The history and impact of air pollution at Čertovo Lake,southwestern Czech Republic     

Josef Vesely  Heather Almquist-Jacobson  Lisa M. Miller  Stephen A. Norton  Peter Appleby  Aruna S. Dixit  John P. Smol 《Journal of Paleolimnology》1993,8(3):211-231

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the umava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from ertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the ²¹⁰Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 g g^-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 g cm^-2 yr^-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 g cm^-2 yr^-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.  相似文献   

Theoretical infrared spectra of some model polycyclic aromatic hydrocarbons: effect of ionization     

De Frees DJ  Miller MD  Talbi D  Pauzat F  Ellinger Y 《The Astrophysical journal》1993,408(2):530-538

In order to test the hypothesis of ionized polycyclic aromatic hydrocarbons (PAHs) as possible carriers of the UIR bands, we realized a computational exploration on selected PAHs of small dimension in order to identify which changes ionization would induce on their IR spectra. In this study we performed ab initio calculations of the spectra of neutral and positively ionized naphthalene, anthracene, and pyrene. The results are significantly important. The frequencies in the cations are slightly shifted with respect to the neutral species, but no general conclusion can be reached from the three molecules considered. By contrast, the relative intensities of most vibrations are strongly affected by ionization, leading to a much better agreement between the calculated CH/CC vibration intensity ratios and those deduced from observations.  相似文献   

Cycle anatomy and variability in the storm-dominated type cincinnatian (Upper Ordovician): coming to grips with cycle delineation and genesis     

Holland SM  Miller AI  Dattilo BF  Meyer DL  Diekmeyer SL 《The Journal of geology》1997,105(2):135-152

Although parasequence and sequence are scale-independent terms, they are frequently applied only to specific scales of cycles. For example, meter-scale cycles are commonly assumed to be parasequences or PACs. In the Upper Ordovician Kope and Fairview Formations of northern Kentucky, we examined a succession of 50 meter-scale cycles that have been variously interpreted as deepening-upward, shallowing-upward, or showing no relationship with water depth. Our analysis shows that these cycles, characterized by shifts in storm-bed proximality, are highly variable in their thickness and internal construction. Most cycles are best considered high-frequency sequences, because deepening-upward intervals are common, and many cycles contain evidence of abrupt basinward shifts in facies as expected at sequence boundaries. A minority fit the parasequence model of shallowing-upward cycles bounded by flooding surfaces. Larger, 20 m scale cycles are defined by systematic thickening and thinning trends of meter-scale cycles. However, meter-scale cycles do not display any systematic trends in cycle anatomy as a function of position within the 20 m cycles or position within the Kope and Fairview Formations. The high cycle variability and the lack of systematic stratigraphic organization with respect to longer-term cyclicity reflect either the irregularity of relative sea-level changes, the poor recording of sea-level changes in this deep-water setting, or the generation of these cycles by climate-induced cyclicity in storm intensity. These three mechanisms would generate similar patterns at the outcrop scale, so it is not possible at the present to distinguish between them.  相似文献   

Association of orogenic activity with the Ordovician radiation of marine life     

Miller AI  Mao S 《Geology》1995,23(4):305-308

The Ordovician radiation of marine life was among the most substantial pulses of diversification in Earth history and coincided in time with a major increase in the global level of orogenic activity. To investigate a possible causal link between these two patterns, the geographic distributions of 6576 individual appearances of Ordovician vician genera around the world were evaluated with respect to their proximity to probable centers of orogeny (foreland basins). Results indicate that these genera, which belonged to an array of higher taxa that diversified in the Middle and Late Ordovician (trilobites, brachiopods, bivalves, gastropods, monoplacophorans), were far more diverse in, and adjacent to, foreland basins than they were in areas farther removed from orogenic activity (carbonate platforms). This suggests an association of orogeny with diversification at that time.  相似文献   

Is C/O enhanced in NGC 253?     

Andrew Harrison  Peter Brand  Adrian Russell  Phil Puxley 《Astrophysics and Space Science》1995,224(1-2):473-474

We have mapped the nuclear region of the starburst galaxy NGC 253 in the³ P ₁ ³ P ₀ line of neutral carbon using the JCMT. Carbon is widespread across the nuclear region with a similiar distribution to CO as expected. Previous studies of Galactic star-forming regions showed that carbon emission is enhanced in photon-dominated regions (where UV photons impinge upon molecular clouds). Previous observations of other PDR tracers such as ionized carbon and FIR continuum constrain the physical conditions in the PDR gas of NGC 253. The carbon we have observed is far brighter than predicted by theoretical models of PDRs with solar elemental values. This indicates that carbon emission is not a reliable diagnostic of the physical conditions in the nuclear region of a galaxy undergoing a burst of star formation.  相似文献   

On the interpretation of Fraunhofer line Doppler shifts at supergranule boundaries     

P. Miller  P. Foukal  S. Keil 《Solar physics》1984,92(1-2):33-46

We have used the SPO tower telescope and echelle spectrograph to study differences in the profiles of three Fei lines, between magnetic network and cells. Ca K slit-jaw pictures were used to identify the network and cell areas, and mean network and cell profiles were computed from digitized spectra for the g = 0 lines 4065, 5434, and the g = 1.5 line 5233. The profile bisectors show that the wings of all three lines are red-shifted in the network by between 75–200 m s^–1 relative to the cell profiles. But the redshift decreases in the line core and becomes less than the standard error of 20 m s^–1 near the line core minimum. This disappearance of the redshift at the cores of all 3 lines formed over the height range 250–500 km above _0.5 = 1, argues against a steady downflow at supergranule boundaries. We show that such red-shifted wings and a relatively unshifted core can result if granular convection is suppressed near the network flux tubes, without implying any downflow in the vicinity of these flux tubes. Our results also indicate that searches for large-scale convective velocity patterns should measure shifts of the line core, rather than the line wings which appear to be very sensitive to inhomogeneities in granule structure.Visiting Astronomers, Sacramento Peak Observatory.  相似文献   

