Reconstruction of millennial-scale variations in the East Asian summer monsoon over the past 300 ka based on the total carbon content of sediment from Lake Biwa,Japan     

Naoya Iwamoto  Yoshio Inouchi 《Environmental Geology》2007,52(8):1607-1616

The total carbon content analysis for Takashima-oki core extracted from Lake Biwa with time resolutions of approximately 150 years was used to reconstruct millennial-scale climate change in the East Asian monsoon region over the past 300 ka. The total carbon content of the Takashima-oki core is an indirect proxy for the East Asian summer monsoon, because the total carbon content reflects primary productivity within the lake, which is controlled by precipitation in the catchment area. Using these data, we clarify temporal variations in the East Asian summer monsoon prior to MIS 5, which were previously unresolved. The observed variations show a ∼1,500-year cycle that is also recorded by paleoclimate indices in the North Atlantic region. We propose that the East Asian summer monsoon underwent abrupt millennium-scale changes during interglacial stages such as MIS 5 and 7.  相似文献   

A 3D magnetic structure of Izu-Oshima Volcano and their changes after the eruption in 1986 as estimated from repeated airborne magnetic surveys     

Yoshio Ueda 《Journal of Volcanology and Geothermal Research》2007

A 3D magnetic inversion method using a conjugate gradient method (CG method) was developed for constructing 3D magnetization models of a volcanic edifice and applied to aeromagnetic anomalies of Izu-Oshima Volcano surveyed in 1986 and in 1997. The calculated results of the 1986 data show that the volcanic edifice of Izu-Oshima Volcano has a mean magnetization intensity ranging from 10.4 to 12.1 A/m. The derived 3D magnetic structure shows low magnetization zones beneath the west-northwest of the western caldera rim, beneath the west-southwest of Mt. Mihara and beneath Mt. Shiroishi. These features may be related with demagnetizations, reflecting a high thermal state due to magma activities in the 1986 eruption. The comparison between 3D magnetization models in 1986 and in 1997, indicates meaningful changes beneath the C-craters erupted in 1986, suggesting a recovery process of demagnetizations and a considerable decrease of magnetization intensities in the foot of Mt. Futago, indicative of demagnetizations. A derived magnetization model including Izu-Oshima Volcano and its surrounding sea areas clarifies the submerged volcanic edifices around Izu-Oshima Island, and suggests that the old volcanic edifices of Fudeshima, Gyojyanoiwaya, and Okata Volcanoes have been affected by eastward migrations due to massive intrusions of a dike-like structure inferred at the base of Izu-Oshima Volcano.  相似文献   

Chemical and structural control of the partitioning of Co, Ce, and Pb in marine ferromanganese oxides   总被引：3，自引：0，他引：3  

Yoshio Takahashi  Alain Manceau  Matthew A. Marcus 《Geochimica et cosmochimica acta》2007,71(4):984-1008

The oxidation state and mineral phase association of Co, Ce, and Pb in hydrogenetic, diagenetic, and hydrothermal marine ferromanganese oxides were characterized by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical extraction. Cobalt is trivalent and associated exclusively with the Mn oxide component (vernadite). Cerium is tetravalent in all genetic-type oxides (detection limit for Ce(III) ∼ 5 at. %), including Fe-rich areas (ferrihydrite) of hydrogenetic oxides, and is associated primarily with vernadite. Thus, the extent of a Ce anomaly does not result from variations in redox conditions, but appears to be kinetically controlled, decreasing when the growth rate increases from hydrogenetic to diagenetic to hydrothermal oxides. Lead is divalent and associated with Mn and Fe oxides in variable proportions. According to EXAFS data, Pb is mostly sorbed on edge sites at chain terminations in Fe oxide and at layer edges in Mn oxide (ES complex), and also on interlayer vacancy sites in Mn oxide (TCS complex). Sequential leaching experiments, spectroscopic data, and electrochemical considerations suggest that the geochemical partitioning in favor of the Mn oxide component decreases from Co to Ce to Pb, and depends on their oxidative scavenging by Mn and Fe oxides.  相似文献   

