A 35 kyr record of organic matter composition and δ13C of n-alkanes in bog sediments close to Lake Baikal: Implications for paleoenvironmental studies

We characterized the compositions of organic compounds in a Cheremushka bog sediment core (deposited over the last 35 kyr), located at the eastern coast of Lake Baikal, to obtain basic information about the terrestrial organic matter (OM) which contributed to Lake Baikal sediments. The bog sediment was analyzed for the molecular composition of n-alkanes, lignin phenols and n-C₂₄ to C₃₀ alkanoic acids, as well as the carbon isotopic composition of plant wax derived n-C₂₇ to C₃₃ alkanes.Concentrations of lignin phenols [vanillyl (V) plus syringyl (S) phenols] normalized to total organic carbon (TOC) in the Holocene are twice those for the last glacial maximum (LGM), while concentrations of TOC-normalized n-C₂₄ to C₃₀ alkanoic acids do not change markedly in this period. Thus, the ratio of lignin phenols to n-C₂₄ to C₃₀ alkanoic acids increases from the LGM to the Holocene. This result is essentially consistent with pollen analysis indicating an expansion of woody plants in the Holocene and a prevailing herb-abundant environment for the LGM. The δ¹³C values of n-C₂₇ to C₃₃ alkanes (e.g. ?29‰ to ?33‰ for C₃₁) indicate the presence of C₃-dominant plants throughout the core.The contribution of terrestrial OM to Lake Baikal sediments was estimated using the biomarkers, on the assumption that the OM in the bog sediments is a representative of the terrestrial OM around the lake. Hence, the estimation using lignin phenol or n-C₂₄ to C₃₀ alkanoic acid parameters indicates that 11–24% of the TOC in the Academician Ridge sediments is land-derived for both the Holocene and the LGM, which is similar to the estimates from C/N values of bulk OM. However, the estimates for terrestrial OM using the n-C₂₇ to C₃₃ alkane parameter are generally higher than those using lignin phenol or n-C₂₄ to C₃₀ alkanoic acid parameters. The difference is thought to be associated with the difference in source and behavior of these biomarkers.     

Reduction of pounding effects in elevated bridges during earthquakes

Pounding of adjacent superstructure segments in elevated bridges during severe earthquakes can result in significant structural damage. The aim of this paper is to analyse several methods of reduction of the negative effects of collisions induced by the seismic wave propagation effect. The analysis is conducted on a detailed three‐dimensional structural component model of an isolated highway bridge. The results show that the influence of pounding on the structural response is significant in the longitudinal direction of the bridge and significantly depends on the gap size between superstructure segments. The smallest response can be obtained for very small gap sizes and for gap sizes large enough to prevent pounding. Further analysis indicates that the bridge behaviour can be effectively improved by placing hard rubber bumpers between segments and by stiff linking the segments one with another. The experimental results show that, for the practical application of such connectors, shock transmission units can be used. Copyright © 2000 John Wiley & Sons, Ltd.     

Development and validation of nonlinear computational models of dispersed structures under strong earthquake excitation

Structural health monitoring of large multispan flexible bridges is particularly important because of their important role in civil infrastructure and transportation systems. In this study, the response of the Yokohama Bay Bridge (YBB), a three‐span cable‐stayed bridge, to the 2011 Great East Japan Earthquake is used to perform multi‐input multi‐output system identification studies. The extensive multicomponent measurements are also used to develop and validate data‐driven nonlinear mathematical models that can predict the response of YBB to various earthquake records and can accurately estimate its damping characteristics when the system is driven into the nonlinear response range. A combination of least‐square (parametric) and neural network (nonparametric) approaches is used to develop the mathematical models, along with time‐marching techniques for dynamic response calculations. It is shown that the nonlinear mathematical models perform better than the equivalent linear models, both for response prediction and damping estimation. The importance of having an accurate approach for quantifying the damping due to the variety of nonlinear features in the YBB response is shown. This study demonstrates the significance of constructing robust mathematical models that can capture the correct physics of the underlying system and that can be used for computational purposes to augment experimental studies. Given the lack of suitable data sets for full‐scale structures under extreme loads, the availability of the long‐duration measurements from the 2011 Great East Japan Earthquake and its many strong aftershocks provides an excellent opportunity to perform the analyses presented in this study. Copyright © 2013 John Wiley & Sons, Ltd.     

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

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.     

