Advances and Issues in Luminescence Dating of Loess Deposits in Arid Central Asia

High-resolution loess deposits are widely distributed in Arid Central Asia (ACA) and provide important records associated with dust transportation, paleoenvironmental and paleoclimatic evolution. The chronology is the foundation of the research into loess deposits as an environmental archive. In recent decades, the gradually developed optical dating method has been increasingly matured and become an important approach to establishing the loess-paleosol sequences. Here, we summarized and discussed previous work on loess chronology mainly based on optical dating approach in ACA. The following understandings have been listed: ① In comparison with optical dating method, the suitable material for ¹⁴C dating is uncommon in ACA. However, the dating range of luminescence dating is more extensive, and the dating materials are accessible. Thus, the optical dating is widely applicable in the establishment of loess framework in this area. ② Until now, the quartz Single Aliquot Regeneration (SAR) method can be applied to the establishment of loess-paleosol sequence since last glacial period. But several issues remain unaddressed. For example, the Optically Stimulated Luminescence (OSL) signal sensitivity of quartz grains are low in some areas. Furthermore, the results of OSL dating of different grain sizes within a single sample are inconsistent in some areas. The solution of these problems still requires more methodological research. ③ The post-IR IRSL (pIRIR) and multiple elevated temperature stimulation (MET-pIRIR) protoCols of feldspar have basically overcome the anomalous fading issue in the traditional IRSL dating process. In ACA, the framework since MIS 7 can be established with K-feldspar luminescence dating method. Compared with quartz luminescence characteristics, the K-feldspar luminescence signals are more sensitive and exhibit a high saturation level. In specific applications, it is necessary to establish the age frame according to the luminescence sensitivity, the age of samples or other factors.     

1949—2019年中国自然地理学与生存环境应用研究进展

自然地理学是一门以基础研究见长的自然科学,其研究对象是与人类生存和发展密切相关的自然环境。中国的自然环境复杂多样,自然地理学家根据国家需求和区域发展在应用基础和应用研究方面同样取得显著成效,为国家重大经济建设、社会发展的规划,宏观生态系统与资源环境保护及区域可持续发展做出了重要贡献。本文总结了1949—2019年中国自然地理学在自然环境区域差异与自然区划、土地利用与覆被变化、自然灾害致灾因子和风险防控、荒漠化过程与防治、黄淮海中低产田改造、冻土区工程建设、地球化学元素异常和地方病防治、自然地理要素定位观测、地理空间分异性识别和地理探测器等方面的实践与应用,指出了未来自然地理学的应用研究方向。     

中国北方地区旧石器时代环境考古学研究进展

旧石器时代环境考古学以研究旧石器时代人类与环境相互作用关系(过去人地关系)为目标,随着材料积累、科学技术进步和研究方法发展,中国北方地区的旧石器时代环境考古学研究在最近三十年发展显著。从古人类对地质资源、石料资源和动植物资源的开发、利用策略角度回顾了相关研究成果,综述了古人类对环境变化事件的响应和行为适应研究,并分别从迁移适应和技术适应两个方面进行了讨论,指出旧石器时代环境考古学的发展需要考古学家与古环境研究学者开展密切合作。     

青藏高原北缘哈拉湖近800年来 湖泊沉积及其环境意义*

文章以青藏高原北缘高山祁连山湖泊——哈拉湖作为研究对象,利用放射性核素²¹⁰ Pb和¹³⁷ Cs测年资料,通过对此高海拔湖泊沉积碳酸盐氧碳同位素、碳酸盐含量、总有机碳含量、磁化率等环境代用指标的分析,揭示了这一地区近800年来的气候环境变化过程。分析表明哈拉湖记录的气候环境变化经历了3个阶段:1206~1700A.D.环境较为寒冷、湿润,并有持续变湿的趋势;1700~1920A.D.环境由冷湿的状况趋向温暖干旱,1771年之后,环境保持相对稳定;1920~2002A.D.是自1206年以来最为温暖干旱的阶段。     

博斯腾湖湖泊沉积物光释光年代测量*

使用光释光年代学的单片再生法测量了博斯腾湖沉积剖面中碳酸盐泥及粉砂质泥底部的浅湖相灰色粉细砂和风成沙的年龄,对剖面上部碳酸盐层中陆生植物残体进行了AMS ¹⁴ C测年。通过不同测片的等效剂量(D_e)值的分布状况评价了样品的晒褪程度,选择不随灵敏度校正后的自然释光信号变化的相对集中的等效剂量(D_e)值计算了样品的埋藏年龄。通过这些年龄结果的对比,发现石英矿物的OSL年龄和AMS ¹⁴ C年龄在地层上是一致的,表明尽管在浅湖相细砂中存在不完全晒褪,但根据相对较小而集中的D_e值计算得到的年龄结果是可靠的。这些年龄结果和地层资料揭示末次冰消期以来至早全新世,博斯腾湖处于无水干盆地向深水湖泊转化的浅水湖泊状态,现代深水博斯腾湖大约形成于距今8ka前后。     

