Deposition rates of polysilicic acid with up to 10 M calcium ions

Cementitious materials used for radioactive waste repository construction complicate the performance assessment of radioactive waste systems because the use of cement may greatly alter the pH (8–13) of groundwater and release constituents such as calcium ions. Under such conditions, it is important to clarify also the dynamic behavior of silica (silicic acid), in order to evaluate the alteration in the chemical and physical properties of the fractured layer or the host rock surrounding the repository. Since silica undergoes polymerization, precipitation or dissolution depending on the pH and/or temperature, the behavior of silica would be greatly complicated in the presence of other ions. This study is focused on the deposition rates of polysilicic acid and soluble silicic acid with up to 10⁻³ M Ca ions. In the experiment, Na₂SiO₃ solution (250 mL, pH > 10, 298 K) was poured into a polyethylene vessel containing amorphous silica powder (0.5 g), and a buffer solution, HNO₃, and CaNO₃ as Ca ions were sequentially added into the vessel. The pH of the solution was set to 8. The silica, initially in a soluble form at pH > 10 (1.4 × 10⁻² M), became supersaturated and either deposited on the solid surface or changed into the polymeric form. Then the concentrations of both poly- and soluble silicic acid were monitored over a 40-day period. The decrease of polysilicic acid became slow with an increase in the concentration of Ca ions in the range of up to 10⁻³ M. In general, the addition of electrolytes to a supersaturated solution accelerates the aggregation and precipitation of polymeric species. However, the experimental result showed that polysilicic acid in the presence of Ca ions is apparently stable in solution, compared with that under a Ca-free condition. On the other hand, the concentration of soluble silicic acid in the presence of Ca ions immediately became metastable, that is, slightly higher than the solubility of soluble silicic acid. Its dynamic behavior was similar to that in the Ca-free condition.     

MIS11–19 pollen stratigraphy from the 250-m Choshi core, northeast Boso Peninsula, central Japan: Implications for the early/mid-Brunhes (400–780 ka) climate signals

Abstract   The 250-m Choshi core (CHOSHI-1), drilled from hemipelagic muds of the Inubo Group, has been physically, geochemically and tephrochronologically analyzed back to 1 Ma. We provide pollen results for the 19–169 m section of the core (400–780 ka) bracketed by the marker tephra Ty1 (equivalent to J4) and the Brunhes–Matuyama paleomagnetic boundary. The results show good agreement with the corresponding oxygen isotope (δ¹⁸O) profile, with high δ¹⁸O intervals dominated by boreal conifers Picea , Abies , Pinus (subgen. Haploxylon ) and Tsuga ( diversifolia ), whereas low δ¹⁸O intervals are dominated by temperate conifers Cryptomeria , Taxaceae-Cephalotaxaceae-Cupressaceae and Sciadopitys . In order to confirm pollen-climate relations for the relevant taxa, a modern surface pollen dataset for the Japanese archipelago was consulted. In this analysis, the ratios of Cryptomeria / Picea and temperate/boreal conifers serve as proxies for the 100-kyr glacial/interglacial cycle during the Middle Pleistocene. Distinct signals for marine isotope stages (MIS) 11, 12, 13–15, 16, 17 and 18–19 are recognized in accordance with the tephrochronology and δ¹⁸O of the same core. Application of the criteria to an independent pollen record from Lake Biwa provides an integrated pollen stratigraphy for mid-latitude Japan during the past 800 ky. Some degree of uncertainty remains in the chronology of the MIS13–15 interval, relating to the uncertainty in the eruption age of widespread tephra Ks11.     

Effect of depositional processes on the origin and composition of organic matter: Examples from the Pleistocene sediments in the Choshi core, Boso Peninsula

Abstract   Both marine and terrigenous organic matter are deposited in shelf and continental slope environments. In the present study, the relationship between environmental changes in the Choshi area and the sedimentation of organic matter was examined. The sediments of the Choshi core were deposited on a shelf environment and their lithology and ichnofacies, as well as the composition of the contained kerogen (insoluble organic matter) indicate a shallowing upward succession. The organic matter preserved in the sediments is of both marine and terrigenous origin, on the basis of C/N ratios (5.90–9.45), δ¹³C values (−21.6‰−24.6‰) and kerogen microscopy. The total organic carbon (TOC) content (0.39–1.08%) of the sediments shows a positive correlation with the increase of terrigenous organic matter before 500 ka, but decreases (0.26–0.61%) after 500 ka as the shelf environment becomes shallower because of dilution, caused by the input of terrigenous inorganic clasts, and oxidation. The variation in TOC contents was thus influenced by the increasing sedimentation rate of terrigenous materials, including both organic and inorganic particles as the basin filled.     

Changing distribution of gender in the Extended Bangkok Region under globalization

This study examines recent changes in the structure of migration and population by gender in the Extended Bangkok Region (EBR) taking the influences of economic globalization into consideration. The EBR is understood here to consist of three concentric zones, namely the Bangkok Metropolis (BM), the Vicinity and the Extended Urban Region (EUR). The spatial policy of the Thai government has encouraged investors to build manufacturing factories outside the BM. Consequently the industrial structure of the BM has turned strongly into service-dominated while the Vicinity and the EUR have attracted factories mainly owned by foreign capitals. Light industries and electronics industries, both of which set up relatively earlier, concentrated on the Vicinity, the adjacent provinces to the BM, while heavy and petrochemical industries are recently have developed in the outer regions, the EUR. Service sectors and light industries as well as electronics industries prefer females to males to employ as workers. As a consequence the population structures of the BM and the Vicinity became female-dominant while male workers were likely to gather in the EUR attracted by heavy and petrochemical industries. The gender imbalance in the population in the areas in concern may have been one of the consequences of the economic globalization of Thailand. The Thai government supported the economic globalization through its investment promotion policy, but it seems that the government did not assume the policy resulted in such gender imbalance. It can be suggested that in the future this gender imbalance may cause changes in family formation behaviors of the Thai population. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gravity change observed near Lake Biwa,Japan

