Meteorological observations 2005 and in a longer perspective at the Sermilik Station,Ammassalik Island,Southeast Greenland     

Sebastian H. Mernild  Bent Hasholt  Birger U. Hansen  Bjarne H. Jakobsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):59-68

Geografisk Tidsskrift, Danish Journal of Geography 107(2):59–68, 2007

Meteorological stations have been in operation since 1993 at Sermilik (65°40'N, 38°10'W), Ammassalik Island, southeast Greenland. This note presents meteorological observations for the year 2005 from the two meteorological stations: Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). The year 2005 was dominated by a temporal break down of Station Nunatak and defect instrument recordings at both stations. Average yearly measurements at both meteorological stations: Station Nunatak (1994–2004) and Station Coast (1998–2005) are presented to illustrate the climatic variability within the Mittivakkat Glacier catchment, and further compared with simultaneous standard synoptic meteorological DMI station climate observations (1994–2004) at the town Tasiilaq (Ammassalik) in order to establish transfer functions (linear regressions) and describe the spatial variability of climate variables.  相似文献   

Extraterrestrial chromite in Middle Ordovician marine limestone at Kinnekulle,southern Sweden—Traces of a major asteroid breakup event     

Birger Schmitz  Therese Hggstrm 《Meteoritics & planetary science》2006,41(3):455-466

Abstract— The distribution of sediment‐dispersed extraterrestrial chromite grains and other Cr‐rich spinels (>63 μm) has been studied in Middle Ordovician Orthoceratite Limestone from two quarries at Kinnekulle, southern Sweden. In the Thorsberg quarry, an ?3.2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment‐dispersed extraterrestrial chromite grains. Typically, 1–3 grains are found per kilogram of limestone. In the nearby Hällekis quarry, the same beds show similarly high concentrations of extraterrestrial chromite grains, but in samples representing the 9 m downward continuation of the section exposed at this site, only 5 such grains were found in a total of 379 kg of limestone. The extraterrestrial (equilibrated ordinary chondritic) chromite grains can be readily distinguished by a homogeneous and characteristic major element chemistry, including 2.0–3.5 wt% TiO₂ and stable V₂O₃ concentrations close to 0.7 wt%. Terrestrial Cr‐rich spinels have a wide compositional range and co‐exist with extraterrestrial chromite in some beds. These grains may be derived, for example, from mafic dykes exposed and weathered at the sea floor. Considering lithologic and stratigraphic aspects variations in sedimentation rate cannot explain the dramatic increase in extraterrestrial chromite seen in the upper part of the composite section studied. Instead, the difference may be primarily related to an increase in the ancient flux of extraterrestrial matter to Earth in connection with the disruption of the L chondrite parent body in the asteroid belt at about this time. The coexistence in some beds of high concentrations of chondritic chromite and terrestrial Cr‐rich spinels, however, indicates that redistribution of heavy minerals on the sea floor, related to changes in sea level and sea‐floor erosion and currents, must also be considered.  相似文献   

Conditioning reservoir models on rate data using ensemble smoothers     

Geir Evensen  Kjersti Solberg Eikrem 《Computational Geosciences》2018,22(5):1251-1270

There are several issues to consider when we use ensemble smoothers to condition reservoir models on rate data. The values in a time series of rate data contain redundant information that may lead to poorly conditioned inversions and thereby influence the stability of the numerical computation of the update. A time series of rate data typically has correlated measurement errors in time, and negligence of the correlations leads to a too strong impact from conditioning on the rate data and possible ensemble collapse. The total number of rate data included in the smoother update will typically exceed the ensemble size, and special care needs to be taken to ensure numerically stable results. We force the reservoir model with production rate data derived from the observed production, and the further conditioning on the same rate data implies that we use the data twice. This paper discusses strategies for conditioning reservoir models on rate data using ensemble smoothers. In particular, a significant redundancy in the rate data makes it possible to subsample the rate data. The alternative to subsampling is to model the unknown measurement error correlations and specify the full measurement error covariance matrix. We demonstrate the proposed strategies using different ensemble smoothers with the Norne full-field reservoir model.  相似文献   

Large spinel grains in a CM chondrite (Acfer 331): Implications for reconstructions of ancient meteorite fluxes     

Karolina Bjärnborg  Birger Schmitz 《Meteoritics & planetary science》2013,48(2):180-194

