Simulation of the Eurasian ice sheet dynamics during the last glaciation     

Pirjo-Leena Forsstrm  Ralf Greve 《Global and Planetary Change》2004,42(1-4):59

The Eurasian Weichselian glaciation is studied with the SICOPOLIS ice-sheet model and UKMO PMIP climate anomaly forcings. A set of sensitivity tests are completed, including runs in cold-ice mode, different positive-degree-day (PDD) factors and modified climatic data-sets. The model set-up with present-day climatology modified by a glacial index brings forth an areally correct Last Glacial Maximum (LGM) extent in the western areas, but the ice-sheet volume is too small compared to reconstructions from rebound rates. Applying modified climate data results in similar extent as indicated by the Quaternary Environment of the Eurasian North (QUEEN) Late Weichselian ice-sheet reconstruction. The simulation results display freshwater fluxes from melting and calving in phase with Heinrich events H3 at 27, H2 at 22, and H1 at 14 ka ago. These peaks correspond to fast flow areas, with main activity at 27 and 22 ka ago in the Nordic Channel area and later in the Bear Island and Storfjorden region. The activity of these areas seems to be shifting from south to north from LGM to the Holocene. The freshwater pulse at 19–18.5 ka could correspond to Dansgaard–Oeschger oscillation, as well as ice volume flux peaks around 18–17 ka ago on the western margin of the ice sheet.  相似文献   

SALT LAKES ON THE INNER MONGOLIAN PLATEAU OF CHINA     

郑喜玉 《中国地理科学(英文版)》1991,1(1):83-94

Salt lakes,the main source of trona resources in China, are widely distributed on the Inner Mongolian Plateau. Their characteristics are large in number, various in type, and short in salt-forming stage, especially their considerable number is well-known at home and abroad. The paper discusses the physical constituents, hydrochemical features, classification, formation, evolution, and salt-forming regularities of salt lakes through analyzing their distribution, lacustrine deposits and salt-forming conditions.  相似文献   

Distinguishing climatic from direct anthropogenic influences during the past 400 years in varved sediments from Lake Holzmaar (Eifel,Germany)   总被引：3，自引：0，他引：3  

Ulrike?KienelEmail author  Markus?J.?Schwab  Georg?Schettler 《Journal of Paleolimnology》2005,33(3):327-347

A 336-year floating varve chronology from Lake Holzmaar (Eifel, Western-Germany) covering the recent period has been established by microfacies analysis of thin sections. This sequence terminates 23 cm below the core top. In the top 23 cm, the varves are disturbed. By means of linear regression, the varve sequence was dated to the period AD 1607–1942. The influences of climatic variability and anthropogenic activities in the lakes catchment (e.g., forestry, agriculture) on lithology, fabric, and microfossil content of the varve sublaminae could be discriminated by applying statistical analyses (ordination and clustering) to the combination of the sublaminae in the varves and their thickness. Four clusters are obtained. Cluster 1 indicates cold springs, and shorter, cooler summers reflected primarily in below-average varve thickness (VT) for two stable phases: from AD 1650–1700 (during the Maunder Minimum) and from AD 1750–1785. Cluster 2 indicates years with conditions transitional to that indicated by cluster 1, characterized by vigorous and prolonged spring circulation with massive blooms of the nordic-alpine Aulacoseira subarctica. The samples assigned to Cluster 3 and Cluster 4 show the imprint of anthropogenic influences. Cluster 3 (AD 1795–1815 and AD 1825–1885) is characterized by above-average VT due to high detritus input throughout the year. The increased soil erosion can be linked to anthropogenic deforestation as a consequence of the production increase of the Eifelian iron industry at the end of the 18th century. This input dampens the climatic signal of a colder Dalton Minimum, which is reflected in a short drop in VT centered around AD 1810. At about AD 1885, Cluster 4 conditions, characterized by increased nutrient concentrations, low detritus input, and longer periods of stable summer stratification, become the stable state in Lake Holzmaar. They indicate the response of the lake to natural reforestation and the use of artificial fertilizers in the catchment, which began, according to historical records, in the 1850s in the Eifel region. The prolonged, stable summer stratification periods may be the first indication of the modern warming trend. A drop in VT centered around AD 1890 and recurring cluster-1 conditions may indicate the Damon Minimum.  相似文献   

Quantification of Holocene lake-level changes in Finnish Lapland using a cladocera – lake depth transfer model     

Atte?KorholaEmail author  Matti?Tikkanen  Jan?Weckstr?m 《Journal of Paleolimnology》2005,34(2):175-190

