Geochemical characteristics of deposits from the 2011 Tohoku‐oki tsunami at Hasunuma,Kujukuri coastal plain,Japan

We examined the geochemical characteristics and temporal changes of deposits associated with the 2011 Tohoku‐oki tsunami. Stable carbon isotope ratios, biomarkers, and water‐leachable ions were measured in a sandy tsunami deposit and associated soils sampled at Hasunuma, Kujukuri coastal plain, Japan, in 2011 and 2014. At this site, the 2011 tsunami formed a 10–30 cm ‐thick layer of very fine to medium sand. The tsunami deposit was organic‐poor, and no samples contained any detectable biomarkers of either terrigenous or marine origin. In the underlying soil, we identified hydrocarbons and sterols derived from terrestrial plants, but detected no biomarkers of marine origin. In the samples collected in 2011, concentrations of tsunami‐derived water‐leachable ions were highest in the soil immediately beneath the tsunami deposit and then decreased gradually with depth. Because of its finer texture and higher organic content, the soil has a higher water‐holding capacity than the sandy tsunami deposit. This distribution suggests that ions derived from the tsunami quickly penetrated the sand layer and became concentrated in the underlying soil. In the samples collected in 2014, concentrations of water‐leachable ions were very low in both soil and sand. We attribute the decrease in ion concentrations to post‐tsunami rainfall, seepage, and seasonal changes in groundwater level. Although water‐leachable ions derived from seawater were concentrated in the soil beneath the tsunami deposit following the tsunami inundation, they were not retained for more than a few years. To elucidate the behavior of geochemical characteristics associated with tsunamis, further research on organic‐rich muddy deposits (muddy tsunami deposits and soils beneath sandy tsunami deposits) as well as sandy tsunami deposits is required.     

A pollution history of Chesapeake Bay

Present day anthropogenic fluxes of some heavy metals to central Chesapeake Bay appear to be intermediate to those of the southern California coastal region and those of Narragansett Bay. The natural fluxes, however, are in general higher. On the bases of Pb-210 and Pu-239 + 240 geochronologies and of the time changes in interstitial water compositions, there is a mixing of the upper 30 or so centimeters of the sediments in the mid-Chesapeake Bay area through bioturbation by burrowing mollusks and polychaetes. Coal, coke and charcoal levels reach one percent or more by dry weight in the deposits, primarily as a consequence of coal mining operations.     

Monte Carlo study on distortion of the space-dimension in COBE monopole data

A concise explanation of studies on distortion of space-time dimension is briefly introduced. Second we obtain the limits (i.e., bounded values) of the dimensionless chemical potential μ, the Sunyaev–Zeldovich (SZ) effect y and distortion of the space-dimension ε by Monte Carlo (MC) analysis of the parameter set (T, d=3+ε, μ, and y) in cosmic microwave data assuming that the SZ effect is positive (y>0). In this analysis, the magnitude of the space-dimension d with distortion of the space-dimension ε is defined by d=3+ε. The limits of μ and y are determined as |μ|<9×10^?5 (2σ) (μ=(?3.9±2.6)×10^?5 (σ)), |y|<5×10^?6 (2σ) (y=(2.0±1.4)×10^?6 (σ)), while the distortion of the space-dimension is |ε|<6×10^?5 (2σ) (ε=(?0.78±2.50)×10^?5 (σ)). The magnitudes of these three estimated limits are ordered as . The estimated limit of |y|<5×10^?6 appears to be related to re-ionization processes occurring at redshift z _ri ～10. We also present data analysis assuming a relativistic SZ effect.     

Kinetic stability of a melted iron globule during chondrule formation. I. Non‐rotating model

Abstract— We have investigated the kinematics of the separation of iron globules from chondrules during chondrule formation. A simple model, which assumes that the system has no angular momentum, was used to calculate the energy of a system with an iron globule and a chondrule. The energies of three different states were calculated: 1) a melted iron globule fully embedded in a melted chondrule, 2) a melted iron globule on the surface of a melted chondrule, and 3) a melted iron globule being separated from a melted chondrule. We also calculated the lowest energy shape for a melted iron globule on the surface of a melted chondrule, and compared our result with the shapes of four natural samples of chondrules and iron globules in thin sections. The shapes were calculated using an assumed value for the interface energy between the four couples of melted chondrules and the iron globules, and agree well with the natural shapes of chondrules and iron globules. The results of our calculations show that the iron globules of these four samples would be strongly bound to the surface of the melted chondrule during chondrule formation, and separation would be difficult, if the iron globules had been on the surface of precursors of these chondrules. Our results also show that if these iron globules were initially inside and transported to the surface of the melted chondrule, most of them would be ejected from the inside to outside because of surface tension forces, as long as the energy losses due to viscous dissipation when the globules pass through the surface of melted chondrules were sufficiently small. Although further improvement of the model is required, our results demonstrate that this ejection process may be responsible for the depletion of siderophile elements in natural chondrules.     

