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Kiloyear-Scale Climate Events and Evolution During the Last Interglacial, Mu Us Desert, China

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Kiloyear-Scale Climate Events and Evolution During the Last Interglacial, Mu Us Desert, China Quaternary International 263 (2012) 63e70 Contents lists available at SciVerse ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint Kiloyear-scale climate events and evolution during the Last Interglacial, Mu Us Desert, China Shuhuan Du a, Baosheng Li b,c,*, Muhong Chen a, David Dian Zhang d, Rong Xiang a, Dongfeng Niu c, Xiaohao Wen c, Xianjiao Ou e a Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China b State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China c Department of Geography, South China Normal University, Guangzhou 510631, China d University of Hong Kong, Pokfulam Road, Hong Kong e School of Geography and Tourism, Jiaying University, Meizhou 514015, China article info abstract Article history: The fifth segment of the Milanggouwan stratigraphical section (MGS 5) in the Mu Us Desert provides Available online 9 January 2012 high-resolution geological information on environmental variations during the Last Interglacial. The analysis of grain content (<50 mm), organic content, SiO2,Al2O3, TOFe, and SiO2e(Al2O3 þ TOFe) ratios in the MGS 5 suggest that there were 17 kiloyear-scale climate fluctuations in the Last Interglacial, including 9 warm events (W1eW9) and 8 cold events (C1eC8), dominated by the East Asian summer monsoon and winter monsoon respectively. The analysis also suggests that the Eemian interglacial was unstable, with 3 warm events (W7eW9) and 2 cold events (C7eC8), indicating that climate fluctuations affected the East Asian monsoon in the Mu Us Desert during the Last Interglacial. The change cycles and the nature of the kiloyear-scale climate events have a close temporal relationship with the Greenland ice-core oxygen isotope data, suggesting that the climate forming mechanism was affected by polar weather, North Atlantic sea ice, range of the Eurasian ice front, and movement of the Arctic frontal, all of which affect the intensity of the SiberianeMongolian high pressure region through the movement of the cold air mass. Ó 2012 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction from a more recent study by the North Greenland Ice Core Project (NGRIP) indicates that the climate of the Eemian interglacial period Climate change during the last interglacial period or MIS 5 was relatively stable (NGRIP members, 2004). The examination of (marine sediments or d18O1 to d18O5 in the continental glaciers) is the benthic foraminifera and the oxygen isotope obtained from the a topic in palaeoclimate study that has attracted considerable drilling conducted in northern Denmark indicated that there were attention. Researchers from around the world including China have two cold events during the Eemian (Solveig and Knudsen, 1997). conducted studies on kiloyear-scale climate fluctuations based on Similarly, the pollen and marine isotope data obtained from the ocean sediments (Wang and Yang, 1995; Tu et al., 2001; Sun and drilling conducted at ODP site 1059 off the southeast coast of the Luo, 2001), polar ice cores (Dansgaard et al., 1993; Grootes et al., USA indicate climate instability (Heusser and Oppo, 2003). 1993; Yao et al., 1997), and terrestrial sediments (An et al., 1991, However, both the terrestrial mollusc record from France (Rousseau 1995; Fang et al., 1996, 1999; An and Porter, 1997; Chen et al., and Puisségur, 1999) and examination of the pollen obtained from 2000, 2003). However, there are conflicting reports about the the lakes in northwestern Germany (Gapers et al., 2002) indicate climate conditions of the MIS 5e sub-segment (Eemian interglacial that climate conditions in the MIS 5e period were quite stable. period). The Greenland Ice-core Project (GRIP) data indicates that There are different records of kiloyear-scale climate events during the climate of MIS 5e was unstable, with rapid changes within the last interglacial in China. The stalagmite records examined by a short time-period (GRIP Members, 1993). On the other hand, data Yuan et al. (2004) suggest that the East Asian summer monsoon was weakest in sub-segment 5d of MIS 5, fluctuated between strengthening and weakening in sub-segment 5c, and remained * relatively stable in sub-segment 5e. Guan et al. (2007) discovered Corresponding author. Department of Geography, South China Normal fi University, No. 55, Zhongshan Road, Guangzhou 510631, China. the occurrence of ve events during MIS 5 in which the summer E-mail address: [email protected] (B. Li). monsoon strengthened and four events in which the winter 1040-6182/$ e see front matter Ó 2012 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2012.01.004 64 S. Du et al. / Quaternary International 263 (2012) 63e70 monsoon strengthened based on their research on two sections in layers from 61LS to 84S. These layers include 10 layers of aeolian