Precise gravity measurements have repeatedly been carried out in the area around Lake Biwa in Japan since 1950 in order to detect the secular change of gravity. The results obtained so far show that gravity change observed on the west line of the first order levelling route around the lake during the period of 1971∼1975 was consistent with the results of levelling surveys. This evidence shows that precise gravity measurement is one of the powerful methods for detecting vertical crustal movement.     

Late-Cenozoic Magnetostratigraphy : Comparisons with Bio-, Climato-, and Lithozones

A workshop conference entitled “Late Cenozoic Magnetostratigraphy: Comparisons with Bio-, Climato-, and Lithozones” took place in Tokyo and Otsu, Japan, between October 28 and November 1, 1974. It was organized by G. J. Kukla and H. Nakagawa as an outcome of the PA-70-17 Project of the International Geological Correlation Programme, launched in 1970 by the International Union of Geological Sciences. The workshop was supported by the Japanese Society for the Promotion of Science, by IGCP, and the National Science Foundation (of the United States). Out of 70 participating geophysicists, geologists, and paleontologists, 37 attended in person, while the remaining 33 contributed by mail.¹ Prior to the conference a questionnaire was distributed in order to collect opinions on several issues. The workshop's objective was to tackle problems in the recognition of depositional polarity and to review the relationship of magneto-stratigraphic units with radiometric data and with regional bio-, litho-, and climatostratigraphic systems of the Pliocene and Pleistocene. The principal conclusions of the conference were summarized as follows:

1. (1) The only practical (though not infallible) way of demonstrating the validity of interpreted depositional polarity and magnetostratigraphic zonation is to reproduce the results in parallel, widely separated sections with different lithology and sedimentation rates.

2. (2) The hazard of unrecognized postdepositional normal overprints must be recognized and considered in all attempted correlations. Multiple sampling of parallel sections and consistency checks of magnetic data are a prerequisite for correct results.

3. (3) Continuous sequences with high sedimentation rates, such as those which originated in subsiding basins, are viewed as prospective candidates for international stratotypes of the Pliocene and Pleistocene. The investigation of such deposits should be accelerated.

4. (4) Magnetostratigraphy must follow basic stratigraphic principles. Magnetic zones should be clearly defined and locally labeled, whether or not their correlation with paleomagnetic chronology appears possible.

5. (5) Improved data on absolute age of reversals are needed. For that purpose, multiple K/Ar and fission-track analyses of key volcanic layers should be performed on a continuing basis.

     

Hg, Zn and Cu levels in the muscle and liver of tiger sharks (Galeocerdo cuvier) from the coast of Ishigaki Island, Japan: relationship between metal concentrations and body length

We analyzed Hg, Zn and Cu concentrations in the liver and muscle of tiger sharks (Galeocerdo cuvier) from the coast of Ishigaki Island, Japan. The Hg concentration in the muscle increased proportionally with body length in the tiger sharks, whereas that in the liver increased rapidly after maturity (defined by a length of over 2.7 m). Muscle Hg levels were higher than liver concentrations in immature sharks, with the inverse trend observed in mature sharks. Notably, the Zn and Cu concentrations in the liver tended to decrease with increasing body length. This rapid increase in hepatic Hg concentration concurrent with the onset of maturity in sharks may result from the continuous intake of Hg via food and the slower growth of mature sharks. The high concentrations of the essential metals Zn and Cu in immature sharks may be explained by the physiological demands related to rapid growth.     

拉萨上空大气气溶胶光学特性的 激光雷达探测

叙述了大气气溶胶激光雷达探测方程的求解方法,以及1998年夏季在拉萨使用激光雷达观测的一些结果,并与日本名古屋市上空的探测资料进行了对比分析,得到了拉萨上空气溶胶光学性质的一般特征,并对其成因进行了讨论。     

Field measurement and modeling of near-bed sediment transport processes with fluid mud layer in Tokyo Bay

Tokyo Bay is one of the estuaries in Japan with a high population of almost 26 million people in the basin area. One of the major concerns for the environment in this water area is the decreasing ecosystem functions including the deterioration of water and sediment qualities caused by various anthropogenic activities. Since the bottom sediments around almost the entire area of the inner bay consist of fine materials with a high organic content, which cause the deterioration of water quality through processes such as hypoxia, an understanding of the fine sediment dynamics in the Bay is crucial for an environmental assessment of the water area. This paper proposes a model for the key processes of fine sediment dynamics, which reflects field data about muddy bed structures and their dynamics obtained during the monitoring campaign in 2007. One of the specific features of the sediment in the Bay at present is the persistent existence of fluid mud layers (water content over 300?%) with a thickness of around a few decimeters, which might be caused by deposition of abundant organic particles due to eutrophication. The present study shows that diffusion flux model delivers quite reliable results for estimating erosion flux from the top of fluid mud layers after calibrating the model parameter against the time series data of vertical flux measured by an acoustic Doppler velocimeter system. This study also derives analytical solutions, based on the Bingham fluid concept, of advection flux in the fluid mud layer on which external shear stress force is applied.