The southern margin of the East European Craton: new results from seismic sounding and potential fields between the North Sea and Poland

The extension of eastern Avalonia from Britain through the NE German Basin into Poland is, in some sense, a virtual structure. It is covered almost everywhere by late Paleozoic and younger sediments. Evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks. During the last two decades, much geophysical and geological information has been gathered since the European Geotraverse (EGT), which was followed by the BABEL, LT-7, MONA LISA, DEKORP-Basin'96, and POLONAISE'97 deep seismic experiments. Based on seismic lines, a remarkable feature has been observed between the North Sea and Poland: north of the Elbe Line (EL), the lower crust is characterised by high velocities (6.8–7.0 km/s), a feature which seems to be characteristic for at least a major part of eastern Avalonia (far eastern Avalonia). In addition, the seismic lines indicate that a wedge of the East European Craton (EEC) (or Baltica) continues to the south below the southern Permian Basin (SPB)—a structure which resembles a passive continental margin. The observed pattern may either indicate an extension of the Baltic crust much farther south than earlier expected or oceanic crust of the Tornquist Sea trapped during the Caledonian collision. In either case, the data require a reinterpretation of the docking mechanism of eastern Avalonia, and the Elbe–Odra Line (EOL), as well as the Elbe Fault system, together with the Intra-Sudedic Faults, appear to be related to major changes in the deeper crustal structures separating the East European crust from the Paleozoic agglomeration of Middle European terranes.     

Seasonal variation of average phytoplankton concentration in the Kattegat—a periodical point model

Seasonal variations in primary production, phytoplankton biomass, chlorophyll-a, dissolved inorganic phosphorus and nitrogen concentrations in the upper 10 m of the Kattegat were analysed by means of monitoring data from 1993–1997. Spatial optimal analysis, based on a stochastic model, was used to reconstruct weekly constituent fields onto a spatial grid. The reconstructed fields were spatially integrated, resulting in a relatively smooth seasonal variability of the average variables. A simple dynamical model, set up as a periodical boundary problem, is suggested for the average phytoplankton concentration, dissolved inorganic nitrogen and entrainment depth as state variables. The model is forced by the solar radiation, nitrogen load from the land sources and atmosphere as well as by nitrogen supply from the lower nutrient-rich layer. The latter process is modelled proportional to the water entrainment into the upper euphotic layer and is driven by atmospheric forcing, river runoff and the Baltic water inflow. Four model coefficient values were fitted by minimising the root mean square difference between the integrated monitoring data and the model output. The suggested diagnostic model reflects the main features in seasonal variability of phytoplankton and nitrogen concentrations by average values, including the magnitude and timing of such dynamic events as the spring and late summer phytoplankton blooms. The importance of different forcing factors is quantified and estimates of unobserved components such as new primary production can be computed.     

New fjords,new coasts,new landscapes: The geomorphology of paraglacial coasts formed after recent glacier retreat in Brepollen (Hornsund,southern Svalbard)

Changes in the properties and dynamics of tidewater glacier systems are key indicators of the state of Arctic climate and environment. Calving of tidewater glacier fronts is currently the dominant form of ice mass loss and a major contributor to global sea-level rise. An important yet under-studied aspect of this process is transformation of Arctic landscapes, where new lands and coastal systems are revealed due to the recession of marine-terminating ice masses. The evolution of those freshly exposed paraglacial coastal environments is controlled by nearshore marine, coastal and terrestrial geomorphic processes, which rework glacial-derived sediments to create new coastal paraglacial landforms and landscapes. Here, we present the first study of the paraglacial coasts of Brepollen, one of the youngest bays of Svalbard revealed by ice retreat. We describe and classify coastal systems and the variety of landforms (deltas, cliffs, tidal flats, beaches) developed along the shores of Brepollen during the last 100 years. We further discuss the main modes of sediment supply to the coast in different parts of the new bay, highlighting the fast rate of coastal transformation as a paraglacial response to rapid deglaciation in the Arctic. This study provides an exemplar of likely coastal responses to be anticipated in similar tidewater settings under future climate change. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

On the origin of seasonal variation of aerosol optical thickness in UV range over Belsk,Poland

