大野 剛

Experimental results are presented showing the variation in the relationship between odd isotopes of tin (Sn) in mass-independent fractionation caused by the magnetic isotope effect (MIE), which has previously only been observed for mercury. These results are consistent with the trend predicted from the difference between the magnitudes of nuclear magnetic moments of odd isotopes with a nuclear spin. However, the correlation between odd isotopes in fractionation induced by the MIE for the reaction system used in this study (solvent extraction using a crown ether) was different from that reported for the photochemical reaction of methyltin. This difference between the two reaction systems is consistent with a theoretical prediction that the correlation between odd isotopes in fractionation induced by the MIE is controlled by the relationship between the spin conversion time and radical lifetime. The characteristic changes in the correlation between odd isotopes in fractionation induced by the MIE observed for Sn in this study provide a guideline for quantitatively determining fractionation patterns caused by the MIE for elements that have multiple isotopes with a nuclear spin. These results improve our understanding of the potential impact of the MIE on mass-independent fractionation observed in natural samples, such as meteorites, and analytical artifacts of high-precision isotope analysis for heavy elements.

In this study, we propose a new method for elucidating zircon growth in granitic plutons, based on the variations in three-dimensional (3D) cathodoluminescence (CL) patterns, U[sbnd]Pb age, titanium concentration, and Th/U. We focused on the zircon growth in the Okueyama granite (OKG) in central Kyushu, Japan, to obtain interpretations of magma chamber processes that result in the formation of granitic plutons. Three lithofacies of the OKG were sampled: biotite granite, hornblende granite, and hornblende granodiorite. To determine the 3D internal structure and growth pattern of zircon, we performed CL observations for multiple crystals that were sectioned in depth intervals of 5–10 μm. The zircon U[sbnd]Pb ages and Ti concentrations for the center sections of the crystals were simultaneously determined. The 3D distribution of the internal structure of zircon crystals comprises the following five textures: 1) oscillatory zoned (OZ), 2) porous, 3) chaotic, 4) locally disturbed, and 5) crystals with inherited cores. The 3D distribution of the OZ can be used to approximate the location of zircon nucleation. The simultaneous determination of zircon U[sbnd]Pb ages and Ti concentrations of the granite samples indicates the time–temperature (t–T) history of granitic magma before its solidification. The three lithofacies record similar cooling histories among the temperatures of zircon crystallization. The magma chamber cooled from 900 °C to 650 °C at approximately 13 Ma and then cooled to the biotite K[sbnd]Ar closure temperature. The simultaneous determination of zircon U[sbnd]Pb age and Ti concentration in the granite also enabled us to correlate the Th/U with apparent temperature. A decrease in zircon Th/U with decreasing temperature indicates progressive fractional crystallization during the cooling of the magma chamber. This decrease in zircon Th/U with decreasing temperature may be related to the co-crystallization of accessory monazite and zircon. The relationship between Th/U and temperature indicates that fractional crystallization in the magma chamber at temperatures above 770 °C was more progressive than that at temperatures below 770 °C. The three lithofacies demonstrate common tendencies in the relationship between Th/U and temperature, which indicate the same path of fractional crystallization among the three lithofacies in the cooling magma chamber.

We examine the historical changes of 236U/238U and 235U/238U in a sediment core collected in Tokyo Bay and elucidate the anthropogenic sources of uranium in the 1960s-2000s. Uranium-236 was detected in samples deposited in the 1960s-2000s, and the 236U/238U ratio of the sediment core shows peak values in the 1970s. The 235U/238U isotopic ratios in samples deposited in the early 1960s are almost identical to that of natural uranium, implying that the 236U might have originated from global fallout. A decrease in 235U/238U was observed in the late 1960s-2000s, suggesting that depleted uranium from nuclear fuel reprocessing increased the 236U/238U ratios in the sediment. The 236U/238U values in sediments from the 1980s-2000s were lower than those in the 1970s but considerably higher than those in the 1960s, suggesting that the main source of depleted uranium still remains around Tokyo Bay. Our results demonstrated that the depleted uranium released in the 1970s should be considered as an important end-member when using uranium isotopic ratios as environmental tracers in closed aquatic environments around industrial cities.

Simultaneous determination of the U-Pb age of zircon and concentration of titanium in a single analysis spot, using inductively coupled plasma mass spectrometry with laser ablation sample introduction, produces paired age and temperature data of zircon crystallisation, potentially revealing time-temperature (t-T) histories for evolved magma. The Kurobegawa granite, central Japan, contains abundant mafic magmatic enclaves (MMEs). We applied this method to evaluate MMEs and their host (enclosing) granites. Cooling behaviour common to both MMEs and host rocks was found between 1.5 and 0.5 Ma. Rapid cooling from the zircon crystallisation temperature to the closure temperature of biotite K-Ar system was within similar to 1 million year. Combining the obtained t-T paths of MMEs and host rocks with petrological information can provide insights into magma chamber processes. This suggests that MME flotation, migration, and spread through the magma chamber ceased at 1.5-0.5 Ma, indicating the emplacement age of the Kurobegawa granitic pluton, as no large-scale reheating episodes have occurred since then.

