The L3–6 chondritic regolith breccia Northwest Africa (NWA) 869: (I) Petrology,chemistry, oxygen isotopes,and Ar‐Ar age determinations     

Knut METZLER  Addi BISCHOFF  Richard C. GREENWOOD  Herbert PALME  Marko GELLISSEN  Jens HOPP  Ian A. FRANCHI  Mario TRIELOFF 《Meteoritics & planetary science》2011,46(5):652-680

Abstract– Northwest Africa (NWA) 869 consists of thousands of individual stones with an estimated total weight of about 7 metric tons. It is an L3–6 chondrite and probably represents the largest sample of the rare regolith breccias from the L–chondrite asteroid. It contains unequilibrated and equilibrated chondrite clasts, some of which display shock‐darkening. Impact melt rocks (IMRs), both clast‐free and clast‐poor, are strongly depleted in Fe,Ni metal, and sulfides. An unequilibrated microbreccia, two different light inclusions and two different SiO₂‐bearing objects were found. Although the matrix of this breccia appears partly clastic, it is not a simple mixture of fine‐grained debris formed from the above lithologies, but mainly represents an additional specific lithology of low petrologic type. We speculate that this material stems from a region of the parent body that was only weakly consolidated. One IMR clast and one SiO₂‐bearing object show Δ¹⁷O values similar to bulk NWA 869, suggesting that both are related to the host rock. In contrast, one light inclusion and one IMR clast appear to be unrelated to NWA 869, suggesting that the IMR clast is contaminated with impactor material. ⁴⁰Ar‐³⁹Ar analyses of a type 4 chondrite clast yield a plateau age of 4402 ± 7 Ma, which is interpreted to be the result of impact heating. Other impact events are recorded by an IMR clast at 1790 ± 36 Ma and a shock‐darkened clast at 2216 ± 40 Ma, demonstrating that NWA 869 escaped major reset in the course of the event at approximately 470 Ma that affected many L–chondrites.  相似文献   

Thermal history of Northwest Africa 5073––A coarse‐grained Stannern‐trend eucrite containing cm‐sized pyroxenes and large zircon grains     

Julia ROSZJAR  Knut METZLER  Addi BISCHOFF  Jean‐Alix BARRAT  Thorsten GEISLER  Richard C. GREENWOOD  Ian A. FRANCHI  Stephan KLEMME 《Meteoritics & planetary science》2011,46(11):1754-1773

Abstract– We report on the bulk chemical composition, petrology, oxygen isotopic composition, trace element composition of silicates, and degree of self‐irradiation damage on zircon grains of the eucrite Northwest Africa (NWA) 5073 to constrain its formation and postcrystallization thermal history, and to discuss their implications for the geologic history of its parent body. This unequilibrated and unbrecciated meteorite is a new member of the rare Stannern‐trend eucrites. It is mainly composed of elongated, zoned pyroxene phenocrysts up to 1.2 cm, plagioclase laths up to 0.3 cm in length, and is rich in mesostasis. The latter contains zircon grains up to 30 μm in diameter, metal, sulfide, tridymite, and Ca‐phosphates. Textural observations and silicate compositions, coupled with the occurrence of extraordinary Fe‐rich olivine veins that are restricted to large pyroxene laths, indicate that NWA 5073 underwent a complex thermal history. This is also supported by the annealed state of zircon grains inferred from μ‐Raman spectroscopic measurements along with U and Th data obtained by electron probe microanalyses.  相似文献   

Atmospheric input of nitrogen into the North Sea: ANICE project overview     

Gerrit de Leeuw  Leo Cohen  Lise Marie Frohn  Gary Geernaert  Ole Hertel  Bjarne Jensen  Tim Jickells  Laura Klein  Gerard J. Kunz  Soren Lund  Marcel Moerman  Frank Müller  Britta Pedersen  Knut von Salzen  K. Heinke Schlünzen  Michael Schulz  Carsten A. Skjth  Lise-Lotte Sorensen  Lucinda Spokes  Susanne Tamm  Elisabetta Vignati 《Continental Shelf Research》2001,21(18-19)

