Climatic and oceanographic changes in the Northeast Atlantic reflected by magnetic properties of sediments deposited on the Portuguese Margin during the last 340 ka   总被引：1，自引：0，他引：1  

Eva Moreno  Nicolas Thouveny  Doriane DelangheI.Nick McCave  Nick J Shackleton 《Earth and Planetary Science Letters》2002,202(2):465-480

Rock magnetic parameters measured along two giant piston cores MD95-2040 (40°34′N, 9°51′W) and MD95-2042 (37°47′N, 10°09′W) collected off the Portuguese Margin, related to other proxy-climatic data, have been used to reconstruct magnetic mineralogical changes of, in relation to environmental and climatic conditions over the North Atlantic, Western Europe and Northwest Africa during the last three climatic cycles (since isotope stage 10). Thin discrete layers containing coarse grains of titano-magnetite are associated with events of iceberg discharge during Heinrich events 1-6 [Heinrich, Quat. Res. 29 (1988) 142] that have equivalent events in isotope stages 5-8. Concentrations of fine-grained (Ti-) magnetite and hematite/goethite, varying in phase opposition, are directly linked with alternations of cold and warm climatic periods. Spectral analyses of the rock magnetic signals reveal Milankovitch periods at 100 and 41 ka, confirming the relationship with long-term climatic changes at high latitudes. The nature (Ti-magnetite) and size range of the finest ferrimagnetic fraction as well as its variation, suggest a control by deep currents carrying a colloidal/clayey fraction from remote sources (Iceland, Faeroes, mid-Atlantic Ridge). Variation of hematite/goethite contents is linked with transport by rivers and winds from the neighbouring continent. A tight correlation with the D-O cycles in Greenland ice records confirms that North Atlantic oceanic regimes and continental wind regimes were strongly influenced by millennial scale climatic changes throughout the last 350 ka.  相似文献   

Aerosol optical thickness retrieval over the Atlantic Ocean using GOES imager data     

M Moula  J Verdebout  H Eva 《Physics and Chemistry of the Earth》2002,27(35):1525-1531

An algorithm based on simulated satellite signal calculated by the 6S radiative transfer model has been developed in order to retrieve the aerosol optical thickness of dust over the Atlantic ocean. The algorithm is applied to the visible channel of Geostationary Operational Environmental Satellite (GOES 8) images. The inversion uses a look-up table giving the satellite signal intensity as a function of surface albedo, viewing geometry, solar illumination and the optical properties of the aerosols. The study consists of assessing the feasibility of monitoring and mapping the transport of suspended particles across the Atlantic from the Sahara to the Caribbean. The study area is between 10 and 25 N and 30 and 65 W. The optical thickness of aerosols has been calculated over a period of 11 days between 10th and 20th of June 1997 for the 14:15 UT GOES image acquisition. The calculated aerosol optical thickness ranges from 0.0 to 0.81 with an important event of dust presence occurring between 13th and 16th of June. The retrieved aerosol optical thickness is in good agreement with the values obtained between 14h UT and 15h UT from ground based sun photometer measurements on the island of Guadeloupe, and a coefficient correlation (R²) of 0.88 has been found between the data sets.  相似文献   

The effect of nitrogen limitation on cellular DMSP and DMS release in marine phytoplankton: climate feedback implications     

William G. Sunda  Rance Hardison  Ronald P. Kiene  Eva Bucciarelli  Hyakubun Harada 《Aquatic Sciences - Research Across Boundaries》2007,69(3):341-351

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The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance   总被引：2，自引：1，他引：2  

Steven P. Oncley  Thomas Foken  Roland Vogt  Wim Kohsiek  H. A. R. DeBruin  Christian Bernhofer  Andreas Christen  Eva van Gorsel  David Grantz  Christian Feigenwinter  Irene Lehner  Claudia Liebethal  Heping Liu  Matthias Mauder  Andrea Pitacco  Luis Ribeiro  Tamas Weidinger 《Boundary-Layer Meteorology》2007,123(1):1-28

An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required to balance the budget. The National Center for Atmospheric Research is supported by the National Science Foundation  相似文献   

An incentive mechanism for reducing emissions from conversion of intact and non-intact forests   总被引：1，自引：0，他引：1  

Danilo Mollicone  Frédéric Achard  Sandro Federici  Hugh D. Eva  Giacomo Grassi  Alan Belward  Frank Raes  Günther Seufert  Hans-Jürgen Stibig  Giorgio Matteucci  Ernst-Detlef Schulze 《Climatic change》2007,83(4):477-493

This paper presents a new accounting mechanism in the context of the UNFCCC issue on reducing emissions from deforestation in developing countries, including technical options for determining baselines of forest conversions. This proposal builds on the recent scientific achievements related to the estimation of tropical deforestation rates and to the assessment of ‘intact’ forest areas. The distinction between ‘intact’ and ‘non intact’ forests used here arises from experience with satellite-based deforestation measurements and allows accounting for carbon losses from forest degradation. The proposed accounting system would use forest area conversion rates as input data. An optimal technical solution to set baselines would be to use historical average figures during the time period from 1990 to 2005. The system introduces two different schemes to account for preserved carbon: one for countries with high forest conversion rates where the desired outcome would be a reduction in their rates, and another for countries with low rates. A ‘global’ baseline rate would be used to discriminate between these two country categories (high and low rates). For the hypothetical accounting period 2013–2017 and considering 72% of the total tropical forest domain for which data are available, the scenario of a 10% reduction of the high rates and of the preservation of low rates would result in approximately 1.6 billion tCO₂ of avoided emissions. The resulting benefits of this reduction would be shared between those high-rate countries which reduced deforestation and those low-rate countries which did not increase their deforestation over an agreed threshold (e.g., half of “global” baseline rate).  相似文献   