Energy balance of the tidal current in the Obatake Seto Strait     

Yoshio Takasugi  Takehiko Higo  Tateki Fujiwara 《Journal of Oceanography》1989,45(1):24-33

Current measurements made with a Doppler Current Profiler were taken along cross sections in the Obatake Seto Strait, a small strait in the western part of the Seto Inland Sea.The energy loss between two cross sections of the strait was estimated using the control volume analysis of the stationary one-dimensional energy equation. The large energy loss observed in the strait cannot be explained in terms of general bottom friction in the coastal region. The loss is attributed to the form loss, which is accompanied by internal turbulence and vortices generated by the specific topography of the strait, in addition to the loss by friction. This is supported by the fact that the energy loss in the strait differs, depending upon the current direction.  相似文献   

Abyssal circulation in the Japan Sea     

Gamo  Toshitaka  Horibe  Yoshio 《Journal of Oceanography》1983,39(5):220-230

Journal of Oceanography - The water below a depth of 1,000 m in the Japan Sea was found to consist of two water masses, the upper layer (the Deep Water) and the lower layer (the Bottom Water). The...  相似文献   

Lethality of increasing CO2 levels on deep-sea copepods in the western North Pacific     

Yuji Watanabe  Atsushi Yamaguchi  Hiroshi Ishida  Takashi Harimoto  Shinya Suzuki  Yoshio Sekido  Tsutomu Ikeda  Yoshihisa Shirayama  Masayuki Mac Takahashi  Takashi Ohsumi  Joji Ishizaka 《Journal of Oceanography》2006,62(2):185-196

The first CO₂ exposure experiments on several species of pelagic copepods inhabiting surface and deep layers in the western North Pacific were conducted. Living organisms were collected from two layers between the surface and 1,500 m between latitudes of 11 and 44°N, and they were exposed aboard ship to various pCO₂ up to about 98,000 μatm. Mortality of copepods from both shallow and deep layers in subarctic to subtropical regions increased with increasing pCO₂ and exposure time. Deep-living copepods showed higher tolerance to pCO₂ than shallow-living copepods. Furthermore, deep-living copepods from subarctic and transitional regions had higher tolerances than the subtropical copepods. The higher tolerances of the deep-living copepods from subarctic and transitional regions may be due to the adaptation to the natural pCO₂ conditions in the subarctic ocean.  相似文献   

Uptake of selenium and other oxyanionic elements in marine ferromanganese concretions of different origins     

Noburu Takematsu  Yoshio Sato  Shiro Okabe  Akira Usui 《Marine Chemistry》1990,31(1-3)

The concentration of selenium in marine ferromanganese concretions varies between 0.02 and 1.2 mg kg⁻¹, with an average of 0.6 mg kg⁻¹. This is about two orders of magnitude lower than previously reported. In contrast to minor cationic elements, the concentrations of selenium are relatively uniform between ferromanganese concretions of different origins, except for hydrothermal crusts. It shows the same trends of element enrichment as other oxyanionic elements. The incorporation of selenium into ferromanganese concretions is attributed to adsorption of selenate on iron and manganese oxides.  相似文献   

Synthesis of crystallographically oriented olivine aggregates using colloidal processing in a strong magnetic field     

Sanae Koizumi  Tohru S. Suzuki  Yoshio Sakka  Kosuke Yabe  Takehiko Hiraga 《Physics and Chemistry of Minerals》2016,43(10):689-706