The aim of the atmospheric nitrogen inputs into the coastal ecosystem (ANICE) project is to improve transport–chemistry models that estimate nitrogen deposition to the sea. To achieve this, experimental and modelling work is being conducted which aims to improve understanding of the processes involved in the chemical transformation, transport and deposition of atmospheric nitrogen compounds. Of particular emphasis within ANICE is the influence of coastal zone processes. Both short episodes with high deposition and chronic nitrogen inputs are considered in the project. The improved transport–chemistry models will be used to assess the atmospheric inputs of nitrogen compounds into the European regional seas (the North Sea is studied as a prototype) and evaluate the impact of various emission reduction strategies on the atmospheric nitrogen loads. Assessment of the impact of atmospheric nitrogen on coastal ecosystems will be based on comparisons of phytoplankton nitrogen requirements, other external nitrogen inputs to the ANICE area of interest and the direct nitrogen fluxes provided by ANICE. Selected results from both the experimental and modelling components are presented here. The experimental results show the large spatial and temporal variability in the concentrations of gaseous nitrogen compounds, and their influences on fluxes. Model calculations show the strong variation of both concentrations and gradients of nitric acid at fetches of up to 25 km. Aerosol concentrations also show high temporal variability and experimental evidence for the reaction between nitric acid and sea salt aerosol is provided by size-segregated aerosol composition measured at both sides of the North Sea. In several occasions throughout the experimental period, air mass back trajectory analysis showed connected flow between the two sampling sites (the Weybourne Atmospheric Observatory on the North Norfolk coast of the UK and Meetpost Noordwijk, a research tower at 9 km off the Dutch coast). Results from the METRAS/SEMA mesoscale chemistry transport model system for one of these cases are presented. Measurements of aerosol and rain chemical composition, using equipment mounted on a commercial ferry, show variations in composition across the North Sea. These measurements have been compared to results obtained with the transport–chemistry model ACDEP which calculates the atmospheric inputs into the whole North Sea area. Finally, the results will be made available for the assessment of the impact of atmospheric nitrogen on coastal ecosystems.  相似文献   

The struggle for fish resources     

Knut Bjørn Lindkvist 《GeoJournal》1996,39(2):195-202

This article discusses problems of economic readjustment facing the peripheral fishery-dependent communes in Norway. The situation in these communes is analyzed using a theory of territorial production systems, focusing in particular on the role played by principal actors in the fishery system. The principal actors' need to defend the prevalent structures of the territorial production system for cultural reasons, is discussed. This defense inhibit important adaptive processes in peripheral industries. In addition the principal actors must defend the socioeconomic systems controlled by the fishing communities in the central parts of Norway if deemed necessary. The principal actors in the periphery thereby stand forward as defenders of the actual centre-periphery structure in the Norwegian fishery system.  相似文献   

Leaning on user-groups: The role of civil society in fisheries governance     

Knut H. Mikalsen  Hans-Kristian HernesSvein Jentoft 《Marine Policy》2007

Fisheries have long been managed through public–private partnerships based on collaboration between government and user-groups. The alleged benefits of involving the latter—as representatives of civil society—are a management system that is more flexible and legitimate than one based exclusively on top–down command and control. A question that is rarely addressed is whether civil society is up to the task. Are voluntary associations fit—‘technically’ and ‘democratically’—to take on management responsibilities? Assessing the pros and cons of involving civil society in fisheries governance requires a closer look at the role of user-groups in public policy-making. This paper attempts to do that by examining certain aspects of the Norwegian system of fisheries management, focusing—in particular—on the role of its most prominent civil society player: the Norwegian Fishers’ Association. The association has long been a privileged partner, virtually monopolizing the attention and goodwill of government. How has this been justified, and does it still serve its original purpose? As the fishery has changed, so—we contend—has the association: from something akin to a public interest group into what is essentially a ‘trade union’ pursuing the economic interests of its most powerful members. How and why did this change—in goals and priorities—come about, and is it tenable that this particular partnership continues? What lessons, if any, can be drawn from the Norwegian case about the pros and cons of user involvement, interactive governance and the role of civil society in fisheries management?  相似文献   

Water balance investigations in Svalbard   总被引：1，自引：0，他引：1  

Ånund Killingtveit  Lars-Evan Pettersson  Knut Sand 《Polar research》2003,22(2):161-174

