Sources of plutonium to the tropical Northwest Pacific Ocean (1943-1999) identified using a natural coral archive     

Patric Lindahl  Ryuji Asami  Paul Worsfold  Min-Seok Choi 《Geochimica et cosmochimica acta》2011,75(5):1346-1356

The Pu isotopes, ²³⁹Pu and ²⁴⁰Pu, were determined in annually-banded skeletons of an accurately dated (1943-1999) modern coral (Porites lobata) from Guam Island to identify historical Pu sources to the tropical Northwest Pacific Ocean. Activity concentrations of ^239+240Pu and ²⁴⁰Pu/²³⁹Pu atom ratios were determined in the dated coral bands using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands and global fallout were identified as the two main sources. The Guam site was dominated by PPG close-in fallout in the 1950s, with an average ²⁴⁰Pu/²³⁹Pu atom ratio of 0.315 ± 0.005. In addition, a higher ²⁴⁰Pu/²³⁹Pu atom ratio (0.456 ± 0.020) was observed that could be attributed to fallout from the “Ivy Mike” thermonuclear detonation in 1952. The atom ratio decreased in the 1960s and 1970s due to increase in the global fallout with a low ²⁴⁰Pu/²³⁹Pu atom ratio (∼0.18). Recent coral bands (1981-1999) are dominated by the transport of remobilised Pu, with high ²⁴⁰Pu/²³⁹Pu atom ratios, from the Marshall Islands to Guam Island along the North Equatorial Current (NEC). This remobilised Pu was estimated to comprise 69% of the total Pu in the recent coral bands, although its contribution was variable over time.  相似文献   

Millennial-scale oscillations of the westerly jet path during the last glacial period   总被引：1，自引：0，他引：1  

Kana Nagashima  Ryuji Tada  Atsushi Tani  Youbin Sun  Yuko Isozaki  Shin Toyoda  Hitoshi Hasegawa 《Journal of Asian Earth Sciences》2011,40(6):239-1220

It has been established that East Asian summer monsoon intensity varies with Dansgaard–Oeschger cycles, suggesting a connection between the climates of East Asia and the North Atlantic on a millennial timescale. However, the dynamics of such a connection are still unsolved. Here we demonstrate that temporal changes in the provenance of aeolian dust in Japan Sea sediments, which we interpret to reflect changes in the westerly jet path over East Asia, exhibit variations in harmony with Dansgaard–Oeschger cycles. The dominance of dust with a Mongolian Gobi provenance during stadials suggests a westerly jet axis located to the south of the Himalaya–Tibetan Plateau throughout most of the year, whereas the co-dominance of dust from both the Taklimakan Desert and the Mongolian Gobi during interstadials suggests that the westerly jet axis jumped to the north of the Tibetan Plateau at latest in summer. As the shift of the westerly jet axis to the north of the Tibetan Plateau is closely related to the onset of the East Asian summer monsoon, changes of the westerly jet path apparently critically affect the teleconnection between the climates of Asia and North Atlantic on a millennial timescale.  相似文献   

Marine artificial structures as amplifiers of Aurelia aurita s.l. blooms: a case study of a newly installed floating pier     

Ryosuke Makabe  Ryuji Furukawa  Mariko Takao  Shin-ichi Uye 《Journal of Oceanography》2014,70(5):447-455

Increase of marine artificial structures, providing more substrate for jellyfish polyps, has been argued to increase jellyfish outbreaks, although no explicit evidence exists. We report a case study demonstrating a remarkable increase of Aurelia aurita s.l. ephyrae after the installation of a floating pier (48 × 6 m) in a fishing port on the Inland Sea of Japan. Monitoring of ephyrae from January 2010, prior to the installation of the floating pier in April 2010, to July 2011, revealed that their time-weighted average density increased 3.5 fold, from 1.1 to 3.9 ephyrae m^?3, and the integrated number of ephyrae exported from the port increased 4.3 fold, from 5.7 × 10⁶ to 25 × 10⁶ ephyrae, after the installation. However, in a nearby port, a control site, the abundance of ephyrae decreased by ca. one third during the same period. Monitoring of polyps showed that they initially colonized the undersurface of the pier by August 2010, followed by a rapid population increase. They strobilated from December 2010 to May 2011. We computed the number of ephyrae released from the strobilae to be ca. 25 × 10⁶, very close to the net increase of ephyrae produced and exported from the port. This study corroborates that the installation of an artificial structure provides new a substrate for polyps, which allows them to produce more ephyrae to induce medusa blooms.  相似文献   

