Putative ice flows on Europa: Geometric patterns and relation to topography collectively constrain material properties and effusion rates

Europa's surface exhibits numerous small dome-like and lobate features, some of which have been attributed to fluid emplacement of ice or slush on the surface. We perform numerical simulations of non-Newtonian flows to assess the physical conditions required for these features to result from viscous flows. Our simulations indicate that the morphology of an ice flow on Europa will be, at least partially, influenced by pre-existing topography unless the thickness of the flow exceeds that of the underlying topography by at least an order of magnitude. Three classes of features can be identified on Europa. First, some (possibly most) putative flow-like features exhibit no influence from the pre-existing topography such as ridges, although their thicknesses are generally on the same order as those of ridges. Therefore, flow processes probably cannot explain the formation of these features. Second, some observed features show modest influence from the underlying topography. These might be explained by ice flows with wide ranges of parameters (ice temperatures >230 K, effusion rates >10⁷ m³ year⁻¹, and a wide range of grain sizes), although surface uplift (e.g., by diapirism) and in situ disaggregation provide an equally compelling explanation. Third, several observed features are completely confined by pre-existing topographic structures on at least one side; these are the best known candidates for flow features on Europa. If these features resulted from solid-ice flows, then temperatures >260 K and grain sizes <2 μm are required. Such small grain sizes seem unlikely; low-viscosity flows such as ice slurries or brines provide a better explanation for these features. Our results provide theoretical support for the view that many of Europa's lobate features have not resulted from solid-ice flows.     

Maximum growth rates of magnetoatmospheric instabilities

Simple bounds on the growth rates of magneto-atmospheric instabilities are derived, both for perturbations along and perpendicular to a horizontal magnetic field. The physical significance of a singular level for stable modes is briefly discussed.     

Abnormal features of Macoma balthica (Bivalvia) in the Baltic Sea: alerting symptoms of environmental adversity?

Recent studies of the Baltic clam Macoma balthica (L.) from the southern Baltic (the Gulf of Gdansk) have revealed striking morphological, histological and cytogenetic features. Strong deformation of the shell, including elongation of the posterior end and the appearance of an easily visible flexure in this part, has been recorded. The population contribution of the deformed blunt shelled ("irregular") clams ranged from 0% to 65% and tended to increase with depth. The morphologically "irregular" clams had higher accumulated tissue concentrations of trace metals (As, Ag, Cd, Pb, Cu and Zn), indicating a different metal handling ability. Adverse conditions in deeper water regions of the Gulf (e.g. hypoxia, hydrogen sulphide, elevated bioavailability of contaminants) have been suggested as inducers of the phenotypical changes (morphological deformation) in part of the population and, in parallel, of the specific physiological adaptations that result in higher metal accumulation in the "irregular" clams. Cytogenetic and histological analyses showed the presence of tumours in gill cells and digestive system of the affected clams, the prevalence of disseminated neoplasia ranging from 0% to 94% depending on the site. The disease was manifested by a modified karyotype (i.e. an abnormal number and morphology of chromosomes), a higher activity of nucleolar organizer regions (AgNORs), and tissue lesions (enlarged cells, actively proliferative with pleomorphic nuclei). Bottom sediments showed acute toxicity and have been proposed as a source of an initialising carcinogenic factor. However, none of the ecotoxicological studies provided was successful in the clear demonstration of a single (or multifactorial) agent that can account for the disseminated neoplasia.     

