Some remarks on isostasy and the long-term behavior of the continental lithosphere     

James R. Cochran 《Earth and Planetary Science Letters》1980,46(2):266-274

The interpretation of linear transfer function (admittance) studies of the relationship between gravity anomalies and topography depends on what assumptions are made in limiting the acceptable set of solutions. However, whatever assumptions are made, the value of the flexural rigidity determined from admittance studies of Australia and the continental United States is less than about 10²⁸ dyne-cm (5-km plate thickness). This is much less than values determined from other studies of the loading of continental lithosphere which consistently give values in the range of 4 × 10³⁰ to 2 × 10³¹ dyne-cm (elastic plate thickness of 35–60 km). It is argued that the latter values represent the long-term rigidity of the continental lithosphere and that the rigidity does not change greatly with age of loading.  相似文献   

Spectrophotometry of Pluto from 3500 to 7350 Å     

Edwin S. Barker  William D. Cochran  Anita L. Cochran 《Icarus》1980,44(1):43-52

We have obtained spectra of Pluto on six nights during February 1979 using the Cassegrain Digicon spectrograph on the 2.1-m Struve reflector and the IDS spectrograph on the 2.7-m reflector of McDonald Observatory. These spectra, with nominal resolution of 6–7 Å, have been reduced to relative fluxes. Relative albedos were then calculated using the solar irradiances of Arvesen et al. (1969). The spectra taken in the blue show no indication of the upturn in albedo at $\text{λ < 3800}\text{A}\text{?}$ previously reported by Fix et al. (1970). The lack of a uv upturn cannot be interpreted in terms of a Rayleigh scattering atmosphere unless the albedo of the underlying surface is known. From the lack of methane absorption at the wavelength of the 6190- or 7270-Å methane bands we derive an upper limit of 1–3 m-am of gaseous CH₄. The albedo curve has a constant slope between 3500 and 7300 Å. The only other solar system body which has this feature is an S-type asteroid.  相似文献   

Terrestrial vegetation redistribution and carbon balance under climate change   总被引：1，自引：0，他引：1  

Wolfgang Lucht  Sibyll Schaphoff  Tim Erbrecht  Ursula Heyder  Wolfgang Cramer 《Carbon balance and management》2006,1(1):6-7

Background  

Dynamic Global Vegetation Models (DGVMs) compute the terrestrial carbon balance as well as the transient spatial distribution of vegetation. We study two scenarios of moderate and strong climate change (2.9 K and 5.3 K temperature increase over present) to investigate the spatial redistribution of major vegetation types and their carbon balance in the year 2100.  相似文献   

Echinoids from the Belpberg Beds (Obere Meeresmolasse, Middle Burdigalian) in the area of Bern (Switzerland)   总被引：1，自引：0，他引：1  

Andreas Kroh  Ursula Menkveld-gfeller 《Eclogae Geologicae Helvetiae》2006,99(2):193-203

The present paper deals with the echinoid fauna of the Belpberg Beds, a lithostratigraphic unit in the Upper Marine Molasse cropping out southeast of Bern (Switzerland). In this unit, echinoids, in contrast to mollusks, are rare and of low diversity. The scarcity of echinoids is related to the environmental setting dominated by monotonous siliciclastic deposits and strong diagenetic alteration. The echinoid fauna consists of three species Psammechinus dubius dubius, Echinocardium deikei and Hemipatagus ocellatus? Psammechinus dubius dubius and H. ocellatus typically occur in Burdigalian sediments in the Paratethys and help to confirm the dating obtained from the microfossils and molluscs of the Belpberg Beds. Furthermore, the Belpberg echinoid fauna is especially relevant for the palaeobiogeography with species common to both the Rh?ne Basin and the Central Paratethyan faunas.

