Crustal structure in the Carpatho-Pannonian region: insights from three-dimensional gravity modelling and their geodynamic significance

A three-dimensional gravity modelling of the Carpatho-Pannonian region was carried out to get a better image of the Moho boundary and the most prominent intra-crustal density heterogeneities. At first, only the major density boundaries were considered: the bottom of the Tertiary basin fill, the Moho discontinuity and the lithosphere to asthenosphere boundary. Density contrasts were represented by relative densities. The improved density model shows a transitional unit of high density at the base of the crust along the Teisseyre-Tornquist Zone. In the Western Carpathians, an extensive, relatively low-density unit was inferred in mid-crustal levels. The border zone between the Southern Carpathians and the Transylvanian basin is characterized by a sharp, step-like contact of the two crustal units. The Moho configuration reveals important information on the tectonic evolution of the region. Zones of continental collision are represented by thick Moho roots (Eastern Alps, Eastern Carpathians). Transpressional orogenic segments, however, are different: in the Western Carpathians, the Moho is a flat surface; in the Dinarides, a medium Moho root is observed; the Southern Carpathians are characterized by a thick crustal root. The differences are explained with the presence or absence of “subductible” oceanic crust along the Carpathians during the extrusion of Pannonian blocks.     

Temporal trends of mercury in marine biota of west and northwest Greenland

Temporal trends in mercury concentrations ([Hg]) during the last two to three decades were determined in liver of shorthorn sculpin, ringed seal and Atlantic walrus from northwest Greenland (NWG, 77 degrees N) and in liver of shorthorn sculpin and ringed seal from central west Greenland (CWG, 69 degrees N) during the last decade. Stable-nitrogen (delta(15)N) and carbon (delta(13)C) isotope values were determined in muscle of ringed seals to provide insight into potential trophic level changes through time. Log-linear regressions on annual median [Hg] did not reveal any temporal trend in shorthorn sculpin from CWG and NWG and walrus from NWG. In ringed seals from NWG, an increase in [Hg] of 7.8% per year was observed. When based on delta(15)N-adjusted [Hg] this rate increased to 8.5% but was still non-significant. In ringed seal from CWG no trend was found in [Hg] during the period 1994-2004. However, during the last part of the period (1999-2004) the [Hg] increased significantly. Including tissue delta(15)N values as a covariate had a marked effect on these results. The annual changes in delta(15)N-adjusted [Hg] was estimated to -5.0% for the whole period and 2.2% during the last 5 years compared to -1.3% and 12.4%, respectively, for the non-adjusted [Hg].     

Modeling aggregated expertise of user contributions to assess the credibility of OpenStreetMap features

The emergence of volunteered geographic information (VGI) during the past decade has fueled a wide range of research and applications. The assessment of VGI quality and fitness‐of‐use is still a challenge because of the non‐standardized and crowdsourced data collection process, as well as the unknown skill and motivation of the contributors. However, the frequent approach of assessing VGI quality against external data sources using ISO quality standard measures is problematic because of a frequent lack of available external (reference) data, and because for certain types of features, VGI might be more up‐to‐date than the reference data. Therefore, a VGI‐intrinsic measure of quality is highly desirable. This study proposes such an intrinsic measure of quality by developing the concept of aggregated expertise based on the characteristics of a feature's contributors. The article further operationalizes this concept and examines its feasibility through a case study using OpenStreetMap (OSM). The comparison of model OSM feature quality with information from a field survey demonstrates the successful implementation of this novel approach.     

Mid‐ and late‐Holocene climatic changes: a test of periodicity and solar forcing in proxy‐climate data from blanket peat bogs

A wide range of palaeoenvironmental evidence from the Holocene has suggested periodicities in the Earth's climate of 10s to 1000s of years. Identifying these millennial‐, century‐ and decadal periodicities, and their impacts, is critical in developing a fuller understanding of natural climate variability. Any solar‐induced climatic change needs to be distinguished from other causes of natural climate variability and from short‐term catastrophic events induced either by external or internal processes. Such events might themselves generate a periodicity, or in combination with other forcing factors they may contribute towards a periodicity (and so spuriously imply a universal and continuing periodicity in the climate record), or they may resonate with a solar‐induced periodicity. Here, evidence from peat records for periodicity in climate change over the mid to late Holocene is reviewed and this is followed by a test of the replicability of claimed periodicities using blanket peat data covering the past 2000 yr from four sites in the British Isles. Results suggest that the mires studied do go through phases of being responsive to periodic forcing factors, with ca. 200, ca. 80 and 60–50 yr wavelengths reflected in some data sets. However, the patterns shown are not consistent. This could be the result of local conditions at individual mires (human impact, sensitivity and vegetation succession) or of changes in the strength or nature of global forcing factors. Assessing a solar–mire link remains difficult because the century‐scale variations of the Sun show different intervals between solar minima, the durations of which are themselves unequal, and because the proxy‐climate data‐sets from peat profiles may themselves not be dated with sufficient precision and/or accuracy. Copyright © 2001 John Wiley & Sons, Ltd.     

A generalized set of discrete frequency distributions with Fortran program

Geologists unfamiliar with the application of probability theory to discrete data in other fields of research are usually acquainted with only three discrete theoretical frequency distributions: Poisson, binomial, and negative binomial distributions. In some situations these distributions may fail to adequately describe a set of experimental data. Other distributions such as the Poisson with zeros, Neyman type A, logarithmic with zeros, Poisson-binomial, and Thomas double Poisson together with the more common Poisson, binomial, and negative binomial form a generalized subset of discrete theoretical distributions, one of which should fit almost any experimental data set. A computer program is presented which allows testing of any combination of these distributions against observed discrete data.     

White light events as photospheric flares

We consider the possibility that white light flares are due to heating of the photosphere by a flux of energetic ions and electrons impinging on it from above. Particles with energy in the range 10 MeV to 1 BeV release most of their energy to the ambient gas at about optical depth unity in the photosphere. This increase in energy produces a temperature perturbation of several hundred degrees in the layer and results in a re-radiation of the energy with a radiative relaxation time of several seconds. The consequences of this model are applied to a study of the great flare of May 23, 1967 and to the very fast event of August 11, 1954. Large numbers of very energetic electrons or protons must be produced in the first few minutes of the primary flare event if our interpretation (or one based on synchrotron emission) is correct.After this paper had been submitted and accepted for publication we received from Dr. vestka a copy of his paper, The Phase of Particle Acceleration in the Flare Development, which was then already in proof. (It appeared in Solar Phys. 13, 471.) A number of the arguments contained in our paper, which we had previously presented in abstract form (Najita and Orrall, 1969) and in part in a dissertation (Najita, 1969), are independently discussed by Dr. vestka who was unaware of our earlier work. Although the ground covered by his and our paper touches in places we have left our paper as originally submitted and believe that this independent agreement supports the conclusions of both.