Does Poisson’s downward continuation give physically meaningful results?

The downward continuation (DWC) of the gravity anomalies from the Earth’s surface to the geoid is still probably the most problematic step in the precise geoid determination. It is this step that motivates the quasi-geoid users to opt for Molodenskij’s rather than Stokes’s theory. The reason for this is that the DWC is perceived as suffering from two major flaws: first, a physically meaningful DWC technique requires the knowledge of the irregular topographical density; second, the Poisson DWC, which is the only physically meaningful technique we know, presents itself mathematically in the form of Fredholm integral equation of the 1st kind. As Fredholm integral equations are often numerically ill-conditioned, this makes some people believe that the DWC problem is physically ill-posed. According to a revered French mathematician Hadamard, the DWC problem is physically well-posed and as such gives always a finite and unique solution. The necessity of knowing the topographical density is, of course, a real problem but one that is being solved with an ever increasing accuracy; so sooner or later it will allow us to determine the geoid with the centimetre accuracy.     

The formation of fan-deltas in mountain lakes: Findings from Zelené Kežmarské Lake (Slovakia)

Fan-deltas are formed in mountain lakes, contributing to changes in shorelines' shapes and filling lake basins with sediments. Factors that condition sediment delivery to the lakes and the formation of fan-deltas are not fully understood. This study aims to identify processes forming fan-deltas in mountain lakes based on the sedimentary architecture of a fan-delta filling Zelené Kežmarské Lake (Slovakia). Our study is based on ground-penetrating radar and seismic refraction surveys conducted over the lake and debris-flow fans in its vicinity, and grain-size analyses of the surface deposits. The internal structure of the fan-delta comprises foreset deposits representing the fan-delta lobes. Mouth bars were identified in the near-shore zone. The fan-delta is built of sands and silty sands whereas an alluvial debris-flow dominated fan west of the lake contains gravels. A general trend of downslope fining of the fan surface sediments, disturbed by zones of coarse gravels, was identified in the surficial sediments forming the fan. The fan-delta was formed by depositional events in humid periods, alternating with dry periods featured with a small or no deposition. The lake-level steadily rose in the humid periods and remained stable in dry periods. The contrast between the coarse sediments forming the alluvial debris-flow dominated fan, and sands forming the fan-delta was caused by a selective deposition. Coarse gravels in the fan were mobilized in humid periods but did not reach the lake-shore. The reason was a basement rock ridge situated parallel to the lake shore. Sands were delivered to the fan-delta in humid periods owing to frequent high-energy flows. A deposition of silts took place in dry periods. The studied fan-delta might preserve the sedimentary record of three humid periods from the last 200 years. However, further studies are needed to establish the timing of the fan-delta formation.     

Oscillations and Waves in Radio Source of Drifting Pulsation Structures

Drifting pulsation structures (DPSs) are considered to be radio signatures of the plasmoids formed during magnetic reconnection in the impulsive phase of solar flares. In the present paper we analyze oscillations and waves in seven examples of drifting pulsation structures, observed by the 800?–?2000 MHz Ond?ejov Radiospectrograph. For their analysis we use a new type of oscillation maps, which give us much more information as regards processes in DPSs than that in previous analyses. Based on these oscillation maps, made from radio spectra by the wavelet technique, we recognized quasi-periodic oscillations with periods ranging from about 1 to 108 s in all studied DPSs. This strongly supports the idea that DPSs are generated during a fragmented magnetic reconnection. Phases of most the oscillations in DPSs, especially for the period around 1 s, are synchronized (“infinite” frequency drift) in the whole frequency range of DPSs. For longer periods in some DPSs we found that the phases of the oscillations drift with the frequency drift in the interval from ?17 to \(+287~\mbox{MHz}\,\mbox{s}^{-1}\). We propose that these drifting phases can be caused (a) by the fast or slow magnetosonic waves generated during the magnetic reconnection and propagating through the plasmoid, (b) by a quasi-periodic structure in the plasma inflowing to the reconnection forming a plasmoid, and (c) by a quasi-periodically varying reconnection rate in the X-point of the reconnection close to the plasmoid.     

