Pleistocene sandur rhythms,cycles and megacycles: Interpretation of depositional scenarios and palaeoenvironmental conditions

The Drawa sandur, which is the largest, coarse‐grained sandur in Poland, dates from the Pomeranian phase of the Weichselian glaciation (c. 16 ka BP). Using Markov chain analysis we infer that five cycles and five rhythms occur in its proximal part. The cycles dominated by Gt and St lithofacies in the lower part of the sandur succession and by a GDm lithofacies in the upper part, are fining‐upward cycles deposited in braided channels during large ablation floods. Three groups of cycles are distinguished based on their genesis: (i) cycles due to channel‐sheet evolution during large floods; (ii) cycles due to braid‐bar development during initial and advanced diminishing of floods; and (iii) cycles developed in the thalweg or interbar channels. The succession as a whole forms a large‐scale coarsening‐up megacycle (‘sandur megacycle’) which corresponds to a phase of ice‐sheet advance. Because the cyclicity was evident from Markov chain analysis of the sedimentary succession, we suggest that this statistical tool is valuable for reconstruction of glacifluvial sedimentary conditions, particularly as it can shed new light on the palaeogeographical development of sandar.     

Water chemistry and hydrometeorology in a glacierized catchment in the Polar Urals,Russia

This study aims to determine the relationships between local meteorological conditions,proglacial river discharge and biogeochemical processes operating in a periglacial basin located in the Polar Ural mountain range, Russia. Fieldwork was conducted in the catchment of Obruchev Glacier(13 km2) during the summer peak flow period in 2008. River discharge was dominated by snowmelt and changed from 3300 l s-1 to less than 1000 l s-1. The mean daily air temperatures of stations situated in the mountain tundra and near Obruchev Glacier from July 11 th to August 1st 2008 were 14.4°C and 10.3°C, respectively. The glacial river had low total dissolved solids varying from 4.5 to 9 mg l-1 and coefficients of correlation between Na+ and Cl-, K+ and Cl-, as well as NH4+ and Cl- were 0.94, 0.90 and 0.84, respectively. Rainfall events affected the snowmelt initiation and provided an essential part of the discharge during the intense snowmelt period, which occurred from July 11 th to July 18 th 2008. Data showed that Na+ and K+ in the surface water derived from snowmelt rather than chemical weathering of silicates. Also, it was obtained that NO3- derived from the melting snowpack, whereas ammonification occurring under the snowpacks was the primary source for NH4+.     

Short and medium term dynamics of the carbon exchange between the Baltic Sea and the North Sea

A detailed analysis of the short and medium term dynamics of the carbon exchange between the Baltic Sea and the North Sea is presented. To quantify the carbon fluxes distinguishing the Baltic and North Sea water masses, the salinity-based End Members (EM) method was successfully applied. The results of 0.63±0.25×10¹² mol C year⁻¹ identify the Baltic Sea as a net source of carbon for the North Sea. Dissolved organic carbon (DOC) was found to contribute significantly (22%) to the bulk of exported carbon. The levels determined suggest the hydrology-dependence of the carbon fluxes in the Danish Straits, which stimulates the high variability of carbon fluxes at both interseasonal and interannual scales.     

Enzymatic activities in spermatozoa and butyltin concentrations in Baltic turbot (Scophthalmus maximus)

Spermatozoal enzymes of fish (NAD+- and NADP-dependent dehydrogenases and creatine kinase (CK)) were previously determined to be sensitive to tributyltin (TBT) in laboratory experiments and were thus indicated for use as biomarkers for TBT exposure. However, the potential ability of spermatozoal enzymes as biomarkers of TBT exposure has never been recapitulated in a field study. For this purpose, the kinetic activities of spermatozoal enzymes of the natural turbot Scophthalmus maximus population from the Gulf of Gdańsk (GDA) and the Pomeranian Bay (POM) in the southern Baltic Sea were measured. Gas chromatography/high-resolution mass spectrometry was used to determine the concentrations of TBT and its breakdown products, dibutyltin (DBT) and monobutyltin (MBT), in the muscle, liver and testes of the male turbot. Males from GDA had significantly higher enzymatic activities and butyltin (BT) content in tissues than those from POM. A general linear model (GLM) showed that lactate dehydrogenase (LDH), malate dehydrogenase (MDH), glucose-6-phosphate dehydrogenase (G6PDH) and CK activities increased significantly with BT concentration in the testes and liver. We indicate the potential effects of TBT pollution on the spermatozoal enzymes of Baltic turbot.     

