A 1000-yr record of environmental change in NE China indicated by diatom assemblages from maar lake Erlongwan

Past environmental changes based on diatom relative abundances have been inferred from the maar Lake Erlongwan in northeast China. The limnology of Lake Erlongwan is affected by the strongly seasonal regional climate. The composition of diatom assemblages, in turn, responds to changes in the seasonal duration of ice cover in winter, water-column turnover in spring and autumn, and thermal stratification in summer. Statistical analysis of the sedimentary diatom assemblages reveals three significant stratigraphic zones over the past 1000 yr. The highest abundance of the planktonic species Discostella species occurs between AD 1050 and 1400 and suggests an annual ice-free period of long duration and well-developed summer stratification of the water column. This planktonic diatom peak between ca. AD 1150 and 1200 suggests that this period was the warmest over the past 1000 yr. The interval between AD 1400 and 1800 is marked by a decline in planktonic diatoms and suggests shorter duration of the ice-free season, weaker water stratification and possibly generally cold conditions. After AD 1800 relative abundances of planktonic diatoms, including Puncticulata praetermissa and Asterionella formosa, increase again, which indicates lengthening of the duration of the annual ice-free period and a stronger overturn of the water column. All these data imply that the pattern of the seasons is different between the MWP and the 20th century.     

Radiocarbon age anomalies of land snail shells in the Chinese Loess Plateau

In the Chinese Loess Plateau, land snail shells are often the only material available for dating in paleoenvironmental and archaeological research. However, the geochronological suitability of land snail shells is limited because of poor knowledge about their deposition dynamics, particularly with regards to the incorporation of inorganic carbonate and the resulting age anomalies. To evaluate the factors controlling these age anomalies, radiocarbon and stable carbon analyses were carried out on surface soils, as well as the shells and organic bodies of different modern snail species from different ecological habitats. The results showed that all specimens were depleted in ¹⁴C, indicating the influence of inorganic, radiocarbon-free carbonate on the ¹⁴C-activity of the snail shells. The apparent ¹⁴C-deficiencies and the resultant age anomalies of both the Cathaica and the Bradybaena snail shells were within close ranges across the Chinese Loess Plateau, indicating that the shells of these species could, after corrections for radiocarbon anomalies, provide reliable age estimates. The apparent ¹⁴C-deficiencies were closely associated with the ecological habitats of the snails. The shells of the ground-dwelling Bradybaena had the smallest age offsets (533 ± 150 a), followed grass-dwelling Cathaica (1107 ± 138 a) and Cathaica living on trees (1550 ± 345 a). These results suggest that the availability of calcium in the respective ecological habitats is an important factor in explaining the apparent ¹⁴C-deficiencies. The influence of carbonate on the stable carbon isotope composition of shells is overwhelmed by the organic diets of snails, making δ¹³C unsuitable for identifying and correcting shell age anomalies. The radiocarbon activities of surface soils (A_calc) increase with weathering intensity. Thus, a significant uncertainty could be caused by assuming that A_calc is zero when estimating the proportions of different carbon sources in shells, as has been the case in most previous studies.     

Sediment Fluxes and Varve Formation in Sihailongwan,a Maar Lake from Northeastern China

Data derived from monthly sediment traps in Sihailongwan, a maar lake in northeastern China, yielded a detailed record of seasonal sediment fluxes. Sediment fluxes correspond to seasonal climatic variations. The diatom flux shows two distinct peaks in September and November, whereas the flux of chrysophyte stomatocysts shows a maximum in May. The blooms of diatoms may be related to the subsequent deepening of the thermocline in September and lake overturn in spring and November, and influx of nutrient-rich groundwater sometime after the onset of the summer monsoon. The fluxes of organic matter and siliciclastics show a distinct seasonal pattern. They are varying between 0.03 and 0.56 g m⁻² d⁻¹ and reach a maximum in May. Quartz in the trap samples indicates that the siliciclastic matter may originate from distant aeolian sources. Sediment trap data and thin section investigations confirm the seasonality of Lake Sihailongwan sediments. Dark-colored layer, which mainly consists of valves of Cyclotella comta, might be deposited during autumn, and then is followed by a light-colored mixed layer starting with siliciclastics deposited after ice-out. The varved sediments in the U-shaped Lake Sihailongwan represent a sensitive siliciclastic and geochemical archive of paleoenvironmental variability in this data-sparse area. Detailed investigations of varved sediments should provide decadal to annual records of seasonal sediment flux and its relation to climatic parameters. Especially the diatomaceous layer is regarded to indicate summer climatic fluctuations, while the thick siliciclastic layer could be an indictor of dust events.     

