Environmental changes and lake level fluctuation recorded by lakes on the plain in northern Xinjiang during the late Holocene

Xinjiang Autonomous Region is located in the arid area of westerly of China and there are many arguments about the changes of past temperature and moisture. Most of the lakes on the plain in northern Xinjiang are sealed lakes and terminal lakes. They can evidently reflect the changes in palaeoclimate. The palaeoenvironmental changes of some plain lakes in northern Xinjiang during the late Holocene will be analysed mainly based on the data of pollen, sedimentary facies, loss on ignition （LOI）, susceptibility and grain size from the Sichang Lake, Dongdaohaizi Lake and Aibi Lake. Results reveal an assembled pattern of temperature and moisture dominated by cold-wet and warm-dry. In addition, the impact factor will be discussed.     

Holocene abrupt climate shifts recorded in Gun Nuur lake core, northern Mongolia

A continuous 7.44 m lake core was successfully drilled at Gun Nuur Lake, northern Mongolia, and analyses on environment magnetic parameters, organic matter content and organic δ^13C were conducted in an attempt to retrieve the Holocene chronosequence of climatic changes based on 6 AMS ^14C dates. We found that the Holocene climate in northern Mongolia has been alternating between cold (or cool)/wet conditions and warm/arid conditions, and also punctuated with a series of abrupt climate shifts. The abrupt climate shifts occurred around 1750, 2800, 4000, 5200, 7200, and 9200 aBP (^14C age), being chronologically correlative to those abrupt climatic events recorded in the high-latitude North Atlantic Ocean. The correlation indicates that the climatic changes in northern Mongolia were linked with those in the North Atlantic Ocean probably via the North Atlantic Oscillation-affected westerly winds. The strength and position of westerly winds might have modulated the Siberian-Mongolian high pressure system (winter monsoon), directly influencing the climate in China.     

Late Pleistocene／Holocene wetland events recorded in southeast Tengger Desert lake sediments, NW China

The area along the eastern and southeastern margins of the Tengger Desert, NW China, which is sensitive to the summer monsoon variations, was selected for studying the environmental conditions surrounding the transition between Paleolithic foragers and Neolithic farmer/pastoral-ists. Short cores were obtained from four lake basins in the southwestern Tengger using a hand-driven piston coringdevice. Proxies from these cores were supplemented by ra-diocarbon ages obtained from lake sediment cores, shoreline features and spring mound deposits. Together these records provide evidence of millennial-scale climate change eventsfrom the Pleistocene-Holocene transition to the present.Lake/wetland events, representing periods of more intensive summer monsoon, occur in the records at-12.7-11.6,-10.1, -9.3, -8.0, -5.4, -1.5, and -0.8 ka BP. They do suggest that century- to miliennial-seale climatic cycles are characteristic of the Holocene in the southeastern Tengger Desert although the chronology must be considered extremely tentative.     

泥炭记录的近2 200年吉林省敦化盆地的气候变化

根据典型泥炭剖面孢粉图示、粒度分布(纤维含量)、pH、沉积速率、吸湿水、C/ N、有机质含量等指标的综合分析,结合地层特征,研究了2 200 a B.P.以来的晚全新世敦化盆地植被和气候的变化.结果表明:敦化大桥泥炭地是从山地森林演替为草甸,继而经沼泽化形成;周围植被经历了以松林(Pinus)为主的温带山地针叶林,桦(Betula)、榛(Corylus)、胡桃(Juglans)等阔叶树和松林共生的针阔混交林,以榛、鹅耳枥(Carpinus)、松为主的针阔混交林和松、桦为主的针阔混交林之后,渐渐进入现代景观;相应地,该区气候经历了四个时期,即冷干((2 045±70)B.P.)～(2 195±70)a B.P.)、暖湿((1 745±70)a B.P.～(2 045±70)a B.P.)、温湿((705±70)a B.P.～1 745±70)a B.P.)和冷湿(公元1245-1950年)时期.     

北极新奥尔松地区环境演变的沉积记录

分析了北极新奥尔松地区伦敦岛的湖泊沉积物L1的16种元素(Hg、Se、Cd、As、Cu、Zn、P、Fe、Ti、K、Mn、Ca、Mg、Na、Si、Al)及TOC(总有机碳)的含量.结果表明:沉积物表层5 cm部分Hg、Se、Cd等重金属元素的污染主要是由20世纪以来新奥尔松煤矿开采活动引起的;而5 cm以下部分属于自然沉积.同时,发现最表层的Hg、Se、Cd含量有降低趋势,很可能是新奥尔松煤矿的关闭导致煤灰沉积的减少.计算了ICV等元素比值,其结果揭示了新奥尔松地区的化学风化作用十分微弱,过去几千年来,该地区气候环境经历了相对暖湿-寒冷-相对暖湿的阶段.     