During recent years, numerous studies dealing with Holocene lake level fluctuations have been conducted in Finnish Lapland. However, no quantification of lake level variations exists to date. Here, we applied a recently developed modern cladocera – lake depth transfer model to subfossil cladocerans analysed from three small and shallow (< 6 m) kettle-hole lakes in northwestern Finnish Lapland to provide estimates of the amplitudes of long-term lake-level changes in the region. The quantitative inferences were compared to pollen, charcoal and geochemical records from one of the study sites. The lake levels were inferred to be high during the early Holocene; they faced marked reduction up to 4–6 m in the mid-Holocene (≈7000–4000 cal yr BP), and rose again during the latter part of the Holocene. There is some indication of lowered lake levels around 1500 cal yr BP, but interpretation of such small-scale changes is hazardous due to large prediction errors in the initial cladoceran model. The overall pattern of the Holocene lake level variation generally followed the regional changes in climate humidity as reconstructed in previous studies by means of other sedimentary proxy indicators, such as pollen and oxygen isotopic compositions. We postulate that changes in winter precipitation may have had a greater influence on lake-levels than variations in summer precipitation or evaporation.  相似文献   

The sulfur flow fields of the Fossa di Vulcano     

Andrew?HarrisEmail author  Roberto?Carniel  Matt?Patrick  Jon?Dehn 《Bulletin of Volcanology》2004,66(8):749-759

Sulfur flow deposits at the Fossa di Vulcano fumarole field (Italy) are dominated by thermal erosion features. These are characteristic of sulfur flows at this location, where most flows are emplaced in a combusting mode such that all flow sulfur is melted and consumed during the emplacement event. Further, thermal erosion during emplacement results in pits and channels that mark the passage of the combusting flow. These thermal erosion pits and channels are typically littered with non-combusted silicate blocks, show overhanging rims and an absence of sulfur. If activity remains confined to a source fumarole basin, then sulfur lake activity will result. Combustion of such a feature leaves thermally eroded pits, typically a few tens of centimeters to a few meters wide and long, and a few tens of centimeters deep. However, the increase in sulfur volume during melting and erosion of pit walls mean that overflow and breaching is common. This leads to capture of new sulfur encrusted fumarole basins and flow extension. Flow extension away from the lake results in thermal erosion channels as much as 1.7 m wide, 0.6 m deep and 23.5 m long. Flow direction is dictated by slope, cinder ejection and sources of new sulfur, thus flows are capable of moving down, across and/or up slope if that is the dominant source of new sulfur. We estimate that sulfur flow activity has combusted 2,000–5,000 m³, or 4,000–10,000 tons, of sulfur at Vulcano. Only one noncombusted unit could be found during seven fumarole-fieldwide surveys during 1998–2003; this was 7.3 m long and 0.3 m wide, and had a viscosity of 0.1–40 Pa s. This viscosity is consistent with emplacement temperatures of 165–180°C, which are lower than sulfurs combustion temperature. At Vulcano the commonality of thermal erosion features over noncombusted sulfur flow units indicates that combusting emplacement has been the main mode of flow emplacement at this volcano. The common occurrence of combustion is also evident from reference to the same phenomenon by Déodat de Dolomieu in 1783.Editorial responsibility: M. Carroll  相似文献   

湖泊和水库营养分类的研究     

王东 《广东海洋大学学报》1992,(2)

根据我国实际情况,并参考国外对湖泊营养分类的标准,建立了湖泊和水库FTE营养分类方法。应用Fuzzy综合评判的理论和方法,对参加分类评判的各项指标参数通过映射的方法,使每一个指标参数转换成在区间[0,1]的特性指数(d_1),同时引入一个能反映每项指标参数在评判中重要程度的权值(a_1),求得一个能统一反映湖库营养程度的综合性评价指数的计算公式:e=∑a_1d_1。以何志辉教授对我国87个湖库营养分类结果为基准,计算并确定出贫、中、富三种营养类型互不相交的FTE指数范围,作为湖库FTE营养分类标准。对任一湖库,根据九项指标参数计算获得的FTE指数e,不仅能客观地反映其营养程度,同时又以它作为唯一的数值来确定该湖库的营养类型的归属。用FTE营养分类方法对我国87个湖库营养分类结果与何氏的分类结果吻合率达97.7％。  相似文献   