We examine the temporal changes of 236U/238U and 235U/238U in atmospheric deposition from samples collected in Tokyo and Akita from 1963 to 1979 and elucidate the spatial distribution and historical changes of the anthropogenic sources of uranium in Japan. The 236U/238U ratio of atmospheric deposition in Tokyo peaked in 1963 and again during the 1970s, while the corresponding 235U/238U ratios of atmospheric deposition during the second peak period were lower than that of natural uranium. The 236U/238U ratios of atmospheric deposition in Akita samples peaked in 1963. The 235U/238U ratios in Akita samples were almost identical to that of the natural uranium ratios. These results suggest that the peak of 236U/238U in 1963 corresponds to what is recognized as representative for global fallout. The increase of 236U/238U and the decrease of 235U/238U observed simultaneously in the 1970s indicate that depleted uranium has subsequently been released into the environment around Tokyo. The cumulative deposition density of 236U for atmospheric fallout samples collected in Tokyo from 1968 to 1979 is an order of magnitude larger than that of the global fallout, suggesting that the depleted uranium in the 1970s is a major component of 236U in Tokyo and should be considered as an end-member when using 236U as an environmental tracer in the industrial city. This knowledge can facilitate future research using 236U as an effective environmental tracer.

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Zircon is one of the most important minerals in geochronologic research. Isotopic ratios and trace elements in zircons are expected to reflect those of their parent magmas. Many geochemical researchers have proposed various discrimination diagrams for zircon to indicate tectonic setting and to identify source rock. Because most detrital zircons accumulated at river mouths are derived primarily from granitoids, the classification of zircon within granitoids is potentially meaningful. In our research, we focused on sediment involvement during granitoid formation and tried to identify trace-element compositions in zircon that are sensitive to variation in sediment incorporation. To accomplish this, we examined trace-element compositions of both the granitoids and the included zircons in the Kofu granitic complex and the Tanzawa tonalitic plutons in Japan. Among the high-field-strength elements (Th, U, Ta, Nb, Hf, and rare earth elements), only Nb and Ta concentrations in the granitoids increased as the rate of sediment contribution increased. However, the zircon did not show such trends in Nb and Ta content. Zircon Y and P contents exhibited a positive correlation, indicating that xenotime substitution occurs to some extent. Because P exists as pentavalent ions in igneous systems, its presence likely affects the concentrations of pentads in zircon. When we divided the Nb and Ta contents by the P content, it became clear that zircon Nb/P and Ta/P ratios increase depending on sediment involvement. While some exceptions exist, we found that zircon Yb/Gd ratios also respond to sediment involvement. Our data further demonstrated that zircons in granitoids with significant sediment incorporation are characterized by low Ce/P contents, which is partly attributable to monazite crystallization before zircon saturation. This study demonstrates that combining these element ratios is useful for indicating sediment incorporation.

Simultaneous determination of zircon U-Pb age and titanium concentration for a single analysis spot gives both the crystallization age and temperature. The crystallization age and temperature pairs in granitic zircons map the time-temperature (t-T) path of granitic magma before its solidification. In laser ablation inductively coupled plasma mass spectrometry (IA-ICP-MS) analysis, it is challenging to quantitatively analyse a low level of titanium concentration. This study employed two approaches using a quadrupole mass spectrometer equipped with a collision/reaction cell (CRC). In the first approach, the MS/MS mass-shift mode with oxygen reaction gas provided reliable and consistent measurement of titanium as (TiO+)-Ti-48-O-16. In the second approach, the titanium concentration was determined quantitatively from the signal intensity of Ti-49 in the non-gas mode (without the inflow of collision/reaction gas into the CRC). The methods were applied to zircon samples of the Kurobegawa granite (KRG), the Okueyama granite (OKG), the Toki granite (TKG), and the Tono plutonic complex (TCP), and provided U-Pb ages and titanium concentrations consistent with previous studies. The crystallization ages and temperatures collected from individual analysis spots of zircon samples in the KRG, OKG, TKG, and TCP were plotted in the t-T diagrams and enabled us to characterize the rapid cooling paths at thermal conditions of zircon crystallization at the sampling sites. (C) 2020 Elsevier B.V. All rights reserved.

Simultaneous determination of zircon U-Pb age and titanium concentration for a single analysis spot gives both the crystallization age and temperature. In laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, it is challenging to quantitatively analyse a low level of titanium concentration. Two approaches were employed using a quadrupole mass spectrometer equipped with a collision/reaction cell (CRC). In the first approach, the MS/MS mass-shift mode with oxygen reaction gas provided reliable and consistent measurement of titanium as 48Ti16O+. In the second approach, the titanium concentration was determined quantitatively from the signal intensity of 49Ti in the non-gas mode (without the inflow of collision/reaction gas into the CRC). The methods were applied to zircon samples of the Kurobegawa granite (KRG), the Okueyama granite (OKG), the Toki granite (TKG), and the Tono plutonic complex (TCP). The biotite K-Ar geochronology were employed for rock samples of the KRG, OKG, and TPC (N = 3) of which the zircon crystals were analysed. The obtained titanium concentrations of the zircon crystals can lead to the crystallization temperatures through Ti-in-zircon geothermometer.