A high-resolution climatic change since Holocene inferred from multi-proxy of lake sediment in westerly area of China

Multi-proxy data are presented and a discuss is made of paleoclimatic and paleoenvironmental changes during Holocene from a 225-cm-long sediment core from Wulungu Lake, located in westerly area of China. The chronology is constructed from six AMS radiocarbon dates on the bulk organic matter. Analyses of pollen, TOC, TN, δ 13Corg, ostracod assemblages and the shell stable isotopes, suggest Holocene climate pattern as follows: temperate and dry (10.0―7.6 cal. ka BP)-warm and wet (7.6―5.3 cal. ka BP) -warm and moist (5.3―3.6 cal. ka BP) -temperate and dry (3.6―2.1 cal. ka BP)-temperate and moist (2.1―1.3 cal. ka BP) -cool and dry (1.3 cal. ka BP―present). With the climatic change, Wulungu Lake experienced two large-scale retreat (5.3―3.6 cal. ka BP and 1.3 cal. ka BP―present) and an obvious transgression (7.6―5.3 cal. ka BP). The records of climatic and environmental evolution of Wulungu Lake were in good accordance with those of adjacent areas. It responded to regional environmental change, global abrupt climate events and followed the westerly climate change mode.     

A high-resolution climatic chanse since Holocene inferred from multi-proxy of lake sediment in westerly area of China

Multi-proxy data are presented and a discuss is made of paleoclimatic and paleoenvironmental changes during Holocene from a 225-cm-long sediment core from Wulungu Lake, located in westerly area of China. The chronology is constructed from six AMS radiocarbon dates on the bulk organic matter. Analyses of pollen, TOC, TN, δ^13Corg, ostracod assemblages and the shell stable isotopes, suggest Holocene climate pattern as follows： temperate and dry （10.0-7.6 cal. ka BP） -warm and wet （7.6-5.3 cal. ka BP） -warm and moist （5.3-3.6 cal. ka BP） -temperate and dry （3.6-2.1 cal. ka BP）-temperate and moist （2.1-1.3 cal. ka BP） -cool and dry （1.3 cal. ka BP-present）. With the climatic change, Wulungu Lake experienced two large-scale retreat （5.3-3.6 cal. ka BP and 1.3 cal. ka BP-present） and an obvious transgression （7.6-5.3 cal. ka BP）. The records of climatic and environmental evolution of Wulungu Lake were in good accordance with those of adjacent areas. It responded to regional environmental change, global abrupt climate events and followed the westerly climate change mode.     

Climatic instability recorded by the mollusk assemblages from the late glacial loess deposits in China

The loess-paleosol sequence in China records abundant and valuable information on the global and regional climate changes. Biological record from the loess sequence is the most direct evidence on variation in pattern of paleo-atmospheric circulation and changes in winter and summer monsoon. A new record of climatic instability, which occurred in the Loess Plateau during the late glacial period, is presented. Through the study of terrestrial mollusks from three loess sequences, the authors intend to characterize the biological response process to rapid climate change and to learn the mechanisms driving the instable climate changes and the possible linkage in different regions. The result shows the striking consistent variability in the ratio records of three mollusk sequences of the late glacial, indicating apparent rapid climate fluctuations. Correlation of our three mollusk records with the oxygen isotopic records from Greenland ice cores and foraminifera1 records from the Northeast Pacific Ocean reveals similar instability climate during the late glacial period, which provides us a new thought probing the climate instability observed in the North Atlantic, the North Pacific and the Loess Plateau. The low-level atmospheric circulation in the Northern Hemisphere may be one possible way to link the unstable climate patterns observed in the above three regions.     

Southwest monsoon changes indicated by oxygen isotope of ostracode shells from sediments in Qinghai Lake since the late Glacial

The δ 18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake can be used as a better proxy to reflect monsoon changes. Low monsoon precipitation between 17.5 and 11 cal. ka BP is indicated by positive δ 18O values averaging 2.37‰. A fast shift in δ 18O from positive at 11 cal. ka BP to negative at 10 cal. ka BP indicates sharp increase of monsoon precipitation. An interval of generally high monsoon precipitation is observed between 10 and 6 cal. ka BP with δ 18O values averaging -2.15‰. Decrease of monsoon precipitation between 6 and 2.5 cal. ka BP is indicated by positive δ 18O values. δ 18O keeps positive values averaging 3.0‰ between 2.5 and 0 cal. ka BP suggesting low high monsoon precipitation. The climatic changes indicated by δ 18O records of ostracode shells in sedi- ments of core QH-2000 from Qinghai Lake and our broader regional comparison show that the climate in Qinghai Lake since the late Glacial is probably controlled by southwest monsoon other than southeast monsoon.     

