Compositional variations of olivines and pyroxenes in chondritic interplanetary dust particles     

Michael E. Zolensky  Ruth A. Barrett 《Meteoritics & planetary science》1994,29(5):616-620

Abstract We report here analyses of olivines and pyroxenes, and petrofabrics of 27 chondritic interplanetary dust particles (IDPs), comparing those from anhydrous and hydrous types. Approximately 40% of the hydrous particles contain diopside, a probable indicator of parent body thermal metamorphism, while this mineral is rarely present in the anhydrous particles. Based on this evidence, we find that hydrous and anhydrous IDPs are, in general, not directly related, and we conclude that olivine and pyroxene major-element compositions can be used to help discriminate between IDPs that are (1) predominantly nebular condensates, and lately resided in anhydrous or icy (no liquids) primitive parent bodies, and (2) those originating from more geochemically active parent bodies (probably hydrous and anhydrous asteroids).  相似文献   

Geochemistry of xenolithic eclogites from West Africa, part 2: origins of the high MgO eclogites   总被引：1，自引：0，他引：1  

Matthias G Barth  Roberta L Rudnick  Ingo Horn  William F McDonough  Michael J SpicuzzaJohn W Valley  Stephen E Haggerty 《Geochimica et cosmochimica acta》2002,66(24):4325-4345

Oxygen isotope, mineral trace element, and measured and reconstructed whole-rock compositions are reported for the high MgO eclogite xenolith suite (16 to 20 wt% MgO in the whole rock) from the Koidu Kimberlite complex, Sierra Leone. In contrast to the previously published data for low MgO eclogites (6 to 13 wt% MgO) from this area, high MgO eclogites equilibrated at higher temperatures (1080 to 1130°C vs. 890 to 930°C) have only mantlelike δ¹⁸O and show variable degrees of light rare earth element (REE) enrichment. Analyses of multiple mineral generations suggest that the heterogeneous REE patterns of the high MgO eclogites reflect variable degrees of metasomatic overprinting. High MgO and Al₂O₃ contents of the eclogites suggest a cumulate origin, either as high-pressure (2 to 3 GPa) garnet-pyroxene cumulates or low-pressure (<1 GPa) plagioclase-pyroxene-olivine cumulates. Trace element modeling suggests a low-P origin for eclogites with flat heavy REE patterns and a high-P origin for eclogites with fractionated heavy REE. Flat heavy REE patterns, the presence of Sr anomalies, and low to moderate transition element contents in the low-P group are consistent with a low-pressure origin as metamorphosed olivine gabbros and troctolites. These metagabbroic high MgO eclogites either could represent the basal section of subducted oceanic crust or foundered mafic lower continental crust. In the former case, the metagabbroic high MgO eclogites may be genetically related to the Koidu low MgO suite. Crystal fractionation trends suggest that the metapyroxenitic high MgO eclogites formed at lower pressures than their current estimated equilibrium pressures (>4 GPa).  相似文献   

The influence of bottom topography on internal seiches in stratified media     

Matthias Münnich 《Dynamics of Atmospheres and Oceans》1996,23(1-4)

Standing internal waves, so-called seiches, are ubiquitous in reservoirs and lakes. Although the stratification in such basin is often continuous, the modeling of seiches has been confined mostly to two-layer models. Such models are unable to give reliable insights into the vertical structure of the seiches, which might be crucial for the understanding of vertical mixing in natural water basins. To obtain this kind of information a two-dimensional computer model has been developed, which takes both continuous stratification and bottom topography into account. The results of this model are presented. The computed seiche modes reveal that (1) several large-scale modes can exist with similar eigenfrequencies, (2) the modes have a tendency to develop narrow jets and (3) only the lowest modes are strongly influenced by the bottom topography.  相似文献   

Optimal temperature for growth and feed conversion of immature cod (Gadus morhua L.)   总被引：1，自引：0，他引：1  

Bjornsson  Bjorn; Steinarsson  Agnar; Oddgeirsson  Matthias 《ICES Journal of Marine Science》2001,58(1):29-38

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Metabolism of 2-acetylaminofluorene by rainbow trout     

Harish C. Sikka  A. Ruth Steward  Sayed A. Elmarakby  Subodh Kumar  U. Devanaboyin  Ramesh C. Gupta 《Marine environmental research》1995,39(1-4)

