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91.
Xianghui Li Chiduru Takashima Akihiro Kano Saburo Sakai Yunhua Chen Baoliang Xu Iodp Expedition Scientists 《第四纪科学杂志》2011,26(2):178-189
Stable isotopes and element compositions of the fine‐grained matrix were measured for IODP Expedition 307 Hole U1317E drilled from the summit of Challenger Mound in Porcupine Seabight, northeast Atlantic, to explore the palaeoceanographic and palaeoclimatic background to development of the deep‐water coral mound. The 155 m long mound section was divided into two units by an unconformity at 23.6 mbsf: Unit M1 (2.6–1.7 Ma) and Unit M2 (1.0–0.5 Ma). Results from 519 specimens show a difference in δ13C value between Unit M1 (?0.6‰ to ?5.0‰) and Unit M2 (?1.0‰ to 1.0‰), but such a distinct difference was not seen in δ18O values (1.0‰–2.5‰), CaCO3 content (40–60 wt%), Sr/Ca ratio (2.0–8.0 mmol mol?1), and Mg/Ca ratio (10.0–20.0 mmol mol?1) through the mound. Positive δ18O and negative δ13C shifts at the mound base are consistent with the oceanographic changes in the northeast Atlantic at the beginning of the Quaternary. The positive δ13C regression in Unit M2 suggests a linkage to the mid Pleistocene intensified glaciation in the Northern Hemisphere. Warm Mediterranean Upper Core Water of Mediterranean Outflow Water, Eastern North Atlantic Water and cold Labrador Sea Water of North Atlantic Deep Water are key oceanographic features that cause spikes and shifts in stable isotope and element composition. However, the stable isotope values of the sediment matrix could not primarily record the glacial–interglacial eustatic/temperature change, but indirectly indicate current regimes of the intermediate oceanic layer where the coral mound grew. Similarly, elemental ratios and CaCO3 content may not represent the productivity and temperature of surface sea water, respectively, but superpose the fractions from both surface and bottom water. It is concluded that palaeoceanographic change coupled to the Pleistocene glacial/interglacial cycles is a key control on the geochemical stratigraphy of the matrix sediments of the carbonate mound developed in Porcupine Seabight. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
92.
93.
Masashi Kusakabe Andrey Andreev Vyacheslav Lobanov Igor Zhabin Yuichiro Kumamoto Akihiro Murata 《Journal of Oceanography》2002,58(5):691-701
Data from the R/V Mirai cruise (May–June 2000) have been examined to discover how mesoscale processes associated with eddy dynamics direct affect
the water masses, the distributions and the vertical fluxes of the dissolved oxygen, nutrients and dissolved inorganic carbon
in the western subarctic Pacific. Using maps of the temperature, salinity, dissolved oxygen, nutrients, chlorophyll and sea-air
pCO2 difference we show that the boundaries of the anticyclone eddies in the study region were composed of high productivity coastal
Oyashio water. The coastal waters were wrapped around the anticyclone eddies (thus creating a high productivity belt) and
intruded inside of them. Using SeaWifs data we demonstrate that temporal variations in the position and the strength of anticyclone
eddies advected the Kuril island coastal high productivity waters to the pelagic part, resulting in temporal variations of
the chlorophyll in the Oyashio region. Computed vertical fluxes of the dissolved oxygen (DO), inorganic carbon (DIC) and silicate
show that the anticylonic eddies in the Kuroshio-Oyashio Zone are characterized by enhanced vertical fluxes of the DO and
DIC between the upper (σθ = 26.7–27.0) and lower (σθ = 27.1–27.5) intermediate layer, probably due to the intrusions of the Oyashio waters into the eddies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
94.
Shigeru Aoki Kazuo Shibuya Akihiro Masuyama Taku Ozawa Koichiro Doi 《Journal of Oceanography》2002,58(3):519-523
Global Positioning System (GPS) measurements of the vertical displacement of fast ice near Syowa Station, Antarctica, were
conducted between April and December 1998 to evaluate measurements of sea level variation derived with a conventional bottom
pressure gauge (BPG). The BPG-derived sea level revealed a seasonal variation of about 0.13 m, with a high in April–June and
a low in November–December. The GPS-derived sea level, combined with observed sea ice thickness, supported the BPG result,
with an RMS error of 0.007 m. Our result also demonstrates that GPS is a powerful technique for monitoring sea level variations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
95.
