Synthesis of γ-Mg2SiO4

Magnesium orthosilicate with spinel structure (γ-Mg₂SiO₄) was synthesized at about 250 kbar and 1000°C. Unit cell dimension was established to be 8.076 ± 0.001Å. X-ray powder diffraction pattern revealed a significant difference between γ-Mg₂SiO₄ and other γ-M₂SiO₄ spinels (M = Fe, Co, and Ni) in the intensities of (111) and (331) reflections, both of which are virtually absent in the Mg₂SiO₄ spinel. This feature could be thoroughly understood by the calculation of the intensities for several silicate spinels.     

A Simple Theoretical Radiation Scheme for Regular Building Arrays

We propose a simple theoretical radiation scheme for regular building arrays. The essential difference of the present radiation scheme from the previous ones is the explicit consideration of the three-dimensional features of the surface geometry. The model is assumed to be an infinitely extended regular array of uniform buildings, each building composed of six faces (roof, floor, and four vertical walls). Without using time-consuming iterations or statistical approaches, we calculated the view factors of the faces, the complicated sunlit--shadow distributions, and the resulting canopy albedo for any time and location. The model was evaluated by comparing to outdoor experiments in a wide range of seasons and surface geometries. The simulated canopy albedos agreed well with measured values, and the accuracy is a significant improvement over two-dimensional-based model outputs.     

The role of pore water in the mechanical behavior of unsaturated soils

Deformation and failure of soils are governed by the stresses acting on the soil skeleton. The isotropic stress acting on the soil skeleton can be divided into two components. One is the stress component which is transmitted through the soil skeleton. This skeleton stress is influenced by the pore water (bulk water) in the soil. The other is the internal stress component which does not contribute to equilibrium with a given external force. The internal stress is induced by the capillary tension of meniscus water clinging to the contact point of soil particles and acts so as to connect the soil particles tightly. Therefore, in modeling the stress and strain relations for unsaturated soils, it is of much importance to quantitatively evaluate how the pore water exists in the soil. This paper discusses the role of pore water on the mechanical behaviour of the soil. In particular, the significance of the water retention curve is emphasized from a mechanical viewpoint. Essential features required in modeling of the constitutive relations for unsaturated soils are discussed and presented.     

http://www.sciencedirect.com/science/article/pii/S167498711200148X

The Earth was born from a giant impact at 4.56 Ga. It is generally thought that the Earth subsequently cooled, and hence shrunk, over geologic time. However, if the Earth's convection was double-layered, there must have been a peak of expansion during uni-directional cooling. We computed the expansion-contraction effect using first principles mineral physics data. The result shows a radius about 120 km larger than that of the present Earth immediately after the consolidation of the magma-ocean on the surface, and subsequent shrinkage of about 110 km in radius within about 10 m.y., followed by gradual expansion of 11 km in radius due to radiogenic heating in the lower mantle in spite of cooling in the upper mantle in the Archean. This was due to double-layered convection in the Archean with final collapse of overturn with contraction of about 8 km in radius, presumably by the end of the Archean. Since then, the Earth has gradually cooled down to reduce its radius by around 12 km. Geologic evidence supports the late Archean mantle overturn ca. 2.6 Ga, such as the global distribution of super-liquidus flood basalts on nearly all cratonic fragments (>35 examples). If our inference is correct, the surface environment of the Earth must have undergone extensive volcanism and emergence of local landmasses, because of the thin ocean cover (3–5 km thickness). Global unconformity appeared in cratonic fragments with stromatolite back to 2.9 Ga with a peak at 2.6 Ga. The global magmatism brought extensive crustal melting to yield explosive felsic volcanism to transport volcanic ash into the stratosphere during the catastrophic mantle overturn. This event seems to be recorded by sulfur mass-independent fractionation (SMIF) at 2.6 Ga. During the mantle overturn, a number of mantle plumes penetrated into the upper mantle and caused local upward doming of by ca. 2–3 km which raised local landmasses above sea-level. The consequent increase of atmospheric oxygen enabled life evolution from prokaryotes to eukaryotes by 2.1 Ga, or even earlier in the Earth history.     

Integrating basin modeling with seismic technology and rock physics

We explore the link between basin modelling and seismic inversion by applying different rock physics models. This study uses the E‐Dragon II data in the Gulf of Mexico. To investigate the impact of different rock physics models on the link between basin modelling and seismic inversion, we first model relationships between seismic velocities and both (1) porosity and (2) effective stress for well‐log data using published rock physics models. Then, we build 1D basin models to predict seismic velocities derived from basin modelling with different rock physics models, in a comparison with average sonic velocities measured in the wells. Finally, we examine how basin modelling outputs can be used to aid seismic inversion by providing constraints for the background low‐frequency model. For this, we run different scenarios of inverting near angle partial stack seismic data into elastic impedances to test the impact of the background model on the quality of the inversion results. The results of the study suggest that the link between basin modelling and seismic technology is a two‐way interaction in terms of potential applications, and the key to refine it is establishing a rock physics models that properly describes changes in seismic signatures reflecting changes in rock properties.     

