Subdecadal‐scale vegetation responses to a previously unknown late‐Allerød climate fluctuation and Younger Dryas cooling at Lake Meerfelder Maar (Germany)          下载免费PDF全文

Stefan Engels  Achim Brauer  Nico Buddelmeijer  Celia Martín‐Puertas  Oliver Rach  Dirk Sachse  Bas van Geel 《第四纪科学杂志》2016,31(7):741-752

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Late-type stars found in the DFBS     

K. S. Gigoyan  P. K. Sinamyan  D. Engels  A. M. Mickaelian 《Astrophysics》2010,53(1):123-132

A list of comparatively faint late M and Carbon type stars detected on the Digitized First Byurakan Survey (DFBS) spectral plates in the zone with +45° ≤ δ ≤ +49° covering 684 deg² is presented. Accurate DSS2 positions, USNO-B1.0 B and R magnitudes, 2MASS near-infrared J, H, and K_s photometry, IRAS PSC/FSC fluxes (when available), approximate spectral types, and luminosity class estimates are given for 72 objects. Nine of them are newly confirmed carbon stars and 63 are M-type stars. For seven Mira variables with known pulsation periods we determined distances of 2 ÷ 8 kpc using a period-luminosity relation. Distances of 17 ÷ 115 pc for five M dwarfs, classified on the base of detected proper motions, were estimated using a color-luminosity relation. The object FBS 0845+466 is classified as a candidate carbon dwarf with distance r ≈ 72 pc.  相似文献   

Chironomid-based water depth reconstructions: an independent evaluation of site-specific and local inference models   总被引：1，自引：1，他引：0  

Stefan Engels  Les C. Cwynar  Andrew B. H. Rees  Bryan N. Shuman 《Journal of Paleolimnology》2012,48(4):693-709

Water depth is an important environmental variable that explains a significant portion of the variation in the chironomid fauna of shallow lakes. We developed site-specific and local chironomid water-depth inference models using 26 and 104 surface-sediment samples, respectively, from seven kettlehole lakes in the Plymouth Aquifer, southeast Massachusetts, USA. Our site-specific model spans a depth gradient of 5.6?m, has an $ {\text{r}}_{\text{jack}}^{2} $ of 0.90, root mean square error of prediction (RMSEP) of 0.5?m and maximum bias of 0.7?m. Our local model has a depth gradient of 11.7?m, an $ {\text{r}}_{\text{jack}}^{2} $ of 0.71, RMSEP of 1.6?m and maximum bias of 2.9?m. Principal coordinates of neighbourhood matrices (PCNM) analysis showed that there is no influence of spatial autocorrelation on the site-specific model, but PCNM variables explained a significant amount of variance (4.8%) in the local model. This variance, however, is unique from the variance explained by water depth. We applied the inference models to a Holocene chironomid record from Crooked Pond, a site for which multiple, independent palaeohydrological reconstructions are available. The chironomid-based reconstructions are remarkably similar and show stable water depths of ~5?m, interrupted by a 2-m decrease between 4,200 and 3,200?cal a BP. Sedimentological evidence of water level fluctuations at Crooked Pond, obtained using the so-called Digerfeldt approach, also shows a drop in water depths around that time. The period of reconstructed lower water levels coincides with the abrupt decline in moisture-dependent hemlock in this region, providing further evidence for this major palaeohydrological event. The site-specific model has the best performance statistics, but the high percent abundance of fossil taxa from the long core that are absent or rare in the training set makes the site-specific reconstruction unreliable for the period before 4,400?cal a BP. The fossil taxa are well represented in the local model, making it the preferred inference model. The strong similarity between the chironomid-based reconstructions and the independent palaeohydrological records highlights the potential for using chironomid-based inference models to determine past lake depths at sites where temperature was not an influencing factor.  相似文献   

Wave propagation in rotating plasmas and influence of the Coriolis force     

E. Engels  F. Verheest 《Astrophysics and Space Science》1975,37(2):427-440

When assessing the influence of the Coriolis force on wave propagation in plasmas or other dielectric media, all the equations and relevant physical quantitities should be expressed in a rotating reference frame. Only then does the Coriolis force appear. However, most treatments for plasmas seem to fail in this respect because the Maxwell equations are used in their customary form, which in general is not valid in a rotating frame. A consistent approach requires the inclusion of Schiff charges and currents in the Maxwell equations. These Schiff sources are fictitious in the same way as the Coriolis force. The resulting wave equation has coefficients depending on the position and this precludes a plane wave solution, even in the slow rotation approximation where the centrifugal force may be neglected in comparison with the Coriolis force. Perturbation analysis then gives a dispersion law as if the system were not rotating. The wave electric field, however, now has a position dependent amplitude, which is not only stretched but also changed in direction compared to the previously known unperturbed or not rotating solution.  相似文献   

