Recent climate changes recorded by sediment grain sizes and isotopes in Erhai Lake

By careful sampling and accurate analysis of recent sediments, the time series of sediment grain sizes and 6" 1B0, S 13C of carbonates in recent 700 years are successfully established, based on which the evolutionary history of the regional climate and environment in Erhai Lake is reconstructed. The results show that the climatic succession type in the region of Erhai Lake is warm-dry and cold-humid alternatively, and there exist 200 and 400 years of quasi-periodical changes in temperature and 100, 200 and 400 years of quasi-periodical changes in aridity/humidity regime. The two coldest periods in recent 700 years occurred in the 14th century and the duration of 1550—1800 AD. The latter period may be the imprint left of the Little Ice Age.     

Climatic variations recorded by the sediments from Erhai Lake, Yunnan Province, southwest China during the past 8000 a

Erhai Lake is a large lake with important climatic significance in Yunnan Province, southwest China. The multi-proxy sedimentary records from Erhai Lake indicate the 9 stages of climatic changes with the alternation of warm-dry and cool-wet during the past 8000 a. The variations of Asian monsoon systems were the main cause for the climatic changes in southwest China. The warm-dry period was coincident with the intensification of India monsoon and Northwest Pacific Sub-tropical High Pressure, and the cool-wet corresponding to weak of India monsoon and its main rain belt moving back to southwest China.     

New progress of lake sediments and environmental changes research in China

Environmental change recorded by lake sediments is one of the important branches of the past global changes study. The new progress of lake sediments and environmental changes in China since the late 1980s has been comprehensively discussed. The highlights emphasized are Asian paleomonsoon migration reflected by lake level fluctuation, uplift of the Qinghai-Xizang Plateau recorded by lacustrine sediments, saltlake sediments and environmental evolution, lake response to the natural-human interaction and modern lake biogeochemical process. Meanwhile important suggestions for the lake sediments and environmental research in the future are proposed, which include studies on the quantitative relationship between lake environment proxies and climate factors, high-resolution evolutionary sequence and spatial differentiation of environments, modern lake dynamic process and environment, Quaternary Chinese lake database and global changes.     

青藏高原湖泊沉积记录与环境变化研究

 过去全球变化研究是人类认识气候与环境变化事实与规律,客观评价现代环境在气候与环境发展历史中位置的重要手段,能够为未来气候与环境变化的预测提供科学的检验工具。介绍了湖泊沉积物环境代用指标与气候要素关系定量化的研究,简要回顾利用湖泊沉积物重建高原最近2万年环境变化历史研究成果,阐述高原湖泊沉积对气候变化的敏感响应。     

洱海夏秋季蓝藻种群动态变化及水华成因分析

目的：为洱海蓝藻污染治理提供依据。方法：通过对2006年洱海蓝藻种群动态变化的跟踪调查和定性、定量分析,探讨洱海夏秋季蓝藻种群动态变化及藻源污染成因。结果：洱海蓝藻种群增殖及水华发生不仅与营养盐积累、环境、气象因子有关,而且与生态系统脆弱、流域面源污染加重等因素密切相关,由于几者共同作用,导致了洱海蓝藻水华的发生。结论：必须加强洱海蓝藻污染治理工作。     

滇池东部第四系浅层湖滨相沉积物磁学特征及其环境意义

为了探究昆明盆地第四纪以来的总体气候特征及滇池湖泊的演化规律。本文综合环境磁学、TOC、pH等指标,对滇池东岸DC1钻孔岩芯沉积物进行了系统研究,测试了包括质量磁化率（χ）、非磁滞剩磁（ARM）、饱和等温剩磁（SIRM）、低频磁化率（χlf）、高频磁化率（χhf）、软剩磁（IRM-300mT）、pH值及总有机碳（TOC）。结果显示：DC1沉积物磁性特征由亚铁磁性矿物主导,反铁磁性的赤铁矿在0.3-3.6 m与14.7-15.6 m两个区段含量相对较高,结合赤铁矿的形成环境,反映了这两个区段对应的沉积环境为湖退时期;另外,结合TOC与磁化率在不同深度上的关系,表明TOC的高值与细颗粒的磁性矿物溶解有关。结合TOC在各区段的含量特征表明整个21 m沉积过程所对应的气候类型以温暖气候为主。     