Die Kristallstruktur von Denningit, (Mn,Ca,Zn) Te2O5. Ein Beispiel für die Koordination um vierwertiges Tellur     

Eva Maria Walitzi 《Mineralogy and Petrology》1965,10(1-4):241-255

Zusammenfassung Denningit, (Mn, Ca, Zn) Te₂O₅ ist tetragonal mit der Raumgruppe P 4₂/n bc und den Gitterkonstanten a=8,82, c=13,04; Z=8. Die Struktur wurde mit Patterson-, Fourier- und (F_o-F_c)-Projektionen parallel [100], [110] und [001] bestimmt und verfeinert. Abschließend konnte eine least-squares-Verfeinerung durchgeführt werden. Je zwei trigonale TeO₃-Pyramiden (Te–O=1,84–2,04 ) sind zu isolierten Te₂O₅-Gruppen verbunden. Mn, Ca und Zn in 8- und in [4+2]-Koordination bilden längs [001] Ketten, die durch Te₂O₅-Gruppen miteinander verknüpft sind.

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Summary Denningite, (Mn, Ca, Zn) Te₂O₅ is tetragonal with spacegroup P 4₂/n bc and unit-cell dimensions a=8,82, c=13,04; Z=8. The structure has been determined and refined by Patterson, Fourier and (F_o-F_c) projections along [100], [110] and [001]. Finally a least-squares refinement has been carried out. Pairs of trigonal TeO₃ pyramids (Te–O=1,84–2,04) are connected to isolated Te₂O₅ groups. Mn, Ca and Zn in 8 coordination and in [4+2] coordination form chains along [001] connected by Te₂O₅ groups.

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Mit 3 Textabbildungen

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet  相似文献   

Die Raumgruppe von Libethenit und Olivenit     

Eva Maria Walitzi 《Mineralogy and Petrology》1962,8(2):275-280

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Climate Impact Response Functions: An Introduction     

Ferenc L. Toth  Wolfgang Cramer  Eva Hizsnyik 《Climatic change》2000,46(3):225-246

The concept of climate impact response function is introduced and placed into the context of integrated assessment models to analyze policy options under climate change constraints. An example of developing such response functions is presented that entails a global model of potential natural vegetation driven by a climate change pattern derived from a general circulation model. A large array of strenuous issues are introduced that will be addressed by the set of papers included in this Special Issue.  相似文献   

Rural restructuring in Hungary in the period of socio-economic transition   总被引：10，自引：0，他引：10  

Eva Kiss 《GeoJournal》2000,51(3):221-233

Rural settlements in Hungary account for 93% of all settlements and 37% of the country's population. Since 1989 they are scenes of spectacular changes. Based on some case studies of less developed villages this paper considers the most important characteristics of the post-socialist rural transformation by examining the local economy and living conditions. The main issues are how local actors (for example, economic corporations, households and individuals) have been affected by the interaction of supralocal and local factors and how they responded to them. Such responses can be considered to be manifestations of survival strategy.  相似文献   

Air–Sea \mathrm{CO}_{2} Gas Transfer Velocity in a Shallow Estuary     

Eva Thorborg Mørk  Lise Lotte Sørensen  Bjarne Jensen  Mikael K. Sejr 《Boundary-Layer Meteorology》2014,151(1):119-138

The air–sea transfer velocity of $\mathrm{CO}_{2}\, (k_{\mathrm{CO}_{2}})$ was investigated in a shallow estuary in March to July 2012, using eddy-covariance measurements of $\mathrm{CO}_{2}$ fluxes and measured air–sea $\mathrm{CO}_{2}$ partial-pressure differences. A data evaluation method that eliminates data by nine rejection criteria in order to heighten parametrization certainty is proposed. We tested the data evaluation method by comparing two datasets: one derived using quality criteria related solely to the eddy-covariance method, and the other derived using quality criteria based on both eddy-covariance and cospectral peak methods. The best parametrization of transfer velocity normalized to a Schmidt number of 600 $(k_{600})$ was determined to be: $k_{600} = 0.3\,{U_{10}}^{2.5}$ where $U_{10}$ is the wind speed in m $\mathrm{s}^{-1}$ at 10 m; $k_{600}$ is based on $\mathrm{CO}_{2}$ fluxes calculated by the eddy-covariance method and including the cospectral peak method criteria. At low wind speeds, the transfer velocity in the shallow water estuary was lower than in other coastal waters, possibly a symptom of low tidal amplitude leading to low intensity water turbulence. High transfer velocities were recorded above wind speeds of 5 m $\mathrm{s}^{-1}$ , believed to be caused by early-breaking waves and the large fetch (6.5 km) of the estuary. These findings indicate that turbulence in both air and water influences the transfer velocity.  相似文献