Chinese Deserts and Sand Fields in Last Glacial Maximum and Holocene Optimum
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector Article Progress of Projects Supported by NSFC August 2013 Vol.58 No.23: 27752783 Geology doi: 10.1007/s11434-013-5919-7 Chinese deserts and sand fields in Last Glacial Maximum and Holocene Optimum LU HuaYu1*, YI ShuangWen1, XU ZhiWei1, ZHOU YaLi2, ZENG Lin1, ZHU FangYing1, FENG Han1, DONG LiNa1, ZHUO HaiXin1, YU KaiFeng1, MASON Joseph3, WANG XiaoYong1, CHEN YingYong1, LU Qi4, WU Bo4, DONG ZhiBao5, QU JianJun5, WANG XunMing5 & GUO ZhengTang6 1 School of Geographic and Oceanographic Sciences, Institute for Climate and Global Change Research, Nanjing University, Nanjing 210093, China; 2 College of Tourism and Environment, Shaanxi Normal University, Xi’an 710062, China; 3 Department of Geography, University of Wisconsin Madison, WI 53706, USA; 4 Institute of Desertification Studies, Chinese Academy of Forestry, Beijing 100091, China; 5 Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China; 6 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Received March 6, 2013; accepted May 14, 2013; published online June 17, 2013 The Last Glacial Maximum (LGM, c. 26–16 ka) and the Holocene Optimum (HO, c. 9–5 ka) were characterized by cold-dry and warm-wet climates respectively in the recently geological Earth. How Chinese deserts and sand fields responded to these distinc- tive climatic changes is still not clear, however. To reconstruct environments of the deserts and sand fields during the LGM and HO is helpful to understand the forcing mechanisms of environment change in this arid region, and to test paleoclimatic modeling results. Through our long-term field and laboratory investigations, 400 optically stimulated luminescence (OSL) ages and more than 100 depositional records in the Chinese deserts and sand fields were obtained; on the basis of these data, we reconstruct spa- tial distributions of the deserts and sand fields during the LGM and HO. Our results show that the sand fields of Mu Us, Hun- shandake, Horqin and Hulun Buir in northern and northeastern China had expanded 25%, 37%, 38% and 270%, respectively, during the LGM; the sand fields of Gonghe in the northeastern Qinghai-Tibetan Plateau had expanded 20%, and the deserts of Badain Jaran, Tengger in central northern China had expanded 39% and 29% separately during the LGM; the deserts of Taklimakan, Gurbantünggüt and Kumtag in northwestern China had expanded 10%–20% respectively, compared to their modern areas. On the other hand, all of the sand fields were nearly completely covered by vegetation during the HO; the deserts in north- western and central northern China were reduced by around 5%–20% in area during this time. Lakes in this arid region were probably expanded during the HO but this conclusion needs more investigation. Compared with the geological distributions of deserts and sand fields, human activity has clearly changed (expanded) the area of active sand dunes at the present time. Our ob- servations show that environmental conditions of Chinese deserts and sand fields are controlled by regional climate together with human activity. deserts and sand fields in China, Last Glacial Maximum, Holocene Optimum, OSL dating, active sand dunes Citation: Lu H Y, Yi S W, Xu Z W, et al. Chinese deserts and sand fields in Last Glacial Maximum and Holocene Optimum. Chin Sci Bull, 2013, 58: 27752783, doi: 10.1007/s11434-013-5919-7 There is an area of around 2.0×106 km2 made up by deserts, their environment and ecosystem are vulnerable to climatic sand fields and potentially desertified land in China [1]; change and human activity. In addition, changes in the de- serts and sand fields have also influenced climate and hu- *Corresponding author (email: [email protected]) man life at local to hemispheric scales, thus, to understand © The Author(s) 2013. This article is published with open access at Springerlink.com csb.scichina.com www.springer.com/scp 2776 Lu H Y, et al. Chin Sci Bull August (2013) Vol.58 No.23 environment changes in these deserts and sand fields is not ment changes during the late Quaternary; in particular in the only a scientific question, it is also important to combating past six years, we investigated the sediments and deposi- desertification. The deserts and sand fields have changed tional records by gridding-route reconnaissance in the field greatly in time and space during late Quaternary, and to and collected numerous samples which were dated by the reconstruct spatial changes in extent of active dunes is par- optically stimulated luminescence (OSL) technique and mea- ticular important [2–6]. There were a few reconstructions of sured to obtaining proxy indexes of the environment changes. desert changes during the Last Glacial Maximum (LGM) On the basis of this long-term study, we try to reconstruct and Holocene Optimum (HO) [7–26], however, because of Chinese deserts and sand fields in the LGM and HO, and, limited dating work and field investigation, the results need compare the reconstruction