Temporal variability in physicochemical properties,phytoplankton standing crop and primary production for 7 years (2002–2008) in the neritic area of Sagami Bay,Japan     

Koichi Ara  Koh Yamaki  Keisuke Wada  Satoshi Fukuyama  Takeshi Okutsu  Sadao Nagasaka  Akihiro Shiomoto  Juro Hiromi 《Journal of Oceanography》2011,67(1):87-111

Seasonal and interannual variations in physicochemical properties (i.e., temperature, salinity, dissolved oxygen and dissolved inorganic nutrients), chlorophyll a (Chl-a), particulate carbon and nitrogen (PC and PN, respectively), and primary production were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from January 2002 to December 2008. These abiotic/biotic variables, except for NH₄ ⁺–N, repeated similar seasonal variations for all 7 years. On the basis of the analysis of data obtained on 167 sampling dates, depth-integrated primary production in this water can be easily estimated from Chl-a at the surface using the regression equations obtained in the present study. Intermittently high values of dissolved inorganic nutrients, Chl-a, PC, PN and primary productivity at the surface during the summer stratified period were induced by high freshwater discharge from the rivers after rainfalls and by the expansion of nutrient-rich Tokyo Bay Water. Temperature, salinity and dissolved inorganic nutrients showed drastic variations within a scale of a few days and/or weeks, and these variations were related to sea levels that represent the intrusion of the Kuroshio Water, Intermediate Oyashio Water or deep water from the continental slope. However, there was no consistent trend in the variations in Chl-a, PC, PN and primary production due to the complex effects of these waters.  相似文献   

Evidence for ocean water invasion into the Chicxulub crater at the Cretaceous/Tertiary boundary     

Kazuhisa Goto  Ryuji Tada  Eiichi Tajika  Timothy J. Bralower  Takashi Hasegawa  Takafumi Matsui 《Meteoritics & planetary science》2004,39(8):1233-1247

Abstract— The possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion.  相似文献   

Diurnal variation of CO₂ concentration, Δ¹⁴C and δ¹³C in an urban forest: estimate of the anthropogenic and biogenic CO₂ contributions     

Hiroshi A. Takahashi  Eiichi Konohira  Tetsuya Hiyama  Masayo Minami  Toshio Nakamura  Naohiro Yoshida 《Tellus. Series B, Chemical and physical meteorology》2002,54(2):97-109

Diurnal variation in the atmospheric CO₂ concentration and the carbon isotopic composition (Δ¹⁴C and δ¹³C) was measured in a forest in an urban area on 9 February 1999. The carbon isotope approach used in the present study differentiated between the quantitative contributions from anthropogenic and biogenic CO₂ sources in the urban atmosphere. The anthropogenic (fossil fuel) and biogenic (soil respiration) contributions was estimated, and they ranged from 1 to 16% and from 2 to 8% of the total atmospheric CO₂. The diurnal variation of the anthropogenic CO₂ was the major cause of the total atmospheric CO₂ variation, while the biogenic CO₂ remained relatively constant throughout the day. Estimating the contribution of soil respired CO₂ provided the mean residence time of soil respired CO₂ within the forest atmosphere.  相似文献   

Age estimation of the Solomon Sea based on heat flow data     

Masato Joshima  Eiichi Honza 《Geo-Marine Letters》1987,6(4):211-217

Several heat flow measurements were made during the NAT83 cruise in the central part of the Solomon Sea Basin. The average value of 87 mW/m² (2.08 HFU) calculated from these and other data indicates that the age of the Solomon Sea Basin may range from 24 to 44 Ma. This is supported by the water depth, of approximately 4,500 m, versus age relationship. There is a possibility that the Solomon Sea Basin is not a back-arc basin associated with an arc but was formerly a relatively large oceanic plate. The agreement in age from both heat flow and water depth data favors the latter hypothesis.  相似文献   

High Resolution, Deep-Tow Seismic Survey to Investigate the Methane Hydrate Stability Zone in the Nankai Trough     

Peter Ward    Eiichi Asakawa  Shoshiro Shimizu 《Resource Geology》2004,54(1):115-124

Abstract. A high frequency deep-tow seismic survey was carried out in the Nankai Trough area in 1996. The objective of the survey was to obtain high resolution seismic sections and velocity profiles of the methane hydrate zone, inferred from the strong BSR events seen on conventional seismic data in the area. A special feature of the survey is that both the source and the streamer cable are towed close to the seabed. This special acquisition geometry requires special data processing to handle the varying source and receiver depths. A CMP floating datum processing sequence was designed which led to high quality sections of the shallow geology. A key step in the processing was devising a residual statics technique to compensate for errors in the measured depths.
The processing sequence was applied to a number of lines, totaling 200 km. The final data quality was highly variable. Some lines produced high quality sections and others, much poorer sections with few interpretable events. Conventional seismic data in the area also shows variation in the data quality so part of the reason is a variation in the sub-sea geology, but the deep-tow data is much more sensitive to change in conditions than conventional data. With the current acquired data and processing sequence the deep-tow system offers most advantages when 1) the water depth is around 1 km or greater, 2) the seabed and underlying geology is not too complex, and 3) the acquisition proceeds smoothly with regular shotpoints, slowly varying depths, and with accurate positioning.  相似文献   

Subduction erosion and accretion in the Solomon Sea region     

Eiichi Honza  Teruki Miyazaki  Jo Lock 《Tectonophysics》1989,160(1-4):49-62

The Solomon Sea region is an area of intense tectonic activity characterized by structural complexity, a high level of seismicity and volcanism, and rapid evolution of plate boundaries. There is little accretion in the eastern New Britain Trench. Accretion gradually increases westward with thick accretion in the western New Britain Trench and in the Trobriand Subduction System. The thick accretion in the western part of the New Britain Trench may be a result of collision from the north of Finisterre-Huon block with New Guinea mainland. The present boundary of the collision is along the Ram-Markham fault. Deformation structures and present day seismicity suggest that the northern block is under compression.