BOOK REVIEWS     

《The Professional geographer》1985,37(2):226-262

Book Reviewed in this article: The City in Cultural Context . John Agnew, John Mercer, David Sopher, eds. Soils and Geomorphology Peter W. Birkeland. Urbanization and Settlement Systems, International Perspectives . L. S. Bourne, R. Sinclair, and K. Dziewoński. eds. An Introduction to Urban Historical Geography . Harold Carter. Overshoot, The Ecological Basis of Revolutionary Change . William J. Catton, Jr. Rivers of the World . Eberhard Czaya. Jewish Communities in Frontier Societies: Argentina, Australia and South Africa . Daniel J. Elazar with Peter Medding. Color in Public Spaces: Toward a Communication-Based Theory of the Urban Built Environment. Kenneth E. Foote. Spatial Statistics and Models. Gary L. Gaile and Cort J. Willmott, eds. Mega-Geomorphology. Rita Gardner and Helen Scoging, eds. Technological Change and Regional Development. Gillespie, ed. The Arid Lands: Their Use and Abuse. R. L. Heathcote. The Location of Industry in Britain. A. G. Hoare. Groundwater as a Geomorphic Agent . R. G. LaFleur, ed. Rural Public Services: International Comparisons. Richard E. Lonsdale and Gyorgy Enyedi, eds. Saving Water in a Desert City. William E. Martin, Helen M. Ingram, Nancy K. Laney, and Adrian H. Griffin. Water Resources: Distribution, Use and Management. John R. Mather. Transnationals and the Third World: The Struggle for Culture. Armand Mattelart. South Hadley, MA: USGS Digital Cartographic Data Standards. R. B. McEwen, R. E. Witmer, and B. S. Ramey, eds. The Ecosystem Concept in Anthropology. Emilio F. Moran, ed. Boulder, CO: Women, Men, and the International Division of Labor. June Nash and Maria Patricia Fernandez-Kelly, eds. Nuclear Power: Assessing and Managing Hazardous Technology. Martin J. Pasqualetti and K. David Pijawka, eds. Mary Somerville and the Cultivation of Science 1815-1840. Elizabeth Chalmers Patterson. An Introduction to Coastal Geomorphology. John Pethick. Late Quaternary Environments of the United States , Vol. 1, The Late Pleistocene. Stephen C. Porter, ed. Planning and Ecology. R. D. Roberts and T. M. Roberts, eds. Regionalism and the Pacific Northwest. William G. Robbins, Robert J. Frank, and Richard E. Ross, eds. Environment and Health. Anthony J. Rowland and Paul Cooper. Sunbelt/Snowbelt: Urban Development and Regional Restructuring. Larry Sawers and William K. Tabb, eds. The Bad Earth. Environmental Degradation in China. Vaclav Smil. Armonk, NY: Voyage into Substance: Art, Science, Nature, and the Illustrated Travel Account, 1760–1840. Barbara Maria Stafford. The Institute of British Geographers: The First Fifty Years. Robert W. Steel. Visions of the Past. Christopher Taylor and Richard Muir. Glacial Lake Agassiz. J. T. Teller and Lee Clayton, eds. The Tule Breakers: The Story of the California Dredge. John Thompson and Edward A. Dutra. The Balkan City 1400–1900. Nikolai Todorov. Explanation, Prediction and Planning: the Lowry model. Michael J. Webber. Mercedes Reales: Hispanic Land Grants of the Upper Rio Grande Region. Victor Westphall. The World Atlas of Revolutions. Andrew J. M. Wheatcroft. The West European City, A Social Geography. Paul White. Urban Elites and Mass Transportation. J. Allen Whitt. Princeton, NJ: Urban Life In Contemporary China. Martin King Whyte and William L. Parish. The Demand for Energy in the Soviet Union. David Wilson. London and Canberra: Rethinking Geographical Inquiry. J. David Wood, ed.  相似文献   

Evidence for Holocene climate variability from the sediments of a Scottish remote mountain lake     

Richard W. Battarbee  Nigel G. Cameron  Paul Golding  Stephen J. Brooks  Roy Switsur  Doug Harkness  Peter Appleby  Frank Oldfield  Roy Thompson  Don T. Monteith  Andrew McGovern 《第四纪科学杂志》2001,16(4):339-346

High resolution sampling of sediment cores covering approximately the last 4000 yr from Lochan Uaine, a small corrie loch in the Scottish Cairngorm Mountains, show quasi‐periodic cycles in organic matter (measured as percentage loss on ignition). Analysis of these cycles show correspondences between loss on ignition, δ¹³C values and chironomid head capsule abundance. We interpret the changes as reflecting changes in lake productivity and hypothesise that they are driven by climate variability. However, it is not yet clear whether the periods of relatively high organic matter production and preservation are associated with colder or with warmer conditions. Nevertheless the results indicate the value of using sediments from remote, undisturbed mountain lakes as recorders of Holocene climate variability. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Sequentially extracted metals in Adirondack lake sediment cores     

Jeffrey R. White  Chad P. Gubala 《Journal of Paleolimnology》1990,3(3):243-252

  相似文献   

Dynamics of a large tropical lake: Lake Maracaibo   总被引：1，自引：0，他引：1  

Bernard E. Laval  Jörg Imberger  Angelos N. Findikakis 《Aquatic Sciences - Research Across Boundaries》2005,67(3):337-349

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