Aspects of rhodium marine chemistry

Rhodium, one of the least abundant of the Pt-group elements in the earth's crust, has the second highest concentration in seawater. This may be a consequence of strong complexing, perhaps kinetically restrained with time constants of the order of centuries to millenia. The element shows a nutrient-like distribution in waters of the Pacific Ocean. Pelagic and coastal sediments have Rh concentrations close to crustal values. There is a remarkable enrichment of Rh in ferromanganese minerals that cannot be explained by oxidative capture. Unlike the other Pt-group elements, Rh is enriched in the high temperature hydrothermal sulfide deposits as well as phosphorites.     

Geochronological and petrological investigations of Miocene felsic igneous rocks in the Amakusa Islands,southwest Japan: Possible extension of the Setouchi Volcanic Belt

The opening of the Japan Sea led to the separation of southwest Japan from the Eurasian continent. Subsequent to this event, a diverse range of igneous activities occurred in southwest Japan. On the back-arc side of the region, igneous activity commenced at approximately 22 Ma and persisted for an extended period. In the trench-proximal region of southwest Japan, magmatism initiated around 15.6 Ma, immediately following the cessation of the Japan Sea opening, in correlation with the subduction of the Philippine Sea plate beneath southwest Japan. The Amakusa Islands in western Kyushu host felsic to intermediate igneous rocks with Miocene radiometric ages. There has been a debate regarding the attribution of the igneous rocks in Amakusa Island among the Miocene igneous rocks in southwest Japan. To address this issue, we conducted zircon U–Pb dating and analyzed the major- and trace-element compositions of felsic igneous rocks in the Amakusa Islands to elucidate their characteristics. The obtained U–Pb ages range from 14.5 to 14.8 Ma, suggesting contemporaneity between magmatism in the Amakusa Islands and the Setouchi Volcanic Rocks in the trench-proximal region of southwest Japan. The major and trace element compositions of the felsic igneous rocks exhibit similarities to the dacites of the Setouchi Volcanic Rocks. These findings support previous suggestions that the magmatism in the Amakusa Islands can be correlated with the Setouchi Volcanic Rocks, based on the discovery of a high-Mg andesite dike and paleo-stress analysis utilizing the direction of dikes and sills. Therefore, the Setouchi Volcanic Belt is proposed to extend further west than the previously identified Ohno volcanic rocks in eastern Kyushu. The subduction of the Shikoku Basin of the Philippine Sea plate toward western Kyushu supports the hypothesis that the Kyushu-Palau Ridge was positioned west of Kyushu at ~15 Ma.     

241Pu/239+240Pu ratios in polar glaciers

The analyses of plutonium isotopes in dated strata of polar ice sheets indicate that the²⁴¹Pu/^239+240Pu activity ratio produced in the U.S.-dominated nuclear tests during the 1950s was about 26, while that in the U.S.S.R.-dominated weapons tests in the early 1960s was between 12 and 14. This difference provides time horizons for sedimentary deposits. Further, the²³⁹Pu/²⁴⁰Pu ratio may show a similar difference in fallout values from these two periods of weapons testing and may provide an additional, and perhaps more sensitive, chronology for sediments.     

Microbial community respiration and structure of dead zone sediments of Omura Bay, Japan

Monitoring sediment microbial community metabolism and structure is instrumental to understanding biogeochemical processes in and ecological impacts on bottom environments. The aim of this study was to determine potential community respiration and to reveal community dynamics of the microorganisms in the dead zone sediments of Omura Bay, Japan. The bay is highly enclosed and develops severe hypoxia in the central regions every summer. We collected sediment core samples from the center of the bay during hypoxia, estimated sediment oxygen consumption by using an adapted in vivo electron transport system activity (in vivo ETSA) assay, enumerated abundance of bacteria, and analyzed bacterial community structure by automated ribosomal intergenic spacer analysis. Higher ETSA and bacterial diversity were found in upper sediments (within 3?cm depth) from the center than the fringe of the bay. Sediment bacterial community structure of the bay center was distinct from that of the fringe. From these results, upper sediment in the dead zone of Omura Bay was characterized by (1) greater community respiration and (2) greater diversity of bacterial components compared with the non-hypoxic sediment of the bay fringe. These characteristics have important implications for understanding the interaction between microbial communities and the development of hypoxia in Omura Bay.     

Reliability analysis of shallow foundations in reference to design codes development

In this study, FORM analysis is carried out for shallow foundation of a typical building in order to evaluate relative magnitude of uncertainties involved in the force and the resistance sides. The distinguished feature of this study is to take into account the uncertainty of the earthquake force as much as possible. Tthis is because, the seismic design dominates major part of structural design in Japan, and without referring to this problem, no useful information of practical value is gained. The results of the FORM analysis exhibited the reliability index values between 2.0 to 3.5, which is considered to be in a reasonable range. Since the 50 year maximum earthquake force is considered in the reliability calculation, calculated reliability index values are for the period of 50 years. The sensitivity factor obtained in a case more realistic ground variability is taken into account exhibited values not very different from those obtained in the upper structures.