Estimation of suspended sediment sources using 137Cs and 210Pbex in unmanaged Japanese cypress plantation watersheds in southern Japan

To analyse suspended sediment sources in unmanaged Japanese cypress plantation watersheds, field measurements and fingerprinting of the suspended sediment was conducted in the Shimanto River basin in southern Japan. For sediment fingerprinting, ¹³⁷Cs and ²¹⁰Pb_ex were detected by means of gamma‐ray spectrometry in the surface soil of the forest floor, stream bank and truck trail and mobilized sediment by interrill erosion. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the forest floor materials were considerably higher than those of the stream bank and truck trail. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the suspended sediment were found to vary with the sampling period. Evidently, the suspended sediment can comprise materials generated from the forest floor by interrill erosion and those from the truck trail and/or stream bank. The multivariate sediment‐mixing model using ¹³⁷Cs and ²¹⁰Pb_ex showed that the contribution of the forest floor varied periodically, ranging from 23–56% in the Hinoki 156 subwatershed and from 18–85% in the Hinoki 155 subwatershed. The difference in the average contribution of the forest floor between Hinoki 156 (46%) and Hinoki 155 (69%) may relate to the presence of truck trail networks in the watershed. The truck trail network can play roles of sediment source and pathway for sediment from forest floor to stream channel due to the concentrated overland flow on the truck trail during heavy rainfall events. These results indicate that the forest floor should be recognized as a major source of suspended sediment in unmanaged Japanese cypress plantation watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

Acute toxicity of temporally varying seawater CO2 conditions on juveniles of Japanese sillago (Sillago japonica)

CO(2) ocean storage by which liquefied CO(2) is injected into the deep-sea to mitigate the climate change would increase the CO(2) concentrations of the surrounding seawater. The biological impacts of such dynamic CO(2) environments are, however, unknown. We examined the acute toxicity of temporally changing seawater CO(2) concentrations on juveniles of Sillago japonica. Step-wise increases in ambient CO(2) to fCO(2) (fractional CO(2) concentration of the gas mixture bubbled into seawater) levels of 7% and 9% resulted in mortalities of 0.15 and 0.40-0.67 after 18 h, respectively. In contrast, one-step increases to these CO(2) levels killed all fish within 15 min. Further, a sudden drop of fCO(2) from 9-10% CO(2) to normocapnia (0.038%) killed all the surviving fish within a few minutes. These results demonstrate that impacts of ocean CO(2) storage need to be examined under conditions mimicking the dynamic changes in CO(2) levels expected to occur by the CO(2) injection procedure.     

Characteristic features in Venus’ nightside cloud-top temperature obtained by Akatsuki/LIR

Mid-infrared images of almost the entire Venus nightside hemisphere obtained by the Longwave Infrared Camera (LIR) onboard Akatsuki on December 9 and 10, 2010 reveal that the brightness temperature of the cloud-top ranges from 237 K in the cold polar collars to 243 K in the equatorial region, significantly higher than the values obtained by Venera 15. Other characteristic features of the temperature distributions observed are zonal belt structures seen in the middle and low latitudes and patchy temperature structures or quasi-periodic streaks extending in a north–south direction in the northern middle latitudes and southern low latitudes.     

Role of tonalite-trodhjemite-granite (TTG) crust subduction on the mechanism of supercontinent breakup

The tonalite-trondhjemite-granite (TTG) crust has been considered to be buoyant and hence impossible to be subducted into the deep mantle. However, recent studies on the juvenile arc in the western Pacific region indicate that immature island arcs subduct into the deep mantle in most cases, except in the case of parallel arc collision. Moreover, sediment trapped subduction and tectonic erosion are also common. This has important implications in evaluating the role of TTG crust in the deep mantle and probably on the bottom of the mantle. Because the TTG crust is enriched in K, U and Th, ca. 20 times more than that of CI chondrite, the accumulated TTG on the Core Mantle Boundary (CMB) would have played a critical role to initiate plumes or superplumes radiating from the thermal boundary layer, particularly after 2.0 Ga, related to the origin of superplume-supercontinent cycle. This is because selective subduction of oceanic lithosphere including sediment-trapped subduction, tectonic erosion and arc- and microcontinent-subduction proceeded under the supercontinent before the final amalgamation ca. 200-300 million years after the formation of the nuclei. We speculate the mechanism of superplume evolution through the subduction of TTG-crust and propose that this process might have played a dominant role in supercontinent breakup.     

