Laser Interferometer Space Antenna double black holes: dynamics in gaseous nuclear discs

We study the inspiral of double black holes, with masses in the Laser Interferometer Space Antenna ( LISA ) window of detectability, orbiting inside a massive circumnuclear, rotationally supported gaseous disc. Using high-resolution smoothed particle hydrodynamics simulations, we follow the black hole dynamics in the early phase when gas-dynamical friction acts on the black holes individually, and continue our simulation until they form a close binary. We find that in the early sinking the black holes lose memory of their initial orbital eccentricity if they corotate with the gaseous disc. As a consequence, the massive black holes bind forming a binary with a low eccentricity, consistent with zero within our numerical resolution limit. The cause of circularization resides in the rotation present in the gaseous background where dynamical friction operates. Circularization may hinder gravitational waves from taking over and leading the binary to coalescence. In the case of counter-rotating orbits, the initial eccentricity (if present) does not decrease, and the black holes may bind forming an eccentric binary. When dynamical friction has subsided, for equal mass black holes and regardless their initial eccentricity, angular momentum loss, driven by the gravitational torque exerted on the binary by surrounding gas, is nevertheless observable down to the smallest scale probed (≃1 pc). In the case of unequal masses, dynamical friction remains efficient down to our resolution limit, and there is no sign of formation of any ellipsoidal gas distribution that may further harden the binary. During inspiral, gravitational capture of gas by the black holes occurs mainly along circular orbits; eccentric orbits imply high relative velocities and weak gravitational focusing. Thus, the active galactic nucleus activity may be excited during the black hole pairing process and double active nuclei may form when circularization is completed, on distance scales of tens of parsecs.     

Lead isotope systematics of Late Cretaceous – Tertiary Andean arc magmas and associated ores between 8°N and 40°S: evidence for latitudinal mantle heterogeneity beneath the Andes

ABSTRACT Lead isotope variability of magmatic arc rocks and associated mineralization of the Central Andes is usually considered to be the result of mixing between a homogeneous mantle and heterogeneous continental crust. About 230 new lead isotope data on the Northern and Central Andes allow us to compare for the first time lead isotope systematics of the Late Cretaceous – Tertiary arc magmatism and associated mineralization along the Andean chain between 8°N and 40°S. Lead isotope compositions indicate mixing between mantle and upper crustal rocks along the whole Andean chain. Additionally, we have found that mantle end-members of the Late Cretaceous – Tertiary magmatism are heterogeneous and systematically shifted towards less radiogenic ²⁰⁶Pb/²⁰⁴Pb compositions from north to south along the Andes. This heterogeneity most likely results from mixing between a low radiogenic mantle, possibly carrying a DMM or EM I component, and a more radiogenic mantle, possibly carrying an HIMU component. Thus, our results imply that lead isotope variability of Andean magmas at the continental scale is caused not only by crustal but also by mantle heterogeneity.     

Wavelength predictions for the 1s 22s-1s2s3p satellite transitions

The experimentally known energies of the 1s ²2s 1s2s(¹ S, ³ S)3p transitions are considered for lithium to calcium. Their differences from the corresponding He-like resonances are fitted to the atomic number by means of a polynomial function and, through interpolation, the wavelengths for nitrogen to sodium are calculated.     

Petrology and U-Pb Zircon Geochronology of Amphibole-rich Cumulates with Sanukitic Affinity from Husky Ridge (Northern Victoria Land, Antarctica): Insights into the Role of Amphibole in the Petrogenesis of Subduction-related Magmas

A microanalytical trace element and geochronological study wascarried out on mafic amphibole-rich cumulates (quartz diorites)cropping out in northern Victoria Land (Antarctica). Associatedtonalites and basement rocks were also investigated. Rock texturesand major and trace element mineral compositions reveal thepresence in quartz diorites of two mineral assemblages: (1)clinopyroxene-I + brown amphibole ± dark mica; (2) clinopyroxene-II+ green amphibole + plagioclase + quartz. Both mineral assemblagescontain mafic phases with elevated Mg-number, but their traceelement signatures differ significantly. In situ U–Pbzircon geochronology was carried out to support petrogeneticand geological interpretations. Quartz diorites were emplacedin the mid-crust probably at 516 ± 3 Ma. Parental meltsof quartz diorites were computed by applying solid/liquid partitioncoefficients. The melt in equilibrium with the first mineralassemblage (melt-I) is extremely depleted in heavy rare earthelements (HREE), Y, Ti, Zr and Hf (at about 0·2 timesnormal mid-ocean ridge basalt) and enriched in B, Th, U, thelarge ion lithophile elements and light REE (LREE). It sharesmany similarities with sanukitic melts (e.g. Setouchi andesites),which originated by equilibration of subduction-derived sedimentmelts with a refractory mantle. The melt in equilibrium withthe second mineral assemblage (melt-II) is characterized bya steep LREE enrichment (La_N/Yb_N up to 39), a U-shaped HREEpattern and low Ti, which is depleted relative to HREE. Thetrace element signature of melt-II can be acquired through amphibolecrystallization starting from a sanukitic melt similar to melt-I,probably in a deeper magma chamber. Our results allow us toconstrain that melts from the subducted slab were produced ona regional scale, in accordance with literature data, belowa large sector of the east Gondwana margin during the mid-Cambrian.Implications for the role of amphibole in petrogenesis of subduction-relatedmagmas are also discussed. KEY WORDS: amphibole; sanukite; high-Mg andesites; Ross Orogeny; Antarctica     

