Exsolution in augite from the Skaergaard Intrusion     

Yoshiharu Nakajima  Stefan S. Hafner 《Contributions to Mineralogy and Petrology》1980,72(2):101-110

The exsolution phenomena of augite from Ferrogabbro 4430 of the Skaergaard Intrusion were examined in detail by single crystal X-ray diffraction and heating experiments to study the stepwise exsolution process. In the augite crystals, five different phases were detected: pigeonite (001), pigeonite (100), orthopyroxene (a), orthopyroxene (p) and a small amount of clinoamphibole. The two different pigeonites nearly share the corresponding (001) and (100) planes with the host. Orthopyroxene (a) and orthopyroxene (p) have (100) in common with the host and with exsolved pigeonite (001), respectively. Clinoamphibole was observed in the form of rather weak reflections in many crystals. It has (010) in common with the host.A large number of augite crystals exhibited a pigeonite (001) phase with curved, rotated reflections and diffuse streaks along the a* direction in (h0l) precession photographs. It appears that these streaks are related to orthopyroxene (p). Orthopyroxene (p) seems to be crystallized from pigeonite (001) by nucleation at (100) stacking fault planes (inverted pigeonite). Pigeonite (100) may be formed at growth ledges between augite host and exsolved orthopyroxene (a) at a later stage of exsolution to stabilize the boundaries.From the X-ray diffraction profiles and the results of the heating experiments, a possible exsolution sequence is suggested. Clinoamphibole appears to be a product of alteration at the latest stage of the exsolution process. It seems to be related to particular conditions of partial water pressure.  相似文献   

Simulated Climate Change Effects on Year-Round Water Temperatures in Temperate Zone Lakes     

H. G. Stefan  X. Fang  M. Hondzo 《Climatic change》1998,40(3-4):547-576

A deterministic, one-dimensional model is presented to simulate daily water temperature profiles and associated ice and snow covers for dimictic and polymictic lakes of the temperate zone. The lake parameters required as model input are surface area (A_s), maximum depth (H_MAX), and Secchi depth (z_s), the latter, used as a measure of light attenuation and trophic state. The model is driven by daily weather data and operates year-round over multiple years. The model has been tested with extensive data (over 5,000 temperature points). Standard error between simulated and measured water temperatures is 1.4°C in the open water season and 0.5°C in the ice cover season. The model is applied to simulate the sensitivity of Minnesota lake water temperature characteristics to climate change. The projected climate changes due to a doubling of atmospheric CO₂ are obtained from the output of the Canadian Climate Center General Circulation Model (CCC GCM) and the Goddard Institute of Space Studies General Circulation Model (GISS GCM). Simulated lake temperature characteristics have been plotted in a coordinate system with a lake geometry ratio (A _s ^0.25 /H_MAX) on one axis and Secchi depth on the other. The lake geometry ratio expresses a lake's susceptibility to stratification. By interpolation, the sensitivity of lake temperature characteristics to changes of water depth and Secchi depth under the projected climate scenarios can therefore be obtained. Selected lake temperature characteristics simulated with past climate conditions (1961–1979) and with a projected 2 × CO₂ climate scenario as input are presented herein in graphical form. The simulation results show that under the 2 × CO₂ climate scenario ice formation is delayed and ice cover period is shortened. These changes cause water temperature modifications throughout the year.  相似文献   

Post-breakup basaltic magmatism along the East Greenland Tertiary rifted margin     

Stefan Bernstein  Peter B Kelemen  Christian Tegner  Mark D Kurz  Jurek Blusztajn  C.Kent Brooks 《Earth and Planetary Science Letters》1998,160(3-4):845-862

Mafic and ultramafic intrusions in East Greenland adjacent to the offshore Greenland–Iceland ridge were emplaced 5–9 My after continental breakup at 55 Ma [1]. Rare earth element (REE) concentrations determined by secondary ion mass spectrometry are reported for cumulus clinopyroxene from these intrusions, and the data are used to estimate REE abundance in equilibrium melts using available partitioning data. Estimated equilibrium melts from intrusions have strongly fractionated REE patterns with Nd/Dy(N) in the range 2 to 5.6 and Yb/Dy(N) 0.55 to 0.92, similar to values for coeval basalts. These melts have markedly higher Nd/Dy(N) than earlier breakup related flood basalts. The moderately low Yb/Dy(N) for the post-breakup volcanism is indicative of residual garnet in the source, while their high Nd/Dy(N) ratios can best be explained by aggregating low degree melts from a light-REE-enriched garnet- and spinel-bearing mantle source. We also report He, Sr, and Nd isotopic data for the intrusions. The highest ³He/⁴He ratios (>10 R/R_a) are found in the samples whose REE data reflect the largest proportion of melts from a garnet-bearing source, and having Sr and Nd isotopic compositions identical with the radiogenic Sr and unradiogenic Nd isotope end of the Iceland compositional field. There is no indication of a MORB-type mantle in the source of the intrusions. We postulate that post-breakup volcanism along the East Greenland coastline reflects the increasing proximity of the mantle plume to the East Greenland continental margin. The low degree of melting at high mean pressure inferred for the parental melts for the intrusions may reflect re-thickening of the lithosphere, which in turn was caused by the vigorous volcanism during breakup, with accompanying depletion of upper mantle and underplating of the crust at the continental margin.  相似文献   

Biofuel and water cycle dynamics: what are the related challenges for hydrological processes research?     