The determination of 90Sr by ICP-MS is capable of providing a high sample throughput compared with radiometric analytical methods. Although the isobaric interference caused by 90Zr ions can be reduced by reaction with oxygen, the high background caused by stable 88Sr has made it difficult to determine 90Sr by conventional ICP-MS. In this study, a rapid and sensitive method was developed for the determination of 90Sr using triple quadrupole ICP-MS. The MS/MS configuration improves the abundance sensitivity by more than two orders of magnitude (5 × 10-12), and the detection limit for 90Sr in 1 g environmental samples was 0.6 Bq kg-1. The applicability of the method to the measurement of 90Sr in environmental samples was demonstrated by analysis of certified reference materials (soil: IAEA 375 plant: IAEA 330, IAEA 373) contaminated by the Chernobyl accident. The measured 90Sr radioactivities in the samples were consistent with values determined by radiometric analysis, within analytical error. The measured 90Sr concentration in IAEA 372 was 610 ± 40 Bq kg-1 (SD, n = 3) (Decay correction was made to December 1, 2016). This method provides a powerful tool for the investigation of radiostrontium contaminations in the Fukushima area and elsewhere.

We report new results for Cu2+ adsorption on d-MnO2 and the resulting changes in Cu isotopic composition due to isotopic fractionation. The adsorption experiments were designed as a pH series (3.22–6.94) and an adsorption-desorption series. 63Cu adsorbs preferentially on d-MnO2, and the degree of isotopic fractionation is 0.45 ± 0.18 (2s, n = 12). Preferential desorption of 65Cu from d-MnO2 was also observed. The isotopic data are consistent with a closed isotopic equilibrium model, and the degree of fractionation indicates no systematic variation with pH or reaction time. Previously reported extended X-ray absorption fine structure study predicted the preferential adsorption of 65Cu on d-MnO2, because of the formation of Cu2+ surface complexes (with 3–4 ligands) from dissolved Cu2+ (with 5 ligands) however, the opposite was observed in this study. The equilibrium in isotopic fractionation is affected by the bonding environment hence, we suggest that dissolved Cu2+ species have a stronger bond than adsorbed ones.

Monohydrocalcite (MHC: CaCO3 center dot H2O), a rare carbonate mineral formed under surface conditions, is usually observed in nature as containing a variable amount of Mg, with a 0.007-0.45 Mg/Ca mole ratio. The variable Mg composition in MHC is anticipated as a promising proxy to assess paleo-hydrochemistry especially in saline lakes. Although the roles of Mg on the formation and stability of MHC have been studied intensively, the Mg speciation in MHC has remained unclear and controversial. This study examined Mg speciation in MHC using X-ray absorption near edge structure (XANES), ab initio molecular simulation, and geochemical modeling. Mg-XANES spectra of MHC with different Mg/Ca ratios prepared from mixing solutions of Na2CO3, CaCl2 and MgCl2 revealed that the Mg in MHC is a mixture of amorphous Mg carbonate (AMC) and other Mg containing phase. The contribution of AMC to total Mg is negatively correlated to the crystallinity of MHC. Results show that AMC might play a protective role in the crystallization and the transformation to stable calcium carbonates. Ab initio calculation of Mg2+ substitution into MHC showed that a limited amount of Mg2+ can be incorporated into the MHC structure. Six-fold coordination of Mg2+ is substituted for eight-fold coordination of Ca2+ in the MHC structure. The other type of Mg in MHC revealed from the XANES analyses most likely corresponds to the structural Mg in MHC. The contribution of the structural Mg is almost constant at 0.06 in Mg/Ca, representing the limit of solid solubility of Mg in MHC. The solubility products of the MHC with the limit of solid solubility of Mg and the AMC associated with MHC were estimated from the reacted solution compositions. Prediction of the Mg/Ca ratio as a function of the initial solution conditions using solubility reasonably reproduces the observed apparent Mg/Ca ratios in MHC from the present study and earlier studies. The apparent Mg/Ca ratio of MHC is useful to elucidate water chemistry, especially for CO3/Ca and Mg concentrations during MHC formation. (C) 2017 Elsevier Ltd. All rights reserved.

Iodine-131 is one of the most critical radionuclides to be monitored after release from reactor accidents due to the tendency for this nuclide to accumulate in the human thyroid gland. However, there are not enough data related to the reactor accident in Fukushima, Japan to provide regional information on the deposition of this short-lived nuclide (half-life = 8.02 d). In this study we have focused on the long-lived iodine isotope, I-129 (half-life of 1.57 x 10(7) y), and analyzed it by accelerator mass spectrometry (AMS) for surface soil samples collected at various locations in Fukushima Prefecture. In order to obtain information on the I-131/I-129 ratio released from the accident, we have determined I-129 concentrations in 82 soil samples in which I-131 concentrations were previously determined. There was a strong correlation (R-2 = 0.84) between the two nuclides, suggesting that the I-131 levels in soil samples following the accident can be estimated through the analysis of I-129. We have also examined the possible influence from Te-129m on I-129, and found no significant effect. In order to construct a deposition map of I-131, we determined the I-129 concentrations (Bq/kg) in 388 soil samples collected from different locations in Fukushima Prefecture and the deposition densities (Bq/m(2)) of I-131 were reconstructed from the results. 2014 Elsevier Ltd. All rights reserved.

