Yusaku Shimizu  Atsushi Ooki  Hiroji Onishi  Tetsuya Takatsu  Seiji Tanaka  Yuta Inagaki  Kota Suzuki  Naoto Kobayashi  Yoshihiko Kamei  Kenshi Kuma 《Journal of Atmospheric Chemistry》2017,74(2):205-225

Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH₂I₂, CH₂ClI, CH₃I, and C₂H₅I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C₂H₅I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO₄ ^3? variation profile. Correlation between C₂H₅I and PO₄ ^3? concentrations (r = 0.93) suggests that C₂H₅I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH₂I₂ and CH₂ClI concentrations increased substantially in the surface and subsurface layers (0–60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring).  相似文献   

    

Tetsuya  Waragai 《Island Arc》2005,14(4):368-377

Abstract   Calcretes can be observed on the surface of old moraines around Batura Glacier in the upper Hunza Valley, Karakoram Mountains, Pakistan. They develop as a calcareous crust cementing small gravels under boulders. In order to understand the genesis of the calcrete crust, a variety of methods were employed: (i) study of mineralogy and geochemistry of a calcrete crust precipitated on the lateral moraine using X-ray diffractometer and electron probe microanalysis; (ii) analysis of solute chemistry of surface water and ice bodies around the Batura Glacier; and (iii) accelerator mass spectrometry ¹⁴C dating of the crust itself. The results indicate that the calcrete crust has definite laminated layers composed of a fine-grain and compact calcite layer, and a mineral fragment layer. The chemical composition of the calcite layer is approximately 60% CaO and 1% MgO. The mineral fragment layer consists of rounded grain materials up to 0.2 mm in diameter. It shows a graded bedding structure with fine grains of quartz, albite and muscovite. Meanwhile, as the Paleozoic Pasu limestone is distributed around the terminal of Batura Glacier, Ca cations dissolve in the melt water of the glacier. Accordingly, the calcrete crust is precipitated by decreases in CO₂ partial pressure from glacier ice and evaporation of the melt water, including high concentration of Ca²⁺ at ephemeral streams and small ponds stagnating between the moraine and glacial ice. On the basis of the AMS ¹⁴C age, the calcrete is considered to have formed approximately 8200 calibrated years bp under the Batura glacial stage.  相似文献   

    

Bethany Behrens  Yosuke Miyairi  Adam D. Sproson  Masako Yamane  Yusuke Yokoyama 《第四纪科学杂志》2019,34(8):603-608

Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (¹⁰Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric ¹⁰Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric ¹⁰Be events to be derived from the deposition of ¹⁰Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric ¹⁰Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

    

Tetsuya Shoji  Hiroaki Kaneda 《Mathematical Geology》1994,26(8):961-972

An interactive computer system has been developed to assist the mineral identification in ore microscopy. The reference file of the system consists of optical, mechanical, and chemical properties of about 130 ore minerals. The properties are name, chemical formula, color, bireflectance, anisotropism, internal reflection, reflectance at wavelengths of 470, 546, 589, and 650 nm, and polishing hardness and micro-indentation hardness. All the properties except reflectance and microindentation hardness are qualitative or semi-qualitative. Most of the properties are given as characters relative to the more common minerals. This implies that most of the identification processes advance on the basis of the comparison between a subject mineral and coexisting minerals. For this reason, the system asks a user at first to input already identified mineral names. This is quite different from the mineral identification procedures used in petrographic microscopy. To reduce the number of possible minerals, the system presents a series of questions to a user, and the user selects any of the prepared answers according to his observation. The user can also choose any desired question independently of the sequence. The user is expected to be able to recognize some common minerals, such as pyrite, chalcopyrite, galena, and hematite, without the assistance of the system.  相似文献   

  总被引：5，自引：0，他引：5  

Masato Tamai  Yuyan Liu  Lian Zhong Lu  Masahiko Yokoyama  Nadir Halim  Haider Zaman  Yo-ichiro Otofuji 《Geophysical Journal International》2004,158(1):297-309

  相似文献   

    

Masaki Yokoyama  Satoshi Masuda 《Solar physics》2010,263(1-2):135-152

It is not clear how trans-equatorial loop systems (TLSs) are formed, although they have been observed often with Yohkoh/SXT. We focus here on a TLS that appeared on 27 May 1998. Yokoyama and Masuda (Solar Phys. 254, 285, 2009) proposed a new scenario for the formation mechanism of the TLS. In this scenario, they pointed out the importance of magnetic interaction between an active region and a coronal hole to make “strong-seed magnetic fields” before a transient (bright and short-lived) trans-equatorial loop was created. The main aims of this study are to verify the scenario and to make the TLS formation mechanism clear, based on observational data. Yohkoh/SXT images, SOHO/MDI magnetograph data, and Kitt Peak coronal-hole maps were mainly used for our analyses. We investigated the TLS in detail from the time that there were no signatures of the TLS to its clear appearance. The following results are obtained: i) an active region emerged in the vicinity of a coronal-hole boundary, ii) the coronal-hole boundary retreated during the period when the active region was developing, iii) temporal variations of soft X-ray intensities were roughly synchronized between the coronal-hole boundary and a trans-equatorial region, and iv) new closed loops were observed in soft X-rays clearly at the coronal-hole boundary. Since i), ii), iii), and iv) are just what we expect in the scenario of YM2009, the scenario found support. We conclude that the TLS was originating with large-scale magnetic fields of the coronal-hole boundary through magnetic reconnection between the active region and a coronal hole.  相似文献   

    