A study on environmental changes based upon cladoceran assemblages from the core sediments in Chen Co,southern Tibet

A consecutive sediment core (CC2) was drilled in Chen Co (lake) of southern Tibet using a PISTON sampler in 1998 AD. Cladoceran remains including their species,amount richness and ecological features are analyzed for the top 117 cm sections of the core, upon which 5 cladoceran assemblages are distinguished. CL0 is an assemblage without any cladocera in the depth between 117-105 cm. CL1 assemblage (depths between I01-77 cm, ca.1407-1533 AD) possesses total 9 cladoceran species that appear in the core,and performs the greatest richness in the whole sequence.This assemblage reflected that there was plenty of exotic cold water and organic debrises inputing to the sedimentary site under the warmer conditions. The lake was wide and shallow that satisfied the big hydrophyte living. Cladoceran species and richnesses of CL2 assemblage (depths between 77-29cm, ca. 1533-1831AD) perform much more decreasing than those of CLI. There was only less Chydorus sphaericus which was acclimatized to wide environmental ranges. This implied that the sedimentary environment is so execrable that most of cladoceran lost their living abilities. Compared with CL1 assemblage, CL3 assemblage (depths between 29-10 cm, ca.1831--1941 AD) possesses nearly the same dominant species but lower richnesses. Especially, the cladoceran preferring organic debris also decrease in their amounts. This meant that the surface vegetation in the drainage basin was still poor though the environment turned to be better. Except the 2 zooplankton species, the other 7 species of cladoceran in this core are found in CL4 assemblage (depths between 10-0cm, ca. 1941-1998 AD), in which the eurythermal species had not performed their competition ability comparing withnarrow-temperatures adapted species. It implied that water temperatures were stable and much more influenced by air temperatures under the shallow-water conditions. The environmental features reflected by cladocera assemblages of CC2 core are fully supported by the evidences from ostracoda assemblages, diatom-salinity transfunction, environmental magnetism and relative proxies of the parallel CC1 core. Cladoceran assemblages in the lake sediments of Tibetan Plateau are sensitive to sedimentary environment and very significant to the studies of environmental changes.     

Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C₄ and C₃ plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C₄ vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C₄ expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C₄ plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C₄ plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.     

洱海北部“两江一河”水污染治理调研报告

为做好保护洱海的工作,对洱海北部为洱海提供主要来水量的两江一河(永安江、罗时江和弥苴河)的水污染治理情况进行调研。针对其水污染严重的现实,在回顾以往治理工作的基础上,分析水污染治理中的制约因素、存在问题及导致水污染的原因,最后提出加强两江一河水污染治理的十条对策建议。     

Climatic changes documented by stable isotopes of sedimentary carbonate in Lake Sugan, northeastern Tibetan Plateau of China, since 2 kaBP

Lake Sugan at the northern edge of the Qaidam Basin was selected as the research object. The temporal sequence of sedimentary cores retrieved from Lake Sugan since 2 kaBP was reconstructed using the ^210Pb, AMS 14C and conventional 14C dating methods. Carbon and oxygen isotopes of carbonate in the fine-grained lake sediments were analysed. Combined with the changes of 8180 values of surface water and air temperature observation data in the study area, it might be thought that the δ^18O value of the carbonate indicates effective moisture, and the changes in δ^13C values are related to annual freeze-up duration of the lake and indirectly indicate air temperature changes in winter half year. From the above, the sequence of climatic changes in the region since 2 kaBP was established. The climatic changes experienced five stages： Warm-dry climate during 0-190 AD： cold-dry climate during 190-580 AD; warm-dry climate during 580-1200 AD （MWP）; cold-wet climate during 1200-1880 AD （LIA）; cold-dry climate during 1880-1950 AD： and climate warming since 1950s. The air temperature changes in winter half year reflected by carbon isotope since 2 kaBP are in good agreement with the historical literature records and other geologic records, which shows that the climate changes recorded by the stable isotopes from Lake Sugan since 2 kaBP are of universal significance.     

