Horizontal distribution of particulate matter and its characterization using phosphorus as an indicator in surface coastal water,Harima-Nada,the Seto Inland Sea,Japan     

Toshimasa Asahi  Kazuhiko Ichimi  Hitomi Yamaguchi  Kuninao Tada 《Journal of Oceanography》2014,70(3):277-287

To study the horizontal distribution and characterization of suspended particulate matter (SPM) in the coastal environment, the distribution and seasonal variation of particulate phosphorus (PP), divided as organic (POP) and inorganic (PIP) fractions with POC, PON, and Chl.a, in 4 seasons throughout Harima-Nada of the Seto Inland Sea, Japan, were investigated. A high concentration of PIP was observed not only in the northern coastal area, which received much freshwater discharge, but also in the channel parts. In winter, when Δσt was low, the difference between surface and bottom σt, resuspension of sinking particles or/and surface sediment which has a high PIP/PP ratio seems to have occurred, and then a high concentration of PIP in surface water was observed. In spring and summer, PIP/PP ratios (0.24) of surface waters were close to those of phytoplankton (0.1–0.2). On the other hand, PIP/PP ratios in autumn and winter, when Δσt was low, were similar to those of surface sediment in Harima-Nada (0.32–0.39). SPM in Harima-Nada showed higher PP contents than other coastal environments, and its mean value of 9.10 mg P/g was close to the phytoplankton P content of 9.75 mg P/g. This suggests that SPM in Harima-Nada was strongly affected by phytoplankton. The C/N ratio in Harima-Nada in spring was high (11), although high Chl.a and low PIP/PP were observed, possibly resulting from preferential decomposition of nitrogen in comparison with carbon. We consider that the PIP/PP ratio is a good indicator to characterize SPM and to predict its origin as well as the C/N.  相似文献   

Total organic carbon and nitrogen contents in surface sediments of Harima Nada,eastern Seto Inland Sea,Japan: a comparison under two different trophic states     

Hitomi Yamaguchi  Naoto Hirade  Miho Kayama  Kazuhiko Ichimi  Kuninao Tada 《Journal of Oceanography》2014,70(4):355-366

Phytoplankton abundance in the surface waters of Harima Nada, eastern Seto Inland Sea of Japan, decreased after around the late 1970s following a reduction of terrestrial phosphorous inputs, and relatively low levels persisted thereafter. This symptom of de-eutrophication in recent decades might have reduced organic matter storage in surficial sediments. To test this possibility, we examined total organic carbon (TOC) and nitrogen (TN) contents of Harima Nada sediments in 2011, and compared the results to past data from more eutrophic states. In 2011, the TOC and TN varied horizontally within the basin, in relation to physicochemical properties (water and mud content) and phytoplankton remnants (pheo-pigments) of the sediments. These horizontal patterns were fundamentally similar to those of the early 1980s (1982–1983), although discrepancies between the periods were observed in some areas. Differences of mean TOC and TN in the 0–2 cm layer at 63 stations from 1982–1983 to 2011 were consequently <10 %. Hence, the recent de-eutrophication in Harima Nada was associated with little overall change of TOC and TN storage in the sediment. In Harima Nada, changes in water clarity and particle size composition of the sediment seem to have occurred during recent decades. The aforementioned paradoxical phenomenon may therefore be explained by factors that are affected by these environmental changes. Such factors include the ratio of export flux to the seafloor to phytoplankton production, phytoplankton biomass and production in the entire euphotic zone, and accumulation rate of surface sediment.  相似文献   

Atoll island vulnerability to flooding and inundation revealed by historical reconstruction: Fongafale Islet, Funafuti Atoll, Tuvalu   总被引：1，自引：1，他引：0  

Hiroya Yamano  Hajime Kayanne  Toru Yamaguchi  Yuji Kuwahara  Hiromune Yokoki  Hiroto Shimazaki  Masashi Chikamori   《Global and Planetary Change》2007,57(3-4):407-416