The Ediacaran-Cambrian was one of the most important periods for the evolution of life. Recent studies have provided detailed chemostratigraphies that decipher the linkages between ambient surface environmental changes and biological evolution. The occurrence of skeletal fossils in Ediacaran rocks suggests that the possible onset of Ca-biomineralization started in the latest Neoproterozoic. Molecular clocks also predict the emergence of animals containing Ca-carbonate spicules in the Neoproterozoic. Therefore, it is important to estimate the transition of the Ca cycle in seawater. Ancient Ca cycles in the oceans are estimated from the calcium isotopic compositions of carbonate rocks. However, the lack of continuous Ca isotopic data in the Ediacaran leaves the Ca cycle unresolved. The almost continuously exposed, Ediacaran and Cambrian strata in South China mainly comprise carbonate rocks with subordinate black shales and sandstones, which contain many fossils, suitable for the study of environmental and biological changes. We conducted drilling from the Liantuo, via the Nantuo, Doushantuo, Dengying and Yanjiahe to the Shuijingtuo formation at four sites in the Three Gorges area in order to obtain continuous, fresh samples without surface alteration and oxidation. We analyzed Ca-44/Ca-42 ratios in carbonate rocks with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) screened for diagenetic alteration. The resultant delta Ca-44/42 ratios exhibit a smooth curve. The values of delta Ca-44/42 are anomalously high relative to those in the Phanerozoic, and they gradually decrease towards the end of the Ediacaran. Our new Ca isotope chemostratigraphy suggests that a different Ca cycle had existed during the Ediacaran. The long-term, high delta Ca-44/42 is not simply explicable by changes in temperature, differences in carbonate mineralogy, or changes in the input/output fluxes of Ca to the ocean. We propose three possible explanations for the observed high delta Ca-44/42 ratios in the Ediacaran: high delta Ca-44/42 ratios of Ca inputs, potential undiscovered sinks of Ca with low delta Ca-44/42 values, and negligible isotope fractionation between carbonate and seawater; we consider that one or all of these contributed to the high delta Ca-44/42 ratios. Of these, we prefer the small isotope fractionation, which implies that the Ca concentration in seawater was initially low in the early Ediacaran and increased throughout that period. (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

A method was developed for the determination of Cs-134/Cs-137 and Cs-135/Cs-137 in rainwater samples using a triple quadrupole ICP-MS, with the objective of investigating radioactive cesium isotope ratios released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The high background caused by Ba ions and Xe impurities in argon plasma gas has made it difficult to carry out determination of the Cs-134/Cs-137 and Cs-135/Cs-137 ratios on conventional ICP-MS instruments without prior chemical separation. In this study, nitrous oxide was used as the reaction gas for reducing the isobaric interference by Ba-134, Ba-135, Ba-137 and Xe-134, and an additional quadrupole in front of the reaction cell was shown to effectively remove Sn and Sb that could have produced possible interference such as SbO and SnO by the N2O reaction. The detection limit for Cs-134, Cs-135 and Cs-137 in solution containing Ba was successfully improved. In order to confirm the applicability of this method to the measurement of Cs-134/Cs-137 and Cs-135/Cs-137 ratios of rainwater, four samples were collected for analysis from 40-200 km away from the FDNPP. The measured Cs-134/Cs-137 ratios in the samples are consistent with the values determined by Ge semiconductor analysis to within the analytical error, suggesting that the developed method can provide reliable isotopic data without any correction of the mass-discrimination effect. No variation was found in the Cs-135/Cs-137 ratios of the four samples, suggesting either the same contamination source or a uniformly consistent mixing ratio between contamination sources. The measured Cs-135/Cs-137 ratios in the samples are different from global fall-out values and from that of Chernobyl. This result indicates that the value of the rainwater samples can be used as a radiocesium tracer in the environment.

We have developed a new analytical method to determine the mass-dependent isotopic fractionations on Ce and Nd in geochemical samples. Mass discrimination effects on Ce and Nd were externally corrected by normalizing Sm-149/Sm-147 and Eu-153/Eu-151, being 0.92124 and 1.0916, respectively based on an exponential law. The reproducibility of the isotopic ratio measurements on Ce-142/Ce-140, Nd-146/Nd-144 and Nd-148/Nd-144 were 0.08 parts per thousand (2SD, n = 25), 0.06 parts per thousand (2SD, n = 39) and 0.12 parts per thousand (2SD, n = 39), respectively. The present technique was applied to determine the variations of the Ce and Nd isotopic ratios for five geochemical reference materials (igneous rocks, JB-1a and JA-2; sedimentary rocks, JMn-1, JCh-1 and JDo-1). The resulting ratios for two igneous rocks (JB-1 a and JA-2) and two sedimentary rocks (JMn-1 and JCh-1) did not vary significantly among the samples, whereas the Ce and Nd isotope ratios for the carbonate samples (JDo-1) were significantly higher than those for igneous and sedimentary rock samples. The 1:1 simple correlation between delta Ce-142 and delta Nd-146 indicates that there were no significant difference in the degree of isotopic fractionation between the Ce and Nd. This suggests that the isotopic fractionation for Ce found in the JDo-1 could be induced by geochemical or physicochemical processes without changing the oxidation status of Ce, since the redox-reaction can produce larger isotopic fractionation than the reactions without changing the oxidation state. The variations in the Ce and Nd isotope ratios for geochemical samples could provide new information concerning the physico-chemical processes of the sample formation.

A method was developed for the determination of 129I in soil samples that uses an ICP-MS equipped with an octopole reaction system. Oxygen was used as the reaction gas for reducing the background intensity of m/z 129, principally by 129Xe+. The contribution of polyatomic ions, such as 127IH2 +, could be effectively corrected for by assuming a production ratio (127IH2 +/127I+ = 3 × 10-8). The measured 129I/127I ratios in a NIST standard solution and Fukushima soil samples are consistent with the expected value within the analytical error. This method provides a powerful tool for investigating radioiodine contamination in Fukushima and elsewhere. © The Japan Society for Analytical Chemistry.

