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  • Articles  (93)
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  • 2015-2019  (93)
  • Nature  (12)
  • Geochemistry Geophysics Geosystems (G3)  (11)
  • Journal of Geophysical Research JGR - Space Physics  (11)
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  • Articles  (93)
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  • 1
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    Auroral evidence of radial transport at Jupiter during January 2014 (2016)
    American Geophysical Union
    Details
    Publication Date: 2016-10-01
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 2
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    Missing western half of the Pacific Plate: Geochemical nature of the Izanagi–Pacific Ridge interaction with a stationary boundary between the Indian and Pacific mantles (2015)
    Wiley
    Details
    Publication Date: 2015-09-15
    Description: The source mantle of the basaltic ocean crust on the western half of the Pacific Plate was examined using Pb–Nd–Hf isotopes. The results showed that the subducted Izanagi–Pacific Ridge (IPR) formed from both Pacific (180–∼80 Ma) and Indian (∼80–70 Ma) mantles. The western Pacific Plate becomes younger westward and is thought to have formed from the IPR. The ridge was subducted along the Kurile–Japan–Nankai–Ryukyu (KJNR) Trench at 60–55 Ma and leading edge of the Pacific Plate is currently stagnated in the mantle transition zone. Conversely, the entire eastern half of the Pacific Plate, formed from isotopically distinct Pacific mantle along the East Pacific Rise and the Juan de Fuca Ridge, largely remains on the seafloor. The subducted IPR is inaccessible; therefore, questions regarding which mantle might be responsible for the formation of the western half of the Pacific Plate remain controversial. Knowing the source of the IPR basalts provides insight into the Indian–Pacific mantle boundary before the Cenozoic. Isotopic compositions of the basalts from borehole cores (165–130 Ma) in the western Pacific show that the surface oceanic crust is of Pacific mantle origin. However, the accreted ocean floor basalts (∼80–70 Ma) in the accretionary prism along the KJNR Trench have Indian mantle signatures. This indicates the younger western Pacific Plate of IPR origin formed partly from Indian mantle and that the Indian–Pacific mantle boundary has been stationary in the western Pacific at least since the Cretaceous. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Geochemical records from loess deposits in Japan over the last 210 kyr: Lithogenic source changes and paleoclimatic indications (2016)
    Wiley
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    Publication Date: 2016-06-24
    Description: The generation, transport, and accumulation of tropospheric dust have changed with the paleoclimatic changes of the Quaternary Period. Such dust has accumulated in Japan ∼3000 km leeward of the source deserts in China. We analyzed the fractions of windblown fine quartz and bulk major and trace elements, and Sr–Nd–Pb isotopic compositions of loess in SW Japan deposited over the past 210 kyr. The results indicated extensive accumulation of tropospheric dust mixed with tephra fragments derived from the nearby Daisen volcano. The accumulation rate of fine quartz and selected elemental/isotopic compositions can be used as climatic proxies that reflect greater accumulation of dust in times of colder climate. Chemical indices for weathering show enhanced effects of weathering during times of warmer climate. The trace element compositions of the loess deposits are surprisingly similar to those of the Chinese loess, hemipelagic sediments in the Sea of Japan and the western Pacific Ocean, and the distal Chinese dust found in Canada. This similarity indicates that the loess dust shares major fractions of these fine-grained sediments, and that geochemical fractionation during the transport was limited. The Sr–Nd–Pb isotope compositions of the SW Japan loess indicate an origin predominantly in the Gobi Desert. The high-latitude Pacific sediments and high-latitude dust in Canada also show the same signature. However, isotopic compositions of samples from the southern Chinese loess plateau and mid- to low-latitude Pacific sediments are largely derived from the Taklimakan desert, which indicates different delivery pathways of the tropospheric dusts. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Origin of geochemical mantle components: Role of subduction filter (2016)
    Wiley
