The unique environment of the most acidified permanently meromictic lake in the Czech Republic

Changes in the water properties and biological characteristics of the highly acidic Hromnice Lake (Western Bohemia) were investigated. This 110-year-old lake, formed as a consequence of the mining of pyritic shales, is permanently meromictic. Two chemoclines separate an extremely acidic (pH ～ 2.6) mixolimnion from a metal-rich anoxic monimolimnion. The absence of spring mixolimnetic turnover due to ice melting and very slow heat propagation through the chemocline with a 6-month delay were observed. Extreme mixolimnetic oxygen maxima (up to 31 mg l^?1) in phosphorus-rich lake (PO₄^3? up to 1.6 mg l^?1) well correlated with outbursts of phytoplankton. Phytoplankton consist of several acido-tolerant species of the genera Coccomyxa, Lepocinclis, Chlamydomonas and Chromulina. Surface phytoplankton biomass expressed as chlorophyll-a varies from 2 to 140 μg l^?1. Multicellular zooplankton are almost absent with the exception of Cephalodella acidophila, a small rotifer occurring in low numbers. Large red larvae of the midge Chironomus gr. plumosus were found at the bottom close to the shore, with larvulae in the open water. Developmental stages (protonemata) of a moss, resembling filamentous algae, dwell in the otherwise plant-free littoral zone.     

Determination of tidal torques independently of densities

Summary The components of the tidal torques along the axes of the inertia ellipsoid of a perfectly elastic Earth have been derived quite independently of the density distribution of masses within the Earth. It has been demonstrated that not only the sectorial, but also the tesseral terms in the tidal forming potential are responsible for the tidal deceleration of the Earth's rotation.

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Seismic regime of a single fault model

A special experimental technique enabled us to study in detail seismic events on a fault model in a uniaxial stress field. The recording system used made it possible to investigate the radiation pattern for all the events observed including the precise determination of the dislocation origin.The aim of the present paper is (1) to find the relation between shear and tensile displacements, (2) to check a possible influence of the process of tensile crack generation on the seismic energy release and (3) to compare the seismic regime of a single fault before and after the tensile crack generation, respectively.Results prove the dominating importance of shear mechanism for the seismic energy release. The tensile displacement can be seismoactive only under special contact conditions on the fault plane.The existence of tensile cracks at the fault tips changed the pattern of seismic energy radiation. This feature is probably caused by subsequent changes in contact conditions on the fault plane and in the stress field around the fault.A comparison of some results of the present model experiments with the already published results of geological and seismological measurements and investigations shows the analogous character in laboratory and in nature of the process of tectonic earthquake preparation, the displacement course on the fault during the earthquake and the manner of seismic energy release on faults.     

Effects of anisotropic diffusion on onset of rotating magnetoconvection in plane layer; stationary modes

ABSTRACT

Turbulence in the Earth's outer core not only increases all diffusive coefficients, but it can lead to their anisotropic properties. Therefore, the model of rotating magnetoconvection in horizontal plane layer rotating about vertical axis and permeated by homogeneous horizontal magnetic field, influenced by anisotropic diffusivities, viscosity and thermal diffusivity, is advanced by considering the magnetic diffusivity as anisotropic too. The case of full anisotropy, i.e. all coefficients anisotropic, is compared with both the case possessing isotropic diffusion coefficients and the case of partial anisotropy, i.e. mixed case with isotropic and anisotropic diffusive coefficients (viscosity and thermal diffusivity anisotropic and magnetic diffusivity isotropic). The existence and preference of instabilities is sensitive to all non-dimensional parameters, as well as on anisotropic parameter, the ratio of horizontal and vertical diffusivities. Two types of anisotropy, BM (introduced by Braginsky and Meytlis) and SA (stratification anisotropy) are studied. BM as well as SA were applied by ?oltis and Brestenský to the study of the partial anisotropy; this study is extended, in this paper, to full anisotropy cases (full SA and full BM) and it is shown that the style of convection given by the onset of stationary modes is more affected by anisotropic diffusivities in BM than in SA anisotropy. The important influence of strong anisotropies in the Earth's core dynamics is stressed.     

Seismic Hazard of the Circum-Pannonian Region,Reprint from Pure and Applied Geophysics (PAGEOPH), Vol.l57(2000), No.1/2, 284 pages

Studia Geophysica et Geodaetica -     

Neue Vorstellungen über den Tiefbau von Vorsenken

Zusammenfassung Der geologische Tiefenbau und die Entwicklungsgeschichte der Kopetdag-, Terek-Kaspi-, Indol-Kuban- und Karpaten-Vorsenke sind ähnlich. Es zeigt sich, daß die genannten Vorsenken keine Zonen kurzzeitiger Durchbiegungen sind, die sich in der orogenen Schlußentwicklungsetappe des alpidischen Faltengebietes gebildet haben, sondern daß sie langlebige negative Strukturen darstellen. Die Intensität ihrer Durchbiegung zu Beginn des alpidischen geotektonischen Zyklus (in der Jura und Kreidezeit) ist mit der Größe der Absenkung im Neogen-Quartär vergleichbar. Im Verlaufe des gesamten alpidischen Zyklus entwickelten sich die Senken posthum.Überall dort, wo notwendige geophysikalische Untersuchungen durchgeführt wurden, wurde unter diesen Senken unterhalb eines mächtigen alpidischen Gesteinskomplexes ein genauso mächtiger Sedimentkomplex variszischen Alters festgestellt. Territorial fallen die Zonen der maximalen Mächtigkeiten des variszischen und alpidischen Gesteinskomplexes zusammen.

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Structure and development of the Pre-Copetdag, Terek-Caspian, Indol-Kuban, and Pre-Carpathian fore deeps are similar. The fore deeps were not zones of short term subsidence during the final stage of orogenic development of the Alpine folded belt, but they were long term subsidence zones. The rates of subsidence at the beginning of the Alpine geotectonic cycle (during Jurassic and Cretaceous) and at the end of the cycle (during Neogene and Quaternary) are comparable.Wherever geophysical investigations were carried out in this zone, beneath the Alpine sediments a Hercynian sediment complex of equal thickness was found. The areas of maximum thickness in both complexes coincide.

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Résumé La structure géologique et le développement historique des avant-fosses de Copetdag, Terek-Caspienne, Indol-Kouban et des Carpates sont semblables. Il appert que ces dépressions ne sont pas des zones d'inflexion de courte durée qui se sont formées pendant l'étape finale du plissement alpin, mais qu'ils présentent des structures négatives de longue durée. L'intensité de leur affaissement au commencement du cycle géotectonique alpin (au Jurassique et au Crétacé) est comparable, en grandeur, avec celui de la période néogène-quaternaire. Au cours de l'ensemble du cycle alpin, les dépressions se sont développées de façon posthume.Partout où ont eu lieu des explorations géophysiques, nous avons découvert sous ces avant-fosses, un épais complexe de roches alpines, et sous elles un complexe aussi puissant de sédiments varisques. Spatialement les zones des puissances maximum des complexes alpins et varisques coïncident.

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