Copper partitioning in a melt-vapor-brine-magnetite-pyrrhotite assemblage

The effect of sulfur on the partitioning of Cu in a melt-vapor-brine ± magnetite ± pyrrhotite assemblage has been quantified at 800 °C, 140 MPa, f_O2 = nickel-nickel oxide (NNO), logf_S2=-3.0 (i.e., on the magnetite-pyrrhotite curve at NNO), logf_H2S=-1.3 and logf_SO2=-1. All experiments were vapor + brine saturated. Vapor and brine fluid inclusions were trapped in silicate glass and self-healed quartz fractures. Vapor and brine are dominated by NaCl, KCl and HCl in the S-free runs and NaCl, KCl and FeCl₂ in S-bearing runs. Pyrrhotite served as the source of sulfur in S-bearing experiments. The composition of fluid inclusions, glass and crystals were quantified by laser-ablation inductively coupled plasma mass spectrometry. Major element, chlorine and sulfur concentrations in glass were quantified by using electron probe microanalysis. Calculated Nernst-type partition coefficients (±2σ) for Cu between melt-vapor, melt-brine and vapor-brine are , , and , respectively, in the S-free system. The partition coefficients (±2σ) for Cu between melt-vapor, melt-brine and vapor-brine are , , and , respectively, in the S-bearing system. Apparent equilibrium constants (±1σ) describing Cu and Na exchange between vapor and melt and brine and melt were also calculated. The values of are 34 ± 21 and 128 ± 29 in the S-free and S-bearing runs, respectively. The values of are 33 ± 22 and60 ± 5 in the S-free and S-bearing runs, respectively. The data presented here indicate that the presence of sulfur increases the mass transfer of Cu into vapor from silicate melt. Further, the nearly threefold increase in suggests that Cu may be transported as both a chloride and sulfide complex in magmatic vapor, in agreement with hypotheses based on data from natural systems. Most significantly, the data demonstrate that the presence of sulfur enhances the partitioning of Cu from melt into magmatic volatile phases.     

Very high resolution rainfall patterns measured by TRMM precipitation radar: seasonal and diurnal cycles

The TRMM Precipitation Radar is used to construct a high resolution (0.05°?×?0.05°) climatology of rainfall over the latitude band extending to about 36° North and South. This study describes climatological patterns of rainfall frequency and intensity at high spatial resolution, with special focus on the seasonal and diurnal cycles in the frequency of rainfall events. We use this Tropics-wide dataset to highlight small-scale precipitation features that are too fine to be captured by the most widely used satellite-based rainfall datasets. The results shed light on the roles of changes in the wind direction, the land-sea thermal contrast, small-scale variations in sea surface temperature, and orography in shaping the seasonal and diurnal cycles of rainfall. In some regions of the tropics, diurnally locked local circulations are largely responsible for sharp gradients in the spatial distribution of seasonal mean precipitation. In other regions, we show that climatological rainfall frequency changes very sharply at coastlines, even though rainfall in these regions is expected to be controlled by relatively large scale weather systems.     

Subduction Influence on Oxygen Fugacity and Trace and Volatile Elements in Basalts Across the Cascade Volcanic Arc

