Soil column experiments for iodate and iodide using K-edge XANES and HPLC–ICP-MS

Radioactive iodine is one of the most problematic radionuclides because of its long half life and high mobility. Mobility of iodine depends on the chemical form to a great extent. This paper reports the results of soil column experiments we conducted to evaluate the mobilities of IO₃⁻ and I⁻. In order to determine the mechanisms of adsorption of IO₃⁻ and I⁻ on soil, adsorption isotherms were obtained by batch experiments. Both adsorption isotherms of IO₃⁻ and I⁻ are well explained by Langmuir model. The adsorption maximum of IO₃⁻ is about five times larger than that of I⁻. In the column experiments, iodine distributions between soil and pore water in the soil column were determined at various depths. Chemical forms of iodine in soil and pore water were determined by X-ray absorption near-edge structure (XANES), and high performance liquid chromatography connected to inductively coupled plasma mass spectrometry (HPLC–ICP-MS), respectively. Vertical profiles of iodine in pore water were simulated using Visual MODFLOW. Our results showed, upon I⁻ infiltration through the column, that a small amount of I⁻ adsorbed on soil, and its mobility is mainly controlled by advection and dispersion. The profile of iodine concentration in pore water was well simulated by assuming equilibrium-controlled Langmuir type adsorption without considering any chemical transformations. For the IO₃⁻ addition system into the column, however, IO₃⁻ adsorbed to soil to a larger degree, which causes a much larger retardation effect than I⁻. In addition, reduction of IO₃⁻ to I⁻ was also confirmed in both soil and pore water by XANES and HPLC–ICP-MS, respectively. The fraction of I⁻ increased toward the deeper end in both phases because of its lower affinity for soil than IO₃⁻, where the reduced I⁻ was released to the pore water and transported by the water flow. In this study, such reduction effect was clearly demonstrated by the speciation analyses of iodine in both soil and water phases, which confirmed that the mobility of I⁻ is a dominant factor that controls the fate of iodine in the surface environment.     

Evidence for a thick and localized ultra low shear velocity zone at the base of the mantle beneath the central Pacific

Prominent postcursors to S/Sdiff waves with delays as large as 26 s are observed in Northern America for Papua New Guinea events. These waves sample the northern side of the Pacific large low shear velocity province revealed by global shear velocity (Vs) tomographic models. The emergence of the postcursors strongly depends on the epicenter-to-station azimuth, indicating that the waveforms are, in general, strongly affected by 3-dimensional (3D) heterogeneities. We limit our focus to an azimuthal range around 60°, measured clockwise from north at the epicenter, where the records show a relatively small azimuthal variation, suggesting a relatively small 3D effect there. In this azimuthal range we attempt 2D structural modelling along the great circle plane towards stations in southern US. First, we use a 2D ray theory to search for a range of models, which generate a postcursor to the main Sdiff phase with a delay time consistent with the observations. Then, for some typical models, we calculated waveforms at periods down to 5 s using the spectral element method. We obtained several models that provide synthetic waveforms in a fair agreement with the observations. The result shows that two types of low Vs regions are required to explain the data. One is a broad and weak anomaly region with a Vs reduction of 5% or so, constituting a part of the Pacific large low shear velocity province at the base of the mantle. The other is a laterally localized strong anomaly region with a more than 25% reduction of Vs within a thickness of at least 80 km and a width on the order of 500 km.     

P–V–T equation of state of Ca3Al2Si3O12 grossular garnet

The thermoelastic parameters of synthetic Ca₃Al₂Si₃O₁₂ grossular garnet were examined in situ at high-pressure and high-temperature by energy dispersive X-ray diffraction, using a Kawai-type multi-anvil press apparatus coupled with synchrotron radiation. Measurements have been conducted at pressures up to 20 GPa and temperatures up to 1,650 K: this P, T range covered the entire high-P, T stability field of grossular garnet. The analysis of room temperature data yielded V _0,300 = 1,664 ± 2 ?³ and K ₀ = 166 ± 3 GPa for K^￠₀ K^{\prime}_{0} fixed to 4.0. Fitting of our P–V–T data by means of the high-temperature third order Birch–Murnaghan or the Mie–Grüneisen–Debye thermal equations of state, gives the thermoelastic parameters: (∂K _0,T /∂T) _P  = −0.019 ± 0.001 GPa K⁻¹ and α _0,T  = 2.62 ± 0.23 × 10⁻⁵ K⁻¹, or γ ₀ = 1.21 for fixed values q ₀ = 1.0 and θ ₀ = 823 (Isaak et al. Phys Chem Min19:106–120, 1992). From the comparison of fits from two different approaches, we propose to constrain the bulk modulus of grossular garnet and its pressure derivative to K _T0 = 166 GPa and K^￠_T0 K^{\prime}_{T0}  = 4.03–4.35. Present results are compared with previously determined thermoelastic properties of grossular-rich garnets.     