In order to examine factors that may contribute to the reported resistance of rainbow trout, Shasta strain, to the well-known hepatocarcinogenic effects of 2-acetylaminofluorene (AAF), the in-vitro and in-vivo metabolism of [¹⁴C]AAF in trout has been examined. Trout (compared to rat) liver microsomes metabolized AAF more efficiently, producing 3-fold larger amounts of ring-hydroxylated metabolites (7-hydroxy-AAF and 5-hydroxy-AAF), but 5-fold less N-hydroxy-AAF. Freshly isolated trout hepatocytes extensively metabolized AAF to form the same ring-hydroxylated metabolites and their respective glucuronide and sulfate conjugates. N-OH-AAF (plus its conjugates) and covalently-bound AAF derivatives amounted, respectively, to < 1% and 1.4–1.6% of total metabolites. Liver DNA of trout treated with AAF contained a single AAF-DNA adduct identified as N-(deoxyguanosin-8-yl)-2-aminofluorene (the major persistent AAF-DNA adduct found in rat liver). The level of this adduct (12 attomoles/μg DNA) was about 1000-fold lower than the level of AAF-DNA adduct previously reported in rat liver. The data show that trout liver, compared to rat liver, is considerably less efficient in metabolizing AAF to carcinogenic metabolites, and more efficient in forming nontoxic products, thus possibly explaining, in part, the resistance of trout to AAF-induced hepatocarcinogenesis.  相似文献   

Polychaete tubes create ephemeral community patterns: Lanice conchilega (Pallas, 1766) associations studied over six years     

Ruth Zühlke 《Journal of Sea Research》2001,46(3-4)

On intertidal sandflats spatial patterns of benthic communities are influenced by biogenic habitat structures such as mussel beds or seagrass meadows. These structures represent ecological islands hosting a different and often more diverse and abundant community than surrounding sandflats. However, few studies have been carried out on tube aggregations of the polychaete Lanice conchilega, although its tube tops are conspicuous habitat features on European intertidal coasts with densities reaching several thousand per m².The aim of this study was to determine differences between benthic communities associated with tube aggregations and tube-free areas, and to investigate the longevity of community patterns around L. conchilega tubes. From 1995 to 2000, the L. conchilega population of an intertidal sandflat off the Eastern Friesian coast was sampled annually. Multivariate analysis showed significant differences between the L. conchilega and reference communities. Species diversity and abundance were higher among tube aggregations. This pattern developed rapidly after L. conchilega colonisation but was also readily destroyed, mainly due to dynamic changes of the L. conchilega population.Five species of benthic macrofauna were exclusively found among L. conchilega tubes, and four species were more abundant in tube aggregations than in reference areas. Only one species, the polychaete Aphelochaeta marioni, was found in lower numbers in dense L. conchilega aggregations.Hence, it is concluded that L. conchilega is a habitat engineer, which alters the composition of the benthic community and contributes to its patchy distribution pattern. However, this pattern is dynamic and ephemeral. Effects of tube aggregations depend on the population dynamic of L. conchilega itself and the species composition in the surrounding sands.  相似文献   

In situ hydrocarbon concentrations from pressurized cores in surface sediments, Northern Gulf of Mexico     

Katja U. Heeschen  Hans Jürgen Hohnberg  Matthias Haeckel  Friedrich Abegg  Manuela Drews  Gerhard Bohrmann   《Marine Chemistry》2007,107(4):498-515

Two newly developed coring devices, the Multi-Autoclave-Corer and the Dynamic Autoclave Piston Corer were deployed in shallow gas hydrate-bearing sediments in the northern Gulf of Mexico during research cruise SO174 (Oct–Nov 2003). For the first time, they enable the retrieval of near-surface sediment cores under ambient pressure. This enables the determination of in situ methane concentrations and amounts of gas hydrate in sediment depths where bottom water temperature and pressure changes most strongly influence gas/hydrate relationships. At seep sites of GC185 (Bush Hill) and the newly discovered sites at GC415, we determined the volume of low-weight hydrocarbons (C₁ through C₅) from nine pressurized cores via controlled degassing. The resulting in situ methane concentrations vary by two orders of magnitudes between 0.031 and 0.985 mol kg^− 1 pore water below the zone of sulfate depletion. This includes dissolved, free, and hydrate-bound CH₄. Combined with results from conventional cores, this establishes a variability of methane concentrations in close proximity to seep sites of five orders of magnitude. In total four out of nine pressure cores had CH₄ concentrations above equilibrium with gas hydrates. Two of them contain gas hydrate volumes of 15% (GC185) and 18% (GC415) of pore space. The measurements prove that the highest methane concentrations are not necessarily related to the highest advection rates. Brine advection inhibits gas hydrate stability a few centimeters below the sediment surface at the depth of anaerobic oxidation of methane and thus inhibits the storage of enhanced methane volumes. Here, computerized tomography (CT) of the pressure cores detected small amounts of free gas. This finding has major implications for methane distribution, possible consumption, and escape into the bottom water in fluid flow systems related to halokinesis.  相似文献   

