Carbon isotope anatomy of a single graphite crystal in a metapelitic migmatite revealed by high-spatial resolution SIMS analysis

High-spatial resolution carbon isotope analyses of natural graphite using secondary ion mass spectrometry (SIMS), together with conventional mass spectrometry techniques, demonstrate isotopic heterogeneity within single graphite crystals precipitated from a partially melted metamorphic rock. SIMS ¹³C/¹²C measurements were calibrated using an internal graphite standard previously analyzed by conventional isotope ratio mass spectrometry, which gave a reproducibility of 0.3‰ (1σ) at a spatial resolution of 2–3 μm. This resolution helped to identify an unusual carbon isotope distribution in a single graphite crystal from a metapelitic leucosome, showing remarkable core to rim variations with sharp δ¹³C steps up to 10‰. The results suggest that the graphite crystal grew from one edge to other forming layers perpendicular to the c-axis. The sharp isotopic steps indicate the presence of disequilibrium carbon isotope zoning in graphite and points to the possible existence of carbon isotope sector zoning. Intra-crystalline carbon isotope disequilibrium in graphite is believed to have resulted from the difference in diffusivity between ¹²C and ¹³C in the growth medium to the interface of graphite precipitation in different growth sectors.     

Evolution and decay of a warm-core ring within the western subarctic gyre of the North Pacific,as observed by profiling floats

This study investigated temporal variations in the vertical structure and water properties of a warm-core ring that migrated into the western subarctic gyre of the North Pacific, based on analyses of temperature and salinity data derived from two profiling floats, together with shipboard and satellite observation data. The floats were initially deployed into cold and fresh Oyashio water in September 2003, and were entrained into a warm-core ring in October 2003, remaining within the ring until detrainment in December 2004. Drastic cooling and freshening of the upper core water of the ring were observed during the above entrainment of the floats with cold and fresh water into the ring, whereas moderate variations in structure and water properties were observed during a quasi-isolated phase from November 2003 to November 2004 when the ring did not experience major interactions with ambient hydrographic features. The upper part of the core water (upper core), with relatively warm/saline water above 26.6 σ _θ , was under the influence of the atmosphere in winter via the formation of a deep mixed layer exceeding 300 dB, and had a prominent pycnostad below the seasonal pycnocline from spring to autumn. In contrast, the lower core, with relatively cold and fresh water below 26.6 σ _θ , was not ventilated throughout the observation period. Isopycnal surfaces showed a shoaling trend of about 50 dB/year during the quasi-isolated phase, suggesting viscous decay over a timescale of several years. Markedly cold and thick water was also frequently observed within the ring, indicating the intrusion of water from the Sea of Okhotsk.     

Analysis of summertime atmospheric transport of fine particulate matter in Northeast Asia

In Northeast Asia, the effect of long-range transport of air pollutants is generally pronounced in spring and winter, but can be important even in summer. This study analyzed summer-time atmospheric transport of elemental carbon (EC) and sulfate (SO₄ ^2?) with the Community Multiscale Air Quality (CMAQ) model driven by the Weather Research and Forecasting (WRF) model. The WRF/CMAQ modeling system was applied to regions ranging from Northeast Asia to the Greater Tokyo Area in Japan in summer 2007. In terms of EC, while the model simulated well the effect of long-range transport, the simulation results indicated that domestic emissions in Japan dominantly contributed (85%) to EC concentrations in the Greater Tokyo. In terms of SO₄ ^2?, the simulation results indicated that both domestic emissions (62%) and long-range transport from the other countries (38%) substantially contributed to SO₄ ^2? concentrations in the Greater Tokyo. Distinctive transport processes of SO₄ ^2? were associated with typical summer-time meteorological conditions in the study region. When a Pacific high-pressure system covered the main island of Japan, domestic emissions, including volcanic emission, dominantly contributed to SO₄ ^2? concentrations in the Greater Tokyo. When a high-pressure system prevailed over the East China Sea and low-pressure systems passed north of Japan, synoptic westerly winds associated with this pressure pattern transported a large amount of SO₄ ^2? from the continent to Japan. In addition, although heavy precipitation and strong wind decreased SO₄ ^2? concentrations near the center of a typhoon, peripheral typhoon winds occasionally played an important role in long-range transport of SO₄ ^2?.     

Sodium‐metasomatism in chondrules in CO3 chondrites: Relationship to parent body thermal metamorphism

Abstract— We have studied the mineralogy and petrology of mesostases of 783 type I chondrules in seven CO3 chondrites that range in petrologic subtype from 3.0 to 3.7. Chondrule mesostases in the CO chondrite of subtype 3.0 consist mainly of primary glass and plagioclase, while chondrule mesostases in the CO chondrites of higher subtypes (3.2–3.7) contain various amounts of nepheline in addition to glass and plagioclase. Nepheline has replaced glass and plagioclase, forming finegrained aggregates and thin parallel lamellar intergrowths with plagioclase. The nephelinization has proceeded preferentially from the outer margins of chondrules toward the inside. Although the degree of nephelinization differs widely among chondrules in each of the metamorphosed chondrites, our modal analyses and bulk chemical analyses of individual mesostases indicate that the amounts of nepheline in chondrules systematically increase with the increasing petrologic subtype of the host chondrites. Nepheline also has a tendency to increase in grain size with increasing petrologic subtype. We conclude that nepheline in chondrules in the CO3 chondrites has formed largely as a result of effects related to heating on the meteorite parent body. We suggest that nepheline initially formed as hydrous nepheline under the presence of aqueous fluids and subsequently was dehydrated after exhaustion of aqueous fluids. The degree of hydrothermal activity must have increased with increasing degree of heating, and thus, chondrules in more thermally metamorphosed chondrites produced larger amounts of nepheline. The results imply that CO3 chondrites have gone through low‐grade aqueous alteration and subsequent dehydration at the early stage of heating on the meteorite parent body.     

