Trace element geochemistry of K-rich impact spherules from howardites   总被引：1，自引：0，他引：1  

Jean-Alix Barrat  Akira Yamaguchi  Richard C. Greenwood  Claire Bollinger  Marcel Bohn  Ian A. Franchi 《Geochimica et cosmochimica acta》2009,73(19):5944-5958

The howardite–eucrite–diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired.The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body.  相似文献   

Negligible effect of the benthic fauna on measuring the nutrient upward fluxes from coastal sediments     

Kuninao Tada  Jidapa Koomklang  Kazuhiko Ichimi  Hitomi Yamaguchi 《Journal of Oceanography》2017,73(3):397-402

Although the influence of benthic fauna on estimating the nutrient upward fluxes from the coastal sediments are a concern, there are few comprehensive studies. We conducted monthly observations in a coastal embayment to examine the effect of benthic fauna on measuring the nutrient flux. Nutrient fluxes were measured by the core incubation method and the densities of organisms in benthic communities were also measured. Numerical composition of benthic communities, according to taxonomic group, was dominated by Polychaeta composed of a few Capitellida and Spionidae species. A negligible effect of the benthic communities on measuring nutrient fluxes was demonstrated.  相似文献   

Mineral classification from quantitative X-ray maps using neural network: Application to volcanic rocks     

Takeshi  Tsuji  Haruka  Yamaguchi  Teruaki  Ishii  Toshifumi  Matsuoka 《Island Arc》2010,19(1):105-119

We developed a mineral classification technique of electron probe microanalyzer (EPMA) maps in order to reveal the mineral textures and compositions of volcanic rocks. In the case of lithologies such as basalt that include several kinds of minerals, X-ray intensities of several elements derived from EPMA must be considered simultaneously to determine the mineral map. In this research, we used a Kohonen self-organizing map (SOM) to classify minerals in the thin-sections from several X-ray intensity maps. The SOM is a type of artificial neural network that is trained using unsupervised training to produce a two-dimensional representation of multi-dimensional input data. The classified mineral maps of in situ oceanic basalts of the Juan de Fuca Plate allowed us to quantify mineralogical and textural differences among the marginal and central parts of the pillow basalts and the massive flow basalt. One advantage of mineral classification using a SOM is that relatively many minerals can be estimated from limited input elements. By applying our method to altered basalt which contains multiple minerals, we successfully classify eight minerals in thin-section.  相似文献   

Correction to: Microphysics and Optical Attenuation in Fog: Observations from Two Coastal Sites     

Wang  Qing  Yamaguchi  Ryan T.  Kalogiros  John A.  Daniels  Zachary  Alappattu  Denny P.  Jonsson  Haflidi  Alvarenga  Oswaldo  Olson  Alex  Wauer  Benjamin J.  Ortiz-Suslow  David G.  Fernando  Harindra Joseph 《Boundary-Layer Meteorology》2021,181(2-3):293-294

Boundary-Layer Meteorology -  相似文献   

Lethality of increasing CO2 levels on deep-sea copepods in the western North Pacific     

Yuji Watanabe  Atsushi Yamaguchi  Hiroshi Ishida  Takashi Harimoto  Shinya Suzuki  Yoshio Sekido  Tsutomu Ikeda  Yoshihisa Shirayama  Masayuki Mac Takahashi  Takashi Ohsumi  Joji Ishizaka 《Journal of Oceanography》2006,62(2):185-196

The first CO₂ exposure experiments on several species of pelagic copepods inhabiting surface and deep layers in the western North Pacific were conducted. Living organisms were collected from two layers between the surface and 1,500 m between latitudes of 11 and 44°N, and they were exposed aboard ship to various pCO₂ up to about 98,000 μatm. Mortality of copepods from both shallow and deep layers in subarctic to subtropical regions increased with increasing pCO₂ and exposure time. Deep-living copepods showed higher tolerance to pCO₂ than shallow-living copepods. Furthermore, deep-living copepods from subarctic and transitional regions had higher tolerances than the subtropical copepods. The higher tolerances of the deep-living copepods from subarctic and transitional regions may be due to the adaptation to the natural pCO₂ conditions in the subarctic ocean.  相似文献   

