Postglacial stratigraphic evolution of a current-influenced sandy shelf: offshore Kujukuri strandplain,central Japan     

Naohisa Nishida  Taku Ajioka  Ken Ikehara  Rei Nakashima  Hajime Katayama  Tomoyuki Sato  Seishiro Furuyama  Toru Tamura 《Sedimentology》2020,67(1):559-575

Sandy shelf sediments are important elements of clastic sedimentary systems because of their wide distribution in the geological record and their significance as hydrocarbon reservoirs. Although many studies have investigated shelf sediments influenced by waves or tidal currents, little is known about shelf sediments influenced by oceanic currents, particularly their lithofacies characteristics and stratigraphic evolution. This study investigated the stratigraphic evolution of shelf sediments off the Kujukuri strandplain facing the Pacific Ocean, which is influenced by the strong Kuroshio Current. Sediment cores were obtained from six locations on the Kujukuri shelf (34 to 124 m water depth) using a vibrocorer. The dominant lithofacies is mud-free sand with low-angle cross-lamination associated with alternating beds of finer and coarser sand with cross-lamination. These display depositional processes influenced by storm waves and the Kuroshio Current, respectively. This finding is consistent with the previously presented modern and historical observations of the Kuroshio Current and estimates of the storm-wave base. Radiocarbon dates show that the sediment succession formed during the last transgressive and highstand stages after 13·1 ka. The depositional processes during the stages represent a transition from storm waves with abundant sediment supply to both storm waves and the Kuroshio Current with sediment starvation mainly due to its trapping in the strandplain. Comparison to other Holocene–Modern shelf systems suggests that the sandy shelf successions are strongly influenced by oceanic currents under conditions of limited riverine input and open coastal geometry. The resultant sand-dominated succession is characterized by reversal of the proximal to distal grain-size trend compared to the fining for most other recognized wave/storm-dominated shelf successions. This is because of seaward increase in the influence of the Kuroshio Current. Thus, shelf deposits are naturally complex, and these may be further complicated by the additional influence of oceanic currents above the usual wave-dominated and tide-dominated end members.  相似文献   

东亚地区春季二氧化硫的输送与转化过程研究I.模式及其验证   总被引：5，自引：0，他引：5  

张美根  徐永福  Itsushi Uno  Hajime Akimoto 《大气科学》2004,28(3):321-329

结合新近评估的东亚地区污染源资料,作者利用一个耦合的区域化学输送模式系统以探讨东亚地区春季期间气象过程、气相与液相化学过程、非均相化学过程、气溶胶过程和干湿沉降过程对二氧化硫输送及转化过程的影响,并研究二氧化硫和硫酸盐气溶胶的空间分布及变化特征.模拟的二氧化硫和硫酸盐气溶胶的浓度值与2001年春季飞机和地面获取的观测值进行了比较.比较结果显示,模拟值与观测值具有很好的一致性,模式系统很好地反映了二氧化硫和硫酸盐气溶胶的分布特征和变化规律,再现了许多观测到的重要特征,为进一步分析模拟结果奠定了基础.  相似文献   

Dense gas in normal and active galaxies     

Kotaro Kohno  Koichiro Nakanishi  Tomoka Tosaki  Kazuyuki Muraoka  Rie Miura  Hajime Ezawa  Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):279-285

Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0) and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO⁺(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO⁺(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these molecular lines are free from dust extinction.  相似文献   

Bed morphology and grain size characteristics around a spur dyke     

Hao ZHANG  Hajime NAKAGAWA  Hideaki MIZUTANI 《国际泥沙研究》2012,27(2):141-155,157,156

This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke.A series of experiments are conducted with different types of sedime...  相似文献   

Detailed measurements of thickness and grain size of a widespread onshore tsunami deposit in Phang‐nga Province,southwestern Thailand     

Shigehiro Fujino  Hajime Naruse  Dan Matsumoto  Norihiko Sakakura  Apichart Suphawajruksakul  Thanawat Jarupongsakul 《Island Arc》2010,19(3):389-398

Measurements of thickness and grain size along flow‐parallel transects across onshore deposits of the 2004 Indian Ocean tsunami revealed macroscopic horizontal variations and provided new insights into tsunami sedimentation. The tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to deposit a kilometer‐wide blanket of sand on the land surface. The tsunami deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and deposited 1 km or more inland. Although the thickness of the tsunami deposits is strongly influenced by local topography, they generally thin landward. In areas of low‐relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland.  相似文献   

