High-reliability zircon separation for hunting the oldest material on Earth: An automatic zircon separator with image-processing/microtweezers-manipulating system and double-step dating     

Yukio Isozaki  Shinji Yamamoto  Shuhei Sakata  Hideyuki Obayashi  Takafumi Hirata  Ken-ichi Obori  Toshinori Maebayashi  Satoshi Takeshima  Toshikazu Ebisuzaki  Shigenori Maruyama 《地学前缘(英文版)》2018,9(4):1073-1083

Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine-an automatic zircon separator(AZS). This is designed particularly for automatic pick-up of100 μm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes:(1) image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray,(2) automatic capturing of the individual zircon grains with microtweezers, and(3) placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical(color) indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e.(1) direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing,(2) high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors(LA-MIC-ICPMS).With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of 150 grains per hour can be achieved with sufficient precision(ca. 0.5%).We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest(4.3 Ga) zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 ± 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons.  相似文献   

Stage-V copepodites of Calanus sinicus and Calanus jashnovi (Copepoda: Calanoida) in mesopelagic zone of Sagami Bay as identified with genetic markers, with special reference to their vertical distribution   总被引：1，自引：0，他引：1  

Takumi Nonomura  Ryuji J. Machida  Shuhei Nishida 《Progress in Oceanography》2008,77(1):45-55

We applied genetic makers to identify Calanus species occurring in Sagami Bay, Japan, in order to investigate their vertical distribution in the upper 1000 m. First, interspecific genetic distances of three gene loci, mitochondrial small ribosomal RNA (srRNA), nuclear internal transcribed spacers 1 (ITS1) and 2 (ITS2), were estimated from morphologically distinguishable adult females of Calanus sinicus, Calanus jashnovi and Calanus pacificus that were collected from Sagami Bay, the Kuroshio Extension and the Oyashio region, respectively. The highest levels of interspecific genetic distance were observed in srRNA, followed by ITS1 and ITS2. The intraspecific genetic distances within C. sinicus were much lower than the interspecific genetic distances, indicating that DNA sequences in these loci are consistent with the morphological differences. This information was used as a criterion for species identification based on DNA sequence variation, and allowed us to identify the fifth copepodites (CVs) or younger stages of these species. Next, the vertical distribution of Calanus species was investigated in Sagami Bay in May 2006, on the basis of a stratified sampling in the upper 1000 m. By applying the genetic markers, 23 individuals comprising all copepodite stages were allocated into either C. sinicus or C. jashnovi, and the small- and large-sized CVs were identified as C. sinicus and C. jashnovi, respectively. The total abundance of C. sinicus was highest at 0-50 m and decreased with depth. On the contrary, CV individuals of C. sinicus were abundant not only in 0-50 m but also below 200 m with minimum occurrences in 150-200 m depth. C. jashnovi was much less abundant than C. sinicus and comprised of only CIV and CV which occurred in the upper 100 m and deeper than 50 m depths, respectively. The abundance of C. sinicus in the 1000-m water column of Sagami Bay was at a level comparable to that in shelf waters, suggesting the importance of off-shelf individuals in the biological production and organic transport in the respective areas.  相似文献   

Surface potential and gravity changes due to internal dislocations in a spherical earth—II. Application to a finite fault     

Wenke Sun  & Shuhei Okubo 《Geophysical Journal International》1998,132(1):79-88

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Quadruple sulfur isotope analysis of ca. 3.5 Ga Dresser Formation: New evidence for microbial sulfate reduction in the early Archean     

Yuichiro Ueno  Shuhei Ono  Douglas Rumble 《Geochimica et cosmochimica acta》2008,72(23):5675-5691

Multiple sulfur isotope system is a powerful new tracer for atmospheric, volcanic, and biological influences on sulfur cycles in the anoxic early Earth. Here, we report high-precision quadruple sulfur isotope analyses (³²S/³³S/³⁴S/³⁶S) of barite, pyrite in barite, and sulfides in related hydrothermal and igneous rocks occurring in the ca. 3.5 Ga Dresser Formation, Western Australia. Our results indicate that observed isotopic variations are mainly controlled by mixing of mass-dependently (MD) and non-mass-dependently fractionated (non-MD) sulfur reservoirs. Based on the quadruple sulfur isotope systematics (δ³⁴S-Δ³³S-Δ³⁶S) for these minerals, four end-member sulfur reservoirs have been recognized: (1) non-MD sulfate (δ³⁴S = −5 ± 2‰; Δ³³S = −3 ± 1‰); (2) MD sulfate (δ³⁴S = +10 ± 3‰); (3) non-MD sulfur (δ³⁴S > +6‰; Δ³³S > +4‰); and (4) igneous MD sulfur (δ³⁴S = Δ³³S = 0‰). The first and third components show a clear non-MD signatures, thus probably represent sulfate and sulfur aerosol inputs. The MD sulfate component (2) is enriched in ³⁴S (+10 ± 3‰) and may have originated from microbial and/or abiotic disproportionation of volcanic S or SO₂. Our results reconfirm that the Dresser barites contain small amounts of pyrite depleted in ³⁴S by 15-22‰ relative to the host barite. These barite-pyrite pairs exhibit a mass-dependent relationship of δ³³S/δ³⁴S with slope less than 0.512, which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation (0.515). The barite-pyrite pairs also show up to 1‰ difference in Δ³⁶S values and steep Δ³⁶S/Δ³³S slopes, which deviate from the main Archean array (Δ³⁶S/Δ³³S = −0.9) and are comparable to isotope effects exhibited by sulfate reducing microbes (Δ³⁶S/Δ³³S = −5 to −11). These new lines of evidence support the existence of sulfate reducers at ca. 3.5 Ga, whereas microbial sulfur disproportionation may have been more limited than recently suggested.  相似文献   

