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Volume 48 (2014)
- Issue 6 Pages 509-
- Issue 5 Pages 423-
- Issue 4 Pages 331-
- Issue 3 Pages 231-
- Issue 2 Pages 113-
- Issue 1 Pages 1-
Volume 48, Issue 2
Displaying 1-9 of 9 articles from this issue
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TRAN THUY HANG, KAZUHIRO KATO, HIDEKI WADA2014 Volume 48 Issue 2 Pages 113-119
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESSAragonite and calcite often coexist; as such, separating these very similar minerals is an important step in undertaking research on these two phases individually. One approach to discriminating between the two phases is to stain a sample using Meigen’s solution, which is a solution of cobalt nitrate, a magnetic substance: aragonite is stained purple while calcite is still white. Magnetic separator can also be employed, and this instrument has been used in a number of environmental and industrial applications. Here, we integrate the use of the magnetic characteristics of Meigen’s solution with magnetic separation to provide an enhanced method of aragonite and calcite separation semi-automatically instead of manually as done in the past. Imperfect staining and/or the aggregation of differing minerals means that, a 250–125 μm is optimal grain size for aragonite separation that is treated at 70 deg.C - 15 minutes treatment as well as of calcite separation that is treated at 80–90 deg.C - 10 minutes treatment. The effectiveness of this approach is demonstrated by defining a radioactive carbon profile of carbonate samples collected from a chimney from Conical Seamount, in the Mariana forearc.View full abstractDownload PDF (1511K) -
TASUKU AKAGI, SAKI YASUDA, YOSHIHIRO ASAHARA, MARIKO EMOTO, KOZO TAKAH ...2014 Volume 48 Issue 2 Pages 121-131
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESSThe Nd and Sr isotopes of the acetic-acid-soluble, hydrochloric-acid-soluble, hydrofluoric-acid-soluble (siliceous) fractions of settling particles collected in the highly diatom productive Bering Sea were measured. The siliceous fraction exhibits εNd values higher than that of the acetic acid extractable fraction or that dissolved in North Pacific seawater. Recent studies concluded that the siliceous fraction of settling particles collected in an area of extremely high diatom production consists almost exclusively of diatom frustules, that diatom frustules are a major Nd transporter in the ocean water column, and that half the Nd in diatom frustules should be supplied from an unknown input other than that diffused/advected from the deep seawater. The Nd isotope system of the siliceous fraction provides the first evidence that diatoms transport the high εNd signature to the oceanic system. The unknown input is the dissolution of silicate rocks which are somehow supplied to the sea surface. In the Bering Sea one of the sources of the high εNd values was identified to be island arcs. This diatom-mediated dissolution of silicate particles may be a mechanism to explain the rather pervasive island arc Nd isotope signature in the Pacific Ocean where there are surrounding island arcs.View full abstractDownload PDF (291K) -
YUJI SANO, MIO TAKADA, NAOTO TAKAHATA, WATARU FUJIYA, NAOJI SUGIURA2014 Volume 48 Issue 2 Pages 133-144
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESS
Supplementary materialWe report here technical details of 26Al–26Mg dating of single plagioclase grains located in a chondrule of the Efremovka CV3 chondrite using a high spatial resolution secondary ion mass spectrometer (NanoSIMS). A ca. 500 pA mass filtered 16O– primary beam was used to sputter 5–7 μm diameter craters. Secondary positive beams were extracted for mass analysis. We detected 27Al++ (at mass 13.5), 24Mg+, 25Mg+, and 26Mg+ simultaneously under a static magnetic field for the first session. To obtain accurate Mg isotopic ratios but at the expense of a longer analytical time, we have also measured Mg isotopes (24Mg, 25Mg, 26Mg) using a single detector with a magnet scanning mode. Apparent 26Mg excesses were observed in small plagioclase grains (#1 and #4) of the chondrule. A positive correlation between the Al/Mg ratio and the excesses 26Mg engender a 26Al–26Mg isochron with an initial 26Al/27Al ratio of (3.3 ± 1.3) × 10–6 for #1 and (1.7 ± 1.4) × 10–6 for #4. In contrast, large plagioclase grains (#2 and #3) show no resolvable excesses 26Mg. The initial 26Al/27Al ratios of −(0.13 ± 0.71) × 10–6 (#2) and −(0.12 ± 1.26) × 10–6 (#3) are consistent with zero. A substantial difference exists among the initial 26Al/27Al ratios of individual grains in the same Efremovka chondrule, which may be attributable to parent body alteration of the meteorite. Careful treatment is necessary to calculate the formation age combining the data from different grains, even in a single chondrule.View full abstractDownload PDF (4885K) -
