Global multi-layer network of human mobility

Recent availability of geo-localized data capturing individual human activity together with the statistical data on international migration opened up unprecedented opportunities for a study on global mobility. In this paper, we consider it from the perspective of a multi-layer complex network, built using a combination of three datasets: Twitter, Flickr and official migration data. Those datasets provide different, but equally important insights on the global mobility – while the first two highlight short-term visits of people from one country to another, the last one – migration – shows the long-term mobility perspective, when people relocate for good. The main purpose of the paper is to emphasize importance of this multi-layer approach capturing both aspects of human mobility at the same time. On the one hand, we show that although the general properties of different layers of the global mobility network are similar, there are important quantitative differences among them. On the other hand, we demonstrate that consideration of mobility from a multi-layer perspective can reveal important global spatial patterns in a way more consistent with those observed in other available relevant sources of international connections, in comparison to the spatial structure inferred from each network layer taken separately.     

Multiple drivers of Holocene lake level changes at a lowland lake in northeastern Germany

Many German lakes experienced significant water level declines in recent decades that are not fully understood due to the short observation period. At a typical northeastern German groundwater‐fed lake with a complex basin morphology, an acoustic sub‐bottom profile was analysed together with a transect of five sediment cores, which were correlated using multiple proxies (sediment facies, μ‐XRF, macrofossils, subfossil Cladocera). Shifts in the boundary between sand and mud deposition were controlled by lake level changes, and hence, allowed the quantification of an absolute lake level amplitude of ~8 m for the Holocene. This clearly exceeded observed modern fluctuations of 1.3 m (AD 1973–2010). Past lake level changes were traced continuously using the calcium‐record. During high lake levels, massive organic muds were deposited in the deepest lake basin, whereas lower lake levels isolated the sub‐basins and allowed carbonate deposition. During the beginning of the Holocene (>9700 cal. a BP), lake levels were high, probably due to final melting of permafrost and dead‐ice remains. The establishment of water‐use intensive Pinus forests caused generally low (3–4 m below modern) but fluctuating lake levels (9700–6400 cal. a BP). Afterwards, the lake showed an increasing trend and reached a short‐term highstand at c. 5000 cal. a BP (4 m above modern). At the transition towards a cooler and wetter late Holocene, forests dominated by Quercus and Fagus and initial human impact probably contributed more positively to groundwater recharge. Lake levels remained high between 3800 and 800 cal. a BP, but the lake system was not sensitive enough to record short‐term fluctuations during this period. Lake level changes were recorded again when humans profoundly affected the drainage system, land cover and lake trophy. Hence, local Holocene water level changes reflect feedbacks between catchment and vegetation characteristics and human impact superimposed by climate change at multiple temporal scales.     

The Influence of Selected Meteorological Parameters on the Concentration of Surface Ozone in the Central Region of Poland

Abstract?This paper presents the results of measurements of the concentration of surface ozone and concurrent standard meteorological parameters: total solar radiation, temperature, relative humidity, pressure, wind speed, and vertical and horizontal components of the wind. The data were collected from 2005 to 2010 at stations located in central Poland (Mazowieckie voivodeship): Warszawa (urban), Legionowo (suburban), Granica and Belsk (rural). Furthermore, Granica is situated in the forested area of Kampinoski National Park. Continuously measured surface ozone concentrations demonstrated the well-known diurnal cycle of surface ozone concentration with a maximum in the afternoon and a minimum in the early morning hours. The averaged diurnal variations over six years reveal that the highest concentrations appear at rural stations (Belsk: 55?µg?m^?3 and Granica: 50?µg?m^?3) and the lowest at the urban station (Warszawa: 41?µg?m^?3). The threshold for high levels of surface ozone (120?µg?m^?3 per 8?h) was exceeded most often at Granica and Belsk. The occurrence of the ozone “weekend effect,” especially at urban stations, has been identified. The difference between weekend and weekday surface ozone concentrations at urban and rural stations was as high as 6.5?µg?m^?3 and approximately 2?µg?m^?3, respectively. Using appropriate statistical tools, it has been shown that meteorological conditions have a significant influence on ozone concentration. High correlation coefficients were found between ozone concentration and solar radiation, temperature, relative humidity, and wind speed. The forward stepwise regression model explains up to 75% of the variations in daily surface ozone concentration in terms of meteorological variability in summer and up to 70% in winter. At the same time, a multilayer perceptron neural network model was used to reconstruct the concentration of surface ozone. High correlation coefficients (up to 0.89) indicate that, on the basis of standard meteorological parameters and NO₂ concentration, we can determine ozone concentration with high accuracy.     