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Zusammenfassung. Die vorliegende Arbeit besch?ftigt sich mit der Echinidenfauna der Belpberg Schichten (Obere Meeresmolasse) bei Bern. Im Gegensatz zu den Mollusken sind die Echiniden selten und wenig divers. Dies kann einerseits auf das sediment?re Regime, und andererseits auf diagenetische Ursachen zurückgeführt werden. Insgesamt konnten drei Arten nachgewiesen werden (Psammechinus dubius dubius, Echinocardium deikei und Hemipatagus ocellatus?). Zwei davon treten in der Paratethys charakteristischerweise im Burdigalium auf und lassen ein ebensolches Alter für die Belpberg Schichten als wahrscheinlich erscheinen. Aus pal?obiogeographischer Sicht ist die Belpberg-Echinidenfauna von besonderem Interesse, das sie ein Bindeglied zwischen Rh?ne Becken und Zentraler Paratethys darstellt.

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Macrophytes and phytobenthos as indicators of ecological status in German lakes — a contribution to the implementation of the water framework directive     

Jochen Schaumburg  Christine Schranz  Gabriele Hofmann  Doris Stelzer  Susanne Schneider  Ursula Schmedtje 《Limnologica》2004,34(4):302-314

A new assessment system for macrophytes and phytobenthos in German lakes according to the Water Framework Directive of the European Community is described. Based on biological, chemical and hydromorphological data from about 100 lake sites covering the main ecoregions, hydromorphological lake types and degradation forms, biocoenotic types could be defined. For developing a classification system the quality element macrophytes and phytobenthos was divided into two components: macrophytes and benthic diatoms. For macrophytes 4 and for benthic diatoms 4 lake types were identified. The benthic vegetation at reference conditions is described and degradation is characterised as deviation in benthic vegetation species composition and abundance from the reference biocoenosis. For classification in five ecological status classes, several metrics were developed and used in combination with existing indices. For a few of the described lake types further investigations are necessary before a classification can be developed.  相似文献   

The Luna 20 lithic fragments,and the composition and origin of the lunar highlands     

G.Jeffrey Taylor  Michael J Drake  John A Wood  Ursula B Marvin 《Geochimica et cosmochimica acta》1973,37(4):1087-1106

Luna 20 soil 22003,1 (250–500 μ) is similar to Apollo 16 soil 61501,47 (250–500 μ) in terms of the percentage of different types of particles. However, among the lithic fragments, the Apollo 16 sample contains a greater percentage of fragments with more than 70 wt. % modal plagioclase and a significantly greater proportion of KREEP-rich particles. Modal analyses of non-mare lithic fragments in Luna 20 and Apollo 11, 14, 15 and 16 indicate that the KREEP-poor highland regions (the bulk of the lunar terrae), though relatively feldspathic, are compositionally inhomogeneous, ranging in plagioclase content from approximately 35 to 100 wt. %. The average plagioclase content lies in the range 45–70 wt.%. Luna 20 pyroxene analyses cluster in two groups, one more magnesian than the other. The groups persist when pyroxene analyses from KREEP-poor noritic, troctolitic and anorthositic lithic fragments from Apollo 11, 14, 15 and 16 and Luna 20 are included. Olivine compositions mimic these pyroxene groups.Within each pyroxene group Cr₂O₃ and TiO₂ decrease as $\text{Fe}\text{(Fe + Mg)}$ increases, suggesting a relationship by fractional crystallization. The two groups suggest that at least two magma compositions were involved. To account for these observations we envisage a Moon-wide magma system in which initial accretionary heterogeneities were imperfectly erased by diffusion and convection. During the cooling of this magma system fractional crystallization was effected by the flotation of plagioclase and sinking of pyroxene, olivine and perhaps ilmenite. The endproduct was an upper layer enriched in plagioclase and a lower layer enriched in mafic silicates. KREEP-rich rocks, which are predominantly noritic in major element composition, may be mechanical mixtures of KREEP-poor norite and material residual after fractional crystallization of the surface magma system.  相似文献   

PHT3D‐UZF: A Reactive Transport Model for Variably‐Saturated Porous Media          下载免费PDF全文

Ming Zhi Wu  Vincent E.A. Post  S. Ursula Salmon  Eric D. Morway  Henning Prommer 《Ground water》2016,54(1):23-34

A modified version of the MODFLOW/MT3DMS‐based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably‐saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D‐UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated‐zone flow (UZF1) package. A volume‐averaged approach similar to the method used in UZF‐MT3DMS was adopted. The PHREEQC‐based computation of chemical processes within PHT3D‐UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional‐scale applications, UZF1 simulates downward‐only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably‐saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns.  相似文献   

Effects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean sea, is it an endocrine disruption?     