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    Publication Date: 2016-07-19
    Description: We quantitatively explore element redistribution at subduction zones using numerical mass balance models to evaluate the roles of the subduction zone filter in the Earth's geochemical cycle. Our models of slab residues after arc magma genesis differ from previous ones by being internally consistent with geodynamic models of modern arcs that successfully explain arc magma genesis, and include element fluxes from the dehydration/melting of each underlying slab component. We assume that the mantle potential temperature ( T p ) was 1400–1650°C at 3.5–1.7 Ga and gradually decreased to 1300–1350°C today. Hot subduction zones with T p ∼1650°C have a thermal structure like modern SW Japan where high-Mg andesite is formed that is chemically like continental crust. After 2.5–1.7 Gyr of storage in the mantle, the residual igneous oceanic crust from hot subduction zones can evolve isotopically to the HIMU mantle component, the residual base of the mantle wedge to EMI, the residual sediment becomes an essential part of EMII, and the residual top of the mantle wedge can become the subcontinental lithosphere component. The Common or Focal Zone component is a stable mixture of the first three residues occasionally mixed with early depleted mantle. Slab residue that recycled earlier (∼2.5 Ga) form the DUPAL anomaly in the southern hemisphere, whereas residues of more recent recycling (∼1.7 Ga) underlie the northern hemisphere. These ages correspond to major continental crust forming events. The east-west heterogeneity of the depleted upper mantle involves sub continental mantle except in the Pacific. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 5
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    Geochemical variations in Japan Sea back-arc basin basalts formed by high-temperature adiabatic melting of mantle metasomatized by sediment subduction components (2015)
    Wiley
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    Publication Date: 2015-04-16
    Description: The Yamato Basin in the Japan Sea is a back-arc basin characterized by basaltic oceanic crust that is twice as thick as typical oceanic crust. Two types of ocean floor basalts, formed during the opening of the Japan Sea in the Middle Miocene, were recovered from the Yamato Basin during Ocean Drilling Program Legs 127/128. These can be considered as depleted (D-type) and enriched (E-type) basalts based on their incompatible trace element and Sr–Nd–Pb–Hf isotopic compositions. Both types of basalts plot along a common mixing array drawn between depleted mantle and slab sediment represented by a sand-rich turbidite on the Pacific Plate in the NE Japan forearc. The depleted nature of the D-type basalts suggests that the slab sediment component is nil to minor relative to the dominant mantle component, whereas the enrichment of all incompatible elements in the E-type basalts was likely caused by a large contribution of bulk slab sediment in the source. The results of forward model calculations using adiabatic melting of a hydrous mantle with sediment flux indicate that the melting conditions of the source mantle for the D-type basalts are deeper and hotter than those for the E-type basalts, which appear to have formed under conditions hotter than those of normal mid-oceanic ridge basalts (MORB). These results suggest that the thicker oceanic crust was formed by greater degrees of melting of a hydrous metasomatized mantle source at unusually high mantle potential temperature during the opening of the Japan Sea. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 6
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    Lypd8 promotes the segregation of flagellated microbiota and colonic epithelia (2016)
    Springer Nature
    In: Nature
    Details
    Publication Date: 2016-04-07
    Description: Lypd8 promotes the segregation of flagellated microbiota and colonic epithelia Nature 532, 7597 (2016). doi:10.1038/nature17406 Authors: Ryu Okumura, Takashi Kurakawa, Takashi Nakano, Hisako Kayama, Makoto Kinoshita, Daisuke Motooka, Kazuyoshi Gotoh, Taishi Kimura, Naganori Kamiyama, Takashi Kusu, Yoshiyasu Ueda, Hong Wu, Hideki Iijima, Soumik Barman, Hideki Osawa, Hiroshi Matsuno, Junichi Nishimura, Yusuke Ohba, Shota Nakamura, Tetsuya Iida, Masahiro Yamamoto, Eiji Umemoto, Koichi Sano & Kiyoshi Takeda Colonic epithelial cells are covered by thick inner and outer mucus layers. The inner mucus layer is free of commensal microbiota, which contributes to the maintenance of gut