Grain-scale iron isotopic distribution of pyrite from Precambrian shallow marine carbonate revealed by a femtosecond laser ablation multicollector ICP-MS technique: Possible proxy for the redox state of ancient seawater     

Manabu Nishizawa  Hiroki Yamamoto  Subaru Tsuruoka  Yusuke Sawaki  Yoshiaki Kon  Tsuyoshi Komiya  Takafumi Hirata 《Geochimica et cosmochimica acta》2010,74(9):2760-8899

The redox state of Precambrian shallow seas has been linked with material cycle and evolution of the photosynthesis-based ecosystem. Iron is a redox-sensitive element and exists as a soluble Fe(II) species or insoluble Fe(III) species on Earth’s surface. Previous studies have shown that the iron isotopic ratio of marine sedimentary minerals is useful for understanding the ocean redox state, although the redox state of the Archean shallow sea is poorly known. This is partly because the conventional bulk isotope analytical technique has often been used, wherein the iron isotopic record may be dampened by the presence of isotopically different iron-bearing minerals within the same sample. Here we report a microscale iron isotopic ratio of individual pyrite grains in shallow marine stromatolitic carbonates over geological time using a newly developed, near-infrared femtosecond laser ablation multicollector ICP-MS technique (NIR-fs-LA-MC-ICP-MS).We have determined that the grain-scale iron isotopic distribution of pyrite from coeval samples shows a bimodal (2.7 and 2.3 Ga) or unimodal pattern (2.9, 2.6, and 0.7 Ga). In particular, pyrite from the 2.7 Ga Fortescue Group shows a unique bimodal distribution with highly positive (+1.0‰ defined as Type 1) and negative δ⁵⁶Fe values (−1.8‰ defined as Type 2). Type 1 and 2 pyrites occasionally occur within different siliceous layers in the same rock specimen. Layer-scale iron isotopic heterogeneity indicates that the iron isotopic ratios of the two types of pyrite are not homogenized by diagenesis after deposition. Some cubic pyrites have a core with a positive δ⁵⁶Fe value (1‰) and a rim with a crustal δ⁵⁶Fe value (0‰). The observed isotopic zoning suggests that the positive δ⁵⁶Fe value is a primary signature at the time of stromatolite formation, while secondary pyrite precipitated during diagenesis.The positive δ⁵⁶Fe value of Type 1 and the large iron isotopic difference between Type 1 and 2 (2.8‰.) suggest partial Fe(II) oxidation in the 2.7-Ga shallow sea, i.e., pyritization of ⁵⁶Fe-enriched ferric oxyhydroxide (Type 1) and ⁵⁶Fe depleted Fe²⁺aq in seawater (Type 2). Type 2 pyrite was probably not produced by microbial iron redox cycling during diagenesis because this scenario requires a higher abundance of pyrite with δ⁵⁶Fe of 0‰ than of −1.8‰. Consequently, the degree of Fe(II) oxidation in the 2.7-Ga shallow sea can be estimated by a Fe²⁺aq steady-state model. The model calculation shows that half the Fe²⁺aq influx was oxidized in the seawater. This implies that O₂ produced by photosynthesis would have been completely consumed by oxidation of the Fe²⁺aq influx. Grain-scale iron isotopic distribution of pyrite could be a useful index for reconstructing the redox state of the Archean shallow sea.  相似文献   

Late Holocene Asian monsoon variations recorded in Lake Rara sediment,western Nepal     

Atsunori Nakamura  Yusuke Yokoyama  Hideaki Maemoku  Hiroshi Yagi  Makoto Okamura  Hiromi Matsuoka  Nao Miyake  Toshiki Osada  Hirofumi Teramura  Danda Pani Adhikari  Vishnu Dangol  Yosuke Miyairi  Stephen Obrochta  Hiroyuki Matsuzaki 《第四纪科学杂志》2012,27(2):125-128

