 :,, ;, [22 ] [23 31 ] [14 ],,, 2 3, ( 5e ),, 2 (L 2 ) ( 5a 5c ), [32 ], 110 [4 ],,,, ( 2 3),, ( 3),, ( 2) [33 ], 13 5e,5a 5c, [34 ], ;,,,,, ( ) ;,,,,,,,,,, 0113Ma,

6 5 : [29 ] [30 ] ( 4), 4 13 Fig. 4 Comparison of the variations of plateau monsoon and East Asian monsoon during the past Ma recorded by loess deposit in North China ( 5), ( 4)

7 ,,, (L 1 SS 1, M IS3), ;, ( 4) : 3 ( L 1 SS 1 ),,,, 4 10, ( ), ( ), [15,35 43 ],,,,, ( 2 3),,,,,,,,,,, [17 ],, 216cmΠ10 3 a,,,,, 14 C,,,,,,

8 5 : , 5 5e,5a 5c ; 3,, Laura van Schagen 1,,..,1957,28 (2) : ,..,1962,28 (2) : ,,..,1979,34 (1) : ,1993,12 (1) : :,,.. :, An Z S, Liu T S, Lu Y C et al. The long2term paleomonsoon variation recorded by the loess2paleosol sequence in cen2 tral China. Quaternary International, 1990,7 8 : Liu T S, Ding Z L. Chinese loess and the paleomonsoon. A nnual Review of Earth and Planetary Sciences, 1998,26 : An Z S. The history and variability of the East Asian paleomonsoon climate. Quaternary Science Reviews, 2000,19 : ,1999,19 (1) : ,..,1995, (1) : ,..,1999, (4) : ,,..,1995,15 (3) : ,,.. (D ),1996,26 (4) : ,..,1999,24 (6) : Chen F H, Bloemendal J, Wang J M et al. High2resolution multi2proxy climate records from Chinese loess : Evidence for rapid climatic changes over the last 75 kyr. Palaeogeography, Palaeoclimatology, Palaeoecology, 1997, 130 : Chen F H, Bloemendal J, Feng Z D et al. East Asian monsoon variations during oxygen isotope stage 5 : Evidence from the northwestern margin of the Chinese Loess Plateau. Quaternary Science Reviews, 1999,18 : Chen F H, Feng Z D, Zhang J W. Loess particle size data indicative of stable winter monsoon during the last interglacial in the western part of the Chinese Loess Plateau. Catena, 2000, 39 : ,..,1997,42 (24), Zhu R X, Zhou L P, Laj C et al. The Blake geomagnetic polarity episode recorded in Chinese loess. Geophysical Re2 search Letters, 1994, 21 :

