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61.
Heterogeneity in supraglacial debris thickness and its role in glacier mass changes of the Mount Gongga 总被引:3,自引:0,他引:3
In the Tibetan Plateau, many glaciers have extensive covers of supraglacial debris in their ablation zones, which affects glacier response to climate change by altering ice melting and spatial patterns of mass loss. Insufficient debris thickness data make it difficult to analyze regional debris-cover effects. Maritime glaciers of the Mount Gongga have been characterized by a substantial reduction in glacier area and ice mass in recent decades. The thermal property of the debris layer estimated from remotely sensed data reveals that debris-covered glaciers are dominant in this region, on which the proportion of debris cover to total glacier area varies from 1.74% to 53.0%. Using a physically-based debris-cover effect assessment model, we found that although the presence of supraglacial debris has a significant insulating effect on heavily debris-covered glaciers, it accelerates ice melting on ~10.2% of total ablation zone and produces rapid wastage of ~25% of the debris-covered glaciers, leading to the similar mass losses between the debris-covered and debris-free glaciers. Widespread debris cover also facilitates the development of active terminus regions. Regional differences in debris-cover effects are apparent, highlighting the importance of debris cover for understanding glacier mass changes in the Tibetan Plateau and other mountain ranges around the world. 相似文献
62.
Recent research has showed increasing interest at the vital role of irrigation ponds that plays at biodiversity conservation, and provides ecological functions at a wide range. However, many irrigation ponds were abolished due to the economic and societal transformation in the rural. In particular, small-scale ponds were abolished and rebuilt to other public uses based on the consensus building process among the community. At the same time, civil organizations also launched initiatives to conserve irrigation ponds for its ecological significance or landscape scenery. However, study pertinent to the small scale ponds in the rural setting is largely neglected. This research aims at revealing the current situation of the utilization and management of small irrigation ponds using a case study of Noto Island in Ishikawa Prefecture. It was found that irrigation ponds are still under the traditional co-management of rural community. The most important finding in this study is that the traditional management of pond water use largely contributes to mitigate the harvest loss from natural disasters such as drought in the face of extreme climate. However, irrigation ponds are facing the threat of degradation due to the sharp decrease of farm population and the existing large number of part time farmers. Therefore, the small scale irrigation ponds and pertinent management and water use allotment should be revalued for its functions at a wide range from the biological and ecological functions and human knowledge system to mitigate disaster threats. 相似文献
63.
Hidetoshi HARA Koji WAKITA Jun-ichiro KURODA Toshiyuki KURIHARA Katsumi UENO Yoshihito KAMATA Ken-ichiro HISADA Punya CHARUSIRI Thasinee CHAROENTITIRAT Pol CHAODUMRONG 《地球学报》2009,30(Z1):12-12
The Paleo-Tethys formed a large ocean basin that existed between Laurasia and Gondwana during Late Paleozoic to Early Mesozoic times. It opened in the Early Devonian by the rifting of Gondwanaland and closed at around latest Triassic time by the collision of the Cimmerian continent to Laurasia (Metcalfe, 1999). We reconstructed opening and closing process of the Paleo-Tethys in Northern Thailand. 相似文献
64.
Koji Shichi Hikaru Takahara Sergey K. Krivonogov Elena V. Bezrukova Kenji Kashiwaya Akihide Takehara Toshio Nakamura 《Quaternary International》2009,205(1-2):98
Climatically driven Late Pleistocene and Holocene vegetation changes were reconstructed based on pollen records from the sediments of Lake Kotokel and Cheremushka Bog, located on the eastern shore of Lake Baikal. The described paleoenvironmental record has higher resolution than records collected from Lake Baikal and unites individual events identified in prior studies of bottom and onshore cores. Remarkable shifts in landscapes and expansions of index plants are as follows. Forest tundra and/or forest steppe landscape with birch, spruce, Artemisia, and Poaceae prevailed at ca. 50–25 14C kyr BP. Tundra and/or steppe vegetation dominated by Artemisia and Poaceae was typical for the Last Glacial Maximum. The expansion of shrub birch and willow occurred at ca. 15.5 14C kyr BP. Two peaks of spruce expansion at ca. 47.5–42.4 14C kyr BP (Karginian time) and at ca. 14.5–13 ka (Bølling-Allerød warm intervals) suggest that the condition were more humid than today. A slight increase in Artemisia at ca. 11–10.5 14C kyr BP (13–12 ka) was indicative of the Younger Dryas event. An expansion of birch forests with fir at ca. 12–6.4 ka suggests higher humidity. The currently dominant Scots and Siberian pine forests with birch expanded since 6.4 ka. 相似文献
65.
Role of Acoustic Emission for Solving Rock Engineering Problems in Indonesian Underground Mining 总被引:2,自引:0,他引:2
Suseno Kramadibrata Ganda Marihot Simangunsong Kikuo Matsui Hideki Shimada 《Rock Mechanics and Rock Engineering》2011,44(3):281-289
In situ stress measurement is not well accepted yet in Indonesia due to the unavailability of technology, high costs and because
it is impractical in remote regions. Alternatively, the Kaiser effect of acoustic emission (AE) can be used as a method for
determining the stress-state at depth, without creating induced stress and is practical in remote areas. This paper is focused
on the development of the AE test. The research has started to study the phenomenon of stress memory in a rock sample, the
factors influencing the phenomenon, and finally, to determine the in situ stresses around underground excavations by applying
the AE method. It is expected that knowledge in gaining the most important input parameters for maintaining the stability
of underground excavations can be well understood and be reliably conducted at a reasonable cost. 相似文献
66.
