Antarctic Glacial Retreats and the Records of Sea Level Change in Deposits at the North Bank of the Shenzhen Bay,South China     

Zheng Honghan  Huang Baolin 《中国地球化学学报》1997,16(2):154-161

In view of the huge ice cover of 24.5 X 10⁶ km³ in Antarctica, which accounts for over 90% by volume of the ice body on earth, the movement of Antarctic glaciers is a major control on global sea-level change and climatic fluctuation. As recorded in the Quaternary deposits in King George Island, West Antarctica, three rapid ablations can be recognized at 11000, 9000 and 6100 years ago and the global climate within the past 6000 years is characterized by small-amplitude warm-cold fluctuation. Intertidal deposits at the north bank of the Shenzhen Bay suggest a periodic variation in sea level in about every 670 years over the last 6000 years with low sea levels recorded in the periods of 5500-4900, 3900-3600, 2400-2200 and 1300-1200 years ago. Between these periods the sea level rised for about 80 cm on average. The modern warming climate in the last century corresponds with a rise of sea level at the rate of 2~3 mm/a. A state key project under the Antarctic Science & Technology Program (No. 905-02-04-03) and is partially financially supported by the Natural Science Foundation of Guangdong Province.  相似文献   

Holocene Climate in the Northern Great Plains Inferred from Sediment Stratigraphy, Stable Isotopes, Carbonate Geochemistry, Diatoms, and Pollen at Moon Lake, North Dakota     

Blas L. Valero-Garcés  Kathleen R. Laird  Sherilyn C. Fritz  Kerry Kelts  Emi Ito  Eric C. Grimm 《Quaternary Research》1997,48(3):359-369

Seismic stratigraphy, sedimentary facies, pollen stratigraphy, diatom-inferred salinity, stable isotope (δ¹⁸O and δ¹³C), and chemical composition (Sr/Ca and Mg/Ca) of authigenic carbonates from Moon Lake cores provide a congruent Holocene record of effective moisture for the eastern Northern Great Plains. Between 11,700 and 9500¹⁴C yr B.P., the climate was cool and moist. A gradual decrease in effective moisture occurred between 9500 and 7100¹⁴C yr B.P. A change at about 7100¹⁴C yr B.P. inaugurated the most arid period during the Holocene. Between 7100 and 4000¹⁴C yr B.P., three arid phases occurred at 6600–6200¹⁴C yr B.P., 5400–5200¹⁴C yr B.P., and 4800–4600¹⁴C yr B.P. Effective moisture generally increased after 4000¹⁴C yr B.P., but periods of low effective moisture occurred between 2900–2800¹⁴C yr B.P. and 1200–800¹⁴C yr B.P. The data also suggest high climatic variability during the last few centuries. Despite the overall congruence, the biological (diatom), sedimentological, isotopic, and chemical proxies were occassionally out of phase. At these times the evaporative process was not the only control of lake-water chemical and isotopic composition.  相似文献   

Seasonal fluctuations in the plankton community in a hypersaline temporary lake (Honda, southern Spain)     

Pablo J. López-González  Francisco Guerrero  M. Carmen Castro 《International Journal of Salt Lake Research》1997,6(4):353-371

Honda saline lake is located in an endorheic basin in the south of Spain. The lake is very shallow, with frequent seasonal drought and a high degree of unpredictability. It was sampled monthly during a relatively dry year (1994–1995, 5 months permanence). To establish a relationship between environmental variables (temperature, depth, salinity and conductivity), variables related to biological activity (organic matter, total solids suspension, and pH) and the planktonic community in the sampled months, various uni-and miltivariate statistical methods were carried out.Dunaliella salina, D. viridis, and ciliates sp. 2 is the principal species group used to average out the dissimilarity between the samples. Muttivariate analysis showed that salinity (as TDS), conductivity and pH made major and significant contributions to the explanation of the variance in the sample data.  相似文献   

Some effects of lateral heterogeneities in the upper mantle on postglacial land uplift close to continental margins   总被引：2，自引：0，他引：2  

G. Kaufmann  P. Wu  D. Wolf 《Geophysical Journal International》1997,128(1):175-187

We investigate the effects of lateral heterogeneities in the upper mantle on the calculation of postglacial land uplift. For the model calculations we use a commercial finite-element code, which enables us to solve the equations governing a layered, isotropic. incompressible, Maxwell-viscoelastic half-space with laterally varying layer thicknesses and physical properties. Following previous investigations performed by Sabadini. Yuen & Portney (1986) and Gasperini & Sabadini (1989), we extend their results using a more realistic loading history and different earth models. We then focus our attention on the question whether lateral heterogeneities in the upper mantle can be modelled correctly using a set of homogeneous earth models. To this end, a comparison of model calculations using both laterally homogeneous and heterogeneous earth models is performed.
We find that lateral heterogeneities in the upper mantle significantly influence the calculated postglacial land uplift. The resolving power of relative sea-level observations for the prescribed lateral heterogeneities used in this study is mainly focused on observations around the load margin and outside the glaciated areas, where differences in predicted land uplift between individual models are large enough to be resolved by observations.
We can qualitatively determine lateral heterogeneities in the upper mantle using a set of laterally homogeneous earth models, if the geological structure, for example a continental margin, is known. However, in order to infer the correct values of lithospheric thickness and asthenospheric viscosity, we need to use laterally heterogeneous models.  相似文献   