YUTA KAWAKUBO, YUSUKE YOKOYAMA, ATSUSHI SUZUKI, TAKASHI OKAI, CHANTAL ...2014 Volume 48 Issue 2 Pages 145-152
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESSCoral skeletal Sr/Ca compositions are valuable tools for the reconstruction of past tropical climate. While solution-based ICP-AES has become the preferred method to obtain monthly-resolved Sr/Ca records as proxy for sea-surface temperature (SST), laser ablation ICP-MS (LA-ICP-MS) allows a more rapid and still precise analysis of multiple elemental ratios at higher spatial resolution and, measurements can easily be replicated. However, the methodology still needs to be refined for long corals. It is applied here to a 435 year old Porites coral from the temperate region of southern Japan. Sr/Ca ratios measured by LA-ICP-MS and ICP-AES for three 10–15 yr periods are shown to be highly consistent. Resolution, data processing and Sr/Ca-SST calibration issues are discussed, and a replicate strategy is proposed to ensure high-precision Sr/Ca records from multi-century corals using LA-ICP-MS.View full abstractDownload PDF (3279K) -
KEI OKAMURA, HIDESHI KIMOTO, MAYUMI HATTA, TAKUROH NOGUCHI, ATSUKO NAK ...2014 Volume 48 Issue 2 Pages 153-163
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESS
Supplementary materialThe total alkalinity (AT) of seawater is one of the parameters required to characterize carbonate systems, which are essential for studying the greenhouse effects of carbon dioxide (CO2) on the Earth’s climate. The AT of seawater was measured by potentiometric open-cell titration using HCl—without the addition of sodium chloride (NaCl)—and calculated by a nonlinear least-squares regression. In addition, the equation for calculating the titrant density was studied over a range of concentrations and temperatures. The similarity of the pH electrode response to the ideal Nernst value (ks) was measured using pH buffers for seawater and pure water. New methods for the calculation of AT using ks were proposed. Open-cell titrations for a certified reference material (CRM) were conducted using two electrodes with ks of 0.997 and 0.989. The measured values for both electrodes were in good agreement with the CRM value of 2356.78 ± 0.26 μmol/kg. AT was successfully calculated using ks. The dilution effect by the titrant, free of NaCl, on electromotive force measurement was also examined and found to be negligible for the calculation of CO2 parameters.View full abstractDownload PDF (193K) -
RAN KUBOTA, ATSUYUKI OHTA, TAKASHI OKAI2014 Volume 48 Issue 2 Pages 165-188
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESSA sequential extraction procedure developed by the European Community Bureau of Reference (BCR) was applied to eight sediment geochemical reference materials provided by the Geological Survey of Japan, AIST (JLk-1, JSd-1–4, JMs-1, JMs-2, and JSO-1). The study aimed to provide reference materials of widely varied geological materials in order to enhance the utility of the sequential extraction procedure in environmental studies. The concentrations of 38 elements extracted by BCR protocols were determined for the eight reference materials. The BCR scheme is designed to extract elements of the intended phase using acetic acid (step 1), hydroxylammonium chloride (step 2), and hydrogen peroxide and ammonium acetate (step 3). The residue of the step 3 extraction was further digested using hydrofluoric acid, perchloric acid, and nitric acid (step 4). The relative standard deviations of elemental concentrations in each extraction stage were generally <30% for steps 1 and 3 and <20% for steps 2 and 4. The sums of the elemental concentrations for the four steps (the total recoveries) ranged from 70% to 100% of the bulk compositions. The speciation of elements in the reference materials obtained by BCR protocols was strongly affected by sediment origin, mineralogical composition, sedimentary environment, and anthropogenic activity. Accordingly, sequential extraction based on the BCR procedure is effective for environmental studies. Eight geochemical reference materials certified/recommended for bulk composition are now further available as reference materials for the sequential extraction procedure.View full abstractDownload PDF (990K) -
SITING ZHANG, YUN LIU2014 Volume 48 Issue 2 Pages 189-205
