Observational Properties of Jets in Active Galactic Nuclei

Parsec scale jet properties are shortly presented and discussed. Observational data are used to derive constraints on the jet velocity and orientation, the presence of velocity structures, and the connection between the pc and kpc scale. Two peculiar sources with limb-brightened jets: 1144+35 and Mkn 501 are discussed in detail.     

Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)

This paper focuses on the chemical and isotopic features of dissolved gases (CH₄ and CO₂) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH₄ and CO₂. The δ¹³C-CH₄ and δD-CH₄ values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH₄ is mainly produced by microbial activity. The δ¹³C-CO₂ values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO₂ contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO₂ source feeding the regional thermal and cold CO₂-rich fluid emissions. In contrast, the relatively low δ¹³C-CO₂ values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO₂. Chemical and isotopic compositions of dissolved CO₂ and CH₄ at different depths are mainly depending on (1) CO₂ inputs from external sources (hydrothermal and/or anthropogenic); (2) CO₂–CH₄ isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO₂ and CH₄ concentrations. In the hypolimnion, where the δ¹³C-CO₂ values progressively increase with depth and the δ¹³C-CH₄ values show an opposite trend, biogenic CO₂ production from CH₄ using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ¹³C-CO₂ values, and measured δ¹³C_TDIC values are not consistent, indicating that CO₂ and the main carbon-bearing ion species (HCO₃ ^?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO₂ and CH₄. This study demonstrates that the vertical patterns of the CO₂/CH₄ ratio and of δ¹³C-CO₂ and δ¹³C-CH₄ are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO₂ input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.     

Layered amphibolite sequence in NE Sardinia,Italy: remnant of a pre-Variscan mafic silicic layered intrusion?

A banded amphibolite sequence of alternating ultramafic, mafic (amphibolite) and silicic layers, tectonically enclosed within Variscan migmatites, outcrops at Monte Plebi (NE Sardinia) and shows similarities with leptyno-amphibolite complexes. The ultramafic layers consist of amphibole (75–98%), garnet (0–20%), opaque minerals (1–5%) and biotite (0–3%). The mafic rocks are made up of amphibole (65–80%), plagioclase (15–30%), quartz (0–15%), opaque minerals (2–3%) and biotite (0–2%). The silicic layers consist of plagioclase (60–75%), amphibole (15–30%) and quartz (10–15%). Alteration, metasomatic, metamorphic and hydrothermal processes did not significantly modify the original protolith chemistry, as proved by a lack of K₂O-enrichment, Rb-enrichment, CaO-depletion, MgO-depletion and by no shift in the rare earth element (REE) patterns. Field, geochemical and isotopic data suggest that ultramafic, mafic and silicic layers represent repeated sequences of cumulates, basic and acidic rocks similar to macrorhythmic units of mafic silicic layered intrusions. The ultramafic layers recall the evolved cumulates of Skaergaard and Pleasant Bay mafic silicic layered intrusions. Mafic layers resemble Thingmuli tholeiites and chilled Pleasant Bay mafic rocks. Silicic layers with Na₂O: 4–6 wt%, SiO₂: 67–71 wt% were likely oligoclase-rich adcumulates common in many mafic silicic layered intrusions. Some amphibolite showing a strong Ti-, P-depletion and REE-depletion are interpreted as early cumulates nearly devoid of ilmenite and phosphates. All Monte Plebi rocks have extremely low Nb, Ta, Zr, Hf content and high LILE/HFSE ratios, a feature inherited from the original mantle sources. The mafic and ultramafic layers show slight and strong LREE enrichment respectively. Most mafic layer samples plot in the field of continental tholeiites in the TiO₂–K₂O–P₂O₅ diagram and are completely different from N-MORB, E-MORB and T-MORB as regards REE patterns and Nd, Sr isotope ratios but show analogies with Siberian, Deccan and proto-Atlantic rift tholeiites. Comparisons with Thingmuli, Skaergaard and Kiglapait rocks and with experimental data suggest that the Monte Plebi intrusion was an open-to-oxygen system with fO₂ FMQ. Mafic and ultramafic samples yielded _Nd(460)=+0.79 /+3.06 and ⁸⁷Sr/⁸⁶Sr=0.702934–0.703426, and four silicic samples _Nd(460)=–0.53/–1.13; ⁸⁷Sr/⁸⁶Sr=0.703239–0.703653. Significant differences in Nd isotope ratios between mafic and silicic rocks prove that both groups evolved separately in deeper magma chambers, from different mantle sources, with negligible interaction with crustal material, and were later repeatedly injected within a shallower magma chamber. The spectrum of Sr and Nd isotope data is consistent with a slightly enriched mantle metasomatized during an event earlier than 460 Ma. The metasomatising component was represented by alkali-Th-rich fluids of crustal origin rather than by sedimentary materials, able to modify alkali and Sr–Nd isotope systematics. Monte Plebi layered amphibolites might represent the first example of a strongly metamorphosed fragment of an early Paleozoic mafic silicic layered intrusion emplaced in a thinning continental crust and then tectonically dismembered by Variscan orogeny.     