By dissolving 30–400 kg of marine limestone in HCl and HF acid, our group has previously recovered common relict chromite grains (approximately 63–250 μm) from ordinary chondritic micrometeorites that fell on ancient sea floors, up to 500 Myr old. Here, we evaluate if CM group carbonaceous chondritic material, which makes up an important fraction of the micrometeorite flux today, contains analogous grains that can be searched for in acid residues. We dissolved 8 g of CM2 meteorite Acfer 331 in HF, which yielded a characteristic assemblage of both transparent Mg‐Al‐ and opaque Cr‐spinels >28 μm. We find on average 4.6 and 130 Mg‐Al‐spinel grains per gram in the 63–250 and 28–63 μm size fractions, respectively. These grains are mostly pink or colorless, and often characterized by heterogeneous Cr‐content. Black, opaque Cr‐spinel grains are absent from the >63 μm fraction, but in the 28–63 μm fraction we find approximately 65 such grains per gram meteorite. The individual grains have a characteristic composition, with heterogeneous major element compositions (e.g., 44.4–61.7 wt% Cr₂O₃), but narrow ranges for maximum TiO₂ (0.6–1.6 wt%) and V₂O₃ (0.5–1.0 wt%) concentrations. The content of spinel grains in the 28–63 μm fraction of CM meteorites appears comparable at the order of magnitude level with the content of >63 μm sized chromite grains in fossil L‐chondrites from Ordovician limestone. Our approach of recovering meteoritic spinel from sediment may thus be extended to include CM meteorites, but the smaller size fraction of the acid residues should be searched.  相似文献   

In situ U-Pb dating and element mapping of three generations of monazite: Unravelling cryptic tectonothermal events in low-grade terranes     

Birger Rasmussen  Ian R. Fletcher 《Geochimica et cosmochimica acta》2007,71(3):670-690

In situ U-Pb dating of monazite and xenotime in sedimentary rocks from the mid-Archean Soanesville Group in the Pilbara Craton, yields ages for provenance, diagenesis and multiple low-grade metamorphic events. Detrital monazite and xenotime grains give dates >3250 Ma, whereas diagenetic xenotime provides a new minimum age of 3190 ± 10 Ma for deposition of the basal Soanesville Group, previously constrained between ∼3235 Ma and ∼2955 Ma. Metamorphic monazite provides evidence for three episodes of growth: at 2.88, 2.16 and 1.65 Ga. Element mapping of monazite for La, Sm, Y and Th reveals distinct cores and rims in some crystals that were used to guide the placement of analytical spots during in situ U-Pb dating by sensitive high-resolution ion microprobe (SHRIMP). Specifically, La and Sm distributions closely correlate with different generations of monazite. The presence of two generations in single monazite crystals highlights the need for characterizing mineral chemistry prior to geochronology. It also shows the importance of using in situ dating techniques rather than methods that rely on the analysis of entire, potentially multi-aged, crystals. The ages recorded by metamorphic monazite span more than one billion years and are interpreted to record cryptic tectonothermal events within the craton. The 2.88 Ga age coincides with a phase of regional deformation, metamorphism and gold mineralization along a major crustal lineament, whereas the most common monazite age population (at 2.16 Ga) corresponds with the migration of a foreland fold-and-thrust belt across the craton. The youngest age (1.65 Ga) coincides with an episode of tectonic reworking in the Capricorn Orogen along the southern Pilbara margin. The prolonged history of monazite growth may, in part, relate to channelized fluid flow during reactivation of long-lived N- to NE-trending crustal structures that transect the craton. Despite repeated episodes of metamorphism, the isotopic system in each generation of monazite remained unperturbed, yielding precise dates. The ability of monazite to record three separate events, and in some instances two events in a single crystal, distinguishes it from most other low-temperature mineral chronometers, which are readily reset during metamorphic overprinting. Low-temperature monazite geochronology can provide a detailed isotopic history of cryptic thermal events and reveal the temporal and spatial patterns of far-field fluid flow related to tectonic processes. The previously unrecognized history of crustal fluid flow in the Pilbara Craton has implications for chemical, mineralogical and isotopic studies seeking to understand conditions on the early Earth.  相似文献   

Intercomparison of Two Hydroxyl Radical Measurement Techniques at the Atmosphere Simulation Chamber SAPHIR     

Eric Schlosser  Birger Bohn  Theo Brauers  Hans-Peter Dorn  Hendrik Fuchs  Rolf Häseler  Andreas Hofzumahaus  Frank Holland  Franz Rohrer  Lutz Olaf Rupp  Manfred Siese  Ralf Tillmann  Andreas Wahner 《Journal of Atmospheric Chemistry》2007,56(2):187-205