Paleosandstorm characteristics and lake evolution history deduced from investigation on lacustrine sediments——The case of Hongjiannao Lake, Shaanxi Province

Sediment cores from desert lakes serve as good records of the frequency and intensity of sandstorms in history. By multi-proxy analysis of grain-size, magnetic susceptibility, TOC and Rb/Sr ratio, the paleosandstorm characteristics and lake evolution history in Yulin Area for the past 80 years, are discussed in this article. It is revealed that Hongjiannao Lake formed in about 1928 A.D. and in its initial stage sandstorms were prevalent with three extremes taking place in 1936 A.D., 1939 A.D. and 1941 A.D.. During the expansion period of 1952-1960 A.D., inflow waters to the lake increased sharply and a lot more weathered materials were carried into the lake. The frequency and intensity of sandstorms have reduced a lot since 1960s and the ＂double peaks＂ feature of the grain-size frequency curve has changed into the ＂single peak＂ feature. Study on the catchment ecology of the lake shows that the occurrence of sandstorms has been effectively restrained by the forest plantation and water and soil conservation.     

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.     

Humid medieval warm period recorded by magnetic characteristics of sediments from Gonghai Lake,Shanxi, North China

Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies. Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (2.8 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP. The results demonstrate that the main magnetic mineral is magnetite. The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation. In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process. The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon. The variations in the and S 300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910–1220), which is supported by pollen evidence. Furthermore, this 3–6-year resolution environmental magnetic record indicates a dry event around AD 980–1050, interrupting the generally humid MWP. The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed. It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments.     

鄂尔多斯盆地南缘晚古生代沉积物源及其对秦岭造山带北部演化的指示

鄂尔多斯盆地南缘位于华北克拉通盆地的西南部,其形成演化和沉积过程与华北克拉通南侧秦岭造山带的活动有紧密的联系.晚古生代沉积的物源特征能够帮助提取关于秦岭造山带的演化信息.基于对鄂尔多斯盆地南缘澄城和韩城2条出露本溪组－石千峰组的剖面岩石学特征的详细研究,从岩石性质、碎屑特征、重矿物组合和碎屑组分的Dickinson三角图解等方面进行分析讨论,获得了鄂尔多斯盆地南缘晚古生代物源的详细信息,并揭示了秦岭造山带北部晚古生代的演化过程.研究表明,本溪组－太原组的物源为秦岭造山带中的华北板块南缘带;山西组－石千峰组的物源来自于北秦岭构造带,物源区有向南迁移的特征.晚泥盆－晚石炭世商丹带的点接触初始碰撞造成华北板块南缘发生抬升,早二叠世秦岭造山带进入面接触碰撞阶段,造成北秦岭弧后盆地和岛弧带依次发生隆升,成为鄂尔多斯南缘沉积区的主要物源供给区.扬子板块与华北板块自东向西剪刀状的碰撞,造成鄂尔多斯南缘沉积的山西组－下石盒子组的古流向由南东－北西方向朝南西－北东方向的转变.     

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.     

Turbidite and bottom-current evolution revealed by anisotropy of magnetic susceptibility of redox sediments in the Ulleung Basin,Sea of Japan

Anisotropy of magnetic susceptibility(AMS) from above and below 7.31 m in a core from the southern Ulleung Basin shows clear differences on an equal area projection of the lower hemisphere.Rather concentrated steep inclination of K 3 and horizontal inclination of K 1 and K 2(K1 ≥K2 ≥K3) are located within the upper part,and the latter two axes lie perpendicular to each other near the bedding plane.In contrast,random distribution of the three axes and extremely high value of shape parameters(Q=(K1-K2)/[(K1+K2)/2-K3]) are evident in the lower part,indicating complete destruction of the original sedimentary structure.This result is consistent with data from X-radiographs,which show numerous conglomerates,distortions and cleavages in the lower part.According to age models by Liu et al.(2010) and Zou et al.(2010),the bottom age at 7.31 m is 48 cal ka BP,and the time domain is discussed below.The degree of AMS(P) is low,1-1.08,and linearly related to the foliation(F)(R2 =0.95,N=176).The relationship between F and linearity(L) implies oblate aligning patterns that are typically sedimentary in origin.At least five redox couplets were found with the aid of S ratios and other rock magnetic parameters,and in most cases,the original signals of climate survived early diagenesis.The paleomagnetically reoriented AMS show corresponding changes with millennial events in the last 48 cal ka.Clearly tilted K 3 directions and reduction of P and F occurred within DO1-BA warm events,when melt water pulse 1A nd the YD cold event took place.The turbulent conditions therein,synchronous with coarsening of sediments,provide evidence of strong bottom currents and possible directional changes,as evidenced by different K3 tilting directions.A NE current direction in the last 4.5 cal ka is consistent with in situ measurements of bottom currents.Responses of AMS,mainly to climatic modulation,show on the one hand,the limited influence of diagenesis on rock magnetic signals and,on the other hand,the dramatic change of hydrodynamic conditions and terrigenous inputs during rapid sea level rise during the last deglaciation.