排序方式： 共有30条查询结果，搜索用时 15 毫秒
11.
Genki I. Matsumoto Yukinori Tani Koji Seto Tomoko Tazawa Masumi Yamamuro Takahiro Watanabe Toshio Nakamura Tetsuo Takemura Satoshi Imura Hiroshi Kanda 《Journal of Paleolimnology》2010,44(2):677-693
Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological
changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica
inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen,
and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm)
overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca.
7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year.
Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine
environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought
about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced
changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine
period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms.
During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the
lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom
of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared
to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface,
ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher
than during the coastal marine period. 相似文献
12.
Environmental impacts of urban growth from an integrated dynamic perspective: A case study of Shenzhen, South China 总被引：5，自引：0，他引：5
China is home to one-fifth of the world's population and that population is increasingly urban. The landscape is also urbanizing. Although there are studies that focus on specific elements of urban growth, there is very little empirical work that incorporates feedbacks and linkages to assess the interactions between the dynamics of urban growth and their environmental impacts. In this study, we develop a system dynamics simulation model of the drivers and environmental impacts of urban growth, using Shenzhen, South China, as a case study. We identify three phases of urban growth and develop scenarios to evaluate the impact of urban growth on several environmental indicators: land use, air quality, and demand for water and energy. The results show that all developable land will be urban by 2020 and the increase in the number of vehicles will be a major source of air pollution. Demand for water and electricity will rise, and the city will become increasingly vulnerable to shortages of either. The scenarios also show that there will be improvements in local environmental quality as a result of increasing affluence and economic growth. However, the environmental impacts outside of Shenzhen may increase as demands for natural resources increase and Shenzhen pushes its manufacturing industries out of the municipality. The findings may also portend to changes other cities in China and elsewhere in the developing world may experience as they continue to industrialize. 相似文献
13.
Eiji Ohtani Hisayoshi Yurimoto Shuji Seto 《Physics of the Earth and Planetary Interiors》1997,100(1-4):97-114
We determined the partition coefficients of 19 elements between metallic liquid and silicate liquid at 20 GPa and 2500°C, and between metallic liquid and silicate perovskite at 27 GPa and 2200°C. Remarkable differences were observed in the partitioning behaviors of Si, P, W, Re, and Pb among the silicate liquid, perovskite, and magnesiowüstite coexisting with metallic liquid, reflecting incompatibility of the elements in the silicate or oxide phase. We could not observe any significant difference in the partitioning behaviors of V, Cr, Mn, Co, Ni, and Cu among the phases coexisting with metallic liquid.
Comparison of the present partitioning data with those obtained previously at lower pressure and temperature suggests that the exchange partition coefficients, Kmet/sil, of Co, Ni, Mo, and W decrease, whereas those of V, Cr, and Mn increase and tend to approach unity with increasing pressure and temperature. We also made preliminary experiments to clarify the effect of sulfur on the partitioning behaviors. Sulfur lowers the exchange partition coefficients, Kmet/sil, of Mo and W between metallic liquid and silicate liquid significantly at 20 GPa and 2300°C.
The mantle abundances of Co, Ni, Cu, Mo, and W calculated for the metal-silicate equilibrium model are lower than those of the real mantle, whereas P, K, and Mn are overabundant in the calculated mantle. The discrepancies in the abundances of Co and Ni could be explained by the chemical equilibrium at higher pressure and temperature. Large discrepancies in Mo and W between the calculated and real mantles could be accounted for by the effect of sulfur combined with the effects of pressure and temperature on the chemical equilibrium. The mantle abundances of P, K, and Cu could be accounted for by volatile loss in the nebula, perhaps before accretion of the Earth, combined with the chemical equilibrium at higher pressure and temperature. Thus the observed mantle abundances of P, K, Co, Ni, Cu, Mo, and W may be consistent with a model of sulfur-bearing metal-silicate equilibrium in lower-mantle conditions. 相似文献
14.
Hiroyuki Takata Satoshi Tanaka Koji Seto Saburo Sakai Katsumi Takayasu Boo-Keun Khim 《Journal of Paleolimnology》2014,51(3):421-435
We investigated responses of shallow-water benthic foraminifera to changes in climate and ocean conditions, using sediment core ASC2 from Aso-kai lagoon, central Japan. Six AMS 14C dates reveal that the studied interval corresponds to sediments deposited from ~AD 700 to 1600. Sulfur content of the bulk sediment and multi-dimensional scaling (MDS) axis 1 of fossil benthic foraminifera indicate that the composition of the benthic foraminifera community was closely related to dissolved oxygen (DO) concentration in the hypolimnion. The sulfur content and MDS axis 1 also revealed two shifts over the 900-year interval. In the first phase (~AD 700–1250), the Shannon–Wiener Index (H′), E (S200), evenness and rank abundance curve (RAC) kurtosis indicate a gradual deterioration in structure of the benthic foraminifera community. In that period, there are statistically significant correlations between the faunal composition (MDS axis 1) and faunal structure [Shannon–Wiener (H′), E (S200), evenness and RAC kurtosis]. In the second phase (~AD 1250–1600), however, faunal composition and structure show no marked correspondence. Instead, abundance of benthic foraminifera fluctuated on a scale of ~200 years. Thus, a shift in the biotic response of benthic foraminifera in Aso-kai lagoon occurred in ca. AD 1250. Gradual deterioration of benthic foraminifera, with taxonomic losses, is consistent with declining DO in the first phase, possibly associated with the increasing influence of the Tsushima Warm Current. The possibility that closure of Aso-kai lagoon and development of the sand bar affected benthic foraminifera cannot, however, be ruled out. No corresponding response was observed in the second phase, during which there was no distinct taxonomic loss. Large variations in abundance, however, were a consequence of strength of the East Asian summer and winter monsoons. The shift in the biotic response of benthic foraminifera in Aso-kai lagoon during the period AD 700–1600 was apparently a result of changes in climate and ocean conditions on the East Asian continental margin. 相似文献
15.