Volume and mass distribution in selected asteroid families

The main focus of this paper is calculation of the diameters of asteroids belonging to five families (Vesta, Eos, Eunomia, Koronis, and Themis). To do that, we used the HCM algorithm applied for a data set containing 292,003 numbered asteroids, and a numerical procedure for choosing the crucial parameter of the HCM, called “the cutting velocity” v_cut. It was established with a precision as high as 1 m s^?1. Thereafter, we used the WISE (Wide‐field Infrared Survey Explorer) catalog to set a range of albedo for the largest members of each family considered. The albedo data were supported by the data concerning color classification (SDSS MOC4). The asteroids with albedo out of this range were classified as interlopers and were therefore disqualified as family members. Sizes were calculated for the asteroids with albedo within the acceptable range. For the other asteroids (those chosen by means of the HCM, but with albedo not listed in the WISE), the value of albedo of the largest member of the family was adopted. Results are given in a set of figures showing the families on the planes (a, e), (a, i), (e, i). Diameters and volumes of the asteroids that are the individual members of a family were calculated on the basis of their known or assumed albedo and on their absolute magnitude. Volumes of the parent bodies of the families were found on the basis of the cumulative volume distribution of these families. We also studied the secular resonances of the family members. We have shown that the locations of members of the considered asteroid families are related to the lines of secular resonances z₁, z₂, and z₃ with Saturn.     

Convection driven by tidal and radiogenic heating in medium size icy satellites

Convection is one of the most important processes responsible for the formation of the surface features on many planetary bodies. Observations of some icy satellites indicate that the satellites’ surfaces are modified due to the internally driven tectonic activity. The tidal heating could be an important source of energy responsible for such internal activity. This suggestion is supported by the correlation of the tidal parameter ψ and tectonic features. Consequently, the tidal and the radiogenic heat sources seem to be of primary importance for the medium size icy satellites. Our research deals with convection in a non-differentiated body. The convection is a results of both uniform radiogenic heating and non-uniform and non-spherically symmetric tidal heating. To investigate the problem a 3D model of convection is developed based on the Navier-Stokes equation, the equation of thermal conductivity, the equation of continuity, and the equation of state. The 3D formulae for the tidal heat generation based on the results of Peale and Cassen [1978. Icarus 36, 245-269] and others are used in the model. To measure the relative importance of radiogenic heating versus tidal heating a dimensionless number C_t is introduced. The systematic investigation of a steady-state convection is performed for different values of the Rayleigh number and for the full range of C_t. The results indicate that for low and moderate value of the Rayleigh number, convection pattern driven by the tidal heating and by the radioactivity in the medium size icy satellites consists of one cell or of two cells. For C_t>0 the critical value of Rayleigh number Ra_cr=0. The one-cell pattern is specific for low Rayleigh numbers but it could be observed for the full range of number C_t. It means that the pattern of convection does not fully follow the pattern of heating. This rather unexpected result could be of great importance for the final stage of convection. All patterns of tidally driven convection are oriented with respect to the direction to the planet. For two-cell patterns the regions of downward motion are situated in the centers of the near and far sides of the satellite, respectively.     

Sticking in moderate velocity oblique impact: Application to planetology

The sticking behavior of metal—metal collisions in the velocity range ～50–650 m/sec—has been investigated experimentally. A map of sticking efficiency versus impact angle and impact velocity has been established for lead. The threshold sticking velocity for normal impact equals approximately 100 m/sec for lead, 140 m/sec for tin, and 500 m/sec for iron in the case of spherical projectiles of 8-mm diameter, and a semi-infinite target. The boundary between the plastic rebound area and the perfect sticking area is found to be a line of constant normal velocity. The case when projectile mass is equal to target. ass ($\text{?3}\text{g}$, lead) has been investigated as well. The experimental results have been extrapolated to higher temperature and then applied to iron, nickel, and magnesium silicate. Near the melting point ($\text{?1800°}\text{K}$), the sticking velocities were estimated as 250–350 m/sec for iron and nickel and about 40% higher for magnesium silicate. It was concluded that metals stick more easily than rocky materials because of their lower sticking velocity and much larger interval of temperature over which sticking is possible.     

Evolution of depressions on Comet 67P/Churyumov-Gerasimenko: Role of ice metamorphism

This work is intended to investigate the influence of temperature-dependent metamorphism of ice on the shape of small depressions in the surface of cometary nuclei. We are mainly interested in the role of initial cohesivity of a nucleus. For this purpose we simulate sublimation of ice from the facets of initially cylindrical depressions in ice of different initial structure. The simulations account for the diurnal and orbital changes of insolation and its dependence on the current shape of the depressions. Our model includes heat transport in the cometary material and metamorphism of ice. We present the results obtained for the nucleus of the Comet 67P/Churyumov-Gerasimenko, target of the ESA cornerstone mission Rosetta.