Stable carbon-isotopic compositions of lipids isolated from the ammonia-oxidizing chemoautotroph Nitrosomonas europaea     

Susumu Sakata  John M. Hayes  Michel Rohmer  Alan B. Hooper  Myriam Seemann 《Organic Geochemistry》2008,39(12):1725

For the ammonia-oxidizing bacterium Nitrosomonas europaea, grown autotrophically using semicontinuous culturing, average biomass was depleted in ¹³C relative to CO₂ dissolved in the medium by ca. 20‰ and the total-lipid extract was depleted in ¹³C relative to biomass by 3.7‰. The n-alkyl lipids (weighted average of fatty acids) and isoprenoid lipids (weighted average of hopanoids) were both depleted in ¹³C relative to biomass by about 9‰. The large depletion in the isoprenoid lipids seems to indicate that isotopic fractionations associated with the biosynthesis of methylerythritol phosphate (MEP) affected at least two carbon positions in each isoprene unit. Among the fatty acids, trans-9-hexadecenoic acid was most depleted (13.0‰ relative to biomass), followed by cis-9- hexadecenoic acid (9.6‰) and hexadecanoic acid (6.9‰). Isotopic relationships between the three acids suggest that significant isotope effects were associated with the desaturation and cis to trans isomerization of fatty acids. Given these observations, hopanoids produced by ammonia-oxidizing bacteria growing in natural waters are likely to be depleted in ¹³C by 26–30‰ relative to dissolved CO₂. Since CO₂ at aquatic oxyclines is often depleted in ¹³C, the range of δ values expected for hopanoids is ca. −34‰ to −55‰. The δ values of geohopanoids observed in numerous studies and attributed to unspecified chemoautotrophs fall within this range.  相似文献   

State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment   总被引：1，自引：0，他引：1  

Toshiyuki Awaji  Shuhei Masuda  Yoichi Ishikawa  Nozomi Sugiura  Takahiro Toyoda  Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943

A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Wave forces on multiple floating bodies     

Akira Masumoto  Yoshio Yamagami  Ryuji Sakata 《Applied Ocean Research》1982,4(1):2-8

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Static Spheroidal Deformation of Degree 1 - Consistency Relation, Stress Solution and Partials     

Shuhei Okubo  Takeshi Endo 《Geophysical Journal International》1986,86(1):91-102

This paper treats the static spheroidal deformation of degree 1 in detail. We give a physical interpretation of the consistency relation imposed on it. the relation serves as a guiding principle to find out all of its members. Following Okubo & Saito, we derive the partial derivatives of the degree 1 Love numbers with respect to density, bulk modulus and rigidity.  相似文献   

Mass-dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles     

Shuhei Ono  Boswell Wing  James Farquhar 《Geochimica et cosmochimica acta》2006,70(9):2238-2252

Sulfur isotope studies of post-Archean terrestrial materials have focused on the ratio ³⁴S/³²S because additional isotopes, ³³S and ³⁶S, were thought to carry little information beyond the well-known mass-dependent relationship among multiple-isotope ratios. We report high-precision analyses of Δ³³S and Δ³⁶S values, defined as deviations of ³³S and ³⁶S from ideal mass-dependent relationships, for international reference materials and sedimentary sulfides of Phanerozoic age by using a fluorination technique with a dual-inlet isotope ratio mass spectrometer. Measured variations in Δ³³S and Δ³⁶S are explained as resulting from processes involve branching reactions (two or more reservoirs formed) or mixing. Irreversible processes in closed systems (Rayleigh distillation) amplify the isotope effect. We outline how this new isotope proxy can be used to gain new insights into fundamental aspects of the sulfur biogeochemical cycle, including additional constraints on seawater sulfate budget and processes in sedimentary sulfide formation. The isotope systematics discussed here cannot explain the much larger variation of Δ³³S and Δ³⁶S observed in Archean rock records. Furthermore, Phanerozoic samples we have studied show a characteristic Δ³³S and Δ³⁶S relationship that differs from those measured in Archean rocks and laboratory photolysis experiments. Thus, high precision analysis of Δ³³S and Δ³⁶S can be used to distinguish small non-zero Δ³³S and Δ³⁶S produced by mass-dependent processes from those produced by mass-independent processes in Archean rocks and extraterrestrial materials.  相似文献   

Reciprocity theorem to compute the static deformation due to a point dislocation buried in a spherically symmetric earth   总被引：4，自引：0，他引：4  

Shuhei Okubo 《Geophysical Journal International》1993,115(3):921-928

Intriguing reciprocity relations exist between the static deformation excited by a point dislocation in a SNREI earth and those generated by external forces, such as tidal force, surface loading and surface shear forces. Coseismic deformations can be rewritten as follows: (1) potential change in terms of the tide deformation field, (2) radial displacement in terms of the load and tidal deformation fields, and (3) tangential displacement in terms of shear and torsional deformation fields. The relations greatly reduce the effort to compute the coseismic crustal deformation in a spherically symmetric earth.  相似文献