eastern and western Liupanshan. An and Porter (1997) studied palaeo-mobile dune sands and palaeo-fixed to semi-fixed dune quartz and grains from the S1 palaeosols of China’s Luochuan Potou sands, 5 layers of palaeosols, and 9 layers of fluvio-lacustrine and Xiaheimu sections and discovered that during the last inter- facies, which overlap among the strata. If a dune sand and its glacial, including MIS 5e, multiple climate fluctuations along with overlying fluvio-lacustrine facies or/and palaeosol are assumed to nine dust events occurred. Fang et al. (1996, 1999) studied the Last represent a sedimentary cycle, then these data suggest that 8.5 Interglacial loess in Lanzhou and Linxia, and discovered that during sedimentary cycles occurred during this stage (because the MIS 5e, there occurred three events in which the East Asian bottom of segment 84S accounts for only half a cycle; Fig. 2). For summer monsoon suddenly strengthened and two events in which convenience, the palaeo-mobile dune sands, palaeo-fixed to semi- the winter monsoon strengthened. fixed dune sands, fluvial facies, lacustrine facies, and palaeosols The Salawusu River valley, located south of China’s Mu Us Desert are labelled in this paper as D, FD, FL, LS, and S, respectively, in in a low-lying part of the southeastern Ordos Plateau, provides Fig. 2. extensive geological information on environmental variations during the Late Quaternary. Li et al. (2000, 2005) reported evidence 3. Materials and methods of kiloyear-scale climate fluctuations in segment 5 of the Milang- gouwan stratigraphical section that corresponded to MIS 5 segment Geochemical analyses of 105 samples taken at 15 cm intervals of the Last Interglacial in the Late Quaternary, and suggested a close were performed using an X-ray fluorescence spectrometer (Type temporal relationship with the mainland ice-core climate data. 3070, Rigaku International Corp., Tokyo, Japan) in the Cold and Arid Based on these studies, the MGS 5 segment was examined further Regions Environment and Engineering Research Institute of the in search of new clues to the regional palaeoclimate. The relation- Chinese Academy of Sciences, with measuring range from 1 ppm to ship between the East Asian monsoons and evolution of the desert 99.99%. Samples were dried, ground, and sifted through a 200- environment, and the climate formation mechanism, was investi- mesh screen, crushing them into smaller pieces (30 mm in diam- gated by determining ages, and proxy palaeoclimatic indices [i.e., eter) for analysis. The test results were compared to sediment GSD9 grain-size, organic content, SiO2,Al2O3, TOFe (total iron), and and GSS1, which are the national standards, and relative deviation e þ SiO2 (Al2O3 TOFe) ratios]. and relative errors were both calculated to be less than 5%. A total of 310 samples was obtained at intervals of 5 cm (a few 2. Regional setting and study site samples were obtained at 3 or 6 cm intervals) to measure the grain size and organic content. The Malvern Mastersizer 2000 M laser The Milanggouwan section (3745047.200 N, 10833005.400 E) is grain-size analyzer (measuring range 0.02e2000 mm) was used to located on the left bank of the Salawusu River’s middle reaches analyze grain-size because the experiment involved the analysis of (Fig. 1). The MGS 5 stratigraphic segment is a series of sedimentary the loess grain-size (Lu and An, 1997). The data was obtained sequences with depths of 36.95e51.93 m (Fig. 2), with a total of 24 through computer processing. Fig. 1. Location and geological characteristics of the region surrounding China’s Milanggouwan stratigraphical section. S. Du et al. / Quaternary International 263 (2012) 63e70 65 Fig. 2. Sequence of the last interglacial period and its time-scale in the Milanggouwan stratigraphic section. The organic matter content was measured using the standard oil including the 62S, 70FD, 76S, 79D, 81D, and 83D strata in MGS 5 bath K2Cr2O7 method (Walkley and Black, 1934) following the and the overlying 60D stratum and underlying 85FD stratum. experimental steps according to the national standard for deter- Quartz grains smaller than 10 mm were collected from the samples. mination of organic matter content of soil (GB 9834-88). The The TL age determination was conducted by Liangcai Lu using detection limit of this measurement is 0e8%, and the error is less a Type 711 age determination instrument (Littlemore Scientific than 0.05%. Instrument Corporation, Oxford, UK) in the TL laboratory of the Guangzhou Institute of Geochemistry, Chinese Academy of 4. Results Sciences, whereas OSL was conducted by Hua Zhao using the Daybreak 2200 optically stimulated luminescence instrument 4.1. Chronology (USA) in the OSL laboratory of the Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences. To date, 8 thermoluminescence (TL) and 2 optically stimulated The age and the relevant parameters of each sample are listed in luminescence (OSL) dates have been obtained from eight layers, Tables 1 and 2.
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