<Emphasis Type="Italic">P</Emphasis>–<Emphasis Type="Italic">V</Emphasis>–<Emphasis Type="Italic">T</Emphasis> equation of state of CaAl<Subscript>4</Subscript>Si<Subscript>2</Subscript>O<Subscript>11</Subscript> CAS phase

The thermoelastic parameters of the CAS phase (CaAl₄Si₂O₁₁) were examined by in situ high-pressure (up to 23.7 GPa) and high-temperature (up to 2,100 K) synchrotron X-ray diffraction, using a Kawai-type multi-anvil press. P–V data at room temperature fitted to a third-order Birch–Murnaghan equation of state (BM EOS) yielded: V _0,300 = 324.2 ± 0.2 Å³ and K _0,300 = 164 ± 6 GPa for K′ _0,300 = 6.2 ± 0.8. With K′ _0,300 fixed to 4.0, we obtained: V _0,300 = 324.0 ± 0.1 Å³ and K _0,300 = 180 ± 1 GPa. Fitting our P–V–T data with a modified high-temperature BM EOS, we obtained: V _0,300 = 324.2 ± 0.1 Å³, K _0,300 = 171 ± 5 GPa, K′ _0,300 = 5.1 ± 0.6 (?K _0,T /?T) _P  = ?0.023 ± 0.006 GPa K^?1, and α_0,T  = 3.09 ± 0.25 × 10^?5 K^?1. Using the equation of state parameters of the CAS phase determined in the present study, we calculated a density profile of a hypothetical continental crust that would contain ~10 vol% of CaAl₄Si₂O₁₁. Because of the higher density compared with the coexisting minerals, the CAS phase is expected to be a plunging agent for continental crust subducted in the transition zone. On the other hand, because of the lower density compared with lower mantle minerals, the CAS phase is expected to remain buoyant in the lowermost part of the transition zone.     

A geochemical study on mud volcanoes in the Junggar Basin, China

A comprehensive study was performed to characterize, for the first time, the mud, water, and gases released from onshore mud volcanoes located in the southern margin of the Junggar Basin, northwestern China. Chemical compositions of mud, along with the geology of the basin, suggest that a source of the mud is Mesozoic or Cenozoic shale. Oxygen and H isotope compositions of the released water suggest a local meteoric origin. Combined with the positive Eu anomalies of the water, a large ¹⁸O shift of the water suggests extensive interaction with rocks. Gases discharged from the mud volcanoes are predominantly thermogenic hydrocarbons, and the high δ¹³C values (>+20‰ VPDB) for CO₂ gases and dissolved carbonate in muddy water suggest secondary methanogenesis with CO₂ reduction after oil biodegradation.The enrichments of Eu and ¹⁸O in water and the low thermal gradient of the area suggest that the water-rock interactions possibly occur deeper than 3670 ± 200 m. On the other hand, considering the relationship to the petroleum reservoir around the mud volcanoes, the depth of the gases can be derived from about 3600 m, a depth that is greater than that generally estimated for reservoirs whose gas is characterized by ¹³C-enriched CO₂. Oil biodegradation with CO₂ reduction likely occurs at a shallower depth along the seepage system of the mud volcano. The results contribute to the worldwide data set of gas genesis in mud volcanoes. Moreover, they further support the concept that most terrestrial mud volcanoes release thermogenic gas produced in very deep sediments and may be early indicators of oil biodegradation, an important problem in the petroleum industry.     

Detection of small earthquakes along the Pacific-Antarctic Ridge from T-waves recorded by abyssal ocean-bottom observatories

A number of seismoacoustic T-wave events were observed between January 2003 and January 2004 by broadband ocean-bottom seismometers installed on the French Polynesia seafloor at depths of 4,000?C5,000?m, well below the conjugate depth of the SOFAR channel. Using T-wave arrival times, we located 89 T-wave events along the Pacific-Antarctic Ridge. Among these, 63 events were not detected by land-based seismic observations of the United States Geological Survey (USGS), which was nearly twice the number of earthquakes reported by the USGS in the area during the observation period. We used a simple method to estimate earthquake magnitude from T-wave energy. The magnitudes of the events unidentified by the USGS ranged from 2.3 to 5.5, whereas magnitudes of the earthquakes reported by the USGS ranged from 4.1 to 6.2. Our study suggests that T-wave observations with abyssal ocean-bottom seismometers can improve the detection of small earthquakes and help our understanding of the seismotectonics of remote oceanic areas.     

Thermal expansion of fayalite,Fe2SiO4

Thermal expansion of single-crystal fayalite has been measured by a dilatometric method at temperatures between 25 °C and 850 °C. The results show the presence of anomalous expansion in the b axis, which is correlated to the anomalous variation of elastic moduli with temperature. Grüneisen's parameter is 1.10 and the thermal Debye temperature is 565 K, which is close to the acoustic Debye temperature of 511 K.     