Accretion has occurred in the sediment filled trenches in the Solomon Sea. The scale of the accretionary wedge depends on the amount of trench-fill sediment available. It is unlikely that there is no sediment supply to the eastern part of the New Britain Trench where no accretion is observed and subduction erosion may be occurring. There are two possible mechanisms for subduction erosion of sediment; either a rapid rate of subduction relative to the supply of sediment inhibiting sediment accumulation in the trench; or horizontal tensional force superimposed on both the forearc and backarc regions of the arc. Seafloor spreading in both the Manus and Woodlark basins is fan-like with nearby poles in the western margins of the basins. This may be a reflection of a horizontally compressional field in the western part and a tensional field in the eastern part of the Solomon Sea. Therefore it is possible to conclude that the consumption of sediment in the eastern New Britain Trench is related to the horizontal tensional field superimposed on both the forearc and backarc regions of the subduction system.

Imbricated thrust and overthrust faults in the western New Britain Trench and Trobriand Trough are not linear over long distance, but form wavy patterns in blocks with unit distance of approximately 10 km.  相似文献   

Apparent Critical Slip Displacement Caused By the Existence of A Fault Zone     

Teruo Yamashita  Eiichi Fukuyama 《Geophysical Journal International》1996,125(2):459-472

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PDF orientations in shocked quartz grains around the Chicxulub crater     

Yoichiro NAKANO  Kazuhisa GOTO  Takafumi MATSUI  Ryuji TADA  Eiichi TAJIKA 《Meteoritics & planetary science》2008,43(4):745-760

Abstract— We measured 852 sets of planar deformation features (PDFs) in shocked quartz grains in impactite samples of the Yaxcopoil (YAX‐1) core and from 4 Cretaceous/Tertiary (K/T) boundary deposits: the Monaca, the Cacarajícara, and the Peñalver formations in Cuba, and DSDP site 536, within 800 km of the Chicxulub crater, in order to investigate variations of PDF orientations in the proximity of the crater. Orientations of PDFs show a broad distribution with peaks at ω {101¯3}, π {101¯2}, and ω {111¯2}, plus r, z {1011¯} orientations with minor c(0001), s{112¯1}, t{224¯1} plus x{516¯1}, and m{101¯0} plus a{112¯0} orientations. Planar deformation features with c(0001) orientation are relatively more abundant in the proximity of the Chicxulub crater than in distal sites such as North America, the Pacific Ocean, and Europe. This feature indicates that in the proximity of the crater, part of the shocked quartz grains in the K/T boundary deposits were derived from the low shock pressure zones. Moreover, the orientations of PDFs with ω {112¯2} plus r, z {101¯1} are high in our studied sites, and frequencies of these orientations decrease with increasing distance from the crater. On the other hand, absence of c(0001) and the rare occurrence of PDFs with ?ω {112¯2} plus r, z {101¯1} orientations in the sample from the YAX‐1 core that was taken at the top of the impactite layer of the Chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz.  相似文献   

Dynamic Overshoot Near Trench Caused by Large Asperity Break at Depth     

Eiichi Fukuyama  Sébastien Hok 《Pure and Applied Geophysics》2015,172(8):2157-2165

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Stick–slip behavior of Indian gabbro as studied using a NIED large-scale biaxial friction apparatus     

Tetsuhiro Togo  Toshihiko Shimamoto  Futoshi Yamashita  Eiichi Fukuyama  Kazuo Mizoguchi  Yumi Urata 《地震学报(英文版)》2015,(2):97-118

This paper reports stick–slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention(NIED), Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 k N, the main frame for holding two large rectangular prismatic specimens with a sliding area of 0.75 m2 and for applying normal stresses rnup to 1.33 MPa, and a reaction force unit holding the stationary specimen to the ground. The shaking table can produce loading rates v up to 1.0 m/s,accelerations up to 9.4 m/s2, and displacements d up to0.44 m, using four servocontrolled actuators. We report results from eight preliminary experiments conducted with room humidity on the same gabbro specimens at v = 0.1–100 mm/s and rn= 0.66–1.33 MPa, and with d of about 0.39 m. The peak and steady-state friction coefficients were about 0.8 and 0.6, respectively, consistent with the Byerlee friction. The axial force drop or shearstress drop during an abrupt slip is linearly proportional to the amount of displacement, and the slope of this relationship determines the stiffness of the apparatus as1.15 9 108N/m or 153 MPa/m for the specimens we used.This low stiffness makes fault motion very unstable and the overshooting of shear stress to a negative value was recognized in some violent stick–slip events. An abrupt slip occurred in a constant rise time of 16–18 ms despite wide variation of the stress drop, and an average velocity during an abrupt slip is linearly proportional to the stress drop.The use of a large-scale shaking table has a great potential in increasing the slip rate and total displacement in biaxial friction experiments with large specimens.  相似文献