Stefan Uhlenbrook 《水文研究》2007,21(26):3647-3650

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Multimodel analysis on the response of the AMOC under an increase of radiative forcing and its symmetrical reversal     

Sgubin  Giovanni  Swingedouw  Didier  Drijfhout  Sybren  Hagemann  Stefan  Robertson  Eddy 《Climate Dynamics》2015,45(5-6):1429-1450

Climate Dynamics - The response of the Atlantic meridional overturning circulation (AMOC) to an increase of radiative forcing (ramp-up) and a subsequent reversal of radiative forcing (ramp-down) is...  相似文献   

Stable Cu and Zn isotope ratios as tracers of sources and transport of Cu and Zn in contaminated soil   总被引：7，自引：0，他引：7  

Moritz Bigalke  Stefan Weyer  Jozef Kobza 《Geochimica et cosmochimica acta》2010,74(23):6801-6813

Copper and Zn metals are produced in large quantities for different applications. During Cu production, large amounts of Cu and Zn can be released to the environment. Therefore, the surroundings of Cu smelters are frequently metal-polluted. We determined Cu and Zn concentrations and Cu and Zn stable isotope ratios (δ⁶⁵Cu, δ⁶⁶Zn) in three soils at distances of 1.1, 3.8, and 5.3 km from a Slovak Cu smelter and in smelter wastes (slag, sludge, ash) to trace sources and transport of Cu and Zn in soils. Stable isotope ratios were measured by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) in total digests. Soils were heavily contaminated with concentrations up to 8087 μg g⁻¹ Cu and 2084 μg g⁻¹ Zn in the organic horizons. The δ⁶⁵Cu values varied little (−0.12‰ to 0.36‰) in soils and most wastes and therefore no source identification was possible. In soils, Cu became isotopically lighter with increasing depth down to 0.4 m, likely because of equilibrium reactions between dissolved and adsorbed Cu species during transport of smelter-derived Cu through the soil. The δ⁶⁶Zn_IRMM values were isotopically lighter in ash (−0.41‰) and organic horizons (−0.85‰ to −0.47‰) than in bedrock (−0.28‰) and slag (0.18‰) likely mainly because of kinetic fractionation during evaporation and thus allowed for separation of smelter-Zn from native Zn in soil. In particular in the organic horizons large variations in δ⁶⁶Zn values occur, probably caused by biogeochemical fractionation in the soil-plant system. In the mineral horizons, Zn isotopes showed only minor shifts to heavier δ⁶⁶Zn values with depth mainly because of the mixing of smelter-derived Zn and native Zn in the soils. In contrast to Cu, Zn isotope fractionation between dissolved and adsorbed species was probably only a minor driver in producing the observed variations in δ⁶⁶Zn values. Our results demonstrate that metal stable isotope ratios may serve as tracer of sources, vertical dislocation, and biogeochemical behavior in contaminated soil.  相似文献   

Links Between Bottom-Water Anoxia,the Polychaete <Emphasis Type="Italic">Nereis diversicolor</Emphasis>, and the Growth of Green-Algal Mats     

Anna Engelsen  Kristina Sundbäck  Stefan Hulth 《Estuaries and Coasts》2010,33(6):1365-1376

Sediment–water incubations were used to study effects of episodic anoxia on filamentous Ulva sp. Treatments included undisturbed sediment with (AnoxSed) and without (NatSed) exposure to 5 days of anoxia, and cores with only the top 0.5 cm of sediment (SurfSed; no macrofauna, restricted pore-water nutrient pool). All three treatments contained Ulva propagules. An Ulva mat developed in the SurfSed, and after the anoxic period in the AnoxSed cores. No growth was observed in the NatSed treatment. In the AnoxSed, Ulva was progressively removed upon reoxygenation through grazing by Nereis. The results suggest that episodic anoxia stimulates the growth of macroalgal mats not only by increasing the availability of nutrients from the sediment, but also by reducing macrofaunal grazing pressure. Infauna (grazing and bioturbation), benthic microalgae (nutrient competition and retention), and pore-water nutrients appear key components in a biogeochemical network with complex feedbacks controlling the growth of green-algal mats in shallow-water systems.  相似文献   

A comparison of three Eurasian chironomid–climate calibration datasets on a W–E continentality gradient and the implications for quantitative temperature reconstructions     

Stefan Engels  Angela E. Self  Tomi P. Luoto  Stephen J. Brooks  Karin F. Helmens 《Journal of Paleolimnology》2014,51(4):529-547