Aerosol optical thickness (AOT) and seasonal variation of AOT over Belsk, Poland, in the UV wavelength range (310–380 nm) have been analysed using results of measurements by Brewer spectrophotometer No. 064 and Cimel sunphotometer data for the 2002–2007 period. The comparison of AOT derived from direct Sun measurements by Brewer spectrophotometer in the 310–320 nm range and retrieved from Cimel measurements at longer wavelengths shows good correlation (R = 0.96), with overestimation of retrieved values compared to the measured ones by about 6%. Basing on aerosol microphysical properties taken from almucantar retrievals and Mie theory, optical properties of aerosol in the UV range has been calculated. Analysis of seasonal variation of AOT at Belsk reveals two maxima: in April and July–August. Analysis of back-trajectories in conjunction with analysis of fire maps from Fire Information For Resource Management System shows that these seasonal maxima are connected with seasonal biomass burning in Eastern and Southern Europe.     

Free core nutation period inferred from the gravity measurements at Józefosław

The Free Core Nutation (FCN) is an important eigenmode which affects both Earth rotation and body tide. The FCN parameters, the resonance period and the quality factor are important for understanding the dynamics of the Earth at nearly diurnal periods. Those parameters are usually estimated either from the Very Long Baseline Interferometry (VLBI) observations of nutation, or from the tidal gravity measurements. In this paper we investigate the determination of the FCN parameters from gravity records covering a period of more than three years, collected with the use of a LaCoste&Romberg Earth Tide no. 26 gravimeter, located at Józefos?aw observatory near Warsaw. From the resonant enhancements of gravimetric factors and phases of diurnal tidal gravity waves, we could infer the FCN period to be equal to 430 sidereal days. This result is in very good agreement with previous gravimetric and VLBI nutation results, confirming the discrepancy in the dynamic flattening of the outer liquid core from its theoretical value based on the hydrostatic equilibrium assumption. The estimated FCN quality factor (Q ≈ 1300) is considerably smaller than the VLBI nutation result, which confirms that the local gravity measurements are more sensitive than VLBI global analyses to site-dependent phenomena (such as atmospheric and indirect ocean tidal effects). We also investigated the importance of gravimetric corrections in the FCN analysis, including numerical tests and simulations. This allowed us to estimate the uncertainty of FCN parameters due to improper or incomplete set of environmental corrections. We took also into account the impact of gravimetric factor errors and tidal wave selection on estimated FCN parameters. We demonstrated that despite relatively noisy measurements due to unfavorable gravimeter location, we were able to obtain very good results in case when proper correction and tidal wave selection were applied.     

Analysis of particulate matter concentrations in mazovia region, central poland, based on 2007–2010 data

Measurement results of PM10 (particulate matter with diameters below 10 μm) concentrations performed at four stations in central Poland (2007–2010) were analyzed in terms of levels and distributions of concentrations, the number of exceedances of the limit values and the causes of these exceedances. PM10 levels were similar at suburban and rural stations, except of one station located in the vicinity of a busy street. The median of PM10 concentration ranged from 26 μg/m³ at suburban station to 44 μg/m³ at Warsaw Kerb station. Seasonal variability analysis of PM10 concentration revealed an additional maximum beyond the usual autumn-winter one. This maximum occurred in April at all stations, and corresponded to seasonal wildfires activity and dust activation in Eastern Europe. Cluster analysis of back-trajectories revealed that PM10 concentrations depend on the direction of advection of the incoming air; the highest values are registered for air of regional and southern origins, while the lowest are for the airmasses coming from the north and northwest direction.     

