Opaque minerals,magnetic properties,and paleomagnetism of the Tissint Martian meteorite     

Jérôme Gattacceca  Roger H. Hewins  Jean‐Pierre Lorand  Pierre Rochette  France Lagroix  Cécile Cournède  Minoru Uehara  Sylvain Pont  Violaine Sautter  Rosa. B. Scorzelli  Chrystel Hombourger  Pablo Munayco  Brigitte Zanda  Hasnaa Chennaoui  Ludovic Ferrière 《Meteoritics & planetary science》2013,48(10):1919-1936

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Reproducibility of spatial and temporal distribution of aseismic slips in Hyuga-nada of southwest Japan     

Ryoko Nakata  Shin’ichi Miyazaki  Mamoru Hyodo  Takane Hori 《Marine Geophysical Researches》2014,35(3):311-317

The Hyuga-nada region of southwest Japan, which is located off the east coast of Kyushu Island, may have the potential to generate great interplate earthquakes along the Nankai trough in the future. In this area, thrust earthquakes of M = 6.7–7.2 have occurred with recurrence intervals of approximately 30 years. In association with these earthquakes, possible local heterogeneities of plate coupling may be expected within 100 km from the coast in the Hyuga-nada region. We investigate numerical experiments to determine the spatial and temporal resolution of slip on the plate interface beneath the Hyuga-nada offshore region. For this purpose, we calculated synthetic displacement data from the result of numerical simulation conducted for the afterslip following an M_w 6.8 earthquake, for existing global positioning system stations on land and planned ocean floor seismic network stations. The spatial and temporal distribution of fault slip is then estimated using a Kalman filter-based inversion. The slip distribution estimated by using ocean floor stations demonstrates that the heterogeneity of plate coupling is resolved approximately within 50 km from the coastal area. This heterogeneity corresponds to the coseismic area of an M_w 6.8 earthquake with a radius of 10 km. Our study quantitatively evaluates the spatial resolution of aseismic slip in the Hyuga-nada region. Analysis based on continuous ocean floor data is useful for resolving the spatial variations of heterogeneities in plate couplings.  相似文献   

Temporal dynamics of dissolved organic carbon (DOC) produced in a microcosm with red tide forming algae <Emphasis Type="Italic">Chattonella marina</Emphasis> and its associated bacteria     

Minoru Wada  Yukiko Takano  Saki Nagae  Yuka Ohtake  Yu Umezawa  Shinichi Nakamura  Makoto Yoshida  Yukihiko Matsuyama  Mitsunori Iwataki  Satoshi Takeshita  Tatsuya Oda 《Journal of Oceanography》2018,74(6):587-593

Acute and severe hypoxia associated with harmful algal bloom has become one of the major causes for the environmental deterioration of coastal areas. Although it is generally thought that a large part of the dissolved oxygen consumption at a bloom site is initiated by heterotrophic bacteria that attack organic matter derived from dead or dying algal cells, precise microbial processes leading to the hypoxia are yet to be examined. Here we show temporal dynamics of extracellular dissolved organic carbon (DOC) of the red tide forming raphidophyte Chattonella marina and bacterial populations associating with the algae under laboratory conditions. During the growth of non-axenic strains of C. marina, we monitored abundance of algae, associated bacteria, and DOC in the culture media. Bacterial cell abundance increased in response to the increase in DOC both at the beginning and the late log phase of the algal growth. Flow cytometric analysis revealed that transient increase in the percentage of respiratory-active bacterial cells also coincided with the timing of the increase in bacterial abundance and DOC. These results strongly suggest that DOC released from growing C. marina fuels respiration and growth of planktonic bacteria surrounding the algae. This has implications for the role of DOC released from C. marina bloom before the collapse in mediating interactions between neighboring algae and bacterial assemblage which may eventually lead to algal bloom-associated hypoxia.  相似文献   

Microbial community respiration and structure of dead zone sediments of Omura Bay, Japan   总被引：1，自引：0，他引：1  

Minoru Wada  Shotaro Suzuki  Tadashi Nara  Yu Umezawa  Motohiro Shimanaga  Kazumi Matsuoka  Hideaki Nakata 《Journal of Oceanography》2012,68(6):857-867