Evidence for ocean water invasion into the Chicxulub crater at the Cretaceous/Tertiary boundary     

Kazuhisa GOTO  Ryuji TADA  Eiichi TAJIKA  Timothy J. BRALOWER  Takashi HASEGAWA  Takafumi MATSUI 《Meteoritics & planetary science》2004,39(7):1233-1247

Abstract The possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion.  相似文献   

Outline of the fault zone drilling project by NIED in the vicinity of the 1995 Hyogo-ken Nanbu earthquake, Japan   总被引：2，自引：0，他引：2  

Ryuji Ikeda 《Island Arc》2001,10(3-4):199-205

Abstract Three boreholes, 1001 m, 1313 m and 1838 m deep, were drilled by the National Research Institute for Earth Science and Disaster Prevention (NIED) in the vicinity of the epicenter of the 1995 Hyogo-ken Nanbu (Kobe) earthquake to investigate tectonic and material characteristics near and in active faults. Using these boreholes, an integrated study of the in situ stress, heat flow, and material properties of drill cores and crustal resistivity was conducted. In particular, the Nojima–Hirabayashi borehole was drilled to a depth of 1838 m and directly intersected the Nojima Fault, and three possible fault strands were detected at depths of 1140 m, 1313 m and 1800 m. Major results obtained from this study include the following: (i) shear stress around the fault zone is very small, and the orientation of the maximum horizontal compression is perpendicular to the surface trace of faults; (ii) from the results of a heat flow study, the lower cut-off depth of the aftershocks was estimated to be roughly 300°C; (iii) cores were classified into five types of fault rocks, and an asymmetric distribution pattern of these fault rocks in the fracture zones was identified; (iv) country rock is characterized by a very low permeability and high strength; and (v) resistivity structure can be explained by a model of a fault extending to greater depths but with low resistivity.  相似文献   

Terrestrial heat flow at Hirabayashi on Awaji Island, south-west Japan   总被引：1，自引：0，他引：1  

Taku Kitajima  Yoji Kobayashi  Ryuji Ikeda  Yoshihisa Iio  Kentaro Omura 《Island Arc》2001,10(3-4):318-325

Abstract Terrestrial heat flow at Hirabayashi in Awaji Island, south-west Japan, was investigated using the deep borehole penetrating through the Nojima Fault, which was activated during the 1995 Hyogo-ken Nanbu earthquake, by measuring the thermal conductivity of basement rocks. Using the temperature logging data, the value of terrestrial heat flow in Hirabayashi was found to be 56.6 ± 5.2 mW/m². The relationship between cut-off depth of aftershocks of the Hyogo-ken Nanbu earthquake in Hirabayashi and terrestrial heat flow are discussed. The cut-off depth roughly corresponds to isotherms of 300°C.  相似文献   

来自于九年后日本海纳霍德卡溢油污染海岸的碳氢化合物降解细菌和石蜡     

Kazue TAZAKI Hiroaki WATANABE Siti Khodijah CHAERUN Koichi SHIRAKI Ryuji ASADA 《地质学报》2006,80(6):924

近十年来，石油类碳氢化合物，尤其是油溢带来的污染引起了广泛的关注。油溢会影响到自然菌落及其受污染菌落点的物理和化学性质。生物降解碳氢化合物是一种主要的除去油类泄漏污染源的方法。1997年1月2日，一艘名为纳霍德卡（Nakhodka）的俄罗斯油轮在日本海发生重油溢漏污染事故。纳霍德卡号油溢事件导致粘稠的流体污染了海岸，影响了周围的生态环境。本文详述了碳氢化合物降解细菌（假单胞菌种）的褪变，确定了九年后来自于纳霍德卡号油溢污染海岸的有机化合物。经过十年的生物修复，纳霍德卡溢油变硬．XRD分析结果中与石墨和方解石有关的0．422，  相似文献   

Distribution of glycerol dialkyl glycerol tetraethers, alkenones and polyunsaturated fatty acids in suspended particulate organic matter in the East China Sea     

Takahiro Nakanishi  Masanobu Yamamoto  Tomohisa Irino  Ryuji Tada 《Journal of Oceanography》2012,68(6):959-970