A method was developed for the determination of I-129 in soil samples using a Triple Quadrupole ICP-MS, with the objective of investigating radioiodine released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The determination of I-129 by ICP-MS is capable of providing a high sample throughput compared to other methods. Nonetheless, the high background caused by Xe-129 impurities in argon plasma gas and polyatomic ions such as (IH2+)-I-127 and (ID+)-I-127 has made it difficult to carry out determinations of this isotope by conventional ICP-MS instruments. In this study, oxygen was used as a reaction gas for reducing the background intensity of m/z 129, principally by Xe-129. The contribution of polyatomic ions such as (IH2+)-I-127 and (ID+)-I-127 could be effectively corrected for by assuming a production ratio of 5 x 10(-9). The detection limit for I-129 in solution was successfully improved. The measured I-129/I-127 ratios in NIST SRM 3231 Level II standard solution are consistent with the certified value of 0.981 x 10(-8) within the analytical error, suggesting the reliability of the method to the measurement of I-129/I-127. In order to confirm the applicability of this method to the measurement of I-129/I-127 ratios of Fukushima soils, samples were collected for analysis from 5-60 km away from the FDNPP. Prior to the ICP-MS measurement iodine fractions were separated from soil by pyrohydrolysis and were purified by solvent extraction. The I-129/I-127 ratios in the samples are consistent with values determined by accelerator mass spectrometry (AMS) within the analytical error. This method provides a powerful tool for the investigation of radioiodine contamination in Fukushima and elsewhere.

In order to understand the behavior of radionuclides released from the Fukushima Daiichi nuclear power plant, the depth distributions of radiocesium and radioiodine were investigated in a wheat field, a rice paddy, an orchard, and a cedar forest in Koriyama, Fukushima Prefecture. Our results demonstrate that, following the nuclear power plant disaster, more than 90% of the radionuclides were distributed in the upper 6 cm of the soil column in the wheat field and within 4 cm of the surface in the rice paddy, orchard, and cedar forest. According to the measurement of radionuclides in the three adjacent agricultural fields, the variation of deposition densities in the wheat field was smaller than that of the orchard and rice paddy, suggesting that the low permeability of the orchard and paddy soils may cause horizontal migration of radionuclides during the initial deposition. This result indicates that the deposition densities in the wheat field should be appropriate for estimating the amount of fallout in the area. The deposition densities of Cs-134, Cs-137, and I-131 in this area were estimated to be 512 +/- 76 (SD, n = 5), 522 +/- 80 (SD, n = 5), and 608 +/- 79 (SD, n = 5) kBq/m(2) (decay corrected to April 1, 2011), respectively. A comparison of the deposition density between the wheat field and the cedar forest suggests that more than half of the radionuclides are distributed in the tree canopies of the evergreen forestland.

The Neoproterozoic-Cambrian Dalradian Supergroup of Scotland contains three glaciogenic sedimentary units, the Port Askaig Formation, the Stralinchy-Reelan Formation, and the Loch na Cille Boulder Bed, in ascending order. Although the idea, that relatively cold climates occurred during the latest Proterozoic, is widely accepted, the cause of the onset of glaciation is still controversial; we use new carbonate Sr-87/Sr-86 data to better constrain this environmental change. Some Dalradian limestones have high strontium contents (&gt;1000 ppm), low manganese contents and Mn/Sr ratios (&lt;0.2) and, according to their silica, aluminum and potassium contents and Rb/Sr ratios, they suffered insignificant contamination from siliciclastic minerals, thus they are suitable for estimating the Sr-87/Sr-86 values of paleoseawater in the Neoproterozoic. The Sr-87/Sr-86 values of limestones of the Islay Formation (ca. 0.7067), sampled on the island of Islay, are similar to the values of previous studies. However, the Sr-87/Sr-86 values of limestones just below the Port Askaig Formation (ca. 0.7064), collected on the island of Garbh Eileach, have the lowest values recorded in the Dalradian Supergroup. Comparing these Sr-87/Sr-86 values with coeval Sr-87/Sr-86 values of other regions in the world, such low Sr-87/Sr-86 (&lt;0.7065) has only been reported from successions pre-dating the older Cryogenian (Sturtian) glaciation, which supports the idea that the Port Askaig Formation was deposited during the older Cryogenian glaciation. We have reconstructed the variations in the Sr-87/Sr-86 ratio from the Tonian through the Cryogenian and Ediacaran to the earliest Cambrian. The results show that the Sr-87/Sr-86 ratio of seawater decreased just before the older Cryogenian glaciation, that it increased by two steps in the early and middle Ediacaran, and that there were at least two abrupt positive excursions in the middle Ediacaran and at the Precambrian-Cambrian boundary. The decline of the Sr-87/Sr-86 ratio of seawater just before the older Cryogenian Sturtian glaciation suggests that enhancement of weathering, related to break-up of the Rodinia supercontinent and continental flood basalt volcanism, was a likely driver for generating global cooling for the Snowball Earth conditions (Godderis et al., 2003; Donnadieu et al., 2004). (C) 2010 Elsevier By. All rights reserved.