Electron microscopy studies of akermanites (Ca1−xSrx)2CoSi2O7 with modulated structure

Single crystals of akermanite (Ca_1–x Sr _x )₂Co-Si₂O₇ solid solution were grown in nitrogen by the floating zone method using a lamp-image furnace. The grown crystals were 6 mm in diameter by 50 mm in length. Microprobe analyses indicate uniform strontium content x except in the initially crystallized part. Synthetic crystals with x from 0.0 to 0.3 give, at room temperature, satellite reflections and circular diffuse scatterings in the electron diffraction pattern, which are related to an incommensurate phase and microdomains, respectively. With increasing Sr content the wavelength of a modulation increases and the intensity of satellites decreases, but the intensity of circular diffuse scattering increases up to x=0.15 and then decreases until eventually the satellites and the circular diffuse scatterings disappear at x = 0.3. The circular diffuse scattering is explained by the cluster model for the transition state, proposed by De Ridder et al. (1976).     

Preferred orientation of antiphase boundaries in pigeonite as a cooling ratemeter

Antiphase domains (APD's) of pigeonite lamellae in natural and heated augite crystals from the Hakonetoge andesite have been examined by a transmission electron microscope (TEM). Antiphase boundaries (APB's) of the pigeonite lamellae in natural specimens have a sigmoidal shape cutting the c axis in (010) sections. APB's in specimens heated at temperatures above the high-low inversion and then quenched are nearly parallel to the c axis with almost straight boundaries. These observations indicate that the preferred orientation of APB's in (010) sections depends on cooling rate; at fast colling rates the APB's are nearly parallel to the c axis, whereas at slower cooling rates they are inclined to the c axis. The cooling rate of the natural augite specimen from Hakonetoge is estimated to be about 0.01 °C/h from the experimentally determined time-temperature-transformation (TTT) diagram for the APB orientations. APD sizes are large in specimens quenched from above the inversion temperature; they are at a minimum after cooling rates of around 1–0.1 °C/h, and then become larger with slower cooling rates.     

Heat capacity anomalies at incommensurate-normal transition of åkermanite solid solution (Ca,Sr)2(Mg,Co, Zn,Fe)Si2O7

The heat capacity of åkermanite solid solutions was measured by a small scale adiabatic calorimeter near the incommensurate-normal (I-N) transition. The heat capacity anomalies caused by the I-N transition show the type characteristic behavior implying the presence of dynamical fluctuations. The heat capacity anomalies were observed over the whole range of the åkermanite solid solutions Ca₂Mg_1-xCo_xSi₂O₇ and Ca₂Mg_1-x-Zn_xSi₂O₂. With increase of Co or Zn atoms, the transition temperature, T_i, rises linearly from ca. 83° C to 220° C and to 130° C, respectively. In the system Ca₂CoSi₂O₇-Ca₂FeSi₂O₇ and Ca₂MgSi₂O₇-Ca₂-FeSi₂O₇ electronic microscopy revealed that the temperature of the heat capacity anomaly decreases with increasing Fe content, whereas the T_i rises. This unusual behavior is ascribed to the microdomains observed in high resolution lattice images.     

Present environment of Dam Lake Sambe,southwestern Japan: a geochemical study of bottom sediments

Geochemical analyses of lakebed and core sediments from Lake Sambe on the outskirts of Oda City in Shimane prefecture in southwestern Japan were carried out in order to assess the water quality and the concentration and distribution patterns of sixteen elements. The lake water showed a stratified condition with respect to dissolved O₂, and As, Fe, and Mn concentrations in the bottom layers which increased in the summer. The chemical composition of the sediments, as measured by X-ray fluorescence, included major and trace elements (P, Ca, Sc, Ti, V, Cr, Fe, Ni, Cu, Zn, As, Sr, Zr, Pb, and Th), and total sulfur (TS). Elevated values of As, Zn, V, Fe, P, and TS were present in several layers of the upper cores (from 0 to 5 cm) and other surface sediments. Increases in the abundances of these metals in lake sediments are probably related to the reducing condition of the sediments, fine-grained organic rich sediments, and post-depositional diagenetic remobilization. Moreover, correlations between the concentrations of trace metals and iron in the sediments suggest their adsorption onto Fe (oxy)hydroxides, whereas correlations with sulfur indicate that they were precipitated as Fe-sulfides. The average abundances of As, Pb, Zn, and Cu exceeded the lowest effect level and Interim Sediment Quality Guideline values that the New York State Department of Environmental Conservation and the Canadian Council of Ministers of the Environment determined to have moderate impact on aquatic organisms. In addition, concentrations of As and Zn exceeded the Coastal Ocean Sediment Database threshold value, indicating potentially toxic levels. Therefore, the presence of trace metals in the lake sediments may result in adverse effects on biota health.