homeostasis. In the small intestine, molecules critical for prevention of bacterial invasion into epithelia such as Paneth-cell-derived anti-microbial peptides and regenerating islet-derived 3 (RegIII) family proteins have been identified. Although there are mucus layers providing physical barriers against the large number of microbiota present in the large intestine, the mechanisms that separate bacteria and colonic epithelia are not fully elucidated. Here we show that Ly6/PLAUR domain containing 8 (Lypd8) protein prevents flagellated microbiota invading the colonic epithelia in mice. Lypd8, selectively expressed in epithelial cells at the uppermost layer of the large intestinal gland, was secreted into the lumen and bound flagellated bacteria including Proteus mirabilis. In the absence of Lypd8, bacteria were present in the inner mucus layer and many flagellated bacteria invaded epithelia. Lypd8−/− mice were highly sensitive to intestinal inflammation induced by dextran sulfate sodium (DSS). Antibiotic elimination of Gram-negative flagellated bacteria restored the bacterial-free state of the inner mucus layer and ameliorated DSS-induced intestinal inflammation in Lypd8−/− mice. Lypd8 bound to flagella and suppressed motility of flagellated bacteria. Thus, Lypd8 mediates segregation of intestinal bacteria and epithelial cells in the colon to preserve intestinal homeostasis.
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 7
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    Reply to comment by Ivan Pineda-Velasco, Tai T. Nguyen, Hiroshi Kitagawa, and Eizo Nakamura on “Diverse magmatic effects of subducting a hot slab in SW Japan: Results from forward modeling” (2015)
    Wiley
    Details
    Publication Date: 2015-07-18
    Description: The Comment by Pineda-Velasco et al . [2015] examined Pb isotope data presented by Kimura et al . [2014]. The authors' points are that (1) there is uncertainty in the analytical results of Kimura et al . [2014] due to the effect of mass fractionation, and therefore, (2) the interpretations of Kimura et al . [2014] based on the extent of crustal assimilation and the estimated Pb isotopic composition of the crustal component are erroneous. In response to the Comment, we report a flaw in the original paper that the samples from the Aono, Daisen, and Kannabe regions were analyzed using conventional TIMS methods and all other samples were analyzed using thallium-spiked multi-collector inductively-coupled-plasma mass spectrometry (TS-MC-ICP-MS). We have re-analyzed the sample powders from Karasugasen, Daisen, and Aono using TS-MC-ICP-MS. Our new results showed considerable overlap with the data in Pineda-Velasco et al . [2015]. Therefore, the isotopic trends shown by the conventional TIMS in Kimura et al . [2014] were analytical artifacts from mass bias. We conclude that the crustal assimilation proposed by Kimura et al . [2014] was erroneous in terms of Pb isotopes, nevertheless some crustal assimilation in the Karasugasen lava is evident from the chemical zoning of hornblende phenocrysts. Although the original Pb isotope argument for crustal contamination was wrong, the ABS4 modeling is unaffected because of no to subtle changes in estimated mantle source compositions in their ABS4 model. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 8
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    Origins of felsic magmas in Japanese subduction zone: Geochemical characterizations of tephra from caldera-forming eruptions (2015)
    Wiley
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    Publication Date: 2015-06-06
    Description: Dacitic to rhyolitic glass shards from 80 widespread tephras erupted during the past 5 Mys from calderas in Kyushu, and SW, central, and NE Japan were analyzed. Laser ablation inductively coupled plasma mass spectrometry was used to determine 10 major and 33 trace elements and 207 Pb/ 206 Pb– 208 Pb/ 206 Pb isotope ratios. The tephras were classified into three major geochemical types and their source rocks were identified as plutonic, sedimentary, and intermediate amphibolite rocks in the upper crust. A few tephras from SW Japan were identified as adakite and alkali rhyolite and were regarded to have originated from slab melt and mantle melt, respectively. The Pb isotope ratios of the tephras are comparable to those of the intermediate lavas in the source areas but are different from the basalts in these areas. The crustal assimilants for the intermediate lavas were largely from crustal melts and are represented by the rhyolitic tephras. A large heat source is required for forming large volumes of felsic crustal melts and is usually supplied by the mantle via basalt. Hydrous arc basalt formed by cold slab subduction is voluminous, and its heat transfer with high water content may have melted crustal rocks leading to effective felsic magma production. Coincidence of basalt and felsic magma activities shown by this study suggests caldera-forming eruptions are ultimately the effect of a mantle-driven cause. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 9