Robert S. Pickart Michael A. Spall G.W.K. Moore Thomas J. Weingartner Rebecca A. Woodgate Knut Aagaard Koji Shimada 《Progress in Oceanography》2011,88(1-4):78-100
The spin up and relaxation of an autumn upwelling event on the Beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models. The event occurred in November 2002 and was driven by an Aleutian low storm. The wind field was strongly influenced by the pack-ice distribution, resulting in enhanced winds over the open water of the Chukchi Sea. Flow distortion due to the Brooks mountain range was also evident. Mooring observations east of Barrow Canyon show that the Beaufort shelfbreak jet reversed to the west under strong easterly winds, followed by upwelling of Atlantic Water onto the shelf. After the winds subsided a deep eastward jet of Atlantic Water developed, centered at 250 m depth. An idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm. The disparity in wave speeds between the sea surface height signal—traveling at the fast barotropic shelf wave speed—versus the interior density signal—traveling at the slow baroclinic wave speed—leads to the deep eastward jet. The broad-scale response to the storm over the Chukchi Sea is investigated using a regional numerical model. The strong gradient in windspeed at the ice edge results in convergence of the offshore Ekman transport, leading to the establishment of an anti-cyclonic gyre in the northern Chukchi Sea. Accordingly, the Chukchi shelfbreak jet accelerates to the east into the wind during the storm, and no upwelling occurs west of Barrow Canyon. Hence the storm response is fundamentally different on the Beaufort slope (upwelling) versus the Chukchi slope (no upwelling). The regional numerical model results are supported by additional mooring data in the Chukchi Sea. 相似文献
67.
Makoto Kagabu Jun Shimada Robert Delinom Maki Tsujimura Makoto Taniguchi 《Journal of Asian Earth Sciences》2011,40(1):226-239
In the Jakarta area (Indonesia), excessive groundwater pumping due to the rapidly increasing population has caused groundwater-related problems such as brackish water contamination in coastal areas and land subsidence. In this study, we adopted multiple hydrogeochemical techniques to demonstrate the groundwater flow system in the Jakarta area. Although almost all groundwater existing in the Jakarta basin is recharged at similar elevations, the water quality and residence time demonstrates a clear difference between the shallow and deep aquifers. Due to the rapid decrease in the groundwater potential in urban areas, we found that the seawater intrusion and the shallow and deep groundwaters are mixing, a conclusion confirmed by major ions, Br?:Cl? ratios, and chlorofluorocarbon (CFC)-12 analysis. Spring water and groundwater samples collected from the southern mountainside area show younger age characteristics with high concentrations of 14C and Ca–HCO3 type water chemistry. We estimated the residence times of these groundwaters within 45 years under piston flow conditions by tritium analysis. Also, these groundwater ages can be limited to 20–30 years with piston flow evaluated by CFCs. Moreover, due to the magnitude of the CFC-12 concentration, we can use a pseudo age indicator in this field study, because we found a positive correlation between the major type of water chemistry and the CFC-12 concentration. 相似文献
68.
Study on the selection of unsaturated flow model for the different types of soil and soft rock 总被引:1,自引:1,他引:0
Sajeewani Rajika Amarasinghe Kunio Watanabe Koji Ishiyama 《Environmental Earth Sciences》2011,64(7):1795-1805
Precise estimation of unsaturated hydraulic properties of porous media is indispensable in various study areas, such as analyzing
the moisture flow, the drying process occurring from the surface, and the pollutant migration beneath the ground surface.
Although many empirical/theoretical models describing the unsaturated hydraulic properties have been proposed by several previous
researchers, the best model for the different types of soil/rock may not be identical. Thus, the model selection process and
the estimation technique of the parameters included in the models should be developed. In the present study, the inverse technique
based on the transient evaporation change was investigated to select the model and estimate the model parameters. The experimental
work was based on a relatively low permeable soft rock and a relatively high permeable sandy soil (Toyoura standard sand).
Experimental equipment was developed to precisely measure the evaporation rate for the high permeable sandy soil. The Genetic
Algorithm (GA) was adopted in the inverse technique as an optimization tool. In order to simplify the problem, only the drying
process from the saturated condition was considered. It was established that the information concerning the transient evaporation
change could be used for the model selection and parameter estimation. Further, the saturation distribution could be used
for the selection of the models. The present study provides important information for the development of the model selection
process. 相似文献
69.
Ratan K. Majumder M. A. Halim B. B. Saha Reo Ikawa Toshio Nakamura Makoto Kagabu Jun Shimada 《Environmental Earth Sciences》2011,64(5):1343-1352
A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers,
Bangladesh using environmental isotope (2H, 18O, 13C, 3H, and 14C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ2H = 7.7 δ18O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ18O and δ2H). The δ18O and δ2H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling
evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the
shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU,
which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of 14C activity is associated with the heavier δ13C values, which indicates the presence of geochemical reactions affecting the 14C concentration along the groundwater flow system. Both vertical and lateral decrease of 14C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which
discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the
Bengal Delta aquifers, Bangladesh. 相似文献
70.
Koji Sugie Kenshi Kuma Satoshi Fujita Satomi Ushizaka Koji Suzuki Tsutomu Ikeda 《Journal of Oceanography》2011,67(2):183-196
We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal
centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates
and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore
desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4–4.2 cell divisions
with 1.2–2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies
were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from
high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions
could often occur in surface waters of the Oyashio region from spring to summer. 相似文献