Metal speciation and attenuation in stream waters and sediments contaminated by landfill leachate

The degree of metal contamination (Zn, Pb, Cu, Ni, Cd) has been investigated in the vicinity of an old unmonitored municipal landfill in Prague, Czech Republic, where the leachate is directly drained into a surface stream. The water chemistry was coupled with investigation of the stream sediment (aqua regia extract, sequential extraction, voltammetry of microparticles) and newly formed products (SEM/EDS, XRD). The MINTEQA2 speciation-solubility calculation showed that the metals (Zn, Pb, Cu, Ni) are mainly present as carbonate complexes in leachate-polluted surface waters. These waters were oversaturated with respect to Fe(III) oxyhydroxides, calcite (CaCO₃) and other carbonate phases. Three metal attenuation mechanisms were identified in leachate-polluted surface waters: (i) spontaneous precipitation of metal-bearing calcite exhibiting significant concentrations of trace elements (Fe, Mn, Mg, Sr, Ba, Pb, Zn, Ni); (ii) binding to Fe(III) oxyhydroxides (mainly goethite, FeOOH) (Pb, Zn, Cu, Ni); and (iii) preferential bonding to sediment organic matter (Cu). These processes act as the key scavenging mechanisms and significantly decrease the metal concentrations in leachate-polluted water within 200 m from the direct leachate outflow into the stream. Under the near-neutral conditions governing the sediment/water interface in the landfill environment, metals are strongly bound in the stream sediment and remain relatively immobile.     

Beta-carotene—A possible biomarker in the Martian evaporitic environment: Raman micro-spectroscopic study

Due to the discovery of the evaporitic environment on the Martian surface, there is a reasonable possibility that evaporites served (or still serve) as habitats for microbial life if ever present on Mars. At the very least, if no signatures of extant life exist within these rocks, it may sustain molecular remnants as evidence for living organisms in the past. β-Carotene, among other carotenoids, could be such a suitable biomarker. In this study, Raman micro-spectroscopy was tested as a nondestructive method of determining the presence of β-carotene in experimentally prepared evaporitic matrices. Samples prepared by mixing β-carotene with powdered gypsum (CaSO₄·2H₂O), halite (NaCl) and epsomite (MgSO₄·7H₂O) were analyzed using a 785 nm excitation source. Various concentrations of β-carotene in the matrices were investigated to determine the lowest β-carotene content detectable by Raman micro-spectroscopy. Mixtures were also measured with a laser beam permeating the crystals of gypsum and epsomite in order to evaluate the possibility of identifying β-carotene inside the mineral matrix.We were able to obtain a clear β-carotene signal at the 10 mg kg⁻¹ concentration level—the number of registered β-carotene Raman bands differed depending on the particular mineral matrix. Spectral signatures of β-carotene were detected even when analyzing samples containing 1 mg kg⁻¹ of this molecule. The 10-100 mg kg⁻¹ of β-carotene in mineral matrices (halite, epsomite) was detected when analyzed through the monocrystal of gypsum and epsomite, respectively. These results will aid both in-situ analyses on Mars and sample analyses on Earth.     

Combined Sr,Nd, Pb and Li isotope geochemistry of alkaline lavas from northern James Ross Island (Antarctic Peninsula) and implications for back-arc magma formation

We present a comprehensive geochemical data set for a suite of back-arc alkaline volcanic rocks from James Ross Island Volcanic Group (JRIVG), Antarctic Peninsula. The elemental and isotopic (Sr, Nd, Pb and Li) composition of these Cenozoic basalts emplaced east of the Antarctic Peninsula is different from the compositions of the fore-arc alkaline volcanic rocks in Southern Shetlands and nearby Bransfield Strait. The variability in elemental and isotopic composition is not consistent with the JRIVG derivation from a single mantle source but rather it suggests that the magma was mainly derived from a depleted mantle with subordinate OIB-like enriched mantle component (EM II). The isotopic data are consistent with mantle melting during extension and possible roll-back of the subducted lithosphere of the Antarctic plate. Magma contamination by Triassic–Early Tertiary clastic sediments deposited in the back-arc basin was only localized and affected Li isotopic composition in two of the samples, while most of the basalts show very little variation in δ⁷Li values, as anticipated for “mantle-driven” Li isotopic composition. These variations are difficult to resolve with radiogenic isotope systematics but Li isotopes may prove sensitive in tracking complex geochemical processes acting through the oceanic crust pile, including hydrothermal leaching and seawater equilibration.     