At the atmosphere simulation chamber SAPHIR in Jülich both Laser-Induced Fluorescence Spectroscopy (LIF) and Long-Path Differential Optical Laser Absorption Spectroscopy (DOAS) are operational for the detection of OH radicals at tropospheric levels. The two different spectroscopic techniques were compared within the controlled environment of SAPHIR based on all simultaneous measurements acquired in 2003 (13 days). Hydroxyl radicals were scavenged by added CO during four of these days in order to experimentally check the calculated precisions at the detection limit. LIF measurements have a higher precision (σ= 0.88×10⁶ cm^–3) and better time resolution (Δt = 60 s), but the DOAS method (σ= 1.24×10⁶ cm^–3, Δt = 135 s) is regarded as primary standard for comparisons because of its good accuracy. A high correlation coefficient of r = 0.95 was found for the whole data set highlighting the advantage of using a simulation chamber. The data set consists of two groups. The first one includes 3 days, where the LIF measurements yield (1 – 2) ×10⁶ cm^–3 higher OH concentrations than observed by the DOAS instrument. The experimental conditions during these days are characterized by increased NO_x concentration and a small dynamic range in OH. Excellent agreement is found within the other group of 6 days. The regression to the combined data of this large group yields unity slope without a significant offset.  相似文献   

Rheological anisotropy of the Earth’s mantle and attenuation of seismic waves     

B. I. Birger 《Izvestiya Physics of the Solid Earth》2006,42(11):877-889

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A new approach to interpreting Rock-Eval S₂ and TOC data for kerogen quality assessment     

Birger Dahl  Jrgen Bojesen-Koefoed  Anders Holm  Holger Justwan  Egil Rasmussen  Erik Thomsen 《Organic Geochemistry》2004,35(11-12):1461

A simple method for application in source potential mapping is used to assess the original oil and gas potentials in source rock horizons based upon Rock-Eval potential (S₂) and total organic carbon (TOC) values. The method assumes that kerogens consist of mixtures of end-members with assigned hydrogen index values. Based on suggested algorithms, the average amounts of oil-prone, gas-prone and inert organic material over source rock intervals are determined in TOC units. The method uses regression lines from plots of remaining hydrocarbon potentials (S₂) versus total organic carbon (TOC), and “quick-look” transparent overlays are used to read the appropriate kerogen mixture.Mineral matrix effects during pyrolysis, when strong, can cause erroneous results. This effect which occurs for oil-prone kerogens and adsorptive minerals can cause problems particularly for lean samples (S₂ = 0–3 mg HC/g rock) whilst the errors for richer samples are less.The method is applied on three sections of Upper Jurassic organic-rich rocks from the Danish North Sea sector, which are at different maturity stages. One of these sections is dominated by gas-prone material, one is dominated by oil-prone material and the third section contains a mixture of oil- and gas-prone material.The method has been compared with other methods that split kerogens in oil and gas generating potential and has given reasonable results.Experience using the method and a presented example suggest that sedimentological, system tract information may be derived from S₂ to TOC cross-plots. A constructed modelling example suggests that the end-member concept used in this approach may be used in forward type source rock prediction models when combined with sedimentological models. The resulting S₂–TOC plots can be used in order to check the forward modelling results against observed values.  相似文献   

The effect of copper-treated net pens on farmed salmon (Salmo salar) and other marine organisms and sediments     

Cathrine Brufsen Solberg  Leif Sthre  Kaare Julshamn 《Marine pollution bulletin》2002,45(1-12)

Samples of Atlantic salmon (Salmo salar), saithe (Pollacius virens), blue mussel (Mytilus edulis), brown seaweed (Ascophyllum nodosum) and sediment were collected from six different fish farms. Five of the farms used net pens treated with copper-containing coatings, whereas one farm did not use copper-containing coating (this was used as a reference location). Samples of muscle, liver and gills of Atlantic salmon and saithe, blue mussel and brown seaweed were freeze dried, homogenised, wet digested and analysed for copper by flame atomic absorption spectrometry. The results showed no significant differences in copper concentrations among the samples from the different locations. The copper contents of some of the samples appeared to be in the upper part of the normal concentration range. From a nutritional point of view, the use of copper-coatings on net pens did not affect the quality of the seafood products either within, or around the net pen.  相似文献   

Protecting the North-East Atlantic: enhancing synergies by institutional interplay     

Jon Birger Skjærseth 《Marine Policy》2006

This article examines the interplay between three different international institutions on marine pollution in the North Sea and the wider North-East Atlantic: the International North Sea Conferences (INSC), the OSPAR-Convention and preceding conventions as well as the European Union (EU). It argues that interplay between these institutions have proved synergetic in two ways. First, the INSC-process has speeded up decision-making within OSPAR and the EU by means of leadership, change in membership and institutional arrangements. Second, OSPAR and the EU have subsequently facilitated domestic implementation of the North Sea Conference Declarations by means of higher authoritativeness and enforcement competence. These three institutions have fulfilled different functions all of which are needed to make international environmental cooperation effective.  相似文献