The Himalayas are a key location for understanding centennial‐ to millennial‐scale variations in the Asian monsoon, yet few studies of the late Holocene have been conducted in this sensitive area. Direct evidence for shifts in monsoonal wind strength is often limited to marine proxy records, while terrestrial reconstructions (e.g. lake levels and spleothems) focus on precipitation. Here, we present the first evidence of terrestrial summer monsoon wind strength changes from Lake Rara, western Nepal, based on Mn/Ti ratios, a proxy for lake stratification. These data indicate a link between the Arabian Sea and the Himalayas, suggesting that centennial‐ to millennial‐scale changes in wind strength occurred synchronously. Distinct similarity is also observed between Lake Rara and the southern part of China, which may support previous suggestions that the southern part of China is influenced by Indian summer monsoon. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Superior solid solubility of MnSiO3 in CaSiO3 perovskite     

Lin Li  Takaya Nagai  Yusuke Seto  Kiyoshi Fujino  Jun Kawano  Shoich Itoh 《Physics and Chemistry of Minerals》2015,42(2):123-129

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Implications for the low latitude cloud formations from solar activity and the quasi-biennial oscillation     

Peng K. Hong  Hiroko Miyahara  Yusuke Yokoyama  Yukihiro Takahashi  Mitsuteru Sato 《Journal of Atmospheric and Solar》2011,73(5-6):587-591

We examined the effect of the 11-year solar cycle and quasi-biennial oscillation (QBO) on the ～27-day solar rotational period detected in tropical convective cloud activity. We analyzed the data of outgoing longwave radiation (OLR) for AD1979–2004, dividing into four different cases by the combination of high and low solar activities in terms of the 11-year variation, and easterly and westerly stratospheric winds associated with QBO. As a result, ～27-day variation has been most significantly detected in high solar activity period around the Indo-Pacific Warm Pool. Based on correlation analysis, we find that solar rotation signal can explain 10–20% of OLR variability around the tropical warm pool region during the high solar activity period. The spatial distribution has been, however, apparently different according to the phases of QBO. It is suggested that the 11-year solar cycle and stratospheric QBO have a possibility to cause large-scale oceanic dipole phenomena.  相似文献   

Redox history of the Three Gorges region during the Ediacaran and Early Cambrian as indicated by the Fe isotope     

Yusuke Sawaki  Miyuki Tahata  Tsuyoshi Komiya  Takafumi Hirata  Jian Han  Degan Shu 《地学前缘(英文版)》2018,9(1):155-172

The Ediacaran-Cambrian transition is characterized by numerous events such as the emergence of large multi-cellular metazoans and surface environmental disturbances.Based on geological evidence,it has been proposed that this transition coincided with the increase in the atmospheric oxygen level that was key to the evolution of life.Even though ancient redox conditions can be inferred from the composition of sedimentary iron mineral species,this method is not necessarily applicable to all rocks.In the Earth system,the cycling of iron is of considerable interest owing to its sensitivity to redox conditions.Information regarding the paleo-oceanic iron cycle is revealed in the iron isotopic composition of ironbearing minerals.Unfortunately,only limited iron isotopic data exists for Ediacaran-to Cambrianperiod oceans.To circumvent this deficiency,we drilled a fossiliferous Ediacaran to Early Cambrian sedimentary succession in the Three Gorges region,South China.We analyzed the iron isotope ratios(δ~(56/54)Fe)of pyrite grains in the drill cores using laser ablation multi collector inductively coupled plasma mass spectrometry.The results demonstrate large variations inδ~(56/54)Fe,from-1.6 to 1.6‰,and positive iron isotope ratios are observed in many successions.The presence of positiveδ~(56/54)Fe in pyrite indicates that the ferrous iron in the seawater was partially oxidized,suggesting that seawater at Three Gorges was ferruginous during the Ediacaran and Early Cambrian periods.However,aggregated pyrite grains in organic carbon-rich black shales at Member 4 of the Doushantuo Formation and the base of the Shuijingtuo Formation yield near-zeroδ~(56/54)Fe values;this suggests that the ocean was transiently dominated by sulfidic conditions during these periods.Notably negativeδ~(56/54)Fe values,lower than-1‰,can be interpreted as a signature of DIR.The DIR also might contribute in part to the re-mineralization of organic matter during the largest negative carbon isotope anomaly in the Ediacaran.  相似文献   