Monitoring sediment microbial community metabolism and structure is instrumental to understanding biogeochemical processes in and ecological impacts on bottom environments. The aim of this study was to determine potential community respiration and to reveal community dynamics of the microorganisms in the dead zone sediments of Omura Bay, Japan. The bay is highly enclosed and develops severe hypoxia in the central regions every summer. We collected sediment core samples from the center of the bay during hypoxia, estimated sediment oxygen consumption by using an adapted in vivo electron transport system activity (in vivo ETSA) assay, enumerated abundance of bacteria, and analyzed bacterial community structure by automated ribosomal intergenic spacer analysis. Higher ETSA and bacterial diversity were found in upper sediments (within 3?cm depth) from the center than the fringe of the bay. Sediment bacterial community structure of the bay center was distinct from that of the fringe. From these results, upper sediment in the dead zone of Omura Bay was characterized by (1) greater community respiration and (2) greater diversity of bacterial components compared with the non-hypoxic sediment of the bay fringe. These characteristics have important implications for understanding the interaction between microbial communities and the development of hypoxia in Omura Bay.  相似文献   

Outline of a small unmanned aerial vehicle (Ant-Plane) designed for Antarctic research     

Minoru Funaki  Naohiko Hirasawa  the Ant-Plane Group 《Polar Science》2008,2(2):129-142

As part of the Ant-Plane project for summertime scientific research and logistics in the coastal region of Antarctica, we developed six types of small autonomous UAVs (unmanned aerial vehicles, similar to drones; we term these vehicles ‘Ant-Planes’) based on four types of airframe. In test flights, Ant-Plane 2 cruised within 20 m accuracy along a straight course during calm weather at Sakurajima Volcano, Kyushu, Japan. During a period of strong winds (22 m/s) at Mt. Chokai, Akita Prefecture, Japan, Ant-Plane 2 maintained its course during a straight flight but deviated when turning leeward. An onboard 3-axis magneto-resistant magnetometer (400 g) recorded variations in the magnetic field to an accuracy of 10 nT during periods of calm wind, but strong magnetic noise was observed during high winds, especially head winds. Ant-Plane 4-1 achieved a continuous flight of 500 km, with a maximum flight altitude of 5690 m. The Ant-Plane can be used for various types of Antarctic research as a basic platform for airborne surveys, but further development of the techniques employed in takeoff and landing are required, as well as ready adjustment of the engine and the development of small onboard instruments with greater reliability.  相似文献   

Kinetic stability of a melted iron globule during chondrule formation. I. Non‐rotating model     

Masayuki UESUGI  Minoru SEKIYA  Tomoki NAKAMURA 《Meteoritics & planetary science》2008,43(4):717-730

Abstract— We have investigated the kinematics of the separation of iron globules from chondrules during chondrule formation. A simple model, which assumes that the system has no angular momentum, was used to calculate the energy of a system with an iron globule and a chondrule. The energies of three different states were calculated: 1) a melted iron globule fully embedded in a melted chondrule, 2) a melted iron globule on the surface of a melted chondrule, and 3) a melted iron globule being separated from a melted chondrule. We also calculated the lowest energy shape for a melted iron globule on the surface of a melted chondrule, and compared our result with the shapes of four natural samples of chondrules and iron globules in thin sections. The shapes were calculated using an assumed value for the interface energy between the four couples of melted chondrules and the iron globules, and agree well with the natural shapes of chondrules and iron globules. The results of our calculations show that the iron globules of these four samples would be strongly bound to the surface of the melted chondrule during chondrule formation, and separation would be difficult, if the iron globules had been on the surface of precursors of these chondrules. Our results also show that if these iron globules were initially inside and transported to the surface of the melted chondrule, most of them would be ejected from the inside to outside because of surface tension forces, as long as the energy losses due to viscous dissipation when the globules pass through the surface of melted chondrules were sufficiently small. Although further improvement of the model is required, our results demonstrate that this ejection process may be responsible for the depletion of siderophile elements in natural chondrules.  相似文献   

Geochemical characteristics of deposits from the 2011 Tohoku‐oki tsunami at Hasunuma,Kujukuri coastal plain,Japan          下载免费PDF全文

Tetsuya Shinozaki  Yuki Sawai  Junko Hara  Minoru Ikehara  Dan Matsumoto  Koichiro Tanigawa 《Island Arc》2016,25(5):350-368