We investigated the spatial distribution of glycerol dialkyl glycerol tetraethers (GDGTs), alkenones, and polyunsaturated fatty acids in particulate organic matter collected at four sites along a depth transect from the continental shelf to the Okinawa Trough in the East China Sea during the spring bloom in 2008. The maximum alkenone concentration appeared in the top 25?m at all sites and the $ U_{37}^{{{\text{K}}'}} $ values were consistent with in situ water temperatures in the depth interval, suggesting that the alkenones were produced mainly in surface water. At the slope and shelf sites, GDGTs in the water column showed a concentration maximum at 74?C99?m depth, and the $ {\text{TEX}}_{86}^{\text{H}} $ agreed with in situ water temperatures, suggesting the in situ production of GDGTs in the depth interval. The low-salinity surface water above 20?m depth was characterized by low GDGT concentrations and low $ {\text{TEX}}_{86}^{\text{L}} $ -based temperatures, suggesting either the production of GDGTs in winter season or the lateral advection of GDGTs by an eastward current. At the slope and Okinawa Trough sites, TEX₈₆-based temperatures were nearly constant in the water column deeper than 300?m and corresponded to temperatures at the surface and near-surface waters rather than in situ temperatures. This observation is consistent with a hypothesis that Thaumarchaeota cells produced in surface waters are delivered to deeper water and also indicates that the residence time of suspended GDGTs in the deep-water column is large enough to mix the GDGTs produced in different seasons.  相似文献   

Evaluating the susceptibility of landslide landforms in Japan using slope stability analysis: a case study of the 2016 Kumamoto earthquake     

Chi-Wen Chen  Hongey Chen  Lun-Wei Wei  Guan-Wei Lin  Tomoyuki Iida  Ryuji Yamada 《Landslides》2017,14(5):1793-1801

This study analyzed 267 landslide landforms (LLs) in the Kumamoto area of Japan from the database of about 0.4 million LLs for the whole of Japan identified from aerial photos by the National Research Institute for Earth Science and Disaster Resilience of Japan (NIED). Each LL in the inventory is composed of a scarp and a moving mass. Since landslides are prone to reactivation, it is important to evaluate the sliding-recurrence susceptibility of LLs. One possible approach to evaluate the susceptibility of LLs is slope stability analysis. A previous study found a good correlation (R ² = 0.99) between the safety factor (F _s ) and slope angle (α) of F _s  = 17.3α ^?0.843. We applied the equation to the analysis of F _s for 267 LLs in the area affected by the 2016 Kumamoto earthquake (M _j  = 7.3). The F _s was calculated for the following three cases of failure: scarps only, moving mass only, and scarps and moving mass together. Verification with the 2016 Kumamoto earthquake event shows that the most appropriate method for the evaluation of LLs is to consider the failure of scarps and moving mass together. In addition, by analyzing the relationship between the factors of slope of entire landslide and slope of scarp for LLs and comparing the results with the Aso-ohashi landslide, the largest landslide caused by the 2016 Kumamoto earthquake, we also found that morphometric analysis of LLs is useful for forecasting the travel distance of future landslides.  相似文献   

多传感器不同分辨率遥感数字图像的尺度转换   总被引：14，自引：0，他引：14  

布和敖斯尔  马建文  王勤学  金子正美  福山龙次 《地理学报》2004,59(1):101-110

针对日益增多的多传感器不同分辨率的遥感数字图像数据,提出其综合利用和尺度转换的有效方法。其中,作为尺度上推 (scaling-up) 技术,本研究选择IHS和小波分解变换两种数据融合方法,应用Landsat ETM+数据和IRS-1C数据进行了实例研究。发现: IHS方法操作简单,对两种待融合的图像的像元大小和像元数 (bit数) 的依赖不是很高,而对原始图像光谱信息的依赖很高,因此适用于不同传感器之间的数据融合上,其缺点就是不能够更多的保留原始多光谱数据的光谱信息。小波分解变换 (WD) 方法可以很好地保留多光谱传感器的所有光谱信息,但是在重采样中对两种待融合的图像的像元配准的要求很高,因此比较适合于对同一传感器的多光谱数据与全色光谱数据的融合上。作为尺度下退 (scaling-down) 技术,通过探讨将札幌野外实验站点数据镶嵌到高时间分辨率遥感图像的问题,提出像元级尺度扩展的具体操作方法和对NDVI图像进行扩展时出现混合像元的识别方法。应用AVHRR, MODIS, ETM+和ASTER的NDVI图像数据进行了像元尺度的扩展研究。得出: 对不同传感器的不同分辨率的数据之间进行像元级的尺度扩展后,能够较好地识别出不同地物的分布边界,较好的分辨混合像元,因此其结果可用于对不同地物分布特征的分类研究或土地覆盖变化中的时间序列变化的研究中。  相似文献