Stabilization versus decomposition in alpine ecosystems of the Northwestern Caucasus: The results of a tea bag burial experiment

Mountainous areas exhibit highly variable decomposition rates as a result of strong local differences in climate and vegetation type. This paper describes the effect of these factors on two major determinants of the local carbon cycle: litter decomposition and carbon stabilization. In order to adequately reflect local heterogeneity, we have sampled 12 typical plant communities of the Russian Caucasus. In order to minimize confounding effects and encourage comparative studies, we have adapted the widely used tea bag index (TBI) that is typically used in areas with low decomposition. By incubating standardized tea litter for a year, we investigated whether (1) initial litter decomposition rate (k) is negatively correlated with litter stabilization (S) and (2) whether k or S exhibit correlations with altitude and other environmental conditions. Our results show that S and k are not correlated. Altitude, pH, and water content significantly influenced the stabilization factor S, while soil-freezing had no influence. In contrast, none of these factors predicted the decomposition rate k. Based on our data, we argue that collection of decomposition rates alone, as is now common practice, is not sufficient to understand carbon input to soils and can potentially lead to misleading results. Our data on community-specific decomposition and stabilization rates further constrain estimates of litter accumulation in subalpine communities and the potential effects of climate change.     

Latitudinal and temporal shifts in the radial growth-climate response of Siberian larch in the Polar Urals

This paper presents a dendroclimatic analysis of Siberian larch trees sampled along a latitudinal 260-km transect located in the Polar Urals,Russia. Three standardised chronologies were built over a length of 230–293 years using 79 individual tree-ring chronologies collected in the southern,middle and northern parts of the Polar Urals.Bootstrapped correlation functions showed that the annual growth of the larches was mainly influenced by the air temperatures in June and July. The relative role of the temperatures increased from south to north. Daily air temperature data analysis revealed that the duration of the growing season in the northern part of the Polar Urals is 24 days less than that in the southern part. At the present time, air temperatures exceeded threshold of 8~℃, 5 days earlier than it did in the beginning of the 20 th century In response to the increase in the duration of the growing season and the changing winter conditions in the Polar Urals over the last 130 years, radial growth–temperature relationships in larches have weakened;this effect was strongly pronounced in the southern part of the Polar Urals.     

New induction sounding tested in Central Europe

The hourly data of nine geomagnetic observatories situated in Central Europe have been analyzed using the generalized magnetovariation (GMV) method designed recently for induction soundings of inhomogeneous media. In this method, impedance is one of transfer functions in the differential relation between spectra of the magnetic components and their derivatives. The peculiarity of this impedance is its correspondence to the magnetotelluric one estimated from the linear relations. Three transfer functions have been estimated simultaneously for data of geomagnetic observatories, using three different routines working in the period range from three hours up to two days. Noises in the source field components have been compared with noise in the estimated plane field divergence. The multivariate errors-in-variables method was used to extract spatially and temporally coherent geomagnetic field structure from the partially incoherent geomagnetic variations. This method allows estimating reliably impedances and gradient tippers for each observatory, taking into consideration the Earth’s sphericity. The obtained responses have been used for induction soundings and for detecting a deep inhomogeneity in the region.     

Bubble growth in visco-elastic magma: implications to magma fragmentation and bubble nucleation

We present a visco-elastic bubble growth model, accounting for viscous and elastic deformations and for volatile mass transfer between bubbles and melt. We define the borders between previous bubble growth models accounting for incompressible viscous melt, and our new model accounting also for elastic deformation; this is done by a set of end-member analytical solutions and numerical simulations. Elastic deformation is most prominent for magma of small vesicularity, where the growth regime depends on the shear modulus. For high shear modulus, bubble growth is slow and follows an exponential law in a viscous growth regime, while for low shear modulus bubbles quickly follow a square-root diffusive solution. Our model provides all the elastic components (stresses, strains and strain rates) required for defining criteria for failure and magma fragmentation. We suggest two failure criteria, a stress related one based on the internal friction and the Mohr-Coulomb failure theory, and a strain related one based on fibre elongation experiments. We argue that both criteria are equivalent if we consider their shear modulus dependency and its effect on magma rheology. Last, we apply our model to the process of bubble nucleation. In the incompressible case, following nucleation, growth is slow and leads to long incubation times during which bubbles may be dissolved back into the melt. The elastic response in magmas with low shear modulus results in a short incubation time, increasing the probability of survival. The above effects emphasize the significance of visco-elasticity for the dynamic processes occurring in magmas during volcanic activity.     