Imaging polarimetry of Comet 9P/Tempel before and after the Deep Impact     

Reiko Furusho  Yuji Ikeda  Wing-Huen Ip  Toshihiro Kasuga  Yusuke Sato  Ming-Shin Chang  Jun-ichi Watanabe 《Icarus》2007,190(2):454-458

The NASA's Deep Impact mission was the first impact experiment to a cometary nucleus. The target of the mission was Comet 9P/Tempel, one of the Jupiter family comets. The impact was performed on July 4th, 2005. Imaging polarimetric observations were carried out by Polarimetric Imager for COmets (PICO) mounted on the Lulin One-meter Telescope (LOT) at Lulin Observatory, Taiwan. Intensity and linear polarization degree maps were obtained on July 3-5, 2005. Impact ejecta plume was clearly recognized in the enhanced intensity map. Furthermore, arc-shaped region of high polarization was recognized in the polarization map. Dust grains in this region had larger expansion velocity than the grains which provided the brightest area in the intensity map. comparing our results with the MIR spectroscopy obtained by Subaru Telescope we conclude that very small carbonaceous grains might be responsible for the region of high polarization.  相似文献   

Changes of environments and human activity at the Sannai-Maruyama ruins in Japan during the mid-Holocene Hypsithermal climatic interval     

Hodaka Kawahata  Hisashi Yamamoto  Ken'ichi Ohkushi  Yusuke Yokoyama  Katsunori Kimoto  Hideki Ohshima  Hiroyuki Matsuzaki 《Quaternary Science Reviews》2009,28(9-10):964-974

Sannai-Maruyama is one of the most famous and best-researched mid-Holocene (mid-Jomon) archaeological sites in Japan, because of a large community of people for a long period. Archaeological studies have shown that the Jomon people inhabi1ted the Sannai-Maruyama site from 5.9 to 4.2 ± 0.1 cal kyr BP However, a continuous record of the terrestrial and marine environments around the site has not been available. Core KT05-7 PC-02, was recovered from Mutsu Bay, only 20 km from the site, for the reconstruction of high-resolution time series of environmental records, including sea surface temperature (SST). C₃₇ alkenone SSTs showed clear fluctuations, with four periods of high (8.4–7.9, 7.0–5.9, 5.1–4.1, and 2.3–1.4 cal kyr BP) and four of low (?8.4, 7.9–7.0, 5.9–5.1, and 4.1–2.3 cal kyr BP) SST. Thus, each SST cycle lasted 1.0–2.0 kyr, and the amplitude of fluctuation was about 1.5–2.0 °C. Total organic carbon (TOC) and C₃₇ alkenone contents, and the TOC/total nitrogen ratio indicate that marine biogenic production was low before 7.0 cal kyr BP, but was clearly increased between 5.9 and 4.0 cal kyr BP, because of stronger vertical mixing. During the period when the community at the site prospered (between 5.9 and 4.2 ± 0.1 cal kyr BP), the terrestrial climate was relatively warm. The high relative abundance of pollen of both Castanea and Quercus subgen. Cyclobalanopsis supports the interpretation that the local climate was optimal for human habitation. Between 5.9 and 5.1 cal kyr BP, in spite of warm terrestrial climates, the C₃₇ alkenone SST was low; this apparent discrepancy may be attributed to the water column structure in the Tsugaru Strait, which differed from the modern condition. The evidence suggests that at about 5.9 cal kyr B.P, high productivity of marine resources such as fish and shellfish and a warm terrestrial climate led to the establishment of a human community at the Sannai-Maruyama site. Then, at about 4.1 ± 0.1 cal kyr BP, abrupt marine and terrestrial cooling, indicated by a decrease of about 2 °C in the C₃₇ alkenone SST and an increase in the pollen of taxa of cooler climates, led to a reduced terrestrial food supply, causing the people to abandon the site. The timing of the abandonment is consistent with the timing (around 4.0–4.3 cal kyr BP) of the decline of civilizations in north Mesopotamia and along the Yangtze River. These findings suggest that a temperature rise of ～2 °C in this century as a result of global warming could have a great impact on the human community and especially on agriculture, despite the advances of contemporary society.  相似文献   