The thermoelastic parameters of Ca3Cr2Si3O12 uvarovite garnet were examined in situ at high pressure up to 13 GPa and high temperature up to 1100 K by synchrotron radiation energy-dispersive X-ray diffraction within a 6-6-type multi-anvil press apparatus. A least-square fitting of room T data to a third-order Birch–Murnaghan (BM3) EoS yielded K0 = 164.2 ± 0.7 GPa, V0 = 1735.9 ± 0.3 Å3 (K’0 fixed to 4.0). P–V–T data were fitted simultaneously by a modified HT-BM3 EoS, which gave the isothermal bulk modulus K0 = 163.6 ± 2.6 GPa, K’0 = 4.1 ± 0.5, its temperature derivative (?K0,T/?T)P = –0.014 ± 0.002 GPa K?1, and the thermal expansion coefficients a0 = 2.32 ± 0.13 ×10?5 K?1 and b0 = 2.13 ± 2.18 ×10?9 K?2 (K’0 fixed to 4.0). Our results showed that the Cr3+ enrichment in natural systems likely increases the density of ugrandite garnets, resulting in a substantial increase of mantle garnet densities in regions where Cr-rich spinel releases chromium through a metasomatic reaction. 相似文献
96.
When one end of an air-dry igneous rock block was uniaxially loaded in laboratory, there appeared an electromotive force that made electric currents flow from the stressed volume to the unstressed volume. Quartz-free rocks such as gabbro also generated this force, stronger than quartz-bearing rocks such as granite. This indicates that the piezoelectric effect of quartz and the electrokinetic effect of pore water do not make a large contribution toward generating the electromotive force. We focus on peroxy bond that is one of the abundant lattice defects in igneous rock-forming minerals. When mechanical loading deforms the lattice structure around this defect and breaks its bond, its energy levels change and act like an accepter. As an electron is trapped at this defect from a neighbor O2- site, a positive hole is activated there. They attempt to diffuse toward the unstressed volume through the valence band and are simultaneously affected by the attractive electric force with the electrons trapped in peroxy bonds. This leads to a polarization in the stressed volume and the generation of electromotive force between the stressed and unstressed volumes. Similar electromotive force may be generated in the Earth's crust where inhomogeneous stress/strain is changing. 相似文献
97.
Yumiko Watanabe Shun'ichi Nakai Akihiro Hiruta Ryo Matsumoto Kunio Yoshida 《Earth and Planetary Science Letters》2008,272(1-2):89-96
We performed U–Th radioactive disequilibrium analyses of carbonate nodules and sediment samples recovered from methane seep sites off Joetsu, of the eastern margin of Japan Sea, to decipher the active period of the methane seep. The carbonates contain 230Th, part of which is located in detritus such as silicate and organics, at the time of precipitation. The initial 230Th renders accurate dating with U–Th radioactive disequilibrium method difficult. We assessed the feasibility of correction using radioactive disequilibrium data of ambient sediment to overcome this difficulty. A (230Th/232Th)–(234U/232Th) isochron drawn by three chips divided from a carbonate nodule (PC05-04-50) passed through data points of local sediments. We conclude that the problem of initial 230Th can be resolved by measurements of local sediments. Results show that carbonate nodules include local sediment as impurities. Furthermore, the results of trace element analyses such as Rb, Zr, Nb, REE, Pb, and Th also support the idea.In all, 18 carbonate samples were dated with correction of initial 230Th using the mean value of local sediment in this study. The U–Th correction ages show 12–35ka with an isochron age of 26 ± 3ka. Results indicate that during the time interval of U–Th ages, from 12ka to 35ka, environmental conditions must have been favorable for enhanced methane flux through sediment. The extensive methane flow period at 20ka accords with the lowest-stand sea level during the last glacial age. Results of this study also suggest that U–Th ages of carbonate are useful as a reliable chronometer with regard to methane seep activation. In order to acquire U–Th ages of carbonate at methane seep sites, however, it is important to evaluate the amount of initial 230Th accurately using the value of sediment. 相似文献
98.
