The distribution of ²¹⁰Pb and ²¹⁰Po in the surface waters of the Pacific Ocean     

Y. Nozaki  J. Thomson  K.K. Turekian 《Earth and Planetary Science Letters》1976,32(2):304-312

By modelling the observed distribution of²¹⁰Pb and²¹⁰Po in surface waters of the Pacific, residence times relative to particulate removal are determined. For the center of the North Pacific gyre these are τ_Po = 0.6years andτ_Pb = 1.7years. The surface ocean τ_Pb is determined by particulate transport rather than plankton settling. The fact that it is about two orders of magnitude smaller than τ_Pb for the deep ocean implies a sharp change in the adsorptive quality of particles during descent through the water column.  相似文献   

Concentrations of Trace Elements in Carbonate Reference Materials Coral JCp-1 and Giant Clam JCt-1 by Inductively Coupled Plasma-Mass Spectrometry   总被引：1，自引：0，他引：1  

Mayuri Inoue  Masato Nohara  Takashi Okai  Atsushi Suzuki  Hodaka Kawahata 《Geostandards and Geoanalytical Research》2004,28(3):411-416

Trace elements in the Geological Survey of Japan carbonate reference materials Coral JCp-1 and Giant Clam JCt-1 were determined by inductively coupled plasma-mass spectrometry after digestion with 2% v/v HNO₃. A standard addition method was adopted in this determination in order to neutralise the Ca matrix effect. In addition, Sc, Y, In and Bi were used as internal standards to control the matrix effect and correct instrumental drift. Of the eighteen elements measured in JCp-1, precisions for fourteen elements, including Cu, Cd and Ba, were better than 10% RSD and concentrations ranged from 0.002 μg g^-1 (Cs) to 8.02 μg g^-1 (Ba). The concentrations of measured trace elements in JCt-1, except for Cu, were lower than those in JCp-1. Precisions for all elements with concentrations higher than 0.04 μg g^-1 in JCt-1 were also better than 10% RSD and concentrations were found to be between 0.001 μg g^-1 (Cs) and 4.84 μg g^-1 (Ba). The concentrations of more than fifteen trace elements in the aragonite reference materials are reported here for the first time. Both reference materials are suitable for use in geochemical studies of environmental reconstruction based upon biogenic carbonate materials.  相似文献   

Subsurface structure under a basaltic monogenetic volcano near the active Atera fault     

T. Tanaka  H. Aoki  A. J. Martin  K. Oshita  K. Nozaki  M. Onishi 《Tectonophysics》2004,378(3-4):197

In this study, we examined the subsurface structure in the vicinity of the active Atera fault beneath at least one monogenetic volcano that forms the Sakashita body of the Ueno basalts, central Japan. Microgravity and seismic reflection surveys over an area of about 3×3 km (horizontal)×1 km (vertical from surface) revealed that (1) a low-density body interpreted as the damaged zone of the Atera fault reaches a depth more than 200 m below sea level; and (2) a weak zone of crust that may exist about 1.5 km southwest of the Atera fault in a direction parallel to it. By combining the shape of the Sakashita body and (2), we propose that a dyke extending in a NW–SE direction with several vent alignments in the same direction may exist along this weak zone. This suggests that the studied area was governed in the NW–SE compressional and NE–SW extensional stress field when the Sakashita body formed.  相似文献   

1986 Values for Fifteen GSJ Rock Reference Samples, "Igneous Rock Series"     

Atsushi ANDO  Naoki MITA  Shigeru TERASHIMA 《Geostandards and Geoanalytical Research》1987,11(2):159-166

During the five-year period (April 1981 - March 1986), a series of fifteen rock reference samples, "Igneous rock series", has been prepared by the Geological Survey of Japan (GSJ). Based on the data available (published and communicated), consensus values for major, minor and trace elements have been derived; these values are presented for this second series of samples as well as for the first series of two samples, Granodiorite JG-1 and Basalt JB-1.  相似文献   

Non-destructive alpha-spectrometry and radiochemical studies of deep-sea manganese nodules     