The reef islands formed on coral atolls are generally small, low, and flat, with elevations of only a few meters. These islands are thus highly vulnerable to elevated sea levels caused by extreme events and global warming. Such vulnerability was recently evidenced at Fongafale Islet, the capital of Tuvalu, when it flooded during accelerated spring high tides possibly related to sea level rise caused by global warming. Many factors, not only environmental but also economic and social, determine the vulnerability of an island to sea level rise. In this study, we used data spanning 108 yrs to reconstruct changes in topography, land use/cover, population, and the distribution of buildings at Fongafale Islet. The results indicate that the vulnerability of Fongafale Islet relates to its original landform characteristics: the central part of the island was formerly dominated by swampland that flooded at high tides. Fongafale Islet experienced greater population in-migration and centralization beginning in the 1970s following the independence of Tuvalu and Kiribati. Migrants were also responding to declines in overseas mining operations and limited options for paid employment. As the population increased, construction took place in vulnerable swampland areas. Our results clearly demonstrate that examinations of global environmental issues should focus on characteristics specific to the region of interest. These characteristics should be specified using historical reconstruction to understand and address the vulnerability of an area to global environmental changes.  相似文献   

Estimation of snow ablation under a dust layer covering a wide range of albedo     

Sunil Adhikary  Yasushi Yamaguchi  Katsuro Ogawa 《水文研究》2002,16(14):2853-2865

Ablation processes of snow under a thin dust cover are complicated compared with those under a thick cover, mainly owing to the effects of aggregation (redistribution) of dust particles on the conditions of surface melting. Aggregation of dust particles causes the snow surface to brighten after the initial dust configuration, thus affecting the relationship between initial dust concentration and surface albedo. In order to estimate snow ablation rate under a thin dust cover, we used a composite energy balance model in which the surface albedo is taken as a measured input variable. The estimated results of snow ablation agreed reasonably well with the observation, considering the measurement errors inherited in the snow depressions. Comparison of the two cases, that is, one considering the aggregation of dust particles (observation: albedo variable) and the other without aggregation (assumption: albedo constant), showed that the ablation rates were noticeably lower on the former case. This suggests that the aggregation of dust particles induces a reduction of snow ablation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Textural variations and impact history of the Millbillillie eucrite     

Akira Yamaguchi  Hiroshi Takeda  Donald D. Bogard  Daniel Garrison 《Meteoritics & planetary science》1994,29(2):237-245

Abstract— We have investigated 10 new specimens of the Millbillillie eucrite to study its textures and mineral compositions by electron probe microanalyser and scanning electron microscope. Although originally described as having fine-grained texture, the new specimens show diversity of texture. The compositions (Mg/Fe ratios) of the host pigeonites and augite lamellae are homogeneous, respectively, in spite of the textural variation. In addition to their chemical homogeneity, pyroxenes in coarse and fine-grained clasts are partly inverted to orthopyroxene. Chemical zoning of plagioclase during crystal growth is preserved. This eucrite includes areas of granulitic breccias and impact melts. Large scale textures show a subparallel layering suggesting incomplete mixing and deposition of impact melt and lithic fragments. An ³⁹Ar-⁴⁰Ar age determination for a coarse-grained clast indicates a strong degassing event at 3.55 ± 0.02 Ga. We conclude that Millbillillie is among the most equilibrated eucrites produced by thermal annealing after impact brecciation. According to the classification of impact breccias, Millbillillie can be classified as a mixture of granulitic breccias and impact melts. The last significant thermal event is characterized by network-like glassy veins that run through clasts and matrices. Consideration of textural observations and requirements for Ar-degassing suggests that the ³⁹Ar-⁴⁰Ar age could in principle date either the earilier brecciation and annealing event or the event which produced the veins.  相似文献   

Effects of topography on the spatial distribution of evapotranspiration over a complex terrain using two‐source energy balance model with ASTER data     

H. K. Kafle  Y. Yamaguchi 《水文研究》2009,23(16):2295-2306

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Petrology and geochemistry of Northwest Africa 5480 diogenite and evidence for a basin‐forming event on Vesta          下载免费PDF全文

A. Yamaguchi  J. A. Barrat  N. Shirai  M. Ebihara 《Meteoritics & planetary science》2015,50(7):1260-1270

We performed a petrological and geochemical study of an olivine diogenite, Northwest Africa (NWA) 5480. NWA 5480 is a crystalline stone, but shows a heterogeneous texture. Olivine aggregates and grains of olivine and chromite display resorption textures set in a crystalline pyroxene matrix. Large olivine aggregates are penetrated by pyroxene matrix. Flow textures are observed near olivine aggregates. Olivine, chromite, and pyroxene show minor chemical zoning, implying relatively rapid cooling. NWA 5480 contains a significant amount of platinum group elements with chondritic relative proportions. All this evidence supports that NWA 5480 is an impact‐melt breccia from a target composed of olivine and pyroxene‐rich lithologies. Such impact melt would have formed by melting crustal materials, possibly during one of the impacts that formed the South Pole basins on Vesta.  相似文献   