Baroclinic instabilities in Jupiter's zonal flow     

Peter J. Gierasch  Andrew P. Ingersoll  David Pollard 《Icarus》1979,40(2):205-212

The baroclinic stability of Jupiter's zonal flow is investigated using a model consisting of two continuously stratified fluid layers. The upper layer, containing a zonal shear flow and representing the Jovian cloudy regions above p ～ 5 bars, is the same as Eady's (1949) model for the Earth. The lower layer has a relatively large but finite depth with a quiescent basic state, representing the deep Jovian fluid bulk below p ～ 5 bars. Due to the presence of the lower layer, the linearized non-dimensional growth rates are drastically reduced from the O(1) growth rates of the original Early model. Only very long wavelengths relative to the upper fluid's radius of deformation L₁ are unstable. Eddy transports of heat are also reduced relative to estimates based on scaling arguments alone. Since the hydrostatic approximation for the lower-layer perturbation breaks down at great depths, a second model is presented in which energy propagates downward in an infinitely deep lower fluid obeying the full linearized fluid equations. In this model, the growth rates are again very small, but now all wavelengths are unstable with maximum growth rates occurring for wavelengths O(1) relative to L₁. These results illustrate the importance for the upper-layer meteorology of the interface boundary condition with the lower fluid, which is radically different from the rigid lower boundary of the Earth's troposphere.  相似文献   

Vertical extent of zonal winds on Venus     

David Crisp  Andrew T. Young 《Icarus》1978,35(2):182-188

Possible interrelationships of different observations have been studied to clear up some obvious inconsistencies and develop a coherent picture of the kinematics of the Venus atmosphere. There is a wind shear in the vicinity of 60 km with vertical dimensions on the order of a scale height. The kinematical model has negligible surface winds, speeds increasing with altitude to approximately 45 km, a layer of high-speed retrograde zonal winds extending from approximately 45 to 60 km, a wind shear between 60 and 65 km, and slow atmospheric motions above this. Spacecraft data show that the region of high-speed winds is thicker on the day side of the planet than on the night side.  相似文献   

Part II. Evaluation of Ar-Ar quartz ages: Implications for fluid inclusion retentivity and determination of initial Ar/Ar values in Proterozoic samples     

M.A. Kendrick  J.McL. Miller  D. Phillips 《Geochimica et cosmochimica acta》2006,70(10):2562-2576

The argon isotope systematics of vein-quartz samples with two different K-reservoirs have been evaluated in detail. Potassium is hosted by ultra-high-salinity fluid inclusions in quartz samples from the Eloise and Osborne iron-oxide-copper-gold (IOCG) deposits of the Mt Isa Inlier, Australia. In contrast, K is hosted by accidentally trapped mica within lower-salinity fluid inclusions of a sample selected from the Railway Fault, 13 km south of the Mt Isa copper mine, Australia. Imprecise apparent ages have been obtained for all of the samples studied and conclusively demonstrate that quartz fluid inclusions are retentive to Ar and have not leaked over billions of years. IOCG samples that host K in fluid inclusions only, have K/Cl values of <1 and the ages obtained represent the maximum ages for mineralization. In contrast, the Railway Fault samples that include accidentally trapped mica have K/Cl values of ?1. Excess ⁴⁰Ar_E plus Cl hosted by fluid inclusions, and radiogenic ⁴⁰Ar_R plus K, are strongly correlated in these samples and define a plane in 3D ⁴⁰Ar-³⁶Ar-K-Cl space. In this case, the plane yields an ‘excess ⁴⁰Ar_E’ corrected age of ∼1030 Ma that is 100’s of Ma younger than nearby Cu-mineralization at Mt Isa. The age is interpreted to reflect ⁴⁰Ar-loss from the accidentally trapped mica into the surrounding fluid inclusions, and is not related to the samples’ age of formation. The initial ⁴⁰Ar/³⁶Ar value of fluid inclusions is widely used to provide information on fluid origin. For the IOCG samples that host K in fluid inclusions only, the initial ⁴⁰Ar/³⁶Ar values are close to the measured values at every temperature of stepped heating experiments. For samples that include accidentally trapped mica, the correction for post-entrapment radiogenic ⁴⁰Ar_R production is significant. Furthermore, because ³⁹Ar_K present in accidentally trapped mica crystals is released at different temperatures to radiogenic ⁴⁰Ar_R lost to the surrounding fluid inclusions, intra-sample ⁴⁰Ar/³⁶Ar variation cannot be reliably documented. The results demonstrate that noble gas analysis is readily applicable to Proterozoic, or older, samples but that if K-mineral impurities are present within quartz the abundance of K must be determined before calculation of mean ⁴⁰Ar/³⁶Ar values that are representative of the samples’ initial composition.  相似文献   

First record of a Cretaceous cheilostome bryozoan from Hokkaido, Japan     

Andrew N. Ostrovsky  Reishi Takashima  Matthew H. Dick  Andrei V. Grischenko  Hiroshi Nishi  Shunsuke F. Mawatari 《Cretaceous Research》2006,27(6):859-862

A small collection of recrystallised, encrusting colonies of a single species from the Mikasa Formation (lower Middle Cenomanian), represents the first record of cheilostome (malacostegan or anascan) bryozoans from Hokkaido, Japan.  相似文献