Dynamics of microphytobenthic biomass in a coastal area of western Seto Inland Sea, Japan   总被引：2，自引：0，他引：2  

Hitomi Yamaguchi  Shigeru Montani  Hiroaki Tsutsumi  Ken-ichiro Hamada  Naoko Ueda  Kuninao Tada 《Estuarine, Coastal and Shelf Science》2007,75(4):423-432

This study focused on the causes of the variation in microphytobenthic biomass and the effects of this variation on macrobenthic animals in the western Seto Inland Sea, Japan, where the importance of microphytobenthos as the primary food source for benthic animals has been recently reported. We investigated the microphytobenthic biomass together with light attenuation of seawater, phytoplanktonic biomass, macrobenthic density and biomass at eight stations (water depth = 5–15 m) during four cruises in 1999–2000. The increased light attenuation coefficient of the water column associated with increased concentration of the phytoplanktonic Chl-a caused a decrease in light flux that reached the seafloor. The biomass of the microphytobenthos within the upper 1 cm of the sediment, 1.9–46.5 mg Chl-a m⁻², was inversely correlated with the phytoplanktonic biomass in the overlying water column, 10.9–65.0 mg Chl-a m⁻². Thus, interception of light by phytoplankton is considered to be a main cause of the variation in the microphytobenthic biomass. The microphytobenthos biomass showed a significant positive correlation with the macrobenthic density (78–9369 ind. m⁻²) and biomass (0.4–78.8 gWW m⁻²). It appears that the increase in oxygen production by the microphytobenthos allowed macrobenthic animals to become more abundant, as a consequence of oxygenation of the organically enriched muddy sediments (14.5 ± 2.69 mg TOC g⁻¹). This study suggests that the variation in the microphytobenthic biomass is influenced by the phytoplanktonic biomass due to shading effect, and the balance between these two functional groups might affect the variability in the macrobenthic density and biomass.  相似文献   

Latitudinal Differences in the Planktonic Biomass and Community Structure Down to the Greater Depths in the Western North Pacific     

Atsushi Yamaguchi  Yuji Watanabe  Hiroshi Ishida  Takashi Harimoto  Kazushi Furusawa  Shinya Suzuki  Joji Ishizaka  Tsutomu Ikeda  Masayuki Mac Takahashi 《Journal of Oceanography》2004,60(4):773-787

As part of the research program WEST-COSMIC Phase I (1997–2001), vertical profiles down to the greater depths (0–2000 m or 5800 m) of the plankton community structure composed of heterotrophic bacteria, phytoplankton, protozooplankton and metazooplankton were studied at one station in each subarctic (44°N) and in transitional region (39°N), and two stations in subtropical region (30°N and 25°N); all in 137–155°E in the western North Pacific Ocean. The biomass of all four taxonomic groups decreased rapidly with increasing depths at all stations, although the magnitude of depth-related decrease differed among the groups. As plankton community structure, metazooplankton biomass and bacterial biomass occupied >50% of the total in 0–2000 and 2000–4000 or 5000 m strata, respectively, at subarctic and transitional stations, while bacterial biomass contributed to >50% of the total consistently from 0 through 4800 or 5800 m at subtropical stations. Metazooplankton biomass integrated over the greater depths exhibited a clear latitudinal pattern (high north and low south), but this was not the case for those of the other taxonomic groups. As a component of metazooplankton, an appreciable contribution of diapausing copepods to the metazooplankton was noted at subarctic and transitional stations, but they were few or nil at subtropical stations. As protozooplankton assemblages, heterotrophic microflagellates (HMF) and dinoflagellates were two major components at subarctic and transitional stations, but were only HMF predominated at subtropical stations. From biomass ratios between heterotrophic bacteria, HMF and dinoflagellates, “sinking POC-DOC-heterotrophic bacteria-HMF-heterotrophic dinoflagellates” link was proposed as a microbial food chain operative in the deep layer of the western North Pacific. All results are discussed in the light of latitudinal differences in the structure and functioning of plankton community contributing to the ‘biological pump’ in the western North Pacific Ocean. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Microbial biomass in the Eutrophic Bay of Shimoda as compared by estimations of several biomass parameters     