洱海流域上游2005-2019年土地利用时空动态特征分析

土地利用对湖泊水质具有重要影响,研究其在重要时间节点的转化对保护洱海水质具有重要意义。基于人机交互解译遥感影像,得到2005年和2019年两期洱海流域上游的土地利用数据,运用地理信息系统（geographic information system,GIS）空间分析、转移矩阵等多种研究方法,分析洱海流域上游近14a来各种土地利用类型在时间、空间及数量上的动态变化情况。结果表明：耕地、林地和草地是洱海流域上游主要地类,耕地分布在中、南部平缓地带,林地和草地呈环状分布在盆地边缘,城镇用地零散分布在耕地中,且靠湖泊区域更为集中;14a间,转换主要在耕地、林地、建设用地和草地四种土地利用类型之间进行。建设用地和草地是总面积增加和减少最多的地类,分别为47.240 km2和97.398 km2;土地利用动态度呈现两极分化态势,园地是动态度最大,为1 549.895%,林地动态度最低,为0.198%。研究结果可为洱海流域上游的土地利用规划、生态保护提供理论支撑。     

全球变化背景下森林生态系统碳循环及其管理

森林生态系统碳循环及其管理是全球变化研究的重要主题,同时也是人类维持全球生态系统的物质、能量平衡和自然资源循环再生的一个重要生态学途径。笔者在分析森林碳循环的基本特征及其与全球变化相互联系的基础上,阐述了碳循环及其管理在全球变化研究中的地位和作用,并提出了森林生态系统碳循环管理的内容、方法、措施及途径。     

Palynological records of environmental changes in the middle part of Inner Mongolia,China

Today, the central part of Inner Mongolia has a continental climate, with cold winters, hot summers, and approximately 70% of the precipitation falling in the summer months. Vegetation is dominated by steppe vegetation with Stipa bungeana and Stipa breviflora. Scattered individuals of Quercus liaotungensis, Populus davidiana, Betula platyplylla are distributed in the mountains, with some Pinus tabluaoformis, near Miaoyu, and with fragmentary Picea above 1700—1800 m a.s.l. The Huitenglian…     

Holocene climatic and environmental changes recorded in Baahar Nuur Lake core in the Ordos Plateau, Inner Mongolia of China

A 5.3 m lake core was drilled in Baahar Nuur Lake in the Ordos Plateau, and measurements of meangrain size, organic δ 13C (δ 13Corg), organic carbon content (TOC), C/N, carbonate content, carbonate δ 13C(δ 13Ccar) and δ 18O (δ 18Ocar) were conducted for retrieving the Holocene chronosequence of climaticchanges based on 15 AMS 14C dates. The record documented four major stages of climate change inthe Ordos Plateau: (IV) a cold and dry condition before ～7.65 14C ka BP; (III) a warm and humid stagebetween ～7.65 and ～5.40 ka BP; (II) a generally drier and cooler climate since ～5.40 ka BP with twohumid events occurring from ～4.70 to ～4.60 ka BP and from ～4.20 to ～3.70 ka BP, and (I) a dry climatecharacterized by complete desiccation of the lake after 3.70 ka BP. Stage III can be further divided intothree sub-stages: (IIIa) a warm and humid episode from ～7.65 to ～6.70 ka BP, (IIIb) a warm and relativelydry episode from ～6.70 to ～6.20 ka BP, and (IIIc) the magthermal and maghumid episode of the Holo-cene from ～6.20 to ～5.40 ka BP.     