Changes in the composition of planktonic ostracod populations across a range of latitudes in the North-east Atlantic   总被引：2，自引：0，他引：2  

Martin V. Angel  Kasia Blachowiak-Samolyk  Ruth Castillo 《Progress in Oceanography》2007,73(1):60-78

A large database representing the bathymetric distribution of 117 species of halocyprid ostracods has been compiled from seven stations forming a transect from the equator to 60°N along 20°W, plus an additional station at 32°N, 65°W. This data base is analysed to examine the latitudinal and bathymetric changes in species composition and diversity of assemblages of this important, yet neglected, holoplanktonic group. At each station stratified sampling of the complete water column from the surface down mostly to 2000 m was carried out both day and night. Each sample resulted from the filtration of at least 2500 m³ of water and was analysed using a consistent protocol. The differences between the day and night profiles are attributable to diel vertical migrations, to local-scale heterogeneity, and possibly to a degree of net avoidance. There is a gradient of increasing species richness and diversity from high to low latitudes. By day, halocyprids are either infrequent or absent from the upper 50 m of the water column, but at night after diel vertical migration they become quite abundant in the epipelagic zone, particularly at low latitudes. Bathymetric profiles show ostracod abundances increase rapidly below the thermocline, reaching maxima at 200-400 m and then declining by at least an order of magnitude at 2000 m. Diversity (both species richness, H′ and evenness, J) also increases below the thermocline and thereafter is either maintained or declines only slightly to 2000 m. There are no relationships among diversity, abundance and productivity, but analysis of the whole database shows that the changes in community structure are consistent with Longhurst’s [Longhurst, A.R., 1998. Ecological Geography of the Sea. Academic Press, San Diego, pp. xiv, 398.] biogeochemical provinces.  相似文献   

Grid point surface air temperature calculations with a fast turnaround: Combining the results of IMAGE and a GCM     

Matthias Jonas  Katharina Fleischmann  Andrey V. Ganopolski  Jaroslav Krabec  Uta Sauer  Krzysztof Olendrzyński  Vladimir K. Petoukhov  Roderick W. Shaw 《Climatic change》1996,34(3-4):479-512

This paper describes a methodology that combines the outputs of (1) the Integrated Model to Assess the Greenhouse Effect (IMAGE Version 1.0) of the Netherlands National Institute of Public Health and Environmental Protection (RIVM) (given a greenhouse gas emission policy, this model can estimate the effects such as global mean surface air temperature change for a wide variety of policies) and (2) ECHAM-1/LSG, the Global Circulation Model (GCM) of the Max-Planck Institute for Meteorology in Hamburg, Germany. The combination enables one to calculate grid point surface air temperature changes for different scenarios with a turnaround time that is much quicker than that for a GCM. The methodology is based upon a geographical pattern of the ratio of grid point temperature change to global mean values during a certain period of the simulation, as calculated by ECHAM-1/LSG for the 1990 Scenarios A and D of the Intergovernmental Panel on Climate Change (IPCC). A procedure, based upon signal-to noise ratios in the outputs, enabled us to estimate where we have confidence in the methodology; this is at about 23% to 83% of the total of 2,048 grid points, depending upon the scenario and the decade in the simulation. It was found that the methodology enabled IMAGE to provide useful estimates of the GCM-predicted grid point temperature changes. These estimates were within 0.5K (0.25K) throughout the 100 years of a given simulation for at least 79% (74%) of the grid points where we are confident in applying the methodology. The temperature ratio pattern from Scenario A enabled IMAGE to provide useful estimates of temperature change within 0.5K (0.25K) in Scenario D for at least 88% (68%) of the grid points where we have confidence; indicating that the methodology is transferable to other scenarios. Tests with the Geophysical Fluid Dynamics Laboratory GCM indicated, however, that a temperature ratio pattern may have to be developed for each GCM. The methodology, using a temperature ratio pattern from the 1990 IPCC Scenario A and involving IMAGE, gave gridded surface air temperature patterns for the 1992 IPCC radiative-forcing Scenarios C and E and the RIVM emission Scenario B; none of these scenarios has been simulated by ECHAM-1/LSG. The simulations reflect the uncertainty range of a future warming.The work reported by the authors was carried out during their stay at the project Forestry and Climate Change of the International Institute for Applied Systems Analysis, Laxenburg, Austria.  相似文献   

Assessing the reliability of the modified three-component spatial autocorrelation technique   总被引：3，自引：0，他引：3  

Andreas Köhler  Matthias Ohrnberger  Frank Scherbaum  Marc Wathelet  Cecile Cornou 《Geophysical Journal International》2007,168(2):779-796

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