The gravitational field of topographic-isostatic masses and the hypothesis of mass condensation   总被引：2，自引：0，他引：2  

E. W. Grafarend  J. Engels 《Surveys in Geophysics》1993,14(4-5):495-524

The topographic masses (TM) load the interfaces within the earth; namely TMs are compensated by an isostatic adjustment which might depend on time. Here we focus on the loading gravitational potential to which we refer as the topographic potential. We aim at a rigorous integral representation for the topographic potential of gravity which results in corollary one and two.In addition, a rigorous computation of the gravitational potential of a massive non-spherical shell is achieved which is limited by shape functions which represent the earth's topography (heights) and the negative topography (depths) which substitutes the internal surface of isostatic compensation. Finally by the third corollary the single layer potential is given of those masses which are condensed onto a reference sphere, the basis for the standard loading potential. The hypothesis of mass condensation is confronted with the exact representation, namely in the external distant zone, the near zone and the internal distant zone.  相似文献   

The oblique Mercator projection of the ellipsoid of revolution IE a 2 ,b     

J. Engels  E. Grafarend 《Journal of Geodesy》1995,70(1-2):38-50

While the standardMercator projection / transverse Mercator projecton maps the equator / the transverse metaequator equivalent to the meridian of referenceequidistantly, theoblique Mercator projection aims at aconformal mapping of the ellipsoid of revolution constraint to anequidistant mapping of an oblique metaequator. Obliqueness is determined by the extension of the area to be mapped, e.g. determined by the inclination of satellite orbits: Satellite cameras map the area just under the orbit geometry. Here we derive themapping equations of theoblique Mercator projection being characterized to beconformal andequidistant on the oblique metaequator extending results ofM. Hotine (1946, 1947).  相似文献   

A multi-proxy record of abrupt cooling events during the Windermere Interstadial at Crudale Meadow,Orkney, UK     

Christopher P. Francis  Stefan Engels  Ian P. Matthews  Adrian P. Palmer  Rhys G. O. Timms  Anne-Lise Jourdan  Ian Candy 《第四纪科学杂志》2021,36(3):325-338

Three clearly defined abrupt cooling events (ACEs) can be observed within Greenland Interstadial (GI)-1 in the Greenland ice-core records. However, the spatial variation in amplitude and timing of these ACEs is poorly understood due to the paucity of well-dated records with quantified temperature reconstructions. This study presents high-resolution chironomid-inferred July air temperature (T_Jul) and oxygen isotope (δ¹⁸O) records from Crudale Meadow (Orkney Isles, UK). Three centennial-scale ACEs punctuate the Windermere Interstadial at Crudale Meadow. The largest ACE shows an amplitude of 5.4 °C and a 1% isotopic decline and is centred on ~14.0 ka bp , consistent with the timing of the GI-1d event in the Greenland stratigraphy. The two other observed ACEs are of smaller magnitude and are centred on ~13.6 ka bp and ~13.2 ka bp , with these smaller magnitude events tentatively correlated with the GI-1cii and GI-1b events, respectively, but lack sufficient chronological constraint to fully assess their timing. When comparing the Crudale Meadow record with other locations in the British Isles a strong relationship can be observed between the magnitude of T_Jul cooling and latitude, with a reduced signal in more southerly locations, indicating that oceanic forcing may be a key driver of the ACEs.  相似文献   

Trans‐dimensional Bayesian inversion of controlled‐source electromagnetic data in the German North Sea          下载免费PDF全文

Romina A. S. Gehrmann  Jan Dettmer  Katrin Schwalenberg  Martin Engels  Stan E. Dosso  Asli Özmaral 《Geophysical Prospecting》2015,63(6):1314-1333