Geophysical evidence of mud diapirism on the Mediterranean Ridge accretionary complex

Mud volcanoes, mud cones, and mud ridges have been identified on the inner portion of the crestal area, and possibly on the inner escarpment, of the Mediterranean Ridge accretionary complex. Four areas containing one or more mud diapirs have been investigated through bathymetric profiling, single channel seismic reflection profiling, heat flow measurements, and coring. A sequence of events is identified in the evolution of the mud diapirs: initially the expulsion on the seafloor of gasrich mud produces a seafloor depression outlined in the seismic record by downward dip of the host sediment reflectors towards the mud conduit; subsequent eruptions of fluid mud may create a flat topped mud volcano with step-like profile; finally, the intrusion of viscous mud produces a mud cone.The origin of the diapirs is deep within the Mediterranean Ridge. Although a minimum depth of about 400 m below the seafloor has been computed from the hydrostatic balance between the diapiric sediments and the host sediments, a maximum depth, suggested by geometric considerations, ranges between 5.3 and 7 km. The presence of thermogenic gas in the diapiric sediments suggests a better constrained origin depth of at least 2.2 km.The heat flow measured within the Olimpi mud diapir field and along a transect orthogonal to the diapiric field is low, ranging between 16 ± 5 and 41 ± 6 mW m^–2. Due to the presence of gas, the thermal conductivity of the diapiric sediments is lower than that of the host hemipelagic oozes (0.6–0.9 and 1.0–1.15 W m^–1 K^–1 respectively).We consider the distribution of mud diapirs to be controlled by the presence of tectonic features such as reverse faults or thrusts (inner escarpment) that develop where the thickness of the Late Miocene evaporites appears to be minimum. An upward migration through time of the position of the décollement within the stratigraphic column from the Upper Oligocene (diapiric sediments) to the Upper Miocene (present position) is identified.     

Vertical Distribution of Meiobenthos in Bathyal Sediments of the Eastern Mediterranean Sea: Relationship with Labile Organic Matter and Bacterial Biomasses

Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments.     

Methodical series tests for fuller ship hull forms

In recent years many fuller ship hull forms have been designed and constructed in various shipbuilding countries, but the data available for the development of the fuller forms are inadequate from the point of view of preliminary ship design. In this paper the authors describe how they have systematically tested vessel forms of block coefficients ranging from 0.80 to 0.90. The analysis and presentation of the test results have been made in such a manner that designers can produce hull forms like those of tankers and other bulk carriers quickly and reliably.     

Thermohaline Anomalies in the Spring and Early Summer of 2000 in the Gulf of Trieste

Abstract. In the framework of the Interreg II Project (July 1998 - June 2001), hydro-logical, chemical and biological data were collected in the Gulf of Trieste.
During spring and summer 2000, some particular thermohaline anomalies were observed in the Gulf of Trieste. Especially in May and June the water body showed: a very strong thermohaline stratification, an increase of advective salt water coming from the south and the presence of sharp pycnoclines. In July the temperature was higher than usual in the whole water column. Moreover, in late May and in June, massive mucilaginous aggregates were observed along the water column and at the surface.
In order to highlight these particular thermohaline features the hydrological data of 16 stations were analysed (Fig. 1). Two stations, in particular, were considered: one offshore (St. AA1, average depth 20 m) and one close to the coast (St. C1, average depth 17 m). For these two stations a best-fit analysis, computed over 11 and 7 years, respectively, was performed on temperature, salinity and density excess data.
Moreover, the hydrological features were compared with the rainfall, air temperature, wind speed data (Istituto Sperimentale Talassografico di Trieste - ISTT) and the Isonzo River's flow rate (Direzione Regionale dell'Ambiente - Regione F. V. G.) collected from January 1998 to December 2000.     

A depocenter of organic matter at 7800 m depth in the SE Pacific Ocean

The Atacama trench, the deepest ecosystem of the southern Pacific Ocean (ca. 8000 m depth) was investigated during the Atacama Trench International Expedition. Sediments, collected at three bathyal stations (1040–1355 m depth) and at a hadal site (7800 m) were analyzed for organic matter quantity and biochemical composition (in terms of phytopigments, proteins, carbohydrates and lipids), bacterial abundance, biomass and carbon production and extracellular enzymatic activities. Functional chlorophyll-a (18.0±0.10 mg m⁻²), phytodetritus (322.2 mg m⁻²) and labile organic carbon (16.9±4.3 g C m⁻²) deposited on surface sediments at hadal depth (7800 m) reached concentrations similar to those encountered in highly productive shallow coastal areas. High values of bacterial C production and aminopeptidase activity were also measured (at in situ temperature and 1 atm). The chemical analyses of the Atacama hadal sediments indicate that this trench behaves as a deep oceanic trap for organic material. We hypothesize that, despite the extreme physical conditions, benthic microbial processes might be accelerated as a result of the organic enrichment.