Origin of the Zálesí U–Ni–Co–As–Ag/Bi deposit,Bohemian Massif,Czech Republic: fluid inclusion and stable isotope constraints

The Zálesí vein-type deposit is hosted by Early Paleozoic high-grade metamorphic rocks on the northern margin of the Bohemian Massif. The mineralization is composed of three main stages: uraninite, arsenide, and sulfide. The mineral assemblages formed at low temperatures (~80 to 130°C, locally even lower) and low pressures (<100 bars). The salinity of the aqueous hydrothermal fluids (0 to 27 wt.% salts) and their chemical composition vary significantly. Early fluids of the oldest uraninite stage contain a small admixture of a clathrate-forming gas, possibly CO₂. Salinity correlates with oxygen isotope signature of the fluid and suggests mixing of brines [δ ¹⁸O around +2‰ relative to standard mean ocean water (SMOW)] with meteoric waters (δ ¹⁸O around −4‰ SMOW). The fluid is characterized by highly variable halogen ratios (molar Br/Cl = 0.8 × 10⁻³ to 5.3 × 10⁻³; molar I/Cl = 5.7 × 10⁻⁶ to 891 × 10⁻⁶) indicating a dominantly external origin for the brines, i.e., from evaporated seawater, which mixed with iodine-enriched halite dissolution brine. The cationic composition of these fluids indicates extensive interaction of the initial brines with their country rocks, likely associated with leaching of sulfur, carbon, and metals. The brines possibly originated from Permian–Triassic evaporites in the neighboring Polish Basin, infiltrated into the basement during post-Variscan extension and were finally expelled along faults giving rise to the vein-type mineralization. Cenozoic reactivation by low-salinity, low-δ ¹⁸O (around −10‰ SMOW) fluids of mainly meteoric origin resulted in partial replacement of primary uraninite by coffinite-like mineral aggregates.     

Eclipsing Binaries with Possible Light-Time Effect

The period changes of six eclipsing binaries have been studied with focus on the light-time effect. With the least squares method we also calculated parameters of such an effect and properties of the unresolved body in these systems. With these results we discussed the probability of presence of such bodies in the systems with respect to possible confirmation by another method. In two systems we also suggested the hypothesis of fourth body or magnetic activity for explanation of the "second-order variability" after subtraction of the light-time effect of the third body.     

Monthly, seasonal and annual temperature reconstructions for Central Europe derived from documentary evidence and instrumental records since AD 1500

Monthly temperature series for Central Europe back to AD 1500 are developed from documentary index series from Germany, Switzerland and the Czech Republic (1500–1854) and 11 instrumental temperature records (1760–2007). Documentary evidence from the Low Countries, the Carpathian Basin and Poland are used for cross-checking for earlier centuries. The instrumental station records are corrected for inhomogeneities, including insufficient radiation protection of early thermometers and the urban heat island effect. For overlapping period (1760–1854), the documentary data series correlate with instrumental temperatures, most strongly in winter (86% explained variance in January) and least in autumn (56% in September). For annual average temperatures, 81% of the variance is explained. Verification statistics indicate high reconstruction skill for most months and seasons. The last 20 years (since 1988) stand out as very likely the warmest 20-year period, accounting for the calibration uncertainty and decreases in proxy data quality before the calibration period. The new reconstruction displays a previously unobserved long-term decrease in DJF, MAM and JJA temperature variability over last five centuries. Compiled monthly, seasonal and annual series can be used to improve the robustness of gridded large-scale European temperature reconstructions and possible impact studies. Further improvement of the reconstruction would be achieved if documentary data from other European countries are further developed.