Hedonic approaches based on spatial econometrics and spatial statistics: application to evaluation of project benefits   总被引：1，自引：0，他引：1  

Morito Tsutsumi  Hajime Seya 《Journal of Geographical Systems》2009,11(4):357-380

This study discusses the theoretical foundation of the application of spatial hedonic approaches—the hedonic approach employing spatial econometrics or/and spatial statistics—to benefits evaluation. The study highlights the limitations of the spatial econometrics approach since it uses a spatial weight matrix that is not employed by the spatial statistics approach. Further, the study presents empirical analyses by applying the Spatial Autoregressive Error Model (SAEM), which is based on the spatial econometrics approach, and the Spatial Process Model (SPM), which is based on the spatial statistics approach. SPMs are conducted based on both isotropy and anisotropy and applied to different mesh sizes. The empirical analysis reveals that the estimated benefits are quite different, especially between isotropic and anisotropic SPM and between isotropic SPM and SAEM; the estimated benefits are similar for SAEM and anisotropic SPM. The study demonstrates that the mesh size does not affect the estimated amount of benefits. Finally, the study provides a confidence interval for the estimated benefits and raises an issue with regard to benefit evaluation.  相似文献   

Thermal alteration of hydrated minerals during hypervelocity capture to silica aerogel at the flyby speed of Stardust     

Takaaki Noguchi  Tomoki Nakamura  Kyoko Okudaira  Hajime Yano  Seiji Sugita  Mark J. Burchell 《Meteoritics & planetary science》2007,42(3):357-372

Abstract— Outside the Earth's atmosphere, silica aerogel is one of the best materials to capture finegrained extraterrestrial particles in impacts at hypervelocities. Because silica aerogel is a superior insulator, captured grains are inevitably influenced by frictional heat. Therefore, we performed laboratory simulations of hypervelocity capture by using light‐gas guns to impact into aerogels finegrained powders of serpentine, cronstedtite, and Murchison CM2 meteorite. The samples were shot at >6 km s^?1 similar to the flyby speed at comet P/Wild‐2 in the Stardust mission. We investigated mineralogical changes of each captured particle by using synchrotron radiation X‐ray diffraction (SR‐XRD), transmission electron microscope (TEM), and field emission scanning electron microscope (FE‐SEM). SR‐XRD of each grain showed that the majority of the bulk grains keep their original mineralogy. In particular, SR‐XRD and TEM investigations clearly exemplified the presence of tochilinite whose decomposition temperature is about 300 °C in the interior of the captured Murchison powder. However, TEM study of these grains also revealed that all the samples experienced melting and vesiculation on the surface. The cronstedtite and the Murchison meteorite powder show remarkable fracturing, disaggregation, melting, and vesiculation. Steep thermal gradients, about 2500 °C/μm were estimated near the surface of the grains (<2 μm thick) by TEM observation. Our data suggests that the interior of >4 μm across residual grains containing abundant materials that inhibit temperature rise would have not experienced >300 °C at the center.  相似文献   

Silver in Tokyo Bay estuarine waters and Japanese rivers     

Yan Zhang  Hajime Obata  Toshitaka Gamo 《Journal of Oceanography》2008,64(2):259-265

Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg⁻¹, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg⁻¹). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients for silver throughout the estuary (log K_d > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y⁻¹ and 15 kg y⁻¹, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged within the Tokyo Bay estuary.  相似文献   

Long-term bottom water warming in the north Ross Sea     

Hirokazu Ozaki  Hajime Obata  Mikio Naganobu  Toshitaka Gamo 《Journal of Oceanography》2009,65(2):235-244

We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer (deeper than 3000 m) over the past four decades. The changes were significantly different from the analytical precisions. Detailed investigation of the temperature, salinity, dissolved oxygen and σ ₃ value distributions and the bottom water flow in the north Ross Sea suggests a long-term change in water mass mixing balance. That is to say, it is speculated that the influence of cool, saline, high-oxygen bottom water (high-salinity Ross Sea Bottom Water) formed in the southwestern Ross Sea has possibly been decreased, while the influences of relatively warmer and fresher bottom water (low-salinity Ross Sea Bottom Water) and the Adélie Land Bottom Water coming from the Australia-Antarctic Basin have increased. The possible impact of global warming on ocean circulation needs much more investigation.  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