Classification of near-surface anomalies in the seismic refraction method according to the shape of the time–distance graph: A theoretical approach

Results obtained by SASW and PS-logging (in-hole) seismic techniques are compared with the relatively new ReMi (Refraction microtremor) method at a common site with a well-known soil profile: a recently constructed high-speed railway embankment. PS-logging is the most accurate technique in identifying the soil profile of the embankment followed by Re-Mi and SASW. Mean shear wave velocity estimations are also higher for PS-logging, followed by SASW and ReMi, while mean deviation is similar in each technique. The ReMi technique has provided very accurate results in the study of the embankment profile, which in addition to its high operability and its fast data processing, makes it a very convenient technique for extensive geotechnical surveys.     

Non-Fickian mass transport in fractured porous media

The paper provides an introduction to fundamental concepts of mathematical modeling of mass transport in fractured porous heterogeneous rocks. Keeping aside many important factors that can affect mass transport in subsurface, our main concern is the multi-scale character of the rock formation, which is constituted by porous domains dissected by the network of fractures. Taking into account the well-documented fact that porous rocks can be considered as a fractal medium and assuming that sizes of pores vary significantly (i.e. have different characteristic scales), the fractional-order differential equations that model the anomalous diffusive mass transport in such type of domains are derived and justified analytically. Analytical solutions of some particular problems of anomalous diffusion in the fractal media of various geometries are obtained. Extending this approach to more complex situation when diffusion is accompanied by advection, solute transport in a fractured porous medium is modeled by the advection-dispersion equation with fractional time derivative. In the case of confined fractured porous aquifer, accounting for anomalous non-Fickian diffusion in the surrounding rock mass, the adopted approach leads to introduction of an additional fractional time derivative in the equation for solute transport. The closed-form solutions for concentrations in the aquifer and surrounding rocks are obtained for the arbitrary time-dependent source of contamination located in the inlet of the aquifer. Based on these solutions, different regimes of contamination of the aquifers with different physical properties can be readily modeled and analyzed.     

An Anisotropic Cosmic-Ray Enhancement Event on 07-June-2015: A Possible Origin

A usual event, called anisotropic cosmic-ray enhancement (ACRE), was observed as a small increase (\({\leq}\,5\%\)) in the count rates of polar neutron monitors during 12?–?19 UT on 07 June 2015. The enhancement was highly anisotropic, as detected only by neutron monitors with asymptotic directions in the southwest quadrant in geocentric solar ecliptic (GSE) coordinates. The estimated rigidity of the corresponding particles is \({\leq}\,1\) GV. No associated detectable increase was found in the space-borne data from the Geostationary Operational Environmental Satellite (GOES), the Energetic and Relativistic Nuclei and Electron (ERNE) on board the Solar and Heliospheric Observatory (SOHO), or the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instruments, whose sensitivity was not sufficient to detect the event. No solar energetic particles were present during that time interval. The heliospheric conditions were slightly disturbed, so that the interplanetary magnetic field strength gradually increased during the event, followed by an increase of the solar wind speed after the event. It is proposed that the event was related to a crossing of the boundary layer between two regions with different heliospheric parameters, with a strong gradient of low-rigidity (\({<}\,1\) GV) particles. It was apparently similar to another cosmic-ray enhancement (e.g., on 22 June 2015) that is thought to have been caused by the local anisotropy of Forbush decreases, with the difference that in our case, the interplanetary disturbance was not observed at Earth, but passed by southward for this event.     

The first record of “spelaeoid” bears in Arctic Siberia

For a long time, “spelaeoid” (cave-bear-like) bears, Ursus (Spelearctos) spp., were believed to be almost purely European animals. Their geographic range has recently been extended to the east, in southern Siberia, Transbaikalia, Kirghizia, Mongolia and Korea. Two unexpected new findings, presented here in detail, significantly change existing views on the distribution of cave bears; both were found in North-Eastern Siberia, far beyond the Arctic Circle, more than 1500 km to the north-east of the previously accepted range.One of the fossils is a mandible, found near the town of Cherskiy at 68.73°N, 161.38°E. The analysis of local geology and accompanying mammal fossils suggests that it comes from the Olyorian Fauna (Early to early Middle Pleistocene). Morphologically, the Cherskiy mandible is closest to Ursus savini, a small middle Pleistocene cave bear from the British Cromer Forest-bed Formation, but differs in having a slightly more advanced dentition, and thus it is described as a new subspecies Ursus savini nordostensis. Another newly recognized fossil of the “spelaeoid” bear is an astragalus found at the Oskhordokh site at 67.54°N, 135.67°E, on a large gravel bar on the right bank of the Adycha River. This specimen is attributed to Ursus cf. deningeri.The paper also presents an interesting example of the interaction between classical and “molecular” palaeontology.The new finds significantly change existing ideas on the ecology and evolution of cave bears, some of the most remarkable members of the extinct Pleistocene megafauna.