This paper reviews and summarizes all known previous water balance studies in Svalbard. An updated water balance computation was then done for the three water catchments with the best data: Bayelva, De Geerdalen and Isdammen/Endalen for 10 hydrological years 1990-2001. The computations were based on the best available data and correction methods. Special emphasis was put on correction of precipitation data, both for catch errors and gradients in precipitation. Areal precipitation in the three catchments is more than two times the measured precipitation at the closest meteorological station: 548 mm/year in De Geerdalen, 486 mm/year in Endalen/Isdammen and 890 mm/year in Bayelva. Compared to this, average measured precipitation is only 199 mm/year at Svalbard Airport, close to Endalen/Isdammen and De Geerdalen, and 426 mm/year in Ny-Ålesund, close to Bayelva. Evaporation is not well understood in Svalbard; the best estimates indicate an average annual evaporation of ca. 80 mm/year from glacier-free areas, and no net evaporation from glaciers. Glacial mass balance has in general been negative in Svalbard during the last 40 years, leading to a significant contribution to the water balance, on the order of 450 mm/year on average. Annual runoff ranges from 545 mm in Endalen/Isdammen, 539 mm/year in De Geerdalen up to 1050 mm/year in Bayelva. Runoff computed from water balance compares well with observed runoff, and average error in water balance is less than ±30 mm/year in all three catchments.  相似文献   

Sorption and anaerobic biodegradation of soluble aromatic compounds during groundwater transport. 1. Laboratory column experiments     

Zuoping Zheng  Per Aagaard  Gijs D. Breedveld 《Environmental Geology》2002,41(8):922-932

. This paper deals with sorption and anaerobic biodegradation of the soluble aromatic fraction of jet fuel and how it is influenced by pore-water velocity during transport in a groundwater aquifer. The study was carried out as controlled laboratory column experiments. A binary mixture of toluene and 1,2,4-trimethylbenzene with a concentration ratio of 2:1 was used through the entire investigations. The column experiments were conducted with contaminated sediments and groundwater, taken from wells at a field research site. The columns were operated anaerobically under continuous-flow conditions at 10 °C in a temperature-controlled refrigerator. Two percent sodium azide was added to the injection solution of two of the columns to prevent biodegradation of the studied organic mixture. Chloride was used as a conservative tracer to characterize the hydrodynamic parameters such as dispersivity and porosity of the columns. The results showed that both compounds in the mixture were attenuated because of sorption and biodegradation processes in the columns. 1,2,4-trimethylbenzene was attenuated more significantly than toluene. Biodegradation of toluene was coupled mainly with the microbial reduction of ferric iron, whereas 1,2,4-trimethylbenzene, in contrast, was mostly sorbed. Their sorption and biodegradation were studied with different pore-water velocities, and a mass balance approach was applied to calculate biodegradation rates. The biodegradation rates of toluene were –0.16, –0.21, and –0.26 (unit: mM day^–1) for pore-water velocities of 96, 82.4, and 54.9 (unit: cm day^–1), respectively. This indicates that a decrease in the pore-water velocity significantly enhanced the biodegradation of toluene, consistent with other reports in the literature. For 1,2,4-trimethylbenzene the biodegradation rates were –0.05, –0.13 (unit: mM day^–1) for pore-water velocities of 96 and 82.4 (unit: cm day^–1), respectively. The biodegradation rate of 1,2,4-trimethylbenzene did not increase at the lowest pore water velocity as expected. This might be a result of substrate competition.  相似文献   

Impregnation of organic lake sediments for palaeomagnetic measurements     

Reidar Løvlie  Knut Krzywinski  Johannes Kjøde 《Physics of the Earth and Planetary Interiors》1979,20(1):p22-p24

A procedure for impregnating high water-content sediments for palaeomagnetic measurements is described and applied to an organic lake sediment core. Comparison of results obtained by a standard sub-sampling procedure, and by the impregnation method, demonstrates a significant improvement in the scatter of the palaeomagnetic directions using the latter method.  相似文献   

Rb-Sr isotope systematics in metamorphic rocks,Kongsberg sector,south Norway     

Stein B. Jacobsen  Knut S. Heier 《Lithos》1978,11(4):257-276

Rb-Sr isotope data are presented for gneisses, migmatite neosome material and granitic and gabbroic intrusive rocks from the southern part of the Kongsberg sector, south Norway. The maximum age of the crust in this area appears to be ～1.6 AE. Two metamorphic episodes at ～1.5–1.6 AE and at ～1.1–1.2 AE are recognized. Initial ⁸⁷Sr/⁸⁶Sr ratios for the granitic rocks give evidence for reworking of sialic crust and indicate that approximately 1.6 AE old crust repeatedly acted as a source for granitic magmas for a timespan of ～0.5 AE.  相似文献   

Multivariate statistics for aquatic ecology     

Knut L. Seip 《Aquatic Sciences - Research Across Boundaries》1995,57(3):181-183

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