137Cs tracing of lacustrine sediments in the Dalian Lake, Qinghai Province, China

Based upon the analysis of Cs and grain-size parameters, the total amounts of ¹³⁷Cs deposition by wind and water in the Dalian Lake of Gonghe Basin, Qinghai Province are defined. The vertical profile of ¹³⁷Cs in the lacustrine sediments exhibits three ¹³⁷Cs activity maxima and one minimum. The major maximum corresponds to the global ¹³⁷Cs fallout in 1963; the two secondary maxima correspond to the leakage of the Chernobyl reactor in 1986 and complete desiccation of the lake in 1994, respectively. The minimum corresponds to aeolian deposition caused by extensive reclamation in the late 1980s and early 1990s. The 137Cs data set was used to evaluate average sedimentation rate of the Dalian Lake since 1963. The deposition was stable in 1963-1986 and 1994-1998, and it was rapid during 1986-1994. This preliminary study reveals that l37Cs has the same potential to trace environmental changes introduce by human interference in arid/semiarid regions as in humid regions.     

Environmental changes reflected by n-alkanes of lake core in Nam Co on the Tibetan Plateau since 8.4 kaB.P.

The n-alkanes are extracted from NMLC-1 core that was drilled in the Nam Co, central Tibet. They are measured by using Gas Chromatography and Mass Spectrometry (GC/MS) for componential and quantitative analyses. According to the constructed depth-age model, the component and concentration of n-alkanes, together with total organic carbon (TOC), total nitrogen (TN) and carbonate are used to elu- cidate palaeoenvironmental changes of Nam Co during the past 8.4 ka. The results indicate that Holo- cene environment performs three stages in the lake area. In the stage of 8.4―6.7 kaB.P., it was warmer while precipitation slightly increased. This stage was ended by an obvious cold/dry event. During 6.7― 5.8 kaB.P., temperature increased rapidly and reached its maximum values at about 6.0 kaB.P. The environments were warm/wet optimum for the blooming of terrestrial plants and submerged aquatic plants. After that, temperature decreased continuously and showed the lowest values at about 3.0 kaB.P. From 2.9 kaB.P. to the present, temperature rose again but alternated with cold and warm. The lake area tended to be dry after 1.4 kaB.P. During 600―400 aB.P., the environmental feature was the reflection of "Little Ice Age".     

Dynamic control on grain-size distribution of terrigenous sediments in the western South China Sea: Implication for East Asian monsoon evolution

High-resolution oxygen isotope stratigraphy of Core MD05-2901, which is located off eastern Vietnam in the western South China Sea （SCS）, was established and indicated that the core spans a time period of the past 450 ka. Based on the bulk density, fractional porosity and lithogenic content of the sediments, terrigenous mass accumulation rate （TMAR） was obtained, which is 4.9-6.0 g cm^-2 ka^-1 on average during interglacial stages, higher than that during glacial stages, i.e. 1.9-5.0 g cm^-2 ka^-1, which is different from northern and southern SCS which show higher TMAR in glacial stages. By principle component analysis of grain size distribution of all the samples, two main control factors （F1 and F2） were obtained, which are responsible for about 80% variance of granularity. The contents of grain size population 1.26-2.66 μm% and 10.8-14.3 μm% which are sensible to F1 show high-frequency fluctuation, and correlate well with the summer insolation at 15^o N. They exhibit a distinct cyclicity with frequencies near 23 ka and 13 ka, in contrast to a strong frequency peak near 100 ka obtained in proxies 4.24-7.42 μm% and 30.1-43.7 μm% controlled mainly by F2. The sedimentary character of this part of the SCS was controlled by variations of input flux from two main source areas, namely the southwest and north SCS, which were transported by different circulations of surface current forced by East Asian summer monsoon and winter monsoon respectively. We believe that the East Asian summer monsoon has fluctuated with high frequency and been forced by changes in solar insolation in low latitude associated with precession and half precession, while ice-volume forcing is probably a primary factor in determining the strength and timing of the East Asian winter monsoon but with less important insolation forcing.