Granite subduction: Arc subduction, tectonic erosion and sediment subduction

Continental growth has been episodic, reflecting the episodic nature of mantle dynamics as well as surface dynamics of the Earth, the net result of which is exhibited by the present mantle with two huge reservoirs of TTG rocks, one on the surface continents and the other on the D″ layer on the Core-Mantle Boundary (CMB). During the early half of the Earth history, the felsic continental crust on the surface which formed in an intra-oceanic environment has mostly been subducted into the deep mantle, except in the rare case of parallel arc collision. The growth history of continental crust shows that with its simultaneous formation, a considerable amount must have also been subducted. Such ongoing subduction processes can be seen in the western Pacific region, through tectonic erosion, arc subduction, and sediment-trapped subduction.     

FeO*-Al2O3-TiO2-Rich Rocks of the Tertiary Bana Igneous Complex, West Cameroon

FeO*‐Al₂O₃‐TiO₂‐rich rocks are found associated with transitional tholeiitic lava flows in the Tertiary Bana plutono‐volcanic complex in the continental sector of the Cameroon Line. These peculiar rocks consist principally of iron‐titanium oxides, aluminosilicates and phosphates, and occur as layers 1–3 m thick occupying the upper part of lava flows on the southwest (site 1) and northwest (site 2) sites of the complex. Mineral constituents of the rocks include magnetite, ilmenite, hematite, rutile, corundum, andalusite, sillimanite, cordierite, quartz, plagioclase, alkali feldspar, apatite, Fe‐Mn phosphate, Al phosphate, micas and fine mixtures of sericite and silica. Texturally and compositionally, the rocks can be subdivided into globular type, banded type, and Al‐rich fine‐gained massive type. The first two types consist of dark globule or band enriched in Fe‐Ti oxides and apatite and lighter colored groundmass or bands enriched in aluminosilicates and quartz, respectively. The occurrence of andalusite and sillimanite and the compositional relations of magnetite and ilmenite in the FeO*‐Al₂O₃‐TiO₂‐rich rocks suggest temperatures of crystallization in a range of 690–830°C at low pressures. The Bana FeO*‐Al₂O₃‐TiO₂‐rich rocks are characterized by low concentrations of SiO₂ (25–54.2 wt%), Na₂O + K₂O (0–1%), CaO (0–2%) and MgO (0–0.5%), and high concentrations of FeO* (total iron as FeO, 20–42%), Al₂O₃ (20–42%), TiO₂ (3–9.2%), and P₂O₅ (0.26–1.30%). TiO₂ is positively correlated with Al₂O₃ and inversely correlated with FeO*. The bulk rock compositions cannot be derived from the associated basaltic magma by crystal fractionation or by partial melting of the mantle or lower crustal materials. In ternary diagrams of (Al₂O₃)?(CaO + Na₂O + K₂O)?(FeO*+ MnO + MgO) and (SiO₂)?(FeO*)?(Al₂O₃), the compositional field of the rocks is close to that of laterite and is distinct from the common volcanic rocks, suggesting that the rocks are derived from lateritic materials by recrystallization when the materials are heated by the basaltic magmas. A hydrothermal origin is discounted because the rocks contain high‐temperature mineral assemblages and lack sulfide minerals. It is proposed that the FeO*‐Al₂O₃‐TiO₂‐rich rocks of the Bana complex were formed by pyrometamorphism of laterite by the heat of basaltic magmas.     