Yoshiyuki Nozaki  Han-Soeb Yang 《Geochimica et cosmochimica acta》1985,49(8):1765-1774

A deep-sea Mn nodule handpicked from top of a 20 cm diameter North Pacific tripod core was directly counted by an α-spectrometer with a silicon surface barrier detector. A distinct ²¹⁰Po peak was recorded for the nodule upper side in contact with bottom seawater. Based on the spectrum, the ²¹⁰Po (supported by ²¹⁰Pb with 22 year half life) is thought to be confined in the top few microns of the nodule. Since the ²¹⁰Po peak diminishes considerably for the bottom side resting on sediment, nondestructive α-spectrometry is useful for determining the sea floor orientation of nodules. This method was tested for a western North Pacific dredged Mn nodule, and was successful in identifying the orientation (and also surface loss of the nodule by dredging).Radiochemical analysis was also carried out for carefully scraped samples from the top and bottom of the two nodules. The growth rates of the hand-picked nodule based on excess ²³⁰Th and ²³¹Pa profiles were 1 to 4 mm/10⁶ y and apparently varied with time. The dredged sample has grown at 2 to 6 mm/ 10⁶ y and the growth has likely been episodic. The radionuclide composition was significantly different between the top and bottom. Evidence was found that the radionuclide fluxes of ²³⁰Th and ²³¹Pa into the nodules considerably changed during the growing histories. The ²³⁰Th/²³²Th activity ratios in the nodule tops are comparable with those in bottom seawater suggesting that the top is growing with metals of seawater origin. However it remains unresolved whether the nodule bottoms are growing by utilizing metals in the sediment pore water.  相似文献   

Determination of Selenium in Twenty-Eight Geological Reference Materials by Atomic Absorption Spectrometry     

Noboru IMAI  Shigeru TERASHIMA  Atsushi ANDO 《Geostandards and Geoanalytical Research》1984,8(1):39-41

Twenty-eight geological reference samples have been analysed for selenium using atomic absorption spectrometry with hydride generation and quartz cell atomizer and/or with solvent extraction and carbon tube atomizer. Data are presented for 5 CCRMP, 6 USGS, 3 NBS, 6 NIM and 8 GSJ reference materials.  相似文献   

High-Mg diorites derived from sanukitic HMA magmas, Kyushu Island, southwest Japan arc: evidence from clinopyroxene and whole rock compositions   总被引：21，自引：0，他引：21  

Atsushi Kamei  Masaaki Owada  Takashi Nagao  Keiichi Shiraki 《Lithos》2004,75(3-4):359-371

High-Mg diorites that have similar whole rock composition to high-Mg andesites (HMAs) should not be simply interpreted as rocks solidified from the HMA magmas, because the high-Mg diorites may be mafic cumulates derived from a different magma from the HMAs.

The HMAs contain unique clinopyroxenes with higher Mg# and Si than those of other sub-alkaline series igneous rocks. The Mg# and Si are controlled by the source magma composition rather than its crystallized conditions such as pressure and temperature. The chemical composition of clinopyroxenes would present important information for the investigation of the source of high-Mg diorites.

We considered the source of Early Cretaceous high-Mg diorites on Kyushu Island, southwest Japan arc, based on their clinopyroxene and whole rock compositions. The clinopyroxenes have similar chemical characteristics to those in HMAs rather than those in other sub-alkaline rocks. Moreover, the whole rock compositions are equivalent to the sanukitic HMA and do not show features of mafic cumulates. This indicates that the high-Mg diorites solidified from sanukitic HMA magmas. It is generally believed that the sanukitic HMA magmas involve the subduction of a young and/or hot oceanic slab was situated in their genesis. Therefore, the occurrence of the high-Mg diorites suggests that Kyushu was situated in the tectonic setting of young and/or hot slab subduction in the Early Cretaceous.  相似文献   

Erratum to Nozaki, Lerche, Alibo And Tsutsumi (2000) dissolved indium and rare earth elements in three Japanese rivers and Tokyo bay: evidence for anthropogenic GD and in, Geochimica Et Cosmochimica Acta64, 3975-3982     