Fluids or melts derived from a subducting plate are often citedas a mechanism for the oxidation of arc magmas. What remainsunclear is the link between the fluid, oxygen fugacity, andother major and trace components, as well as the spatial distributionof the impact of those fluids. To test the potential effectsof addition of a subduction-derived fluid or melt to the sub-arcmantle, olivine-hosted melt inclusions from primitive basalticlavas sampled from across the central Oregon Cascades (43°–45°N)have been analyzed for major, trace and volatile elements andfO₂. Oxygen fugacity was determined in melt inclusions fromsulfur speciation determined by electron microprobe and fromolivine–chromite oxygen geobarometry. The overall rangein fO₂ based on sulfur speciation measurements is from <–0·25log units to + 1·9 log units (FMQ, where FMQ is fayalite–magnetite–quartzbuffer). Oxygen fugacity is positively correlated with fluid-mobiletrace element and light rare earth element contents in basaltsgenerated by relatively low-degree partial melting. Establishinga further correlation between fO₂ and fluid-mobile trace elementabundances with position along the arc requires the basaltsto be subdivided into shoshonitic, calc-alkaline, low-K tholeiiteand enriched intraplate basalt groups. Melt inclusions fromenriched intraplate and shoshonitic lavas show increasing fO₂and trace element abundances closer to the trench, whereas calc-alkalinemelt inclusions exhibit no significant across-arc variations.Low-K tholeiitic melt inclusions record an increase in incompatibletrace elements closer to the trench; however, there is no correlatedincrease in fO₂. The correlation observed in enriched intraplateand shoshonitic melt inclusions is interpreted to reflect aprogressively greater proportion of a fluid-rich, oxidized subductioncomponent in magmas generated nearer the subduction zone. Significantly,calc-alkaline melt inclusions with high ratios of large ionlithophile elements to high field strength elements, characteristicof ‘typical’ arc magmas, have oxidation states indistinguishablefrom low-K tholeiite and enriched intraplate basalt melt inclusions.The lack of across-arc geochemical variation in calc-alkalinemelt inclusions may suggest that these basalts are not necessarilythe most appropriate magmas for examining recent addition ofa subduction component to the sub-arc mantle. Flux and batchmelt model results produce a wide range of predicted amountsof melting and subduction component added to the mantle source;however, general trends characterized by increased melting andproportion of the subduction component from enriched intraplate,to low-K tholeiite, to calc-alkaline are robust. The model resultsdo not require enriched intraplate, low-K tholeiite and calc-alkalinemagmas to be produced from the same more fertile mantle source.However, enriched intraplate magmas, in contrast to calc-alkalineand low-K tholeiite magmas, cannot be generated from a depletedmantle source. Flux or batch melting of either the more fertileor depleted mantle sources used to generate the low-K tholeiite,calc-alkaline, and enriched intraplate magmas cannot reproduceshoshonitic compositions, which require a significantly depletedmantle source strongly metasomatized by a subduction component.The potential mantle source for shoshonitic basalts has a predictedfO₂ (after oxidation) from + 0·3 to + 2·4 logunits (FMQ) whereas the mantle source for low-K tholeiite, calc-alkaline,and enriched intraplate magmas may range from –1·1to + 0·7 log units (FMQ). KEY WORDS: basalt; Cascades; melt inclusions; oxidation state; volatiles     

Cognitive and Affective Predictors of Illinois Residents’ Perceived Risks from Gray Wolves

Abstract

Increasing wolf populations are a concern for wildlife managers in the Midwestern U.S. Understanding the psychological mechanisms that contribute to public perceptions of risk will enable development of strategies that seek to mitigate these risks, and suggest where outreach efforts may facilitate acceptance of wolves. We examined the psychological factors that influence Illinois residents’ perceived risks from wolves. We hypothesized that individuals’ perceived risks from wolves were a function of their attitudes toward wolves, negative affect toward wolves, and basic beliefs about wildlife. Data were obtained from a survey of the Illinois public (n?=?784). Negative affect and attitudes toward wolves were direct predictors of perceived risks. Basic beliefs predicted attitudes and negative affect toward wolves. Negative affect predicted attitudes. Basic beliefs had direct and indirect effects on perceived risks.     

Are modern metaheuristics successful in calibrating simple conceptual rainfall–runoff models?

In recent years sampling approaches have been used more widely than optimization algorithms to find parameters of conceptual rainfall–runoff models, but the difficulty of calibration of such models remains in dispute. The problem of finding a set of optimal parameters for conceptual rainfall–runoff models is interpreted differently in various studies, ranging from simple to relatively complex and difficult. In many papers, it is claimed that novel calibration approaches, so-called metaheuristics, outperform the older ones when applied to this task, but contradictory opinions are also plentiful. The present study aims at calibration of two simple lumped conceptual hydrological models, HBV and GR4J, by means of a large number of metaheuristic algorithms. The tests are performed on four catchments located in regions with relatively similar climatic conditions, but on different continents. The comparison shows that, although parameters found may somehow differ, the performance criteria achieved with simple lumped models calibrated by various metaheuristics are very similar and differences are insignificant from the hydrological point of view. However, occasionally some algorithms find slightly better solutions than those found by the vast majority of methods. This means that the problem of calibration of simple lumped HBV or GR4J models may be deceptive from the optimization perspective, as the vast majority of algorithms that follow a common evolutionary principle of survival of the fittest lead to sub-optimal solutions.