Long-range transport of particulate polycyclic aromatic hydrocarbons at Cape Hedo remote island site in the East China Sea between 2005 and 2008

Particle-associated polycyclic aromatic hydrocarbons (PAHs) in outflow from East Asia were observed at Cape Hedo, Okinawa, Japan between 2005 and 2008. The filter samples of the total suspended particles were analyzed by means of gas chromatography-mass spectrometry. The total concentration of fourteen 3–7-ring PAHs was 0.01–24 ng m^?3 (average 1.6 ng m^?3). The average PAH concentration increased in the winter-spring season and decreased in the summer-fall season. The average benzo(a)pyrene to benzo(e)pyrene ratio was 0.49 in the winter-spring season and was lower than the literature values for East Asian cities in the same season. This result shows that aging of organic aerosol particles proceeds during long-range transport from East Asia. In the Asian Pacific region, these pollutants are transported from East Asia in the winter-spring season, whereas clean air mass is transported from the Pacific Ocean in the summer-fall season.     

Depth Variability of Compressive Strength Test Results of Toki Granite from Shobasama and Mizunami Construction Sites,Japan

This paper studies the depth variability of uniaxial compressive laboratory test results on intact Toki granite (i.e., sound rock without macroscopic fractures) from the Shobasama and Mizunami Construction Sites, Japan. Some of the depth variability observed in the laboratory results can be indirectly attributed to the high fracture frequency of the “upper highly fractured rock domain” from which some of the samples were taken. For samples taken from the “lower sparsely fractured rock domain,” however, the uniaxial compressive strength of the granite seems to be very strongly correlated to the level of in situ rock stress (i.e., maximum shear stress) determined by measurement results obtained from hydrofracturing tests. The correlation between the laboratory results and the level of in situ stress is explained by the damage due to the complex stress path that the cores undergo during drilling, besides the stress concentrations at the drill-bit/rock contact, which can also affect the microcracking of the samples. An attempt to adjust laboratory test results to estimate the in situ intact rock strength of Toki granite based on its correlation with in situ stresses was carried out.     

The stability and origin of sodicgedrite in ultrahigh-temperature Mg-Al granulites: a case study from the Gondwana suture in southern India

Mg-Al-rich rocks from the Palghat-Cauvery Shear Zone System (PCSZ) within the Gondwana suture zone in southern India contain sodicgedrite as one of the prograde to peak phases, stable during T = 900–990°C ultrahigh-temperature metamorphism. Gedrite in these samples is Mg-rich (Mg/[Fe + Mg] = X _Mg = 0.69–0.80) and shows wide variation in Na₂O content (1.4–2.3 wt.%, Na^A = 0.33–0.61 pfu). Gedrite adjacent to kyanite pseudomorph is in part mantled by garnet and cordierite. The gedrite proximal to garnet shows an increase in Na^A and Al^IV from the core (Na^A = 0.40–0.51 pfu, Al^IV = 1.6–1.9 pfu) to the rim (Na^A = 0.49–0.61 pfu, Al^IV = 2.0–2.2 pfu), suggesting the progress of the following dehydration reaction: Ged + Ky → Na-Ged + Grt + Crd + H₂O. This reaction suggests that, as the reactants broke down during the prograde stage, the remaining gedrite became enriched in Na to form sodicgedrite, which is regarded as a unique feature of high-grade rocks with Mg-Al-rich and K–Si-poor bulk chemistry. We carried out high-P-T experimental studies on natural sodicgedrite and the results indicate that gedrite and melt are stable phases at 12 kbar and 1,000°C. However, the product gedrite is Na-poor with only <0.13 wt.% Na₂O (Na^A = 0.015–0.034 pfu). In contrast, the matrix glass contains up to 8.5 wt.% Na₂O, suggesting that, with the progressive melting of the starting material, Na was partitioned into the melt rather than gedrite. The results therefore imply that the occurrence of sodicgedrite in the UHT rocks of the PCSZ is probably due to the low H₂O activity during peak P-T conditions that restricted extensive partial melting in these rocks, leaving Na partitioned into the solid phase (gedrite). The occurrence of abundant primary CO₂-rich fluid inclusions in this rock, which possibly infiltrated along the collisional suture during the final amalgamation of the Gondwana supercontinent, strengthens the inference of low water activity.