Seasonal changes in runoff characteristics on a permafrost watershed in the southern mountainous region of eastern Siberia     

Yusuke Yamazaki  Jumpei Kubota  Tetsuo Ohata  Varely Vuglinsky  Takahisa Mizuyama 《水文研究》2006,20(3):453-467

We attempted to clarify the runoff characteristics of a permafrost watershed in the southern mountainous region of eastern Siberia using hydrological and meteorological data obtained by the State Hydrological Institute in Russia from 1976 to 1985. We analysed seasonal changes in the direct runoff ratio and recession gradient during the permafrost thawing period. Thawing depth began to increase from the beginning of May and continued to increase until the end of September, exceeding 150 cm. Annual precipitation and discharge were in the range 525–649 mm and 205–391 mm respectively. The sum of the annual evapotranspiration and changes in water storage ranged from 235 to 365 mm. The mean daily evapotranspiration in June, July, August and September was 1·5 mm day^?1, 1·7 mm day^?1, 1·5 mm day^?1, and 0·5 mm day^?1 respectively. The direct runoff ratio was highest in June, decreasing from 0·8 in June to 0·2 in September. The recession gradient also decreased from June to September. Since the frozen soil functioned as an impermeable layer, the soil water storage capacity in the thawing part of the soil, the depth of which changed over time, controlled the runoff characteristics. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Surf zone fishes in an exposed sandy beach at Sanrimatsubara,Japan: Does fish assemblage structure differ among microhabitats?     

Takashi Inoue  Yusuke Suda  Mitsuhiko Sano 《Estuarine, Coastal and Shelf Science》2008

To assess differences in fish assemblage structures among microhabitats within the surf zone of an exposed sandy beach, three microhabitats (onshore current, rip current, and river adjacent sites) were sampled at Sanrimatsubara Beach, western Japan, in May, August, and November 2002 and 2003. Although several physical variables (e.g. wave height, current speed, turbidity, salinity, and sand particle size) and major prey abundances (calanoid copepods and mysids) differed among the sites, no significant differences were apparent in the numbers of fish species and individuals among the sites in any month in either year. In addition, species and individual numbers of two dominant feeding groups (zooplankton feeders, and epiphytic and benthic crustacean feeders) did not show any significant responses to among-site differences in prey abundance. Cluster and ordination analysis confirmed the similarity in fish species composition among the three sites. These results indicated that the surf zone fish assemblage structures were similar among the microhabitats in spite of there being microhabitat-related differences in abiotic and biotic environments.  相似文献   

Supercooled drizzle formed by condensation–coalescence in the mid-winter season of the Canadian Arctic     

Masahiro Kajikawa  Katsuhiro Kikuchi  Yoshio Asuma  Yusuke Inoue  Noboru Sato 《Atmospheric Research》2000,52(4):377

Supercooled drizzle (freezing drizzle) was observed at Inuvik, N.W.T., Canada (68°22′N, 133°42′W) on December 20, 21 and 27, 1995. Meteorological conditions in which the supercooled drizzle could form under low temperatures (colder than −20°C) in the mid-winter season of the Canadian Arctic were examined from the sounding data and data measured by a passive microwave radiometer at ground level. The following results were obtained. (1) Supercooled drizzle fell to the ground with ice pellets and frozen drops on snow crystals. (2) The maximum size of supercooled drizzle particles increased as the depth of cloud layer saturated with respect to water increased. (3) Because a layer of air temperature higher than 0°C was not detected from the sounding data at Inuvik, melting of snow particles was impossible. It was concluded, therefore, that supercooled drizzle was formed by the condensation–coalescence process below freezing temperature.  相似文献