Eberhard Gischler  Alex L. Thomas  André W. Droxler  Jody M. Webster  Yusuke Yokoyama  Bernd R. Schöne 《Sedimentology》2013,60(6):1432-1466

During Integrated Ocean Drilling Program Expedition 325, 34 holes were drilled along five transects in front of the Great Barrier Reef of Australia, penetrating some 700 m of late Pleistocene reef deposits (post‐glacial; largely 20 to 10 kyr bp ) in water depths of 42 to 127 m. In seven holes, drilled in water depths of 42 to 92 m on three transects, older Pleistocene (older than last glacial maximum, >20 kyr bp ) reef deposits were recovered from lower core sections. In this study, facies, diagenetic features, mineralogy and stable isotope geochemistry of 100 samples from six of the latter holes were investigated and quantified. Lithologies are dominated by grain‐supported textures, and were to a large part deposited in high‐energy, reef or reef slope environments. Quantitative analyses allow 11 microfacies to be defined, including mixed skeletal packstone and grainstone, mudstone‐wackestone, coral packstone, coral grainstone, coralline algal grainstone, coral‐algal packstone, coralline algal packstone, Halimeda grainstone, microbialite and caliche. Microbialites, that are common in cavities of younger, post‐glacial deposits, are rare in pre‐last glacial maximum core sections, possibly due to a lack of open framework suitable for colonization by microbes. In pre‐last glacial maximum deposits of holes M0032A and M0033A (>20 kyr bp ), marine diagenetic features are dominant; samples consist largely of aragonite and high‐magnesium calcite. Holes M0042A and M0057A, which contain the oldest rocks (>169 kyr bp ), are characterized by meteoric diagenesis and samples mostly consist of low‐magnesium calcite. Holes M0042A, M0055A and M0056A (>30 kyr bp ), and a horizon in the upper part of hole M0057A, contain both marine and meteoric diagenetic features. However, only one change from marine to meteoric pore water is recorded in contrast with the changes in diagenetic environment that might be inferred from the sea‐level history. Values of stable isotopes of oxygen and carbon are consistent with these findings. Samples from holes M0032A and M0033A reflect largely positive values (δ¹⁸O: ?1 to +1‰ and δ¹³C: +1 to +4‰), whereas those from holes M0042A and M0057A are negative (δ¹⁸O: ?4 to +2‰ and δ¹³C: ?8 to +2‰). Holes M0055A and M0056A provide intermediate values, with slightly positive δ¹³C, and negative δ¹⁸O values. The type and intensity of meteroric diagenesis appears to have been controlled both by age and depth, i.e. the time available for diagenetic alteration, and reflects the relation between reef deposition and sea‐level change.  相似文献   

    

Richard A. Staff  Takeshi Nakagawa  Gordon Schlolaut  Michael H. Marshall  Achim Brauer  Henry F. Lamb  Christopher Bronk Ramsey  Charlotte L. Bryant  Fiona Brock  Hiroyuki Kitagawa  Johannes van der Plicht  Rebecca L. Payne  Victoria C. Smith  Darren F. Mark  Alison Macleod  Simon P. E. Blockley  Jean‐Luc Schwenninger  Pavel E. Tarasov  Tsuyoshi Haraguchi  Katsuya Gotanda  Hitoshi Yonenobu  Yusuke Yokoyama  Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).  相似文献   

    

Takeshi Ohmura  Takeo Moriya  Chengshi Piao  Takaya Iwasaki  Toshikastu Yoshi  Shin'ichi Sakai  Tetsuya Takeda  Kaoru Miyashita  Humihito Yamazaki  Kiyoshi Ito  Akira Yamazaki  Yoji Shimada  Katsuya Tashiro  Hiroki Miyamachi 《Island Arc》2001,10(3-4):215-227

Abstract The 1995 Kobe (Hyogo-ken Nanbu) earthquake (M_JMA 7.2, M_w 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribution and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES) . The profile including 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island. The charge of each shot was 350–700 kg. The P-wave velocity structure model showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crystalline upper crust, and the boundary between the upper and lower crust.
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed.  相似文献   

    

Tetsuya Komabayashi  Soichi Omori  Shigenori Maruyama 《Physics of the Earth and Planetary Interiors》2005,153(4):191-209

Fluid-undersaturated experiments were conducted to determine the phase relations in the simplified peridotite system MgO-SiO₂-H₂O (MSH) at 11.0-14.5 GPa and 800-1400 °C. Stability relations of dense hydrous magnesium silicates (DHMSs) under fluid-undersaturated conditions were experimentally examined. From the fluid-absent experimental results, we retrieved thermodynamic data for clinohumite, phase A, phase E, and hydrous wadsleyite, consistent with the published data set for dry mantle minerals. With this new data set, we have calculated phase equilibria in the MSH system including dehydration reactions. The dehydration reactions calculated with lower water activities of 0.68-0.60 match the fluid-present experiments of this study above 11.0 GPa and 1000 °C, indicating that considerable amounts of silicate component were dissolved into the fluid phase. The calculated phase equilibria illustrate the stability of the post-antigorite phase A-bearing assemblages. In the cold subducting slab peridotite, phase A + enstatite assemblage survives into the transition zone, whereas phase A + forsterite + enstatite assemblage forms hydrous wadsleyite at a much shallower depth of about 360-km. The slab is subducted with no dehydration reactions occurring when entering the transition zone. The phase equilibria also show the high temperature stability of phase E. Phase E is stable up to 1200 °C at 13.5 GPa, a plausible condition in the mantle of relatively low temperature, i.e., beneath subduction zones. Phase E is a possible water reservoir in the mantle as well as wadsleyite and ringwoodite.  相似文献