Exploring the dynamics of migration to mega-delta cities in Asia and Africa: Contemporary drivers and future scenarios 总被引：1，自引：0，他引：1
This paper uses a content analysis of the published literature to take stock of current understanding of key social and policy drivers of migration to cities in 11 Asian and African mega-deltas and identifies commonalities and differences among them. The analysis shows that migration to urban centers in mega-deltas is an outcome of many forces: economic policies and incentives, local and destination institutions, government policies to develop small towns, and the geographic concentration of investments. Massive influx of capital to many deltas has transformed the local economic base from a primarily agricultural one to a manufacturing and processing economy. This has created uneven spatial economic development which is the underlying driver of migration to cities in the mega-deltas regardless of geographic context or size. Going forward to 2060, one critical challenge for all the deltas is to increase the labor skill of their workforce and foster technology innovation. Continued economic growth in these regions will require substantial investments in education and capacity building and the ability of urban centers to absorb the migrant labor pool. 相似文献
16.
Temporal trends in wet deposition of major ions were explored at nationwide remote sites in Japan from April 1991 to March 2009 by using the seasonal Kendall slope estimator and the nonparametric seasonal Kendall test. For the trend analysis, datasets from eight remote sites (Rishiri, Echizenmisaki, Oki, Ogasawara, Shionomisaki, Goto, Yakushima, and Amami) were selected from the Japanese Acid Deposition Survey (JADS) conducted by the Ministry of the Environment. Deposition of H+ has been increasing at remote sites in Japan on a national scale. Significant (p????0.05) increases in H+ deposition were detected with changes of +3?C+9?%?year?1 at seven sites, while insignificant increases were observed at one site. Depositions of non-sea salt (nss)-SO 4 2? and NO 3 ? significantly increased at four and six sites, respectively, with changes of +1?C+3?%?year?1. Significant increases in precipitation at four sites would have contributed to the increase in depositions of H+, nss-SO 4 2? , and NO 3 ? . The emission trends of SO2 and NOx did not corresponded to the deposition trends of nss-SO 4 2? and NO 3 ? . The different trends indicated that temporal variation of precipitation amount trend dominated the deposition trends. 相似文献
17.
Microfracturing of rock is a complicated damage evolution process. Inaccurate prediction of micro-fracturing behaviours suggests a need for the development of a better modelling method. Analysis of acoustic emission (AE) measurements in double-torsion tests indicates that micro-fracturing behaviours during the loading stage have fractal time structures. This fractal behaviour can be described by C(t) ∝ tD, where D is the correlation exponent, t is the time and C(t) is the correlation integral. Furthermore, by utilizing measured AE data, a new method has been developed to model the AE behaviours of micro-fracturing in rock, in air, and following soaking in water and in a chemical solution of DTAB. The neutral models NN (10,21,2) and NN (10,20,2) were found to describe reasonably well the AE behaviours of micro-fracturing in rock under air and DTAB conditions, and water conditions, respectively. The cumulative AE events and the cumulative AE counts predicted by the neural models agreed well with those measured in experiments. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
18.
Veena Srinivasan Karen C. Seto Ruth Emerson Steven M. Gorelick 《Global Environmental Change》2013,23(1):229-239
While there is consensus that urbanization is one of the major trends of the 21st century in developing countries, there is debate as to whether urbanization will increase or decrease vulnerability to droughts. Here we examine the relationship between urbanization and water vulnerability for a fast-growing city, Chennai, India, using a coupled human–environment systems (CHES) modeling approach. Although the link between urbanization and water vulnerability is highly site-specific, our results show some generalizable factors exist. First, the urban transformation of the water system is decentralized as irrigation wells are converted to domestic wells by private individuals, and not by the municipal authority. Second, urban vulnerability to water shortages depends on a combination of several factors: the formal water infrastructure, the rate and spatial pattern of land use change, adaptation by households and the characteristics of the ground and surface water system. Third, vulnerability is dynamic, spatially variable and scale dependent. Even as household investments in private wells make individual households less vulnerable, over time and cumulatively, they make the entire region more vulnerable. Taken together, the results suggest that in order to reduce vulnerability to water shortages, there is a need for new forms of urban governance and planning institutions that are capable of managing both centralized actions by utilities and decentralized actions by millions of households. 相似文献
19.
On the basis of a key model of the appearance of hematite and goethite in some Chinese and European loess successions, paleosols generally contain higher proportions of hematite formed by pedogenic processes during warm and humid interglacials, while loess contains sedimentary goethite deposited during colder, glacial periods. Rock magnetic measurements were conducted on samples from Paks (Hungary) loess, revealing an anomalous case. Sediments were found to contain higher amounts of hematite and/or goethite, while the well‐developed paleosols were found to be lacking in hematite but had significant amounts of magnetite and maghemite. This observation demonstrates that the character of pedogenic magnetic mineral alteration and neoformation differs from the hematite/goethite model; the model is therefore not applicable to the Paks succession, possibly due to differences in the regional paleoclimate and pedogenic environment. The results indicate the existence of a further model, in which hematite formation is not significant in the course of pedogenesis. 相似文献
20.