Aeolian Facies Belts in the Taklimakan Desert   总被引：4，自引：0，他引：4  

Li Baosheng  Dong Guangrong  Zhang Jiasheng  Li Sen  Jin Heling  Chen Huizhong  Wen Xiangle  Wang Yao  Lanzhou Desert Research Institute  Chinese Academy of Sciences  Lamhou  Gansuand Zhu YizhiXi''an Open Laboratory of Loess  Quaternary Geology  Chinese Academy of Sciences  Xi''an  Gansu Fei Zhenbi 《《地质学报》英文版》1995,69(3)

At least at the beginning of the last glacial epoch, the facies belts of dune sand, sandy loam and loess formed by winds had existed in the Taklimakan desert and areas south of it. There were no appreciable changes in the NE and NW wind systems and their wind fqrces that deposited dune sand, sandy loam and loess in the global cold stage since the last glacial epoch (accordingly no marked shifts of the boundaries of these aeolian facies belts took place. In the global warm stage since then, the climate in the Taklimakan desert and areas south of it became warm and dry, resulting in ablation of substantial volumes of ice and snow in their surrounding mountains and thus forming alluvial and diluvial deposits in the region. The alluvial-diluvial actions, however, failed to change the general framework of aeolian facies belts.  相似文献   

Factors affecting water chemistry of alpine lakes   总被引：2，自引：0，他引：2  

A. Marchetto  R. Mosello  R. Psenner  G. Bendetta  A. Boggero  D. Tait  G. A. Tartari 《Aquatic Sciences - Research Across Boundaries》1995,57(1):81-89

During a four-year study (1988–1991), 413 lakes in the Central Alps (Italy, Switzerland and Austria) were investigated to quantify their acidification. The ionic content of the lakes was generally low: 68% of them had alkalinity values of less than 200 µeq 1^–1 and were regarded as sensitive to acidification. Moreover, 36% of the lakes showed alkalinity values of less than 50 µeq 1^–1. Redundancy Analysis was used to relate the hydrochemistry of 187 lakes to their catchment characteristics. Calcite weathering was the main factor influencing lake chemistry. The same analysis, applied to a subset of 101 lakes lying in watersheds exclusively composed of silicic rocks, showed that lake chemistry was influenced by silicate weathering and nitrogen uptake. These processes were found to be mainly related to lake altitude and the fraction of the watershed not covered by vegetation, i.e. controlled by temperature. The importance of these relations to explain the pH shift produced by climatic variation is also discussed.  相似文献   

Mega-scale glacial lineations and cross-cutting ice-flow landforms     

Chris D. Clark 《地球表面变化过程与地形》1993,18(1):1-29

Landsat images reveal a previously unsuspected large-scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow. Such a glacial grain can be regarded as a landform assemblage comprised of a number of components. Drumlins and megaflutes form part of the pattern, but in addition there are two previously undocumented ice-moulded landform elements: streamlined lineations of much greater proportions, referred to as mega-scale glacial lineations, and a distinctive cross-cutting topology within the grain. The ice-moulded landform assemblage is described and illustrated with reference to examples from Canada. Possible modes of genesis of such landforms are discussed and their glaciological implications outlined. The discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment, and demands a radical re-interpretation of ice sheet dynamics.  相似文献   

天山冰川资源及其分布规律     

韩添丁  刘潮海 《干旱区地理》1993,16(4):11-18

本文从天山冰川数量，冰储量、类型以及分布特征等方面系统地分析了天山冰川的资源及其分布规律，为经济建设提供可靠的山地水资源论据。  相似文献   

天山独库公路北段泥石流形成的水文气象条件   总被引：5，自引：0，他引：5  

朱宁森 《干旱区地理》1993,16(4):45-50

分析了新疆独库公路泥石流的形成特点及其水文气象条件，得出周期性气候背景是泥石流形成的有利条件，气温连续升高或高强度暴雨则是泥石流发生的关键。  相似文献   

Glacial rebound of the British Isles—II. A high-resolution, high-precision model     

Kurt Lambeck 《Geophysical Journal International》1993,115(3):960-990

Observations of ice movements across the British Isles and of sea-level changes around the shorelines during Late Devensian time (after about 25 000 yr BP) have been used to establish a high spatial and temporal resolution model for the rebound of Great Britain and associated sea-level change. The sea-level observations include sites within the margins of the former ice sheet as well as observations outside the glaciated regions such that it has been possible to separate unknown earth model parameters from some ice-sheet model parameters in the inversion of the glacio-hydro-isostatic equations. The mantle viscosity profile is approximated by a number of radially symmetric layers representing the lithosphere, the upper mantle as two layers from the base of the lithosphere to the phase transition boundary at 400 km, the transition zone down to 670 km depth, and the lower mantle. No evidence is found to support a strong layering in viscosity above 670 km other than the high-viscosity lithospheric layer. Models with a low-viscosity zone in the upper mantle or models with a marked higher viscosity in the transition zone are less satisfactory than models in which the viscosity is constant from the base of the lithosphere to the 670 km boundary. In contrast, a marked increase in viscosity is required across this latter boundary. The optimum effective parameters for the mantle beneath Great Britain are: a lithospheric thickness of about 65 km, a mantle viscosity above 670 km of about (4-5) 10²⁰ Pa s, and a viscosity below 670 km greater than 4 × 10²¹ Pa s.  相似文献