Modeling radar-rainfall estimation uncertainties using parametric and non-parametric approaches

There are large uncertainties associated with radar estimates of rainfall, including systematic errors as well as the random effects from several sources. This study focuses on the modeling of the systematic error component, which can be described mathematically in terms of a conditional expectation function. The authors present two different approaches: non-parametric (kernel-based) and parametric (copula-based). A large sample (more than six years) of rain gauge measurements from a dense network located in south-west England is used as an approximation of the true ground rainfall. These data are complemented with rainfall estimates by a C-band weather radar located at Wardon Hill, which is about 40 km from the catchment. The authors compare the results obtained using the parametric and non-parametric schemes for four temporal scales of hydrologic interest (5 and 15 min, hourly and three-hourly) by means of several different performance indices and discuss the strengths and weaknesses of each approach.     

Improved evaluation of inelastic displacement demands for short‐period masonry structures

This work discusses the simplified estimation of earthquake‐induced nonlinear displacement demands as required by nonlinear static procedures, with particular attention on short‐period masonry structures. The study focuses on systems with fundamental periods between 0.1 and 0.5 s, for which inelastic amplification of the elastic displacement demand is more pronounced; hysteretic force‐displacement relationships characteristic of masonry structures are adopted, because these structures are more commonly found within the considered period range. Referring to the results of nonlinear dynamic analyses of single‐degree‐of‐freedom oscillators, some limitations of the Eurocode 8 and Italian Building Code formulations are first discussed, then an improved equation is calibrated that relates inelastic and elastic displacement demands. Numerical values of the equation parameters are obtained, considering the amount of hysteretic energy dissipation associated with various damage mechanisms observed in masonry structures. Safety factors are also calculated to determine several percentiles of the displacement demand. It is shown that the proposed equation can be extended to more dissipative systems. Finally, the same formulation is adapted to the estimation of seismic displacements when elastic analysis procedures are employed. Copyright © 2017 John Wiley & Sons, Ltd.     

Biogeochemistry of mineral-organic associations across a long-term mineralogical soil gradient (0.3-4100 kyr), Hawaiian Islands

Organic matter (OM) in mineral-organic associations (MOAs) represents a large fraction of carbon in terrestrial ecosystems which is considered stable against biodegradation. To assess the role of MOAs in carbon cycling, there is a need to better understand (i) the time-dependent biogeochemical evolution of MOAs in soil, (ii) the effect of the mineral composition on the physico-chemical properties of attached OM, and (iii) the resulting consequences for the stabilization of OM. We studied the development of MOAs across a mineralogical soil gradient (0.3-4100 kyr) at the Hawaiian Islands that derived from basaltic tephra under comparable climatic and hydrological regimes. Mineral-organic associations were characterized using biomarker analyses of OM with chemolytic methods (lignin phenols, non-cellulosic carbohydrates) and wet chemical extractions, surface area/porosity measurements (N₂ at 77 K and CO₂ at 273 K), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The results show that in the initial weathering stage (0.3 kyr), MOAs are mainly composed of primary, low-surface area minerals (olivine, pyroxene, feldspar) with small amounts of attached OM and lignin phenols but a large contribution of microbial-derived carbohydrates. As high-surface area, poorly crystalline (PC) minerals increase in abundance during the second weathering stage (20-400 kyr), the content of mineral-associated OM increased sharply, up to 290 mg C/g MOA, with lignin phenols being favored over carbohydrates in the association with minerals. In the third and final weathering stage (1400-4100 kyr), metastable PC phases transformed into well crystalline secondary Fe and Al (hydr)oxides and kaolin minerals that were associated with less OM overall, and depleted in both lignin and carbohydrate as a fraction of total OM. XPS, the N₂ pore volume data and OM-mineral volumetric ratios suggest that, in contrast to the endmember sites where OM accumulated at the surfaces of larger mineral grains, topsoil MOAs of the 20-400-kyr sites are composed of a homogeneous admixture of small-sized PC minerals and OM, which originated from both adsorption and precipitation processes. The chemical composition of OM in surface-horizon MOAs, however, was largely controlled by the uniform source vegetation irrespective of the substrate age whereas in subsoil horizons, aromatic and carboxylic C correlated positively with oxalate-extractable Al and Si and CuCl₂-extractable Al concentrations representing PC aluminosilicates and Al-organic complexes (r² > 0.85). Additionally, XPS depth profiles suggest a zonal structure of sorbed OM with aromatic carbons being enriched in the proximity of mineral surfaces and amide carbons (peptides/proteins) being located in outer regions of MOAs. Albeit the mineralogical and compositional changes of OM, the rigidity of mineral-associated OM as analyzed by DSC changed little over time. A significantly reduced side chain mobility of sorbed OM was, however, observed in subsoil MOAs, which likely arose from stronger mineral-organic bindings. In conclusion, our study shows that the properties of soil MOAs change substantially over time with different mineral assemblages favoring the association of different types of OM, which is further accentuated by a vertical gradient of OM composition on mineral surfaces. Factors supporting the stabilization of sorbed OM were (i) the surface area and reactivity of minerals (primary or secondary crystalline minerals versus PC secondary minerals), (ii) the association of OM with micropores of PC minerals (via ‘sterically’ enhanced adsorption), (iii) the effective embedding of OM in ‘well mixed’ arrays with PC minerals and monomeric/polymeric metal species, (iv) the inherent stability of acidic aromatic OM components, and (iv) an impaired segmental mobility of sorbed OM, which might increase its stability against desorption and microbial utilization.