Direct observation of Cm(III)-fulvate species on fulvic acid-montmorillonite hybrid by laser-induced fluorescence spectroscopy

Particulate matter plays an important role in the removal of metal ions from water in natural aquifers. Some of the most important of these materials consist of associations of inorganic particles (clay minerals, oxides) with humic substances, associations that can form readily in such an environment due to the strong affinity between inorganic particles and humic substances. These associations are referred to in this paper as organic-inorganic hybrids. However, it is not clear whether the sorbed species of metal ions in such organic-inorganic hybrids are organic or inorganic species because of the complexity of such hybrids and the lack of appropriate methods for characterizing the trace metal ions incorporated in them. In this study, laser-induced fluorescence spectroscopy (LIF) was used successfully to characterize the Cm(III) species on an FA(fulvic acid)-montmorillonite hybrid, an example of such organic-inorganic hybrids. The LIF clearly showed that Cm(III) can be sorbed as Cm(III)-fulvate complex in the FA-montmorillonite hybrid. These results were consistent with those of experiments of solid-water partitioning of Cm(III) (or Eu(III) used as an analogue) and speciation calculations based on the stability constants of Cm(III)-fulvate complexes determined in this study. The results of LIF and the partitioning experiments showed that the solid-water distribution of humic substances governed that of Cm(III) under our experimental conditions. The Cm(III) preference for forming Cm(III)-fulvate complexes was also evident under a condition that would be found in a natural aquifer with a fairly low concentration of organic matter in freshwater (dissolved organic carbon: 2 mg/dm³), as determined by our speciation calculations. These findings on the importance of humic substances in the migration of Cm(III) indicate that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Cm(III), or actinide(III) and lanthanide(III) ions, in natural aquifers.     

Reconstruction of a climate record for the past 140 kyr based on diatom valve flux data from Lake Biwa, Japan

To reconstruct the pattern of past climate change in central Japan during the last 140 kyr, total planktonic diatom valve concentrations (valves g^–1) and fluxes (valves cm^–2 year^–1) of total planktonic diatoms flux (PVF) and individual species were examined using a 140-m core taken from Lake Biwa, Shiga Prefecture. Most records had a sample resolution between approximately 150 and 300 yr. Based on characteristics of past and modern diatom responses to possible climate variables, we interpreted changes in Stephanodiscus suzukii flux (SVF) to reflect changes in phosphorus levels, which reflect, in turn, summer precipitation levels; changes in Aulacoseiva nipponica flux (AVF) reflect winter vertical lake-water mixing induced by winter temperatures and snowfall levels. Thus, changes in total planktonic diatom flux reflect a combination of summer precipitation, winter temperature, and snowfall values. During the 140–101 ka interval, changes in S. suzukii productivity at a millennial timescale may correspond to changes in summer rainfall in central Japan. The disappearance of A. nipponica during the same period could indicate weaker vertical mixing, possibly caused by increased temperatures and decreased snowfall levels in winter. During the 101–70 ka interval, the AVF record shows levels near or above those observed in present times, indicating that winter water temperatures fell within the optimal range for A. nipponica to prosper. Generally low AVF values during the 70–7 ka interval indicate weak winter vertical mixing and cold winters. The many intervals with low PVF values during the same period suggest decreased summer precipitation levels. Between 7 and 0 ka, PVF, SVF, and AVF records show levels near or above those of the present, suggesting winter temperatures favorable for A. nipponica growth, and snowfall and summer precipitation levels probably similar to or above those currently recorded.     

Simulation analysis of ground liquefaction induced by earthquake

A dynamic effective stress analysis with the finite element method has long been recommended to predict the liquefaction phenomena of sandy soil by authors and Zienkiewicz et al. as well as the similar approaches by the others. Our approach of the analysis is summarized in the first.

Until recently, however, these approaches has not commonly been used as the means of design, although its capability of prediction is appreciated by geotechnicians. This method has been neglected because of the lack of verification studies of soil models of sand and mathematical formulation for boundary problems of liquefaction phenomena. Therefore the verification of the numerical method to evaluate liquefaction potential are urgent requirement of the recent engineering practice. To respond this requirement, extensive numerical studies on the liquefation simulations are performed by DIANA program for shaking table tests which have been conducted by the authors. The test models are soil-structure type models with combination of homogenous ground and partially improved ground by compaction.

The good performance of our approach is proved by the results of numerical simulation showing good agreement with experimental data in terms of response acceleration, excess pore pressure, and deformation profile. It is also demonstrated that the numerical results can provide substantial information to understand the mechanisms of soil ground behavior which is not easily obtained by experiments.

The procedure to identify soil constants for the reflecting surface model is also reported in details.