Multiple regional chironomid–climate calibration datasets are available to reconstruct quantitatively July air temperatures from fossil chironomid assemblages. We examined the relationship between July air temperature and the 40 most common chironomid taxa in three independent Eurasian calibration (training) sets. The estimated temperature optimum of each chironomid taxon is systematically lower (by ~1–2 °C) in a Norwegian calibration set compared to Finnish and Russian calibration sets. This result might partly be explained by the fact that the Norwegian calibration set extends further at the cold end of the temperature gradient. A difference in continentality between the Russian sites and the European sites might also contribute to this pattern. The number of taxa that show a statistically significant unimodal response to temperature is higher in the Norwegian calibration set (34 out of 40 taxa) compared to the modern Finnish (11 of 37 taxa; 3 common taxa absent) and the Russian calibration set (20 of 40 taxa), probably due to the longer temperature gradient incorporated in the Norwegian calibration set. We applied all three calibration sets to fossil chironomid assemblages from the high-latitude study site of Sokli (northeast Finland), a site with a unique series of lacustrine deposits covering (amongst others) the Holocene, part of early MIS 3 (at ~53 ka) and MIS 5d–c (at ~110–95 ka) and with independent proxy-records for comparison. In the early Holocene and during MIS 5c, the chironomid-based temperature inferences from all three inference models had similar values. Temperature reconstructions based on the Norwegian calibration set are 2–4 °C lower for the late Holocene, early MIS 3 and MIS 5d than the inferred temperatures based on the other calibration sets. Although the lakes included in the Finnish calibration set are located closest to the site of Sokli, evaluation tests and a comparison with independent proxy data suggests that the Norwegian calibration set provides the most suitable analogues for reconstruction purposes for most of the fossil assemblages. Our results imply that when choosing a calibration set for quantitative climate reconstructions on glacial timescales, regional proximity of the fossil site may not be a sufficient basis, and the length of the temperature gradient of the calibration dataset and factors such as the continentality gradient covered by the calibration set must also be considered.  相似文献   

Airborne near-real-time monitoring of assembly and parking areas in case of large-scale public events and natural disasters     

Hannes Römer  Jens Kersten  Ralph Kiefl  Stefan Plattner  Alexander Mager  Stefan Voigt 《International journal of geographical information science》2014,28(4):682-699

A critical requirement for an effective and coordinated response by public entities tasked with management, security, and relief during large-scale public events or natural disasters is the availability of current situational information. However, today there is a lack of comprehensive operational systems allowing a near-real-time (NRT) collection, visualization, and provision of situational information for larger areas. In this study a methodological framework is proposed, which allows an NRT extraction and visualization of situational information based on aerial image acquisition. The framework combines digital image analysis using a generic supervised information extraction approach based on statistical modeling with a downstream web-based visualization component realized through an automatic update of web services. Even though being applicable for different scenarios, the workflow will be demonstrated for the specific use-case of a NRT monitoring of open spaces including assembly and parking areas. Compared to other approaches, image analysis results indicate a high robustness and a low demand for computational power sources (7 seconds per image). Due to a high degree of automation, the proposed workflow contributes to a NRT ‘end-to-end’ monitoring system, which was developed within the VABENE (German acronym for ‘traffic management under large-scale public events and disaster conditions’) project covering all parts from the acquisition of raw aerial imagery to the dissemination of information products to end-users.  相似文献   

The importance of reduced meat and dairy consumption for meeting stringent climate change targets     

Fredrik Hedenus  Stefan Wirsenius  Daniel J. A. Johansson 《Climatic change》2014,124(1-2):79-91

For agriculture, there are three major options for mitigating greenhouse gas (GHG) emissions: 1) productivity improvements, particularly in the livestock sector; 2) dedicated technical mitigation measures; and 3) human dietary changes. The aim of the paper is to estimate long-term agricultural GHG emissions, under different mitigation scenarios, and to relate them to the emissions space compatible with the 2 °C temperature target. Our estimates include emissions up to 2070 from agricultural soils, manure management, enteric fermentation and paddy rice fields, and are based on IPCC Tier 2 methodology. We find that baseline agricultural CO₂-equivalent emissions (using Global Warming Potentials with a 100 year time horizon) will be approximately 13 Gton CO₂eq/year in 2070, compared to 7.1 Gton CO₂eq/year 2000. However, if faster growth in livestock productivity is combined with dedicated technical mitigation measures, emissions may be kept to 7.7 Gton CO₂eq/year in 2070. If structural changes in human diets are included, emissions may be reduced further, to 3–5 Gton CO₂eq/year in 2070. The total annual emissions for meeting the 2 °C target with a chance above 50 % is in the order of 13 Gton CO₂eq/year or less in 2070, for all sectors combined. We conclude that reduced ruminant meat and dairy consumption will be indispensable for reaching the 2 °C target with a high probability, unless unprecedented advances in technology take place.  相似文献