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    Jupiter's X-ray and EUV auroras monitored by Chandra, XMM-Newton, and Hisaki satellite (2016)
    Wiley
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    Publication Date: 2016-02-06
    Description: Jupiter's X-ray auroral emission in the polar cap region results from particles which have undergone strong field-aligned acceleration into the ionosphere [ Cravens et al. , 2003]. The origin of precipitating ions and electrons and the time variability in the X-ray emission are essential to uncover the driving mechanism for the high energy acceleration. The magnetospheric location of the source field line where the X-ray is generated is likely affected by the solar wind variability. However, these essential characteristics are still unknown because the long-term monitoring of the X-rays and contemporaneous solar wind variability has not been carried out. In Apr 2014, the first long-term multi-wavelength monitoring of Jupiter's X-ray and EUV auroral emissions was made by the Chandra X-ray Observatory, XMM-Newton, and Hisaki satellite. We find that the X-ray count rates are positively correlated with the solar wind velocity and insignificantly with the dynamic pressure. Based on the magnetic field mapping model, a half of the X-ray auroral region was found to be open to the interplanetary space. The other half of the X-ray auroral source region is magnetically connected with the pre-noon to post-dusk sector in the outermost region of the magnetosphere, where the Kelvin-Helmholtz (KH) instability, magnetopause reconnection, and quasi-periodic particle injection potentially take place. We speculate that the high energy auroral acceleration is associated with the KH instability and/or magnetopause reconnection. This association is expected to also occur in many other space plasma environments such as Saturn and other magnetized rotators.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    The Impact of an ICME on the Jovian X-ray Aurora (2016)
    Wiley
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    Publication Date: 2016-01-31
    Description: We report the first Jupiter X-ray observations planned to coincide with an Interplanetary Coronal Mass Ejection (ICME). At the predicted ICME arrival time, we observed a factor of ∼8 enhancement in Jupiter‘s X-ray aurora. Within 1.5 hours of this enhancement, intense bursts of non-Io decametric radio emission occurred. Spatial, spectral and temporal characteristics also varied between ICME arrival and another X-ray observation two days later. Gladstone et al. [2002] discovered the polar X-ray hot spot and found it pulsed with 45minute quasi-periodicity. During the ICME arrival, the hot spot expanded and exhibited two periods: 26minute periodicity from sulfur ions and 12minute periodicity from a mixture of carbon/sulfur and oxygen ions. After the ICME, the dominant period became 42minutes. By comparing Vogt et al. [2011] Jovian mapping models with spectral analysis, we found that during ICME arrival at least two distinct ion populations, from Jupiter‘s dayside, produced the X-ray aurora. Auroras mapping to magnetospheric field lines between 50-70R J were dominated by emission from precipitating sulfur ions (S 7+,...,14+ ). Emissions mapping to closed field lines between 70-120R J and to open field lines were generated by a mixture of precipitating oxygen (O 7+,8+ ) and sulfur/carbon ions, possibly implying some solar wind precipitation. We suggest the best explanation for the X-ray hot spot is pulsed dayside reconnection perturbing magnetospheric downward currents, as proposed by Bunce et al. [2004]. The auroral enhancement has different spectral, spatial and temporal characteristics to the hot spot. By analysing these characteristics and coincident radio emissions, we propose that the enhancement is driven directly by the ICME through Jovian magnetosphere compression and/or a large-scale dayside reconnection event.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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