Two modes of climatic control in the Holocene stalagmite record from the Japan Sea side of the Japanese islands
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Tomomi Sone Akihiro Kano Kenji Kashiwagi Taiki Mori Tomoyo Okumura Chuan‐Chou Shen Masako Hori 《Island Arc》2015,24(3):342-358
The Holocene stalagmite FG01 collected at the Fukugaguchi Cave in Itoigawa, central Japan provides a unique high‐resolution record of the East Asian winter monsoon. Because of the climate conditions on the Japan Sea side of the Japanese islands, the volume of precipitation during the winter is strongly reflected in the stalagmite δ18O signal. Examination of the carbon isotopes and the Mg/Ca ratio of FG01 provided additional information on the Holocene climate in Itoigawa, which is characterized by two different modes separated at 6.4 ka. Dripwater composition and the correlation between the δ13C and Mg/Ca data of FG01 indicate the importance of prior calcite precipitation (PCP), a process that selectively eliminated 12C and calcium ions from infiltrating water from CO2 degassing and calcite precipitation. In an earlier period (10.0–6.4 ka), an increase in soil pCO2 associated with warming and wetting climate trends was a critical factor that enhanced PCP, and resulted in an increasing trend in the Mg/Ca and δ13C data and a negative correlation between the δ13C and δ18O profiles. A distinct peak in the δ13C age profile at 6.8 ka could be a response to an increase of approximately 10% in C4 plants in the recharge area. At 6.4 ka, the climate mode changed to another, and correlation between δ18O and δ13C became positive. In addition, a millennial‐scale variation in δ18O and pulsed changes in δ13C and Mg/Ca became distinct. Assuming that δ18O and PCP were controlled by moisture in the later period, the volume of precipitation was high during 6.0–5.2, 4.4–4.0, and 3.0–2.0 ka. In contrast, the driest interval in Itoigawa was during 0.2–0.4 ka, and broadly corresponds to the Little Ice Age. 相似文献
99.
Large earthquake-induced displacements of a bridge abutment can occur, when the bridge is built on a floodplain or reclaimed area, i.e., liquefiable ground, and crosses a water channel. Seismic responses of a bridge abutment on liquefiable ground are the consequence of complex interactions between the abutment and surrounding soils. Therefore identification of the factors dominating the abutment response is important for the development of simplified seismic design methods. This paper presents the results of dynamic three-dimensional finite element analyses of bridge abutments adjacent to a river dike, including the effect of liquefaction of the underlying ground using earthquake motions widely used in Japan. The analysis shows that conventional design methods may underestimate the permanent abutment displacements unless the following two items are considered: (1) softening of the soil beneath the liquefiable layer, due to cyclic shearing of the soil surrounding the piles, and (2) the forces acting on the side faces of the abutment. 相似文献
100.
Yamada M Takada H Toyoda K Yoshida A Shibata A Nomura H Wada M Nishimura M Okamoto K Ohwada K 《Marine pollution bulletin》2003,47(1-6):105-113
Polycyclic Aromatic Hydrocarbons (PAHs) are one of the components found in oil and are of interest because some are toxic. We studied the environmental fate of PAHs and the effects of chemical dispersants using experimental 500 l mesocosm tanks that mimic natural ecosystems. The tanks were filled with seawater spiked with the water-soluble fraction of heavy residual oil. Water samples and settling particles in the tanks were collected periodically and 38 PAH compounds were analyzed by gas chromatography-mass spectrometry (GC-MS). Low molecular weight (LMW) PAHs with less than three benzene rings disappeared rapidly, mostly within 2 days. On the other hand, high molecular weight (HMW) PAHs with more than four benzene rings remained in the water column for a longer time, up to 9 days. Also, significant portions (10-94%) of HMW PAHs settled to the bottom and were caught in the sediment trap. The addition of chemical dispersant accelerated dissolution and biodegradation of PAHs, especially HMW PAHs. The dispersant amplified the amounts of PAHs found in the water column. The amplification was the greater for the more hydrophobic PAHs, with an enrichment factor of up to six times. The increased PAHs resulting from dispersant use overwhelmed the normal degradation and, as a result, higher concentrations of PAHs were observed in water column throughout the experimental period. We conclude that the addition of the dispersant could increase the concentration of water column PAHs and thus increase the exposure and potential toxicity for organisms in the natural environment. By making more hydrocarbon material available to the water column, the application of dispersant reduced the settling of PAHs. For the tank with dispersant, only 6% of chrysene initially introduced was detected in the sediment trap whereas 70% was found in the trap in the tank without dispersant. 相似文献