Pollen-based reconstructions of Holocene vegetation and climatic change of Tibetan Plateau

A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards     

A high resolution,multiproxy Late‐glacial record of climate change and intrasystem responses in northwest England

A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd.     

Postglacial history of a cedar swamp in southeastern Connecticut

Stratigraphic and palynologic analyses of sediment cores from a large mire, combined with geologic and hydrologic studies of its watershed, provide a late Quaternary record of environmental change at Cedar Swamp in southeastern Connecticut. Since deglaciation of the area, the basin has evolved from an open lake characterized by the rapid accumulation of allochthonous inorganic sediments to an ombrotrophic mire with peat accumulation keeping pace with the gradual rise in the water table. Lithostratigraphic, pollen, and chronologic evidence suggest that the long-term trend of basin infilling and paludification was interrupted by two intervals (14 000–13 000 and 8000–4700 yr B.P.) when the water table elevation dropped at least 1 m.     

A high‐resolution pollen and geochemical analysis of late Holocene human impact and vegetation history in southern Cumbria,England

The historic era, which in Cumbria begins with the Roman invasion of AD 71, is a frequently neglected period in palaeoecological research, but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records. Pollen and geochemical data are presented for late Holocene records from Deer Dyke and Hulleter Mosses in southern Cumbria. The records show initially low levels of anthropogenic impact, followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries AD. The timing of these clearances suggests that they were initially Anglo‐Saxon in origin, rather than Norse. Further clearances in the 16th century AD are interpreted as a response to monastic dissolution and late Tudor population pressures; the landscapes reached their contemporary form following extensive clearances in the 17th century AD. Silicon and titanium concentrations at Deer Dyke Moss were used to reconstruct past levels of atmospheric dust loading, which is broadly related to soil erosion. Geochemical influx was found to peak during periods of landscape transition rather than from established land use. This relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region, which changes as substantial woodland clearances during the 16th century AD and continuous land use pressure since then have greatly increased the supply of airborne dust. Copyright © 2008 John Wiley & Sons, Ltd.     

不同年度收存的褶皱臂尾轮虫休眠卵的孵化及滞育胚胎“激活”效果的研究

比较了 1 985— 1 998年间由同一褶皱臂尾轮虫 (Brachionusplicatilis)种群在实验室内历年产生并收存的休眠卵的孵化效果 ,并初步探讨了胚胎“激活”处理对孵化的影响。结果表明 ,休眠卵的收存年度或时间对其在一定孵育期内的总孵化率 (THR)和日孵化率 (DHR)有极显著影响 (x2 检验 ,p<0 .0 0 1 ) ,但THR和DHR与储存时间间均无显著的相关性 ,而是呈极大波动。同时发现“激活”作用具有促使孵化高峰提前到来、增强孵化同步性的双重功效 ,从而可明显缩短孵育时间 ,提高孵化速率。但“激活”前后多数卵样的总孵化率无显著变化 (p >0 .0 5 )。详细讨论了可能导致孵化率波动的多种因素 ,例如遗传变异、培养历史、储存及孵化的环境条件等。     

近2600年神农架大九湖泥炭的气候变化记录

神农架大九湖沼泽泥炭柱状样提供了分辨率为25a的约2600a来的气候变化记录。对样品进行了环境磁学参数测量、X射线荧光分析(XRF)、孢粉鉴定和统计建模，结果表明，大九湖气温的变化曲线与竺可桢中国东部的物候温度曲线以及格陵兰氧同位素变化曲线大体一致，与青藏高原东部希门错湖泊沉积物温度代用指标的变化曲线也十分相似。特别是550—1300AD间的相对温暖期，与竺可桢首次提出来的中国东部隋唐温暖期(约600-1000AD)和欧洲的中世纪暖期(930-1240AD)在时间跨度上大致对应。可划分为4个阶段：(1)600BC—550AD，气候相对冷湿；(2)550—1300AD，气候相对凉干；(3)1300—1900AD，气候又转变为冷湿，其中最冷期1400—1900AD可与欧洲的小冰期对应；(4)1900AD至今，气候又开始转向相对凉干。同时发现低频磁化率χlf与铁元素含量之比(χlf／Fe)的变化曲线与利用孢粉分析数据恢复的大九湖气候变化曲线对应得很好，特别是二者都清晰地显示了500—1300AD为一相对暖期。这预示着χlf／Fe可能是泥炭剖面的一个更好的气候记录代用指标。     