Oxygen and magnesium isotopic compositions of amoeboid olivine aggregates from the Semarkona LL3.0 chondrite

Abstract— Amoeboid olivine aggregates (AOAs) in the LL3.0 Semarkona chondrite have been studied by secondary ion mass spectrometry. The AOAs mainly consist of aggregates of olivine grains with interstitial Al‐Ti‐rich diopside and anorthite. Oxygen‐isotopic compositions of all phases are consistently enriched in ¹⁶O, with δ^17,18O = ～?50‰. The initial ²⁶Al/²⁷Al ratios are calculated to be 5.6 ± 0.9 (2σ) × 10^?5. These values are equivalent to those of AOAs and fine‐grained calcium‐aluminum‐rich inclusions (FGIs) from pristine carbonaceous chondrites. This suggests that AOAs in ordinary chondrites formed in the same ¹⁶O‐rich calcium‐aluminum‐rich inclusion (CAI)‐forming region of the solar nebula as AOAs and FGIs in carbonaceous chondrites, and subsequently moved to the accretion region of the ordinary chondrite parent body in the solar nebula.     

内蒙古达里湖全新世有机碳氮同位素记录与环境演变

内蒙古中东部的达里湖为一水文封闭型湖泊,位于现今东亚夏季风的北部边缘区,对区域环境变化十分敏感.本文对达里湖沉积中心提取的岩芯(DL04沉积岩芯)顶部8.5m沉积物进行了有机地球化学分析.15个全岩样品有机质的放射性碳测年结果表明:岩芯顶部8.5m涵盖了过去大约11500年.按约50年分辨率分析的225个总有机碳(TOC)、总氮(TN)含量、总有机碳/总氮(C/N)原子比值数据以及221个有机碳和有机氮稳定同位素(δ13C和δ13C)数据,详细揭示了全新世东亚夏季风边缘区的水文和生态变化历史.在距今11500 ～ 9800日历年(ca1.aB.P.)期间,所有地球化学指标均呈逐渐增大趋势,指示入湖河流逐渐增强,达里湖开始扩张,水生植物生产率逐渐升高;在9800 ～ 7700cal.aB.P.期间,TOC和TN含量以及C/N比值维持稳定高值,δ13C和δ15N值较小,指示湖泊维持高湖面状态,陆源输入和浮游植物生产率较高;在7700～ 5900cal.aB.P.期间,C/N比值和δ15N维持低值,TOC和TN含量呈现更高值,并且波动变化,δ13C值逐渐增大,表明湖面维持高水平,湖水显著变暖,浮游植物生产率显著升高,流域植被大幅度扩张;在5900 ～ 4850cal.aB.P.期间,TOC和TN含量,C/N比值以及δ13C值显著减小,δ15N值显著增大,暗示地表径流显著减弱,达里湖湖面显著下降,湖泊生产率快速下降;从4850cal.a B.P.开始,TOC和TN含量以及C/N比值呈逐渐减小趋势,δ13C和δ15N值呈逐渐增大趋势,表明湖面逐渐下降,湖水盐度、碱度升高,湖水可能变冷,湖泊生产率逐渐下降,流域植被收缩.全新世东亚夏季风边缘区水文和生态环境的变化可能直接或间接受北半球夏季太阳辐射量和区域季风降水强度的共同控制.     

Diurnal variation of urban structure in terms of time distance: A spatio-temporal analysis of an urban area

The purpose of this paper is to clarify the diurnal variations in structure of an urban area from the viewpoint of time distance. To accomplish this, for one entire day, and for the morning, noon, and evening periods, time maps are delineated by using MDS; also, the indices of accessibility and circuity are computed from the time distances. As a result, the difference in shape between the time and actual maps becomes clear especially in the morning and also in the evening. Both the accessibility and circuity measured from the time distance show a concentrically shaped pattern where the regional disparity is especially distinct within the morning and evening periods. The diurnal variations as described above are thought to occur against the backdrop of the topological traffic conditions within the study area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal and annual change in community structure of meso-sized copepods in Tokyo Bay, Japan

Seasonal change in the meso-sized copepod community structure in the central part of Tokyo Bay was investigated from January 2006 to December 2008. Three seasonal community groups were detected, and seasonal shifts of these communities are explained by life history characteristics of indicator species and seasonal changes in the hydrographical environment. In the winter-spring community, Acartia omorii and Centropages abdominalis dominate because of high growth rates at low temperature. A shift to the early summer community is caused by a diapause of Ce. abdominalis as resting eggs and an increase in the growth and egg-production rate of Pseudodiaptomus marinus at high temperature. A shift to the summer-fall community is caused by a diapause of A. omorii at hypoxic and high temperature conditions and an increase of Temora turbinata, Paracalanus parvus and other oceanic species by an enhancement of the estuary circulation. Then, the community returns to a winter-spring one by the recovery of A. omorii and Ce. abdominalis with low temperatures and oxygenation of bottom water and by the disappearance of oceanic warm-water species at low temperature. Seasonal community shifts occurred almost regularly, but the shift from a winter-spring community to an early summer one occurred 1 month early in 2007 when the water temperature was warmer than in other years.