Thermo-mechanical facies representative of fast and slow flowing ice sheets: the Weichselian ice sheet,a central west Poland case study

This study deals with an issue of thermo-mechanical facies, reflecting specific thermal and mechanical properties of the subglacial environment. The main objective of this study was to develop a model of glacitectionic deformation and its sedimentary record beneath fast and slow flowing ice sheets, based on investigations conducted in Wielkopolska (west central Poland). Sedimentary structures, mainly at the contact between subglacial tills and glacifluvial sediments, were recognized to delineate typical facies associations in a Weichselian glacigenic succession. Each association was interpreted as a record of the different depositional environments related to different subglacial conditions. Those investigations suggest the substratum was composed of frozen and dry, and wet and mobile spots, and four thermo-mechanical facies were distinguished: A – is representative of slower ice flow, dry and cold subglacial conditions, where driving stresses and normal effective pressure were high; B – is also related to slow ice flow and occurrence of cold subglacial permafrost, but with little amount of unfrozen water (however, higher than in facies A), with similar physical characteristics of the ice sheet as facies A; thermo-mechanical facies C and D represent wet and warm ice sole, with low normal effective pressure and driving stresses, thus lowering sediments’ shear strength and enabling high ice-flow velocities. We suggest that these facies have specific and non-random location, thereby revealing the relationship between subglacial thermo-mechanical conditions and ice sheet dynamics. Slow moving, cold-based ice occurred along ice sheet margins and inter-stream areas, whereas fast-moving, warm-based, well-lubricated ice, was typical of the axial parts of ice streams.     

Long-Term Ozone Changes Over the Northern Hemisphere Mid-Latitudes for the 1979–2012 Period

Abstract

The solar backscattered ultraviolet (SBUV/SBUV-2) merged ozone datasets, version 8.6, including column ozone and ozone profiles for the 1979–2012 period are examined for the 35°N–60°N zonal belt in the northern hemisphere mid-latitudes and four sub-regions: central Europe, continental Europe, North America, and East Asia. The residual long-term patterns for total ozone and ozone profiles are extracted by smoothing the time series of differences between the original and the modelled ozone time series. Modelled ozone is obtained using the standard trend model accounting for ozone variability due to changes in stratospheric halogens and various dynamical factors commonly used in previous ozone trend analyses. Since about 2005 spring and summer total ozone in the troposphere and lower stratosphere has decreased in some regions (central and continental Europe, North America, and the 35°N–60°N zonal belt) compared with modelled ozone. The negative departure from modelled ozone in 2010 is approximately 2–3% of the overall 1979–2012 monthly mean level. It seems that this decrease is a result of yet unknown dynamical processes rather than to chemical destruction because the differences have a longitudinal structure, and total ozone in the upper stratosphere still follows changes in stratospheric halogen loading.     

Intraspecific Variability and Problematic Dimorphism in the Early Cretaceous (Valanginian) Ammonite Saynoceras verrucosum (d’Orbigny, 1841)

The population of Saynoceras verrucosum (d’Orbigny) from the Polish basin (W?wa? section, central Poland) shows no significant intraspecific variability. Dimorphism has not been found in this population. Statistical analyses of material from the shallow epicratonic Polish basin and the relatively deep Vocontian basin (southeastern France) indicated two populations. Forms from the Polish basin are somewhat more inflated and smaller than forms from the Vocontian basin.     

Holocene climate vs. catchment forcing on a shallow,eutrophic lake in eastern Poland

This paper presents a sedimentary record from Lake ?ukie located in the southeastern part of the Central European Plain, beyond the reach of the maximum extent of the last glaciation. The lake has thermokarstic origin and developed during the last glacial termination due to subsidence of the sub‐Quaternary carbonate basement triggered by permafrost thawing. A sediment core was investigated to reconstruct water trophic state and lake depth changes during the Holocene. We aimed at showing the relationship between ecological and geochemical changes in the lake and regional/supraregional climatic and hydrological trends throughout the Holocene. Results of subfossil Cladocera analysis were combined with data on the geochemistry and stable C and O isotopes in sedimentary carbonates. Isotopic and geochemical proxies helped to detect sources of sedimentary particles in the lake and thus to reconstruct changes in the intensity of atmospheric and catchment processes (e.g. precipitation and surface runoff). The Cladocera analysis results indicated endogenic processes in the lake such as trophic changes. Our data revealed that Lake ?ukie has always been a rather eutrophic water body and the periods of particularly high productivity were in the lower Preboreal and upper Subatlantic. Periods of increased water depth were recorded in the lower Preboreal, lower Boreal and upper Subboreal, whereas low water stands were obtained during the late Preboreal, late Boreal, late Atlantic and Atlantic/Subboreal transition as well as during the lower Subboreal. The sediment succession from Lake ?ukie provides the first full Holocene record of carbon and oxygen stable isotopes in lacustrine carbonates from the eastern part of the Central European Lowland. The record is characterized by uncommonly high δ¹³C and δ¹⁸O values of the carbonates resulting from a combination of within‐lake processes and dissolution of the carbonate bedrock of Cretaceous age. The impact of the old carbonates on isotope values was helpful in the reconstruction of the catchment forcing on the lake.