艾比湖地区冰消期以来气候演化的植物学证据

本文根据植物生态学分析方法，通过对艾比湖ＺＫｏｏＢ孔中孢粉组合及植被生态的定量分析，阐述了北疆内陆干旱区冰消期以来的气候演化状况。孢粉组合特征及其植被生态的定量分析研究表明，受大气降水以及大气和土壤中相对湿度波动变化的影响，艾比湖地区的生态环境特征在最近１５０００ａ中至少经历了１０次比较明显的波动变化，并且与全球气候变化过程基本符合，表明中国西部干旱半干旱地区晚更新世以的气候环境演化过程是在全球变     

The history and impact of air pollution at Čertovo Lake,southwestern Czech Republic

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the umava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from ertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the ²¹⁰Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 g g^-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 g cm^-2 yr^-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 g cm^-2 yr^-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.     

寒武系古流体地球化学特征及其对页岩气保存的指示意义 ——以中扬子地区寒武系页岩气发现井宜地2井为例

保存条件是中扬子地区页岩气富集的关键因素之一，宜地2井是中扬子寒武系页岩气发现井，通过对该井全井段岩芯裂缝古流体的地球化学分析，探讨了寒武系古流体成因和对水井沱组页岩气保存条件的指示意义。结果认为：① 覃家庙组膏岩层之上方解石脉缺少Fe2+、Mn2+，且δ13C和δ18O值较围岩偏负，指示其形成于氧化的环境，石牌组方解石脉δ13C偏负，黄铁矿脉δ34S值与膏盐相似，表明其成因与TSR密切相关；水井沱组脉体δ13C和δ18O与围岩相似，形成于封闭的环境。② 方解石脉包裹体群SO42-、Ca2+、Mg2+含量整体上由覃家庙组向上向下分别递减，钠氯系数以水井沱组最低，整体上向上升高，表明覃家庙组是高盐度卤水的主要来源，水井沱组受外来流体影响弱；包裹体水溶液δD和δ18O也指示娄山关组、石牌组方解石脉成因分别与大气水、TSR相关。③ 古流体地球化学研究表明宜昌地区页岩气保存条件整体较好，页岩气散失的主要通道是垂直裂缝，页岩气保存条件好与膏盐盖层发育、后期构造破坏弱、脉体对裂缝的及时封闭以及白垩系盖层等因素密切相关。     

Surface pollen and its relationship to vegetation on the southern slope of the eastern Qilian Mountains

The objective of this study is to investigate pollen-vegetation relationship in the Qilian Mountains. The eastern Qilian Mountains are located in the transitional zone of the Tibetan Plateau, the Loess Plateau and the arid region of Northwest China, which is one of the key areas of global environmental change. A total of 13 surface pollen samples from main vegetation have been collected. Pollen percentages were calculated in all samples. In order to reveal the relationship between pollen composition and the vegetation types from which the soil samples have been collected, Detrended Correspondence Analysis (DCA) ordination method was employed on the pollen data. The results show that dominating vegetation types can be recognized by their pollen spectra: Picea crassifolia forest, alpine shrub and alpine meadow as well. Altitude and temperature determine the distribution of the surface pollen and the vegetation. The good agreement between modern vegetation and surface samples across this area provides a measure of the reliability of using pollen data to reconstruct paleoenvironment and paleovegetation patterns in this or other similar regions. However the loss of Betula pollen in forest needs further investigation. Pollen oxidation is the most important factor contributing to the damage of modern pollen in the study area. Pollen concentrations decrease with the increase of pH values of soils, and decrease sharply when the pH exceeds 7.6.