This study develops a fabrication technique to obtain Fe-free and Fe-bearing (Fe:Mg = 1:9) olivine aggregates not only with high density and fine grain size but with crystallographic preferred orientation (CPO). A magnetic field (≤12 T) is applied to synthetic, fine-grained (~120 nm), olivine particles dispersed in solvent. The alignment of certain crystallographic axes of the particles with respect to a magnetic direction is anticipated due to magnetic anisotropy of olivine. The dispersed particles are gradually consolidated on a porous alumina mold covered with a solid–liquid separation filter during drainage of the solvent. The resultant aligned consolidated aggregate is then isostatically pressed and vacuum sintered. We find that (1) preparation of fully reacted olivine particles, with less propensity to coalesce; (2) preparation of a suspension with highly dispersed particles; and (3) application of a certain strength of the magnetic field are essential to obtain well-sintered and well-aligned aggregates. High density (i.e., <1 vol% porosity) and fine grain size (~1 μm) Fe-free and Fe-bearing olivine aggregates were successfully synthesized with uniaxially aligned a- and c-axes, respectively. Attempts to uniaxially align the magnetization hard axis and to triaxially align Fe-bearing olivine by rotating the suspension in the magnetic field succeeded in obtaining weakly developed CPO aggregates.  相似文献   

Characterization of Fe(III) (hydr)oxides in arsenic contaminated soil under various redox conditions by XAFS and Mössbauer spectroscopies     

Satoshi Mitsunobu  Yoichi Sakai  Yoshio Takahashi 《Applied Geochemistry》2008

Characterization of Fe(III) (hydr)oxides in soils near the Ichinokawa mine was conducted using X-ray absorption fine structure (XAFS) and Mössbauer spectroscopies, and the structural changes were correlated with the release of As into pore-water. The Eh values decreased monotonically with depth. Iron is mainly present as poorly-ordered Fe(III) (hydr)oxides, such as ferrihydrite, over a wide redox range (from Eh = 360 to −140 mV). Structural details of the short-range order of these Fe(III) (hydr)oxides were examined using Mössbauer spectroscopy by comparing the soil phases with synthesized ferrihydrite samples having varying crystallinities. The crystallinity of the soil Fe (hydr)oxides decreased slightly with depth and Eh. Thus, within the redox range of this soil profile, ferrihydrite dominated, even under very reducing conditions, but the crystalline domain size, and, potentially, particle size, changed with the variation in Eh. In the soil–water system examined here, where As concentration and the As(III)/As(V) ratio in soil water increased with depth, ferrihydrite persisted and maintained or even enhanced its capacity for As retention with increased reducing conditions. Therefore, it is concluded that As release from these soils largely depends on the transformation of As(V) to As(III) rather than reductive dissolution of Fe(III) (hydr)oxide.  相似文献   

Evaluation of intrinsic vulnerability to nitrate contamination of groundwater: appropriate fertilizer application management     

Yoshio Mishima  Masayuki Takada  Rie Kitagawa 《Environmental Earth Sciences》2011,63(3):571-580

In agricultural areas, fertilizer application is the main source of nitrate contamination of groundwater. To develop fertilizer management strategies to combat this problem, arable land in Hokkaido, Japan was evaluated using geographic information system techniques for intrinsic groundwater vulnerability to nitrate contamination. The DRASTIC method was modified to adapt it to the Hokkaido environment and used for the evaluation. Of the seven original DRASTIC factors, the depth to water (D), net recharge (R), soil media (S), topography (T), and impact of vadose zone media (I) were selected and used to explain the vertical movement of contaminants to the aquifer. The rating for the net recharge factor was also modified to a dilution factor for contaminants, rather than as a transporter. The frequency of wells with nitrate concentrations exceeding the Japanese environmental standard (10 mg/L) was reasonably explained by vulnerability evaluation results (GLM: logit-link, quasi-binomial distribution, Y = [1 + exp(6.873765 − 0.045988 × X)]⁻¹, p < 0.001). However, in the paddy fields and pastures, vulnerability did not exhibit a clear relationship with the frequency of wells exceeding the standard. This suggests that the modified DRASTIC method is applicable for fertilizer application management in upland fields. In addition, under the ongoing policy for acreage allotment for rice production, this method will be useful for deciding the arrangement of arable land and crop rotation taking into consideration the potential risk of fertilizer-induced nitrate contamination of groundwater.  相似文献