9 Zhou L P, Oldfield F, Wintle A G et al. Partly pedogenic origin of magnetic variations in Chinese loess. Nat ure, 1990, 346 : ,,Heller F..,1990, (1) : ,2000,23 : :, An Z S, Kukla G, Porter S C et al. Late Quaternary dust flow on Chinese Loess Plateau. Catena, 1991, 18 : Ding Z L, Yu Z W, Liu T S. Ice2volume forcing of East Asian winter monsoon variations in the past years. Quaternary Research, 1995, 44 : Ding Z L, Yu Z W, Rutter N W et al. Towards an orbital time scale for Chinese loess deposits. Quaternary Science Reviews, 1994, 13 : Ding Z L, Sun J M, Rutter N W et al. Changes in sand content of loess deposits along a North2South Transect of the Chinese Loess Plateau and the implications for desert variations. Quaternary Research, 1999,52 : Vandenberghe J, An Z S, Nugteren G et al. New absolute time scale for the Quaternary climate in the Chinese loess re2 gion by grain2size analysis. Geology, 1997, 25 : Lu H Y, An Z S, Vandenberghe J et al. Evidence for paleoclimatic significance of grain size composite of loess deposit in central Chinese Loess Plateau. In : An Z S, Zhou W J eds. Proceedings of 30th International Geological Congress (21). Netherlands : VSP, Lu H Y, An Z S. Paleoclimatic significance of grain size of loess2palaeosol deposit in Chinese Loess Plateau. Science in China ( Series D), 1998, 41 : Lu H Y, Huissteden K V, An Z S et al. East Asia winter monsoon changes on millennial time scale before the last gla2 cial2interglacial cycle. Journal of Quaternary Sciences, 1999,14 : Lu H Y, Sun D H. Pathways of dust input to the Chinese Loess Plateau during the last glacial and interglacial periods. Catena, 2000, 40 : ,, ka.,1999, 44 (14) : Petit J R, Jouzel J, Raynaud D. et al. Climate and atmospheric history of the past years from the Vostok ice core, Antarctica. Nat ure, 1999, 399 : Porter S C, An Z S. Correlation between climate events in the North Atlantic and China during the last glaciation. Na2 t ure, 1995, 375 : Lu H Y, Li L, Huang X P et al. East Asia winter monsoon oscillation and its correlation with the North Atlantic Hein2 rich events during the last glaciation. Progress in Nat ural Science, 1996, 6 : ,,.. (D ),1996,26 (2) : ,,. 60ka.,1999,44 : (4) : An Z S, Porter S C. Millennial2scale climatic oscillations during the last interglaciation in central China. Geology, 1997, 25 : Zhang X Y, Arimoto R, An Z S. Dust emission from Chinese desert sources linked to variations in atmospheric circula2 tion. Journal of Geophysical Research, 1997, 102 (D23) : ,,. -. (D ), 1996,26 (5) : ,,. Heinrich.,1996, (1) : ,,..,2000,45 (6) :

10 5 : PLATEAU MONSOON VARIATIONS D URING THE PAST MA IND ICATED BY LOESS DEPOSIT AT XINING, NORTHEAST QINGHAI, CHINA Lu Huayu Ma Haizhou Tan Hongbing Li Zhen Miao Xiaodong An Zhisheng Wang Xiaoyong Cao Guangchao Jef Vandenberghe ( State Key L aboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi an ; Institute of S aline L ake, Chinese Academy of Sciences, Xining ; Depart ment of Geography, Qinghai Normal U niversity, Xining ; Faculty of Earth Sciences, Free U niversity, A msterdam) Abstract Climate variations at Xining area, northeast Qinghai2Xizang Plateau is characteristic of alterna2 tions of plateau summer and winter monsoon circulation, which is generated by thermodynamic and kinetic effect of the immense Qinghai2Xizang Plateau. The plateau monsoon variation in geological time was paid less attention previously. However, changes of the plateau monsoon is important for our understanding of climate change above and around the plateau, the process of the plateau uplift as well as the mechanism of East Asian monsoon changes. Loess deposit s at Xining, nort heast Qinghai2Xizang Plateau, present an excellent record of t he plateau monsoon variations in t he Pleistocene and even in t he Pliocene Epochs. loess sediment is more than 200 meters thick, interceded by paleosols. It was showed that loess was deposited in cold2dry time, where t he paleosol was developed during warm2humid episodes. The loess and paleosol formations are correlated to t he glacial and interglacial peri2 ods, respectively. The loess2paleosol sequence of the last 0. 13Ma were sampled by digging ditch and well in order to obtain un2contaminated samples, since secondary loess cover in t his region is quite thicker. The loess deposit, located at low terrace of Huangshui River, was sampled at inter2 val of 5 10 centimeter. A 442m loess2paleosol profile at Tuxiangdao was sampled. Black loam is found in upper part of the exposure, and it is regarded as typical sediment formed during the Holocene Optimums in North China. Malan loess, which was formed during the last glacial period and correlated to marine isotope stage 2 4,is interceded with very thin2 ner, weak paleosols. Underlying t he Malan loess is reddish paleosol, correlated to t he time of marine isotope stage 5. The Thermoluminescence ( TL ) and optically stimulated luminescence (OSL) dating of the loess deposit proved that the loess was formed during the last glacial cy2 cle. In order to get parallel records, we sampled a loess deposit at high altitude terrace at Panzishan, Xining, from a well. The well is 17 meters in depth, and the bottom of the last interglacial paleosol is at 13. 5m deep. St ratigraphic correlation between two sites is very good and shows t he loess2paleosol deposit was formed during t he last glacial cycle. A detailed palaeomagnetic investigation hasn t found t he Blake excursion. However, st ratigaphic corre2