Yoshiyuki Nozaki 《Geochimica et cosmochimica acta》2002,66(20):3673

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Increase in medium-size rainfall events will enhance the C-sequestration capacity of biological soil crusts     

CuiHua Huang  Fei Peng  Itaru Shibata  Jun Luo  Xian Xue  Kinya Akashi  Atsushi Tsunekawa  Tao Wang 《寒旱区科学》2019,11(1):81-92

Biological soil crusts(BSCs) play important roles in the carbon(C) balance in arid regions. Net C balance of BSCs is strongly dependent on rainfall and consequent activation of microbes in the BSCs. The compensation-rainfall size for BSCs(the minimum rainfall amount for a positive net C balance) is assumed to be different with BSCs of different developmental stages. A field experiment with simulated rainfall amount(SRA) of 0, 1, 5, 10, 20, and 40 mm was conducted to examine the C fluxes and compensation-rainfall size of BSCs in different parts of fixed dunes in the ecotone between the Badain Jaran Desert and the Minqin Oasis. We found algae-lichen crust on the interdunes and crest, algae crust on the leeward side, and lichen-moss crust on the windward. Even a small rainfall(1 mm) can activate both photosynthesis and respiration of all types of BSCs. The gross ecosystem production, ecosystem respiration, and net ecosystem exchange were significantly affected by SRA, hours after the simulated rainfall, position on a dune, and their interactions. The rapid activation of photosynthesis provides a C source and therefore could be responsible for the increase of C efflux after each rewetting. C-uptake and-emission capacity of all the BSCs positively correlated with rainfall size, with the lowest C fluxes on the leeward side. The compensation rainfall for a net C uptake was 3.80, 15.54, 8.62, and 1.88 mm for BSCs on the interdunes, the leeward side, the crest, and the windward side, respectively. The whole dune started to show a net C uptake with an SRA of 5 mm and maximized with an SRA of about 30 mm. The compensation-rainfall size is negatively correlated with chlorophyll content. Our results suggest that BSCs will be favored in terms of C balance, and sand dune stabilization could be sustained with an increasing frequency of 5-10 mm rainfall events in the desert-oasis transitional zone.-  相似文献   

Mineralogical study of brown olivine in Northwest Africa 1950 shergottite and implications for the formation mechanism of iron nanoparticles          下载免费PDF全文

Atsushi Takenouchi  Takashi Mikouchi  Toshihiro Kogure 《Meteoritics & planetary science》2017,52(12):2491-2504

Martian meteorites, in particular shergottites, contain darkened olivine (so‐called “brown olivine”) whose color is induced by iron nanoparticles formed in olivine during a shock event. The formation process and conditions of brown olivine have been discussed in the Northwest Africa 2737 (NWA 2737) chassignite. However, formation conditions of brown olivine in NWA 2737 cannot be applied to shergottites because NWA 2737 has a different shock history from that of shergottites. Therefore, this study observed brown olivine in the NWA 1950 shergottite and discusses the general formation process and conditions of brown olivine in shergottites. Our observation of NWA 1950 revealed that olivine is heterogeneously darkened between and within grains different from brown olivine in NWA 2737. XANES analysis showed that brown olivine contains small amounts of Fe³⁺ and TEM/STEM observation revealed that there is no SiO‐rich phase around iron metal nanoparticles. These observations indicate that iron nanoparticles were formed by a disproportionation reaction of olivine (3Fe²⁺_olivine → Fe⁰_metal + 2Fe³⁺_olivine + V_olivine, where V_olivine means a vacancy in olivine). Some parts of brown olivine show lamellar textures in SEM observation and Raman peaks in addition to those expected for olivine, implying that brown olivine experienced a phase transition (to e.g., ringwoodite). In order to induce heterogeneous darkening, heterogeneous high temperature of about 1500–1700 K and shock duration of at least ~90 ms are required. This heterogeneous high temperature resulted in high postshock temperature (>900 K) inducing back‐transformation of most high‐pressure phases. Therefore, in spite of lack of high‐pressure phases, NWA 1950 (= Martian meteorites with brown olivine) experienced higher pressure and temperature compared to other highly shocked meteorite groups.  相似文献