results with the modern deserts tested. Moreover, some previous reconstructions were spec- and sand fields, to investigate possible forcing mechanisms ulation based on comparison with paleoclimatic records, of environmental change in the deserts and sand fields. without direct and specific stratigraphic evidence; therefore, the conclusions [7–26] should be clarified. In China, some early investigations have advanced our knowledge of envi- 1 Methods and data ronment changes in the desert and sand fields, but there were quite a few issues that were not well resolved in this Figure 1 shows distribution of the modern deserts, Gobi and previous research, including: (1) Because of the limitation sand fields in northern China [32]. We produced this map of dating techniques, accurate, independent high-quality based on combination of remote sensing (RS) including En- ages for the deserts and sand fields were limited in number; hanced Thematic Mapper (ETM) images and the spectral previous research always compared the sand deposition angle method, observations located with global positioning with established time series such as that of Chinese loess- systems (GPS), and geographic information system (GIS) paleosol sequence and marine oxygen isotope stages to ob- analysis. We first applied geometric precision correction, tain age control [9,10,15–17,21–26] which was quite spec- image mosaicking, wave band combination and image en- ulative. (2) The ages were not well-distributed spatially hancement to ETM images from 2010; then bands 7, 5 and across the deserts and sand fields. (3) By reconstructing 2 of these enhanced ETM images were used to establish changes in the boundaries of deserts and sand fields only markers of desertification. Third, the spectral angle method indirectly from paleoclimatic zone migration, without direct was used to identify margins of active dunes, soil and vege- evidence, has probably led to misleading conclusions. (4) tation covers. Observations in the field, located by GPS There was not a clear distinction made between the deserts were used to correct the boundary data. An existing data set and sand fields dominated by Asian monsoon circulation, was combined with our results to create a new GIS database the North Hemisphere westerlies and even local landform for the deserts and sand fields, containing numerical data of effects on climate, therefore, it was difficult to identify landforms, soils and vegetation. forcing mechanisms of change in specific deserts and sand Figure 2 shows the detailed field reconnaissance in Chi- fields. These previous limitations hindered proper under- nese deserts and sand fields as an example; we have chosen standing of the spatial changes of Chinese deserts and sand good outcrops for sampling through extensive field recon- fields during the late Quaternary. naissance. At each site, the location, stratigraphic and sedi- Chinese deserts and sand fields are mainly located in mentary characteristics were carefully logged. Samples northern China, with dry climate (we do not discuss the were dated by OSL technique and measured for grain size, scattered and fragmentary sand fields in southeast China magnetic susceptibility and organic matter content in order and on the Qinghai-Tibetan Plateau), controlled separately to identify depositional environment. Previous studies by Asian monsoon circulation and/or the Northern Hemi- [8–10,18,21] have shown that the aeolian deposits in mar- sphere westerlies. The sand fields of Mu Us, Hunshandake, ginal regions of these deserts and sand fields can be used as Horqin and Hulun Buir in central northern China are domi- indicators of desert and sand field expansion and contrac- nated by the monsoon climate, whereas the deserts of tion during the late Quaternary. That is, when the East Taklimakan, Gurbantünggüt and Kumtag are not influenced Asian winter monsoon circulation was strengthened, the by the monsoon climate (some suggest that these deserts are climate in these regions was dry and the wind velocity was dominated by the westerlies [27–31]). The deserts between increased, the sand dune would be active and the deserts northwestern and northeastern China such as Badain Jaran, and sand fields expanded along direction of the strength- Tengger, Ulan Buh and Hobq are located in the marginal ened monsoon wind; on the other hand, the strengthened region of the Asian monsoon climate, and are also very dry. East Asian summer monsoon circulation brought more pre- Therefore, the different atmosphere circulations that control cipitation to this dry region, vegetation cover expanded and the deserts and sand fields’ environments should be sepa- stabilized the active sand dunes, so the desert and sand field rately investigated. were probably covered by loess and sandy soil. The sand, Since the spring of 1997, we have investigated these de- loess and soil in the depositional sequences can be used as serts and sand fields in order to reconstruct their environ- proxy indicators of the deserts and sand fields change in the Lu H Y, et al.