11 lation, absolute dating and geomorphologic observations tend to suggest t hat t he loess2pa2 leosol deposits were formed during the last glacial cycle. We measured magnetic susceptibility, f requency2dependent susceptibilit y, calcium car2 bonate content, which are regarded as good proxy of the plateau summer monsoon ( PSM) st rengt h. The grain2size dist ribution is regarded as a sensitive proxy index of t he plateau winter monsoon ( PWM) strength. The results show that the summer monsoon was unusual2 ly strengthened during the period correlating to the marine isotope stage 5e, and strength of the PSM in 5a and 5c was close to the stage 3. The PWM was frequently changed in the stage 3 indicated by the grain size record. There are existed phase lag and lead between the PWM and PSM records, the two systems were not co2variations during the last 0. 13Ma. There are sub2orbital time scale variations in bot h t he grain2size and f requency2depend2 ent susceptibility records, but we can not separate the local and regional climate signals from t hese records. We believe that, mixture of local and regional climatic signals, lower time reso2 lution aswell as non2detailed dating of t he loess2paleosol sequences might have caused many uncertainties in t he long2distance climatic correlation in t he Pleistocene period. The previous conclusion that the climatic correlation in East Asia and the North Atlantic should be further examined. Our ongoing investigations in nort heast Qinghai2Xizang Plateau will spatially and tem2 porally extend t he environmental records. A preliminary result of grain2size and magnetic susceptibility measurement of a 2 Ma continuous loess2paleosol sequence has shown t he PWM was high2frequency variations in the past, and there existed clear and regular 10 4 year time scale cycles in the PWM changes. The period of the strengthened PSM was shorter than that of the PWM. However, there may be other explanation : the record is partly misleading because implication of t he proxy index of paleoclimate such as magnetic susceptibility of t he loess in Qinghai2Xizang Plateau is not very effective. A preliminary paleosol investigation has shown high variability of the soil deposits with space, this certainly indicates the local envir2 onment is acutely heterogeneous in Qinghai2Xizang Plateau. The environment changes are related to the uplift process of the plateau. Therefore, investigations of the origin, trend and variability of t he plateau monsoon climate may provide information of t he uplift process of t he plateau. To understand t he changing plateau monsoon will be f undamental to predict t he en2 vironment changes in and around t he Qinghai2Xizang Plateau, and t his region is sensitive and vulnerable to global change. There are still some uncertainties in reconst ructing t he paleocli2 mate of the last glacial cycle by the loess deposit. Investigations of the origin, implications of the proxy indexes and ages of the loess deposits will be required, and these will certainly offer much more information about t he plateau monsoon changes during t he late Cenozoic Era. Key words Qinghai2Xizang Plateau, loess, plateau monsoon, the past 0. 13Ma, cli2 matic event correlation

14 17.,., Fig. 1 Bougeur gravity map of research region 2 Fig. 2 Magnetic map of research region

14 17.,., Fig. 1 Bougeur gravity map of research region 2 Fig. 2 Magnetic map of research region 1 7 1 Vol. 17 No. 1 2002 3 (13 23) PROGRESS IN GEOPHYSICS March 2002 (,,100101) [ ],, 39.,,. [ ] ; ; [] P738 [] A [ ]100422903 (2002) 0120013211 0,,.,,, NE [1 ],.., ( NE, EW,NE ),.,.,,. 1 20 20 km ( 10