CDM potential in the power-generation and energy-intensive industries of China     

Mitsutsune Yamaguchi 《Climate Policy》2013,13(2):167-184

Reducing emissions from deforestation and forest degradation (REDD+) has emerged as an important carbon governance mechanism. However, forest governance is weak in most REDD+ countries, which undermines efforts to establish REDD+. This study analyses the factors that enable national REDD+ processes in the context of weak governance using a two-step ‘qualitative comparative analysis’ (QCA) of 12 REDD+ countries. Assuming that actor-related factors can be effective only if certain institutional preconditions are met, six factors were divided into two categories that were analysed separately: institutional setting (pressure from forest-resource shortage; forest legislation, policy, and governance; already initiated policy change) and the policy arena (national ownership; transformational coalitions; inclusiveness of the policy process). The factors were analysed to determine their role in efforts to establish comprehensive REDD+ policies that target transformational change. The results reveal path dependencies and institutional stickiness in all the study countries. Only countries already undertaking institutional change have been able to establish REDD+ policies in a relatively short period – but only in the presence of either high pressure from forest-resource shortages or key features of effective forest legislation, policy, and governance. Furthermore, where an enabling institutional setting is in place, the policy arena conditions of national ownership and transformational coalitions are crucial.Policy relevance Although the aim of REDD+ is to provide performance-based payments for emissions reductions, the outcomes in terms of actual emission reductions or co-benefits are not yet observable. Most REDD+ countries are still at the design and implementation stage for policies and measures. Indicators and criteria to measure progress in this phase are required to identify which factors enable or hinder countries' performance in delivering necessary policy change to provide targeted financial incentives to support countries' efforts. This study analyses the factors that shape national REDD+ processes in the context of weak governance using a two-step QCA of 12 REDD+ countries. The results show a set of enabling conditions and characteristics of the policy process under which REDD+ policies can be established. These findings may help guide other countries seeking to formulate REDD+ policies that are likely to deliver efficient, effective, and equitable outcomes.  相似文献   

An anomalous eucrite,Dhofar 007, and a possible genetic relationship with mesosiderites     

Akira Yamaguchi  Takehiko Setoyanagi  Mitsuru Ebihara 《Meteoritics & planetary science》2006,41(6):863-874

Abstract— We studied the texture, mineralogy, and bulk chemical composition of Dhofar 007, a basaltic achondrite. Dhofar 007 is a polymict breccia that is mostly composed of coarse‐grained granular (CG) clasts with a minor amount of xenolithic components, such as a fragment of Mg‐rich pyroxene. The coarse‐grained, relict gabbroic texture, mineral chemistry, and bulk chemical data of the coarse‐grained clast indicate that the CG clasts were originally a cumulate rock crystallized in a crust of the parent body. However, in contrast to monomict eucrites, the siderophile elements are highly enriched and could have been introduced by impact events. Dhofar 007 appears to have experienced a two‐stage postcrystallization thermal history: rapid cooling at high temperatures and slow cooling at lower temperatures. The presence of pigeonite with closely spaced, fine augite lamellae suggests that this rock was cooled rapidly from higher temperatures (>0.5 °C/yr at ˜1000 °C) than typical cumulate eucrites. However, the presence of the cloudy zone in taenite and the Ni profile across the kamacite‐taenite boundaries indicates that the cooling rate was very slow at lower temperatures (˜1–10 °C/Myr at <600–700 °C). The slow cooling rate is comparable to those in mesosiderites and pallasites. The two‐stage thermal history and the relative abundance of siderophile elements similar to those for metallic portions in mesosiderites suggest that Dhofar 007 is a large inclusion of mesosiderite. However, we cannot rule out a possibility that Dhofar 007 is an anomalous eucrite.  相似文献   

Application of fiber optics for deep-sea exploration systems     

Yamaguchi  M. 《Oceanic Engineering, IEEE Journal of》1990,15(3):238-243

Optical fibers, optical transmission systems, and optical Accessories to apply fiber optics to deep-sea exploration systems are described. The discussion of fibers cover the construction of the fiber and cable and the useful life of optical fibers. Considerations in designing a system (number of fibers and multiplexing method) are discussed. Accessories such as optical feedthroughs, optical connectors, and optical rotary connectors are examined. A composite fiber-optic/coaxial cable system successfully operated for one year is described  相似文献