This paper presents the first controlled‐source electromagnetic survey carried out in the German North Sea with a recently developed seafloor‐towed electrical dipole–dipole system, i.e., HYDRA II. Controlled‐source electromagnetic data are measured, processed, and inverted in the time domain to estimate an electrical resistivity model of the sub‐seafloor. The controlled‐source electromagnetic survey targeted a shallow, phase‐reversed, seismic reflector, which potentially indicates free gas. To compare the resistivity model to reflection seismic data and draw a combined interpretation, we apply a trans‐dimensional Bayesian inversion that estimates model parameters and uncertainties, and samples probabilistically over the number of layers of the resistivity model. The controlled‐source electromagnetic data errors show time‐varying correlations, and we therefore apply a non‐Toeplitz data covariance matrix in the inversion that is estimated from residual analysis. The geological interpretation drawn from controlled‐source electromagnetic inversion results and borehole and reflection seismic data yield resistivities of ～1 Ωm at the seafloor, which are typical for fine‐grained marine deposits, whereas resistivities below ～20 mbsf increase to 2–4 Ωm and can be related to a transition from fine‐grained (Holocene age) to unsorted, coarse‐grained, and compacted glacial sediments (Pleistocene age). Interface depths from controlled‐source electromagnetic inversion generally match the seismic reflector related to the contrast between the different depositional environments. Resistivities decrease again at greater depths to ～1 Ωm with a minimum resistivity at ～300 mbsf where a seismic reflector (that marks a major flooding surface of late Miocene age) correlates with an increased gamma‐ray count, indicating an increased amount of fine‐grained sediments. We suggest that the grain size may have a major impact on the electrical resistivity of the sediment with lower resistivities for fine‐grained sediments. Concerning the phase‐reversed seismic reflector that was targeted by the survey, controlled‐source electromagnetic inversion results yield no indication for free gas below it as resistivities are generally elevated above the reflector. We suggest that the elevated resistivities are caused by an overall decrease in porosity in the glacial sediments and that the seismic reflector could be caused by an impedance contrast at a thin low‐velocity layer. Controlled‐source electromagnetic interface depths near the reflector are quite uncertain and variable. We conclude that the seismic interface cannot be resolved with the controlled‐source electromagnetic data, but the thickness of the corresponding resistive layer follows the trend of the reflector that is inclined towards the west.  相似文献   

Understanding carbon trading: Effects of delegating CO2 responsibility on organizations’ trading behaviour     

Juan Miguel Rodriguez Lopez  Anita Engels  Lisa Knoll 《Climate Policy》2013,13(3):346-360

The establishment of a carbon market assumes that there is an effective means of transforming price information into technical carbon reduction measures. However, empirical evidence reveals that the links between price information and carbon management strategies are far from obvious. To understand how delegating CO₂ responsibility affects CO₂ trading behaviour, this article proposes a neo-institutionalist approach to answering the question of why companies became sellers, buyers or a combination of both during phase I of the European Emissions Trading Scheme (EU ETS). Original data from a survey on companies that participated in this scheme were collected and analysed. It was assumed that the trading scheme offered two ways to delegate decisions regarding emissions trading: decoupling from technical knowledge and financialization (i.e. delegating to financial departments) or coupling using technicalization (i.e. delegating to manufacturing departments). The results support the hypothesis that a company that adopts a decoupling strategy is more likely to buy certificates to fulfil their emissions targets. Adopting a coupling strategy indicates that a company is more likely to become a seller, all else equal. Professional identity is the theoretical basis for this relationship. Delegating carbon management to different departments represents either a stronger coupling or a stronger decoupling from core technological processes.

Policy relevance

The transaction data from phase I of the EU ETS open new questions and possibilities regarding the reasons that drive selling and buying in companies. It is important to look not only at the traditional sources of transaction costs, but rather also at the reasons for these tensions. One important source is the professional education of the people in charge of the EU ETS. Tailored information that directly addresses the different professional backgrounds of managers working in both financial departments and more technical departments might help to lower these types of transaction costs. In today's context, important emitter countries, such as China and Korea, have launched their own emissions markets, copying many aspects of the EU ETS. For the positive development of these markets and as a way of establishing a global emissions market, these new schemes should learn from the EU ETS experience.  相似文献   

Ascospores of the parasitic fungus Kretzschmaria deusta as rainstorm indicators during a late Holocene beech-forest phase around lake Meerfelder Maar, Germany     

Bas van Geel  Stefan Engels  Celia Martin-Puertas  Achim Brauer 《Journal of Paleolimnology》2013,50(1):33-40

Discrete reddish-brown, predominantly minerogenic detrital layers along the Holocene, annually laminated sediment sequence of Lake Meerfelder Maar represent extreme runoff events. We conducted detailed microfacies analyses and a high-resolution palynological investigation, focusing on ten detrital layers throughout the Holocene. We studied triad samples taken directly under, in and above the detrital layer. Fagus sylvatica (beech) was a dominant species in the regional forest around Lake Meerfelder Maar after ca. 3,800 years ago. Three detrital layers occurring during the Fagus phase exhibit short-term maxima of ascospores of the parasitic fungus Kretzschmaria deusta. In contrast, the ascospore contents are low in the event layers deposited during the early and middle Holocene. Fagus is a vulnerable host species for Kretzschmaria deusta and the fungus is common on Fagus. Ascospores are formed on the trunk base, and under normal weather conditions, few spores appear outside the forest. We interpret the short peaks in abundance of K. deusta in the event layers as indicators for rainstorms during which material was transported from the forest floor into the lake by strong winds and stormwater runoff. The open beech forest facilitated wind transport of the ascospores. We recommend analysis of fungal spores in lake sediments because fungal records may help to identify extreme weather events, even when such events are not macroscopically visible in the sediment sequence.  相似文献