The Ediacaran period was one of the most important times for the evolution of life. However, the scarcity of well-preserved outcrops of Ediacaran rocks still leaves ambiguity in decoding ambient surface environmental changes and biological evolution. The Ediacaran strata in South China are almost continuously exposed, comprise mainly carbonate rocks with subordinate black shales and sandstones, and they contain many fossils, suitable for study of environmental and biological changes in the Ediacaran. We conducted drilling through the Doushantuo I&apos;m at four sites in the Three Gorges area to obtain continuous, fresh samples without surface alteration and oxidation. We analyzed (87)Sr/(86)Sr and (88)Sr/(86)Sr ratios of the fresh carbonate rocks, selected on the basis of microscopic observations and the geochemical signatures of Sr contents, Mn/Sr and Rb/Sr ratios, and delta(18)O values, with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS). The chemostratigraphy of the (87)Sr/(86)Sr ratios of the drilled samples displays a smooth curve and two large positive shifts during Ediacaran time. The combination of the detailed chemostratigraphies of delta(13)C, delta(18)O and (87)Sr/(86)Sr values and Mn and Fe contents enables us to decode the surface environmental changes and their causes in the Ediacaran. The first large positive excursion of (87)Sr/(86)Sr occurred together with negative delta(13)C and positive delta(18)O excursions. The higher (87)Sr/(86)Sr values indicate an enhancement of continental weathering, whereas the positive delta(18)O excursion suggests global cooling. Global regression due to global cooling enhanced the oxidative decay of exposed marine organic sediments and continental weathering. Accelerated influx of nutrients promoted primary productivity, resulting in oxidation of dissolved organic carbon (DOC), whereas active sulfate reduction due to a higher sulfate influx from the continents caused remineralization of the large DOC, both of which caused a negative delta(13)C anomaly. The 580 Ma Gaskiers glaciation accounts for the close correlation among the positive (87)Sr/(86)Sr, negative delta(13)C and positive delta(18)O excursions. The second large positive shift of (87)Sr/(86)Sr firstly accompanied a positive delta(13)C excursion, and continued through the Shuram delta(13)C negative excursion. The positive correlation of delta(13)C and (87)Sr/(86)Sr values is consistent with an enhanced continental weathering rate due to continental collisions that built Trans-Gondwana mountain chains, and with a higher primary activity due to the enhancement of continental weathering and consequent higher nutrient contents in seawater. The accompanied increase in Mn and Fe contents implies a gradual decline of the seawater oxygen content due to more active aerobic respiration and oxidation of reductive materials flowing in the oceans. In the Shuram excursion, higher (87)Sr/(86)Sr values and a transition from increase to decrease in Mn and Fe contents were accompanied by the large negative delta(13)C excursion. The higher (87)Sr/(86)Sr values are the first compelling evidence for enhanced continental weathering, which was responsible for the large delta(13)C anomaly through the remineralization of the DOC by more active sulfate reduction due to a higher sulfate influx. Higher Mn and Fe contents in the early and middle stages of the excursion suggest a decline in the oxygen content of seawater due to oxidative decay of the DOC, whereas in the late stages the decrease in Mn and Fe contents is consistent with oceanic oxygenation. The emergence of Ediacara biota after the Gaskiers glaciation and the prosperity of the latest Ediacaran is concomitant with the formation of more radiogenic seawater with high (87)Sr/(86)Sr values, suggesting that enhanced continental weathering, and the consequent higher influx of nutrients, played an important role in biological evolution. (C) 2009 Elsevier B.V. All rights reserved.

We measured both mass-dependent isotope fractionation of delta Sr-88 (Sr-88/Sr-86) and radiogenic isotopic variation of Sr (Sr-87/Sr-86) for the Neoproterozoic Doushantuo Formation that deposited as a cap carbonate immediately above the Marinoan-related Nantuo Tillite. The delta Sr-88 and Sr-87/Sr-86 compositions showed three remarkable characteristics: (1) high radiogenic 87Sr/86Sr values and gradual decrease in the Sr-87/Sr-86 ratios, (2) anomalously low delta Sr-88 values at the lower part cap carbonate, and (3) a clear correlation between Sr-87/Sr-86 and delta Sr-88 values. These isotopic signatures can be explained by assuming an extreme greenhouse condition after the Marinoan glaciation. Surface seawater, mixed with a large amount of freshwater from continental crusts with high Sr-87/Sr-86 and lighter delta Sr-88 ratios, was formed during the extreme global warming after the glacial event. High atmospheric CO2 content caused sudden precipitation of cap carbonate from the surface seawater with high Sr-87/Sr-86 and lighter delta Sr-88 ratios. Subsequently, the mixing of the underlying seawater, with unradiogenic Sr isotope compositions and normal delta Sr-88 ratios, probably caused gradual decrease of the Sr-87/Sr-86 ratios of the seawater and deposition of carbonate with normal delta Sr-88 ratios. The combination of Sr-87/Sr-86 and delta Sr-88 isotope systematics gives us new insights on the surface evolution after the Snowball Earth. (C) 2007 International Association for Gondwana Research. Published by Elsevier B.V All rights reserved.