Spatial distribution characteristics of stable carbon isotope compositions in desert plant Reaumuria soongorica (Pall.) Maxim

In order to investigate the distribution characteristics of stable carbon isotope ratios (δ ¹³C) in the desert plant Reaumuria soongorica, the δ ¹³C values of leaves were measured in 407 individuals of 21 populations. Soil physicochemical properties including soil water content, soil total dissolved solids, soil total nitrogen, soil total phosphorus and soil organic content were also analyzed in order to survey the major factors influencing δ ¹³C values on spatial variation. Leaves and soil samples were simultaneously collected from the ten major distribution areas in Northwest China at altitudes from 394 m to 1 987 m above sea level, at latitudes from 36°10′N to 44°33′N, and at longitudes from 81°43′E to 106°37′E. These ten areas include Shihezi, Baicheng, Yiwu areas in Xinjiang Uygur Autonomous Region; Anxi, Zhangye, Baiyin, Lanzhou areas in Gansu Province; Shapotou, Yinchuan areas in Ningxia Hui Autonomous Region; and Alashan County in Inner Mongolia Autonomous Region. The results show that the δ ¹³C value of R. soongorica ranges from −22.77‰ to −29.85‰ with an average of −26.52‰. Foliar d13C values in R. soongorica are not significantly correlated with altitude, latitude or longitude, and a spatial distribution trend of d13C values of R. soongorica is not obvious on a large scale. However, when d13C values of two R. soongorica populations under the same climate conditions are compared, δ ¹³C values increase obviously from east to west and from north to south. As none of the soil total dissolved solids, soil total nitrogen, soil total phosphorus, and soil organic content shows a uniform trend from east to west and from north to south, we suppose that the small-scaled spatial distribution pattern of δ ¹³C values of R. soongorica is mainly controlled by the soil water content. Translated from Quaternary Sciences, 2006, 26(6): 947–954 [译自: 第四纪研究]     

Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China

Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating re- sults. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000―1500 AD, a humid climate during the Little Ice Age (LIA) (c. 1500―1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indi- cate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concen- trations, decreased carbonate content and increased grain size. The humid period during the LIA re- corded by the Bosten Lake sediments is representative of arid central Asia and is supported by nu- merous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipita- tion increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA.     

我国二氧化碳排放的区域分析

利用我国能源统计数据,对我国及各省区的CO2排放总量、排放强度、人均排放量和排放密度进行了计算.通过分析发现我国CO2排放具有较为明显的东西部差异,总体表现为东部发达省区排放总量大、排放强度低、人均排放多、排放密度高的特点,而中西部尤其是西部地区则表现出相反的特征.在分析我国CO2排放区域特征的基础上,分析出现以上地域差异的主要原因,并针对区域减排行动可能存在的问题进行了探讨,提出以省区为单位,降低排放强度可以取得实际的、可跟踪的减排效果,但需要考虑到全国各省区在功能定位、减排成本、资源环境条件等方面的差别,以及建立基于技术与资金合作的联合减排机制的可行性和障碍等因素.     

Comparisons of drought variability between central High Asia and monsoonal Asia: Inferred from tree rings

Severe drought is a serious natural disaster that frequently strikes East Asia, highlighting the need to understanding its drought regime and the associations with Asian monsoon. Tree-ring-based drought reconstructions provide invaluable paleoclimatic archives for detecting regional and large-scale drought variability and their potential forcings. We herein reviewed many drought reconstructions from central High Asia and monsoonal Asia and compared their similarities and differences, as well as their linkages to Asia monsoon. We compared the decadal-scale variability of six drought reconstructions for the central High Asia, where differing drought variations were found between the western and eastern portions. Seven drought reconstructions were reviewed for monsoonal Asia, from which a difference in drought variability was observed between the northern and southern parts. Therefore, we compared the drought variations of the four sub-regions of western and eastern parts of central High Asia, as well as northern and southern portions of monsoonal Asia. ENSO activity and sea surface temperature of western Pacific and northern Indian Oceans, coupled with Asian monsoon, play an important role in modulating drought variability of much area of the East Asia. An improved denser multi-index tree-ring network of longer length for East Asia is necessary for the establishment of more reliable large-scale drought reconstruction.