Schnitzler JG  Koutrakis E  Siebert U  Thomé JP  Das K 《Marine pollution bulletin》2008,56(10):1755-1764

We evaluated the alterations of organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) on the thyroid in wild and cultured sea bass (Dicentrarchus labrax) at environmental concentrations. These compounds influence the endocrine system of many fish species and are qualified as endocrine disruptors. The thyroid seems to be a target organ. Two alteration endpoints: the thyroid histology and the muscular thyroid hormone concentrations, were used simultaneously.High concentrations in PCBs and DDT were detected in muscles, supporting the idea that the Mediterranean fauna could be more polluted than the Atlantic fauna. The high abundance of DDE indicates a progressive degradation of remnant DDT load and the absence of new inputs in this area. Aquaculture sea bass shows a significant higher amount of pollutants on fresh weight basis (especially PCBs) in their muscles compared to the wild sea bass. Those differences may be related mainly to the contaminations of diet.Thyroid parameters vary between wild and aquaculture sea bass, wild sea bass were characterized by higher follicle diameters, epithelial cell heights and muscular T₄ concentrations. A significant relationship between persistent organic pollutants (muscular PCBs and DDT concentration) and the different thyroid parameters (diameters of follicles, epithelial cell heights and muscular T₄ levels) could be observed, which support the hypothesis that these compounds have an adverse impact on thyroid morphometry and function.  相似文献   

The Meteoritical Society and Meteoritics and Planetary Science: Past and future     

Ursula B. Marvin 《Meteoritics & planetary science》2000,35(1):4-4

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Assessing the Transport of Pharmaceutical Compounds in a Layered Aquifer Discharging to a Stream     

Nicola Balbarini  Majken Frederiksen  Vinni Rønde  Ingelise Møller  Anne T. Sonne  Ursula S. McKnight  Jørn K. Pedersen  Philip J. Binning  Poul L. Bjerg 《Ground water》2020,58(2):208-223

A groundwater plume containing high concentrations of pharmaceutical compounds, mainly sulfonamides, barbiturates, and ethyl urethane, in addition to chlorinated ethenes and benzene was investigated. The contamination originating from a former pharmaceutical industry discharges into a multilayered aquifer system and a downgradient stream. In this study, geological and hydrogeological data were integrated into a numerical flow model to examine identified trends using statistical approaches, including principal component analysis and hierarchal cluster analysis. A joint interpretation of the groundwater flow paths and contaminant concentrations in the different compartments (i.e., groundwater and hyporheic zone) provided insight on the transport processes of the different contaminant plumes to the stream. The analysis of historical groundwater concentrations of pharmaceutical compounds at the site suggested these compounds are slowly degrading. The pharmaceutical compounds migrate in both a deep semiconfined aquifer, as well as in the shallow unconfined aquifer, and enter the stream along a 2-km stretch. This contrasted with the chlorinated ethenes, which mainly discharge to the stream as a focused plume from the unconfined aquifer. The integrated approach developed here, combining groundwater flow modeling and statistical analyses of the contaminant concentration data collected in groundwater and the hyporheic zone, lead to an improved understanding of the observed distribution of contaminants in the unconfined and semiconfined aquifers, and thus to their discharge to the stream. This approach is particularly relevant for large and long-lasting contaminant sources and plumes, such as abandoned landfills and industrial production sites, where field investigations may be very expensive.  相似文献