We present a method to determine (88)Sr/(86)Sr and (87)Sr/(86)Sr simultaneously. The former variation reflects the mass-dependent isotopic fractionation through the physico-chemical processes, and the latter originates from beta(-)-decay of the parent nuclide (87)Rb as well as the mass-dependent isotopic fractionation. In order to determine the mass-dependent isotopic fractionation, the mass-discrimination effect on (88)Sr/(86)Sr was externally corrected by an exponential law using Zr. For the radiogenic growth of (88)Sr/(86)Sr, the mass-dependent isotopic fractionation effect on (87)Sr/(86)Sr was corrected by a conventional correction technique using the (88)Sr/(86)Sr ratio. The reproducibility of the (88)Sr/(86)Sr and (87)Sr/(86)Sr measurements for a high-purity Sr chemical reagent was 0.06 parts per thousand (2SD, n = 20) and 0.07 parts per thousand (2SD, n = 20), respectively. Strontium isotopic ratios ((88)Sr/(86)Sr and (87)Sr/(86)Sr) were measured on six geochemical reference materials (igneous rock: JB-1a and JA-2; carbonate mineral: JLs-1, JDo-1, JCp-1 and JCt-1) and one seawater sample. The resulting (87)Sr/(86)Sr ratios obtained here were consistent with previously published data within the analytical uncertainties. The resulting (88)Sr/(86)Sr ratios for igneous rock samples did not vary significantly within the samples, whereas the carbonate samples showed enrichments of the lighter Sr isotopes over the seawater sample. The (88)Sr/(86)Sr ratio of geochemical samples could reflect the physicochemical processes for the sample formation. Also, a combined discussion of (88)Sr/(86)Sr and (87)Sr/(86)Sr of samples will render multi-dimensional information on geochemical processes.

Precise Zn-66/Zn-64 and Zn-68/Zn-64 isotopic ratios of biochemical samples have been measured using multiple collector-ICP-mass spectrometry (MC-ICPMS). In order to eliminate the mass spectrometric interferences on Zn isotopes (e.g., Ni-64+ and Ba-136(2+)), we chemically purified the analyte using an ion chromatographic technique. The resulting precisions of the Zn-66/Zn-64 and Zn-68/Zn-64 ratio measurements were 0.05 parts per thousand and 0.10 parts per thousand (2SD), respectively, which were enough to detect the isotopic variation of Zn in nature. Red blood cell (RBC) samples were collected from five volunteers (four males and one female), including a series of 12 RBC samples from one person through monthly-based sampling over a year. These were analyzed to test possible seasonal changes and variations in Zn-66/Zn-64 and Zn-68/Zn-64 ratios among the individuals. The Zn-66/Zn-64 and Zn-68/Zn-64 ratios for a series of 12 RBC samples collected over a year were 0.43 parts per thousand and 0.83 parts per thousand higher than the values of highly purified Zn metal (JMC Zn), and no seasonal change could be found. The Zn-66/Zn-64 and Zn-68/Zn-64 ratios for RBC samples collected from five volunteers did not vary significantly. In order to investigate Zn isotopic heterogeneity in a human body, Zn isotopic ratios of a hair sample collected from one of the volunteers was also analyzed. The Zn-66/Zn-64 and Zn-68/Zn-64 ratios for the hair sample were 0.59 parts per thousand and 1.14 parts per thousand lower than the mean value of RBC samples. This result demonstrates that detectable isotopic fractionation occurs in the human body. The data obtained here suggest that the isotopic ratios of trace metals could provide new information about transportation of metal elements in vivo.

誘導結合プラズマ（ICP）質量分析法は，迅速かつ高感度な元素分析装置として，地球科学的試料の化学にはなくてはならない分析法となっている．特にレーザーアブレーション試料導入法は，固体試料の直接分析が可能な上，レーザービームを絞り込むことにより局所分析も可能であり，更にICP質量分析法の最大の特徴である分析の迅速性を最大限に引き出すことができる優れた試料導入法として注目されている．レーザーアブレーション法において正確な元素分析，同位体分析を行うためには，感度の向上，レーザーサンプリング時における元素分別の低減，信号強度の安定化，妨害信号の除去，イオン検出器の感応性の改良などが不可欠である．そこで著者らは，分析感度を向上するために窒素混合法を，またレーザーサンプリング時における元素分別を低減法するためにソフトアブレーション法あるいは化学支援レーザーアブレーション法を，そして信号強度を安定化する手法としてスタビライザー法を，更にイオン検出器の感応性の違いに起因する同位体分析精度の低下を抑える検出器補正法や，スペクトル干渉を低減するための低出力プラズマ法などを開発してきた．本稿では，これらの手法の動作原理の解説と，得られる効果を紹介する．&lt;br&gt;