10Be和26Al在地表形成和演化研究中的应用

地球表面丰富多样的地形、地貌是地球内外动力相互作用的结果。宇宙射线辐射地表岩石、沉积物等产生的¹⁰Be和²⁶Al放射性核素（半衰期分别为1．5Ma和0．71Ma）,它们的浓度主要取决于由地理位置和地形、地貌条件所决定的宇宙射线辐射的通量和时间,从而能够记录地表的形成和演化历史。因此,宇宙成因核素是研究地表形成历史和作用过程的有力工具。     

基于ObjectARX的用户地图符号库系统的设计与开发

随着数字地图学的不断发展,AutoCAD本身的符号库系统已无法满足相关领域的专业需求,所以设计一个能够让用户能自己管理的地图符号库系统是非常有必要。基于此种考虑,本文以点状、线型符号的设计、用户地图符号库系统的建立与程序设计的思想为文章核心内容。详细论述了用户地图符号库系统在CAD2002和Visual C++ 6.0平台下的设计与开发的全过程。系统可以让用户自己创建各种符号,包括点状符号、线状符号,并且可以可视化地修改已创建符号的属性,删除不用的符号,系统可以自动为每个符号创建对应的幻灯片。     

灵台黄土-红粘土序列的磁性地层及粒度记录

甘肃灵台县任家坡黄土－红粘土剖面的磁性地层学研究表明;中国北方连续的风成堆积可下推到705MdB．P。第三纪红粘土的粒度组成从上到下变化很小,与黄土－古土壤序列的粒度大幅度变化形成强烈的反差,意味着晚第三纪时期的气候总体上要比第四纪时期稳定。在705～2．6MaB．P．的红粘土沉积中,可分出的110～115个土壤B层与钙质结核层的组合,初步表明在这个时期有约110～115次气候旋回。     

中国南方红土年代地层学与地层划分问题

南方红土是我国热带、亚热带以各类岩石和第四纪松散沉积物为母质发育的红色风化壳,也是我国分布最广的第四纪土状堆积。本文在探讨第四纪松散沉积物上红色风化壳的形成机制的基础上,根据风化壳发育程度将其划分为砖红土风化壳、红壤土风化壳和红化土风化壳3种类型。南方地区第四纪松散沉积物主要有河流相沉积、滨海相海滩砂和海岸风成砂——"老红砂"以及以下蜀土为主的风尘堆积。近年来在上述沉积物中多处发现旧石器遗址,促进了南方红土的地层年代学研究。根据前人及近期对南方红土的研究成果,讨论了南方红土的年代地层学问题,提出了以风化壳岩性特征为基础的岩石地层单位初步划分框架:老红砂划分为中更新统北海组、晚更新统晋江组;风尘堆积划分为中更新统宣城组、晚更新统下蜀组;河流相沉积只划出中更新统白沙井组,晚更新统留待以后研究再划出。     

10Be DATED BOULDERS FROM THE THIRD TERRACE OF NUJIANG RIVER AT BINGZHONGLUO,YUNNAN PROVINCE,CHINA

宇宙成因核素可用于河流阶地测年,然而保存于阶地面上的漂砾暴露年龄是否能代表其形成年代还缺乏深入研究.应用宇宙成因核素10Be对怒江丙中洛河段第三级阶地上的花岗岩漂砾进行测年研究,结果显示继承性组分可以忽略,而风化侵蚀将对其暴露年龄产生较大影响.基于采集自第三级阶地保存较好的基岩中石英脉样品,应用有效暴露年龄、暴露时间与风化速率间的关系图解出花岗岩漂砾的风化速率为0.3cm/ka,并据此得到第三级阶地的形成年代大约为 150～203 ka.     

Decoupled warming and monsoon precipitation in East Asia over the last deglaciation

Our understanding of the continental climate development in East Asia is mainly based on loess–paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes (δ¹⁸O) of stalagmites from several Chinese caves. Based on these records, it is thought that East Asian Summer Monsoon (EASM) precipitation generally follows Northern Hemisphere (NH) summer insolation. However, not much is known about the magnitude and timing of deglacial warming on the East Asian continent. In this study we reconstruct continental air temperatures for central China covering the last 34,000 yr, based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess–paleosol sequence from the Mangshan loess plateau. The results indicate that air temperature varied in phase with NH summer insolation, and that the onset of deglacial warming at ~ 19 kyr BP is parallel in timing with other continental records from e.g. Antarctica, southern Africa and South-America. The air temperature increased from ~ 15 °C at the onset of the warming to a maximum of ~ 27 °C in the early Holocene (~ 12 kyr BP), in agreement with the temperature increase inferred from e.g. pollen and phytolith data, and permafrost limits in central China.Comparison of the tetraether membrane lipid-derived temperature record with loess–paleosol proxy records and stalagmite δ¹⁸O records shows that the strengthening of EASM precipitation lagged that of deglacial warming by ca. 3 kyr. Moreover, intense soil formation in the loess deposits, caused by substantial increases in summer monsoon precipitation, only started around 12 kyr BP (ca. 7 kyr lag). Our results thus show that the intensification of EASM precipitation unambiguously lagged deglacial warming and NH summer insolation, and may contribute to a better understanding of the mechanisms controlling ice age terminations.     

A risk-based approach for crowd evacuation performance evaluation under metro fire

This paper aims to evaluate the crowd evacuation performance in a metro fire by using the limit state equation to describe the egress process. The limit state equation is established by the available time margin in fire evacuation, which comprises the evacuee's response time, behaviour time and movement time to an exit. Here, the available time margin in a fire evacuation is determined by the duration of time the smoke takes to exceed the evacuee's respiration level, the time that the smoke is detected by fire alarm and the time that the evacuee needs to respond and move to an exit during evacuation. Further, Monte Carlo simulation approach has been employed to integrate the fatality rates and the probabilities of occurrence of different scenarios in a typical metro in Xiaobailou station of station-Tianjin Line 1. Through this case study, it is shown that the evacuee's response time, behaviour time and movement time to exits can be integrated in a stochastic process model.