We examined the geochemical characteristics and temporal changes of deposits associated with the 2011 Tohoku‐oki tsunami. Stable carbon isotope ratios, biomarkers, and water‐leachable ions were measured in a sandy tsunami deposit and associated soils sampled at Hasunuma, Kujukuri coastal plain, Japan, in 2011 and 2014. At this site, the 2011 tsunami formed a 10–30 cm ‐thick layer of very fine to medium sand. The tsunami deposit was organic‐poor, and no samples contained any detectable biomarkers of either terrigenous or marine origin. In the underlying soil, we identified hydrocarbons and sterols derived from terrestrial plants, but detected no biomarkers of marine origin. In the samples collected in 2011, concentrations of tsunami‐derived water‐leachable ions were highest in the soil immediately beneath the tsunami deposit and then decreased gradually with depth. Because of its finer texture and higher organic content, the soil has a higher water‐holding capacity than the sandy tsunami deposit. This distribution suggests that ions derived from the tsunami quickly penetrated the sand layer and became concentrated in the underlying soil. In the samples collected in 2014, concentrations of water‐leachable ions were very low in both soil and sand. We attribute the decrease in ion concentrations to post‐tsunami rainfall, seepage, and seasonal changes in groundwater level. Although water‐leachable ions derived from seawater were concentrated in the soil beneath the tsunami deposit following the tsunami inundation, they were not retained for more than a few years. To elucidate the behavior of geochemical characteristics associated with tsunamis, further research on organic‐rich muddy deposits (muddy tsunami deposits and soils beneath sandy tsunami deposits) as well as sandy tsunami deposits is required.  相似文献   

Quasi-static slip on the plate boundary associated with the 2003 M8.0 Tokachi-oki and 2004 M7.1 off-Kushiro earthquakes, Japan     

Naoki Uchida  Satoshi Yui  Satoshi Miura  Toru Matsuzawa  Akira Hasegawa  Yoshinobu Motoya  Minoru Kasahara 《Gondwana Research》2009,16(3-4):527-533

We analyzed small repeating earthquakes recorded over a 13-year period and GPS data recorded over an 8-month period to estimate interplate quasi-static slip associated with the 2003 Tokachi-oki earthquake (M8.0) and the 2004 off-Kushiro earthquake (M7.1). The repeating-earthquake analysis revealed that the slip rate near the source region of the Tokachi-oki earthquake was relatively low (< 5 cm/year) prior to the earthquake; however, in the last 3 years leading up to the event, a minor acceleration in slip occurred upon the deeper extension of the coseismic slip area of the earthquake. Repeating-earthquake and GPS data indicate that large amounts of afterslip occurred around the rupture area following the earthquake; the afterslip mainly propagated to the east of the coseismic slip area. We also infer that the occurrence of the 2004 off-Kushiro earthquake, located about 100 km northeast of the epicenter of the Tokachi-oki earthquake, was advanced by the afterslip associated with the Tokachi-oki earthquake.  相似文献   

A Numerical Simulation of the Seasonal Cycle of Temperature, Salinity and Velocity Fields in Tokyo Bay     

Fumio Horiguchi  Joji Yamamoto  Kisaburo Nakata 《Marine pollution bulletin》2001,43(7-12):145-153

To understand when oxygen-depleted waters occur, how they develop and when they dissipate in inner Tokyo Bay, realistic simulations were attempted with fine spatial and temporal resolution by applying realistic time dependent external forcing. A 3D hydrodynamic model was driven by time-dependent external forcing factors/parameters such as solar radiation, air temperature, relative humidity, wind velocity, and fluvial discharge, under the open boundary conditions of 1995. A simulated time series of salinity and temperature agreed fairly well with observed data, except in summer. The model failed to reproduce the development of the surface mixed layer in summer. Several sensitivity analyses on the external forcing parameters such as wind velocity and vertical diffusivity were conducted to reproduce the mixed layer. However, changing these parameter values did not improve the model results.  相似文献   

²⁴¹Pu/^239+240Pu ratios in polar glaciers     

Minoru Koide  Edward D. Goldberg 《Earth and Planetary Science Letters》1981,54(2):239-247

The analyses of plutonium isotopes in dated strata of polar ice sheets indicate that the²⁴¹Pu/^239+240Pu activity ratio produced in the U.S.-dominated nuclear tests during the 1950s was about 26, while that in the U.S.S.R.-dominated weapons tests in the early 1960s was between 12 and 14. This difference provides time horizons for sedimentary deposits. Further, the²³⁹Pu/²⁴⁰Pu ratio may show a similar difference in fallout values from these two periods of weapons testing and may provide an additional, and perhaps more sensitive, chronology for sediments.  相似文献