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESSThe mechanisms of quartz dissolution are affected intricately by pH conditions and electrolyte types. Most previous studies have focused on the mechanisms of quartz dissolution under one specific condition (e.g., temperature, pH, saturation or electrolyte type); however, this study investigates molecular-level mechanisms under combinations of electrolyte and pH conditions, which are more complex but closer to the reality. Under neutral and alkaline pH conditions with Ca2+, Mg2+ or Na+ aqua ions in the solution, the dissolution of Q1 (Si) and Q2 (Si) sites on the quartz surface, which represents the predominant part of the quartz dissolution story, is investigated by first-principles quantum chemistry calculation methods. Our results confirm that quartz dissolution can be enhanced significantly by the presence of electrolytes under neutral pH conditions. However, under alkaline pH conditions, the surface complexes of aquo ions are different, depending on where and how those electrolytes bond onto the quartz surfaces. The energy barriers of all possible hydrolysis reaction pathways are calculated carefully. The activation energies for the reaction between the negatively charged quartz surface and H2O have never been reported before. Our results of activation energy are closer to experimental values than previous calculations have been, suggesting that the cluster models and theoretical levels used here are more reasonable. Such information provides a molecular-level understanding of the differences of quartz dissolution rates between pure water and ion-containing solutions.View full abstractDownload PDF (414K) -
MASANOBU YAMAMOTO, FUKASHI OHIRA, FUJIO KUMON2014 Volume 48 Issue 2 Pages 207-217
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESSWe generated a record of lignin and fatty acid compositions from the TK-2004 core in Takano Basin, central Japan, during 39–162 ka by TMAH-thermochemolysis-GC/MS. We tested lignin and fatty acid compositions in the sediments of a small lake (1.88 km2 watershed) as a paleovegetation proxy to understand the responses of terrestrial vegetation in central Japan to global climate change. Variation in terrestrial organic carbon contents estimated by C/N and ∑8 was parallel to the total organic content (TOC) variation, suggesting that the inflow of terrestrial organic matter was a major factor determining the TOC. The ratio of mid-chain C20–C24 n-fatty acids to short-chain C14–C18 n-fatty acids (MFA/SFA ratio) and the ratio of cinnamyl to vanillyl phenols (C/V ratio) of lignin gradually increased from mid-MIS 6 to early MIS 3. The increase in both parameters suggested increase in the contribution of submerged and floating plants as the flats were expanded in the lake margin. The ratio of syringyl to vanillyl phenols (S/V ratio) corresponded to the pollen vegetation index. This correspondence indicated that the S/V ratio reflected the relative abundance of angiosperms to gymnosperms in the Takano Basin. The consistency of the S/V ratio at the site of core TKN-2004 and the other two locations suggests that the S/V ratio in a small basin is a robust proxy for terrestrial vegetation on a regional scale.View full abstractDownload PDF (2086K) -
KASUMI SAKATA, HIKARU YABUTA, TADASHI KONDO2014 Volume 48 Issue 2 Pages 219-230
Published: March 20, 2014
Released on J-STAGE: March 28, 2014
JOURNAL FREE ACCESSThe recent discovery of active deep-sea hydrothermal systems venting high-pH fluids suggests that the prebiotic chemistry of the hydrothermal systems of early Earth may have been more diverse than previously thought. To determine the most favorable conditions for prebiotic oligomerization, the effects of metal ions (Ca2+, Mg2+, Zn2+, Fe2+, Mn2+, and Cu2+) and pH on the formation and decomposition rates of glycylglycine (GlyGly), glycylglycylglycine (GlyGlyGly), and diketopiperazine (DKP) in aqueous solution were investigated. Glycine (Gly) solutions containing metal ions were heated for 1–74 days at 140°C under various pH conditions and the samples were analyzed by high-performance liquid chromatography. GlyGly and DKP were produced in all samples regardless of the presence or absence of metal ions. GlyGly yields were higher under basic conditions (pH 9.8–9.9) than under acidic or neutral conditions. Moreover, GlyGly yields in the presence of Cu2+ and Zn2+ were higher than in the absence of Cu2+ and Zn2+; in the presence of metal ions other than Cu2+ and Zn2+, GlyGly yields were lower. The dimerization rate constant of Gly (k1) increased in the presence of Cu2+. GlyGlyGly was only produced in samples with Cu2+ and the yield was 5 times higher under basic conditions (pH 9.8) than under acidic (pH 3.4) or neutral (pH 7.1) conditions. However, other metal ions inhibited prebiotic peptide synthesis by catalyzing hydrolysis or chelation with amino acids. These results reflect the high stability of Cu2+ complexes with amino acids or peptides in the salt-induced peptide formation reaction, particularly at high pH. Although elongation of oligopeptides was not favored, formation of metal–amino acid or metal–short peptide chelates may have facilitated primitive biological functions and expanded prebiotic reaction fields because of their mobility in the Earth’s early oceans.View full abstractDownload PDF (1783K)
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