Precise Fe-56/(54) Fe and Fe-57/Fe-54 isotopic ratios on human red blood cell (RBC) samples have been measured using multiple collector-ICP-mass spectrometry (MC-ICPMS). The mass spectrometric interferences on Fe isotopes (e.g., (ArO+)-Ar-56 and (ArOH+)-Ar-57) were successfully minimized by a dry plasma condition achieved by a desolvating nebulizer sample-introduction technique. In order to eliminate possible variations in the measured isotopic ratios due to non-mass spectrometric interferences, Fe was separated from remaining organic compounds and major co-existing elements using an ion chromatographic technique. The resulting precisions of the Fe-56/Fe-54 and Fe-57/Fe-54 ratio measurements were 0.12parts per thousand and 0.20parts per thousand, respectively, which were high enough to detect the isotopic variation of Fe in nature. For an inter-laboratory comparison, all of the Fe isotopic ratio data were normalized by the ratios for the IRMM-014 international isotopic standard. A series of 12 RBC samples were collected from one person through monthly-based sampling over a period of one year. These were analyzed to test possible seasonal changes in the Fe-56/Fe-54 and Fe-57/Fe-54 ratios. Moreover, in order to test possible variations in the Fe-56/Fe-54 and Fe-57/Fe-54 ratios among different people, RBC samples were collected from five volunteers (four males and one female). The Fe-56/Fe-54 and Fe-57/Fe-54 ratios for a series of 12 RBC samples collected over a one-year period show 3.06parts per thousand and 4.51parts per thousand lower than the values of IRMM-014, and no significant seasonal change could be found in the ratios. The lack in seasonal changes in the Fe isotopic ratios could be explained by a small contribution of the daily net-intake of Fe (1 - 2 mg/day) onto the total amount of Fe in the human body (2 - 4 g). The Fe-56/Fe-54 and Fe-56/Fe-54 ratios for RBC samples collected from four male samples did not vary measurably, whereas the Fe isotopic ratios for a female RBC were 0.3parts per thousand/amu heavier than the mean value of four male samples. This difference in Fe isotopes among the individuals can be the result of a difference in uptake efficiency of the Fe through a dietary process from the digestive tract. The data obtained here demonstrate that the isotopic ratios of trace metals can provide new information about metabolic efficiencies of the metallic elements.

A short course on inductively coupled plasma-mass spectrometry (ICP-MS) was held from 6th to 7th September, just before the Goldschmidt Conference at Kurashiki. This short course covered the entire range of ICP-MS techniques, including basic principles of ICP-MS, laser ablation sample introduction techniques, and various applications to the Earth and planetary science. The course also covered basic theoretical aspects of the mechanism of isotopic fractionation. Lectures given by Dr. Detlef Gunther (ETH, Switzerland), Dr. Alex Halliday (ETH, Switzerland), Dr. Toshiyuki Fujii (Kyoto Univ., Japan), Dr. Simon E. Jackson (GEMOC, Australia) and Dr. Keith O'Nions (Oxford Univ., UK) will be reviewed in this paper.

Cu-65/Cu-63 and Fe-56/Fe-54 isotopic ratios for two metal reference materials (NIST SRM 976 and NIST SRM 665) have been measured by a laser ablation-multiple collector-inductively coupled plasma mass spectrometer (LA-MC-ICPMS). A time resolved analysis (TRA) data acquisition technique was used to monitor the time profile in Cu-65/Cu-63 and Fe-56/Fe-54 isotopic ratios. An ArF excimer laser (193 nm) which produces pit sizes of 16-63 mm was used to ablate Cu and Fe from metal samples. Measured Cu-65/Cu-63 ratios increased systematically (1 similar to 2parts per thousand) with prolonged ablation, suggestive of isotopic fractionation during the laser ablation or ionisation process in the ICP. However, systematic increase in the measured Cu-65/Cu-63 ratio could be minimised down to &lt; 1&PTSTHOUSND; level when a newly developed correction technique for slow response of a Faraday preamplifier (0.2 &SIM; 1 s) was applied. The resulting precision or repeatability of the isotopic ratio measurements was improved to the 0.7&PTSTHOUSND; level, which was almost half the level achieved by the conventional measurements. The validity of this correction technique was also demonstrated by the Fe-56/Fe-54 isotopic ratio measurement for metal Fe. The systematic increase in the measured Fe-56/Fe-54 ratio could also be minimised to the &lt; 1parts per thousand level after the correction of slow response of the Faraday preamplifier. The data obtained here demonstrated that the time-dependent changes in measured isotopic ratios can be minimised by the careful control of the intensity change and correction of slow response of the Faraday preamplifier.

In-situ Fe-54/Fe-56 and Fe-57/Fe-56 ratio measurements for solid samples have been carried out using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Using a dry plasma condition achieved by laser sample introduction technique, mass spectrometric interferences such as (ArN+)-Ar-54, (ArO+)-Ar-56 or (ArOH+)-Ar-57 could be successfully reduced. Although these argide interference signals were not completely eliminated, the contribution of the remnant signals could be effectively corrected by an "on-peak" baseline subtraction technique. Resultant repeatability or external precision of the measurement over the four month period was almost 0.5-1%, which was insufficient to detect the isotopic variations of Fe in natural samples (typically smaller than 0.3%). We found that the poor repeatability in Fe isotopic ratio measurements was mainly due to instability or poor reproducibility of the high voltage power supply, especially for ion acceleration voltage, of our instrument. The mass discrimination effect on Fe isotopic ratios was strongly correlated with accelerating energy (ion energy) of analyte ions. To overcome this, Fe isotopic ratios of NIST Standard Reference Material (SRM) 665 metallic standard were measured between the sample measurements. This sample-standard bracketing method successfully results in internal precisions of the Fe-54/Fe-56 and Fe-57/Fe-56 ratios of better than 0.1% at the 95% confidence level. The analysis time for one sample was about 50 s, and the total amount of Fe used for an analysis was about 30 ng. The Fe-54/Fe-56 and Fe-57/Fe-56 ratios measured for NIST SRM 661 steel, three Fe-bearing minerals, and six iron meteorites, show no significant variations within the analytical uncertainties achieved in this study. The good agreement between samples suggests that our approach successfully compensates for both the instrumental drift and the background correction. The data presented here demonstrate clearly that the Fe isotopic ratios obtained by the LA-MC-ICP-MS technique can give strong clues to elucidate the Fe isotopic fractionation occurring in biochemical reactions, which may cause a larger isotopic fractionation effect in nature.