Mercury mobility and bioavailability in soil from contaminated area

The mobility and bioavailability of mercury in the soil from the area near a plant using elemental mercury for manufacturing thermometers, areometers, glass energy switches and other articles made of technical glass has been evaluated. Mercury has been determined by sequential extraction method and with additional thermo desorption stage to determine elemental mercury. The procedure of sequential extraction involves five subsequent stages performed with the solutions of chloroform, deionized water, 0.5 M HCl, 0.2 M NaOH and aqua regia. The mean concentration of total mercury in soil was 147 ± 107 μg g⁻¹ dry mass (range 62–393), and the fractionation revealed that mercury was mainly bound to sulfides 56 ± 8% (range 45–66), one of the most biounavailable and immobile species of mercury in the environment. The fractions that brought lower contribution to the total mercury content were semi-mobile humic matter 22 ± 9% (range 11–34) and elemental mercury 17 ± 5% (range 8–23). The contributions brought by the highly mobile and toxic organomercury compounds were still lower 2.3 ± 2.7% (range 0.01–6.5). The lowest contributions brought the acid-soluble mercury 1.5 ± 1.3% (range 0.1–3.5) and water-soluble mercury 1.0 ± 0.3% (range 0.6–1.7). The surface layer of soil (0–20 cm) was characterized by higher mercury concentrations than that of the subsurface soil (60–80 cm), but the fractional contributions were comparable. The comparison of mercury fractionation results obtained in this study for highly polluted soils with results of fractionation of uncontaminated or moderately contaminated samples of soil and sediments had not shown significant statistical differences; however, in the last samples elemental mercury is usually present at very low concentrations. On the basis of obtained correlation coefficients it seems that elemental mercury soils from “Areometer” plant are contaminated; the main transformation is its vaporization to atmosphere and oxidation to divalent mercury, probably mainly mediated by organic matter, and next bound to humic matter and sulfides.     

Method of predicting tremors on the basis of seismicemission registered in exploitation workings

A method of tremor risk estimation on the basis of seismic emission registered in mining exploitation zones is presented in this paper. A considerable part of the emission registered in these conditions, is generated by mechanical devices used in the mine (miner transporters etc.). Therefore, it is not possible to evaluate the risk of mining rock-bursts properly on the basis of interpretation of emission using known theories and models describing rock mass fracturing. In a new approach presented in this paper, the tremor risk is determined on the basis of time variation of a parameter describing the attenuation of seismic vibrations of the rock medium. The attenuation is assessed from the analysis of seismic emission registered in the frequency range from 30 Hz to 1000 Hz. Information about this parameter is encapsulated in the seismic emission regardless of the means of its generation. The method of estimating the temporal variations of attenuation is based on the analysis of signal envelopes of the microseismic emission. Attenuation trends can be interpreted in a straightforward way. As the stress values keep increasing, the following processes take place in the rock mass: compaction (hardening), dilatancy (softening), and then possibly tremors. At the compaction stage attenuation values are lower, while they increase at the dilatancy stage. This mechanism has been proven in practice. Our results can be used for monitoring tremor risk.     

Fluvial response to Holocene climate change in low‐order streams of central Mexico

Alluvial sequences constitute a recognised source of information on past environmental change, but one that has scarcely been tapped in central Mexico. This paper reviews what is currently known about the Holocene alluvial stratigraphy of the region, focusing on the interplay between climate and the pace and style of sedimentation in the incised headwater reaches of stream networks. The records obtained in five different drainage basins – four in the state of Tlaxcala and one in Guanajuato – are presented and compared to published reconstructions of climate change. A near‐synchronous incision of all stream networks occurred close to 10 200 ¹⁴C a BP in response to an increase in precipitation and stream discharge. A spell of very humid but markedly seasonal conditions ensued, resulting in the formation of wet meadows along streams and the accumulation of thick fine‐textured valley fills dominated by cumulic soil A horizons. After 9100 ¹⁴C a BP a transition to a warmer and more arid climate provoked the thinning of vegetation cover on slopes, accelerated runoff and increased sediment delivery to streams. The aggradation of coarser‐textured valley fills poor in organic matter set in. It ceased or slowed down significantly after a few millennia as the studied stream reaches achieved a near‐graded condition adjusted to the relatively stable climate. Arid mid Holocene conditions are also reflected in the abundant precipitation of secondary carbonates in Guanajuato. At 3100 ¹⁴C a BP higher precipitation caused more frequent flooding and a resumption of aggradation. Shortly after that date sedentary farmers colonised Tlaxcala. Agriculture altered runoff and sediment delivery to streams and accelerated cut‐and‐fill cycles on a scale that masked the impact of any climatic fluctuations. Guanajuato was colonised later and its alluvial record suggests the persistence of a humid climate at least until 1000 ¹⁴C a BP. Copyright © 2009 John Wiley & Sons, Ltd.