Geochemical and hydrological controls on biannual lamination of tufa deposits

Fluvial tufa deposits in southwest Japan commonly develop biannual lamination consisting of dense summer layers and porous winter layers, and the clearness of the laminae varies among the sites. The laminae have been largely attributed to a seasonally variable inorganic precipitation rate of calcite. This rate-controlled hypothesis was examined by using quantitative data for calcite packing-density (CPD) and the precipitation rate of calcite (PWP rate) calculated from water chemistry. The results for four tufa-depositing sites in SW Japan show that a positive correlation between CPD and PWP rate becomes less certain with increasing PWP rate. In the temperature realm of SW Japan, tufas develop regular distinct seasonal change in CPD when deposited in water containing Ca values less than 65 mg/l, which results in a relatively low precipitation rate. The CPD of tufa deposits rarely exceeds 65%, owing to pore space between fine-grained calcite crystals and to porosity derived from decomposed cyanobacteria and other microorganisms. By increasing the Ca content to more than 65 mg/l, the CPD often attains an upper limit and becomes insensitive to seasonal changes in the PWP rate. Therefore, seasonal variations in CPD at sites with a higher Ca content are unclear, as seen in two examples from tropical islands in southern Japan and in one locality in a temperate climate. The flow rate and microbial density on the tufa surface are subordinate factors with respect to the CPD. Seasonal changes in these two factors often enhance the porous/dense contrast of biannual lamination in SW Japan.     

Spatial distribution and temporal trends of rainfall and erosivity in the Eastern Africa region

Soil erosion by water is one of the main environmental concerns in the drought‐prone Eastern Africa region. Understanding factors such as rainfall and erosivity is therefore of utmost importance for soil erosion risk assessment and soil and water conservation planning. In this study, we evaluated the spatial distribution and temporal trends of rainfall and erosivity for the Eastern Africa region during the period 1981–2016. The precipitation concentration index, seasonality index, and modified Fournier index have been analysed using 5 × 5‐km resolution multisource rainfall product (Climate Hazards Group InfraRed Precipitation with Stations). The mean annual rainfall of the region was 810 mm ranging from less than 300 mm in the lowland areas to over 1,200 mm in the highlands being influenced by orography of the Eastern Africa region. The precipitation concentration index and seasonality index revealed a spatial pattern of rainfall seasonality dependent on latitude, with a more pronounced seasonality as we go far from the equator. The modified Fournier index showed high spatial variability with about 55% of the region subject to high to very high rainfall erosivity. The mean annual R‐factor in the study region was calculated at 3,246 ± 1,895 MJ mm ha^?1 h^?1 yr^?1, implying a potentially high water erosion risk in the region. Moreover, both increasing and decreasing trends of annual rainfall and erosivity were observed but spatial variability of these trends was high. This study offers useful information for better soil erosion prediction as well as can support policy development to achieve sustainable regional environmental planning and management of soil and water resources.     

Temporal changes in benthic communities of seagrass beds impacted by a tsunami in the Andaman Sea,Thailand

Seagrass beds are susceptible to various natural and human-induced disturbances. Disturbances affect not only seagrasses, but also the abundance and diversity of associated macrofaunal communities. The Andaman Sea coast of Thailand was heavily affected by the tsunami of December 26, 2004. To examine its impact on seagrass macrofaunal communities, we compared the abundance, diversity and taxa composition by quantitative samplings in 2001 (before the tsunami) and in 2005 and 2006 (after the tsunami). Macrobenthic animals and sediments were collected from vegetated and nonvegetated areas of two sites that had received different levels of tsunami disturbances. A large decline in abundance and diversity was observed in the nonvegetated areas after the tsunami, whereas an increase was observed in the vegetated areas. The magnitude of decline and subsequent recovery of abundance and diversity of macrobenthic animals in nonvegetated areas were similar between the two sites, suggesting that their temporal changes were not solely related to the magnitude of the tsunami disturbance. Similarity of the benthic animals differed greatly between 2001 and 2005–2006 at the nonvegetated areas, whereas it varied less among the 3 years at the seagrass-vegetated areas. This study demonstrated that the presence of seagrass vegetation alters the patterns of temporal variation in macrofaunal assemblages and subsequent recovery processes following a tsunami.     

Experimental Study of Geoneutrinos with KamLAND

The Kamioka liquid scintillator antineutrino detector (KamLAND), which consists of 1000 tones of ultra-pure liquid scintillator surrounded by 1879 photo-multiplier tubes (PMT), is the first detector sensitive enough to detect geoneutrinos. Earth models suggest that KamLAND observes geoneutrinos at a rate of 30 events/10³²-protons/year from the ²³⁸U decay chain, and 8 events/10³²-protons/year from the ²³²Th decay chain. With 7.09×10³¹ proton-years of detector exposure and detection efficiency of 0.687 ± 0.007, the ‘rate-only’ analysis gives geoneutrino candidates. Assuming a Th/U mass concentration ratio of 3.9, the ‘rate + shape’ analysis gives the 90% confidence interval for the total number of geoneutrinos detected to be from 4.5 to 54.2. This result is consistent with predictions from the Earth models. The 99% C.L. upper limit is set at 1.45×10⁻³¹ events per target proton per year, which is 3.8 times higher than the central value of the model prediction that gives 16 TW of radiogenic heat production from ²³⁸U and ²³²Th. Although the present data have limited statistical power, they provide by direct means an upper limit for the Earth’s radiogenic heat of U and Th. Sanshiro Enomoto (on behalf of the KamLAND Collaboration)