Yukuya Yamaguchi  Humitake Seki 《Journal of Oceanography》1977,33(1):38-44

Microbial biomass in seawater of Shimoda Bay was assessed using some biomass parameters, such as ATP, DNA, RNA, protein, chlorophylla, and bacterial number and every estimate is in the same order. The estimates based on the amounts of ATP, DNA and RNA showed good correlation.  相似文献   

Vertical changes in abundance,biomass and community structure of copepods down to 3000 m in the southern Bering Sea     

Tomoe Homma  Atsushi Yamaguchi 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(8):965-977

Vertical changes in abundance, biomass and community structure of copepods down to 3000 m depth were studied at a single station of the Aleutian Basin of the Bering Sea (53°28′N, 177°00′W, depth 3779 m) on the 14th June 2006. Both abundance and biomass of copepods were greatest near the surface layer and decreased with increase in depth. Abundance and biomass of copepods integrated over 0–3000 m were 1,390,000 inds. m^?2 and 5056 mg C m^?2, respectively. Copepod carcasses occurred throughout the layer, and the carcass:living specimen ratio was the greatest in the oxygen minimum layer (750–100 m, the ratio was 2.3). A total of 72 calanoid copepod species belonging to 34 genera and 15 families occurred in the 0–3000 m water column (Cyclopoida, Harpacticoida and Poecilostomatoida were not identified to species level). Cluster analysis separated calanoid copepod communities into 5 groups (A–E). Each group was separated by depth, and the depth range of each group was at 0–75 m (A), 75–500 m (B), 500–750 m (C), 750–1500 m (D) and 1500–3000 m (E). Copepods were divided into four types based on the feeding pattern: suspension feeders, suspension feeders in diapause, detritivores and carnivores. In terms of abundance the most dominant group was suspension feeders (mainly Cyclopoida) in the epipelagic zone, and detritivores (mainly Poecilostomatoida) were dominant in the meso- and bathypelagic zones. In terms of biomass, suspension feeders in diapause (calanoid copepods Neocalanus spp. and Eucalanus bungii) were the major component (ca. 10–45%), especially in the 250–3000 m depth. These results are compared with the previous studies in the same region and that down to greater depths in the worldwide oceans.  相似文献   

Characterization and evaluation of MODIS-derived Drought Severity Index (DSI) for monitoring the 2009/2010 drought over southwestern China     

X. Q. Zhang  Y. Yamaguchi 《Natural Hazards》2014,74(3):2129-2145

This article investigates whether the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived global terrestrial Drought Severity Index (DSI) had the capability of detecting regional drought over subtropical southwestern China. Monthly, remotely sensed DSI data with 0.05° spatial resolution were used to characterize the extent, duration, and severity of drought from 2000 to 2010. We reported that southwestern China suffered from incipient to extreme droughts from November 2009 to March 2010 (referred to as the “drought period”). The area affected by drought occupied approximately 74 % of the total area of the study region, in which a moderate drought, severe drought, and an extreme drought accounted for 20, 12.7, and 13.2 % of the total area, respectively; particularly in March 2010, droughts of severe and extreme intensity covered the largest areas of drought, which were 16.1 and 18.6 %, respectively. Spatially, eastern Yunnan, western Guizhou, and Guangxi suffered from persistent droughts whose intensities ranged from mild to extreme during the drought period. Pearson’s correlation analyses were performed between DSI and the in situ meteorological station-based Standardized Precipitation Index (SPI) for validating the monitoring results of the DSI. The results showed that the DSI corresponded favorably with the time scales of the SPI; meanwhile, the DSI showed its highest correlation (mean: r = 0.58) with a three-month SPI. Furthermore, similar spatial patterns and temporal variations were found between the DSI and the three-month SPI, as well as the agro-meteorological drought observation data, when monitoring drought. Our analysis suggests that the DSI can be used for near-real-time drought monitoring with fine resolution across subtropical southwestern China, or other similar regions, based solely on MODIS-derived evapotranspiration/potential evapotranspiration and Normalized Difference Vegetation Index data.  相似文献